Extended Tubular Heat Exchanger Instruction Manual HT36

Extended Tubular Heat Exchanger
Instruction Manual
HT36
ISSUE 4
June 2010
Table of Contents
Copyright and Trademarks ...................................................................................... 1
General Overview ....................................................................................................... 2
Equipment Diagrams................................................................................................... 3
Important Safety Information....................................................................................... 6
Introduction.............................................................................................................. 6
Electrical Safety....................................................................................................... 6
Hot Surfaces and Liquids ........................................................................................ 6
Water Borne Hazards .............................................................................................. 6
Description .................................................................................................................. 8
Overview.................................................................................................................. 8
Baseplate................................................................................................................. 8
End Housings .......................................................................................................... 8
Cold Water Circuit Manual Configuration Valves .................................................... 8
Thermocouples........................................................................................................ 9
Connections for Flexible Tubing .............................................................................. 9
Installation ................................................................................................................. 10
Advisory................................................................................................................. 10
Installation Process ............................................................................................... 10
Operation .................................................................................................................. 12
Operating the Software.......................................................................................... 12
Operating the Equipment....................................................................................... 22
Equipment Specifications.......................................................................................... 29
I/O Port Pin Connections ....................................................................................... 29
USB Channel Numbers ......................................................................................... 30
Environmental Conditions...................................................................................... 31
Routine Maintenance ................................................................................................ 33
Responsibility ........................................................................................................ 33
General.................................................................................................................. 33
Laboratory Teaching Exercises................................................................................. 34
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Table of Contents
Index to Exercises ................................................................................................. 34
Nomenclature ........................................................................................................ 34
Reference Tables .................................................................................................. 36
Calculating Reynolds Number ............................................................................... 37
Exercise A: Indirect Heating/Cooling Demonstration ................................................ 39
Exercise B: Energy Balance and Overall Efficiency.................................................. 45
Exercise C: Cocurrent and Countercurrent Flow ...................................................... 48
Exercise D: Overall Heat Transfer Coefficient .......................................................... 55
Exercise E: Effect of Flow Rate................................................................................. 59
Exercise F: Driving Force.......................................................................................... 65
Exercise G: Project Work .......................................................................................... 70
Contact Details for Further Information ..................................................................... 72
iii
Disclaimer
This document and all the information contained within it is proprietary to Armfield
Limited. This document must not be used for any purpose other than that for which it
is supplied and its contents must not be reproduced, modified, adapted, published,
translated or disclosed to any third party, in whole or in part, without the prior written
permission of Armfield Limited.
Should you have any queries or comments, please contact the Armfield Customer
Support helpdesk (Monday to Friday: 0800 – 1800 GMT). Contact details are as
follows:
United Kingdom
International
(0) 1425 478781
(calls charged at local rate)
+44 (0) 1425 478781
(international rates apply)
Email: support@armfield.co.uk
Fax: +44 (0) 1425 470916
Copyright and Trademarks
Copyright © 2009 Armfield Limited. All rights reserved.
Any technical documentation made available by Armfield Limited is the copyright
work of Armfield Limited and wholly owned by Armfield Limited.
Brands and product names mentioned in this manual may be trademarks or
registered trademarks of their respective companies and are hereby acknowledged.
1
General Overview
This instruction manual should be used in conjunction with the manual supplied with
the HT30XC Heat Exchanger Service Unit.
This Manual provides the necessary information for operating the equipment in
conjunction with the HT30XC Service Unit and a connected PC running the Armfield
HT36-304 software. It includes a range of Teaching Exercises designed to
demonstrate the basic principles of Heat Exchanger theory and use.
This instruction manual describes the operation of the HT36 Extended Tubular Heat
Exchanger which must be used in conjunction with the HT30XC Heat Exchanger
Service Unit (supplied separately). Details of the service unit are given in a separate
instruction manual, which is supplied with the unit. The service unit provides the hot
and cold water streams for the heat exchanger along with flow and temperature
measurement and control and the facility for computerised data logging of the results.
The HT36 Extended Tubular Heat Exchanger is one model in a range of heat
exchangers designed for use with the HT30XC service unit. A full description of the
exchanger is provided in the DESCRIPTION section of this manual (page 2-1). Other
heat exchangers available in the range include the HT31 Tubular, HT32 Plate, HT33
Shell and Tube, HT34 Jacketed Vessel with Coil and Stirrer and HT37 Extended
Plate with Regeneration. These modules are interchangeable on the service unit and
each come with their own product manual.
HT36 Extended Tubular Heat Exchanger
2
Equipment Diagrams
Figure 1 Plan View of HT36
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Armfield Instruction Manual
Figure 2 Side View of HT36
4
Equipment Diagrams
Figure 3 Diagram of Countercurrent Operation
Figure 4 Diagram of Cocurrent Operation
5
Important Safety Information
Introduction
All practical work areas and laboratories should be covered by local safety
regulations which must be followed at all times.
It is the responsibility of the owner to ensure that all users are made aware of
relevant local regulations, and that the apparatus is operated in accordance with
those regulations. If requested then Armfield can supply a typical set of standard
laboratory safety rules, but these are guidelines only and should be modified as
required. Supervision of users should be provided whenever appropriate.
Your HT36 Extended Tubular Heat Exchanger has been designed to be safe in use
when installed, operated and maintained in accordance with the instructions in this
manual. As with any piece of sophisticated equipment, dangers exist if the equipment
is misused, mishandled or badly maintained.
Electrical Safety
The equipment described in this Instruction Manual operates from a mains voltage
electrical supply. It must be connected to a supply of the same frequency and voltage
as marked on the equipment or the mains lead. If in doubt, consult a qualified
electrician or contact Armfield.
The equipment must not be operated with any of the panels removed.
To give increased operator protection, the unit incorporates a Residual Current
Device (RCD), alternatively called an Earth Leakage Circuit Breaker, as an integral
part of this equipment. If through misuse or accident the equipment becomes
electrically dangerous, the RCD will switch off the electrical supply and reduce the
severity of any electric shock received by an operator to a level which, under normal
circumstances, will not cause injury to that person.
At least once each month, check that the RCD is operating correctly by pressing the
TEST button. The circuit breaker MUST trip when the button is pressed. Failure to
trip means that the operator is not protected and the equipment must be checked and
repaired by a competent electrician before it is used.
Hot Surfaces and Liquids
The heat exchanger is capable of producing temperatures that could cause burns.
Do not touch the heat exchanger while it is in operation and allow sufficient time for it
to cool after use before handling the exchanger or pipework. If the model needs to be
changed it should be handled by the white base on which the exchanger is mounted.
Do not open the circulator unit on the service unit except in accordance with the
safety instructions included in the HT30XC Heat Exchanger Service Unit product
manual.
Water Borne Hazards
The equipment described in this instruction manual involves the use of water, which
under certain conditions can create a health hazard due to infection by harmful
micro-organisms.
For example, the microscopic bacterium called Legionella pneumophila will feed on
any scale, rust, algae or sludge in water and will breed rapidly if the temperature of
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Important Safety Information
water is between 20 and 45°C. Any water containing this bacterium which is sprayed
or splashed creating air-borne droplets can produce a form of pneumonia called
Legionnaires Disease which is potentially fatal.
Legionella is not the only harmful micro-organism which can infect water, but it
serves as a useful example of the need for cleanliness.
Under the COSHH regulations, the following precautions must be observed:

Any water contained within the product must not be allowed to stagnate, ie.
the water must be changed regularly.

Any rust, sludge, scale or algae on which micro-organisms can feed must be
removed regularly, i.e. the equipment must be cleaned regularly.

Where practicable the water should be maintained at a temperature below
20°C. If this is not practicable then the water should be disinfected if it is safe
and appropriate to do so. Note that other hazards may exist in the handling of
biocides used to disinfect the water.

A scheme should be prepared for preventing or controlling the risk
incorporating all of the actions listed above.
Further details on preventing infection are contained in the publication “The Control
of Legionellosis including Legionnaires Disease” - Health and Safety Series booklet
HS (G) 70.
7
Description
Where necessary, refer to the drawings in the Equipment Diagrams section.
Overview
The tubular heat exchanger is the simplest form of heat exchanger and in its basic
form consists of two concentric (coaxial) tubes carrying the hot and cold fluids. Heat
is transferred to/from one fluid in the inner tube from/to the other fluid in the outer
annulus via the metal wall which separates the two fluids.
In this miniature version, four sets of concentric tubes are arranged in series in the
form of a coil to reduce the overall length and allow the temperature mid way along
both fluid streams to be measured.
In normal operation (see Figure 3 and 4) the hot fluid from the hot water circulator
passes through the inner stainless steel tube and cold fluid from the cold water
supply passes through the annulus created between each inner metal tube and clear
acrylic outer tube. This arrangement minimises heat loss from the exchanger without
the need for additional insulation and allows the construction of the exchanger to be
viewed.
Baseplate
The tubular heat exchanger is mounted on a PVC base plate (1) which incorporates
four holes (2) which locate it on four studs at the left hand end of the HT30X service
unit. The PVC base plate is secured to the service unit using thumb nuts.
End Housings
PVC housings (3), bonded to each end of the clear acrylic outer tubes, incorporate
'O' rings between each inner tube and outer annulus. These provide a liquid seal,
accommodate differential expansion between the metal and plastic parts and allow
the inner metal tubes to be removed for cleaning. The end housings also incorporate
the necessary fittings for sensors to measure the fluid temperatures and connections
to the hot and cold water supplies.
Cold Water Circuit Manual Configuration Valves
The manual valves on the cold water circuit allow the cold water to be passed
through one, two, three or four of the outer annuli, hence allowing active heat
exchange through 1, 2, 3 or 4 sections of the Heat Exchanger. This allows the effect
of differing heat exchanger lengths to be investigated.
8
Description
Thermocouples
The ten thermocouple temperature sensors (4) are labelled T1 to T10 for
identification and each lead is terminated with a miniature thermocouple plug (5) for
connection to the appropriate socket on the front of the service unit.
Connections for Flexible Tubing
Flexible tubing attached to each fluid inlet/outlet is terminated with a ferrule (6). This
allows rapid connection to the appropriate quick release fittings on the HT30XC
service unit. The fittings on the HT30XC service unit and HT36 are colour coded red
for hot water and blue for cold water to aid identification.
Details of the connections are given in the Installation and Operation sections of this
manual.
9
Installation
Advisory
Before operating the equipment, it must be unpacked, assembled and installed as
described in the steps that follow. Safe use of the equipment depends on following
the correct installation procedure.
Installation Process
The HT36 Extended Tubular Heat Exchanger must be used in conjunction with the
HT30X Heat Exchanger Service Unit.
Before mounting the HT36 Extended Tubular Heat Exchanger on a HT30XC Heat
Exchanger Service Unit ensure that the service unit has been assembled and
connected to the appropriate services as described in the instruction manual supplied
with the HT30XC.
1. Check that the HT30XC service unit and the Armfield HT30 range software
has been installed as described in the HT30XC product manual (provided
with the service unit). The PC on which the software has been installed
should be located close to the service unit.
2. Remove the HT36 accessory from any packaging and position the accessory
on the HT30XC plinth so that the holes in the HT36 baseplate are located
over the studs on the HT30XC.
3. Secure the HT36 to the plinth using the thumb nuts provided.
4. Connect the flexible tubing on the HT36 to the quick-release fittings on the
service unit as shown in the following diagram:
5. Direct the tubing carrying the cold water out of the exchanger into a suitable
drain.
6. Check that the HT30XC service unit is connected to suitable mains water and
mains electricity supplies (as described in the HT30XC manual), and that the
water and electricity supplies are switched on.
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Installation
7. Check that the HT30XC service unit is connected to the PC using the USB
cable provided, and that the PC is switched on. Check that the red and green
USB indicator lights on the front panel of the HT30XC are illuminated.
8. Switch on the HT30XC service unit (using the mains switch on the front of the
unit), and check that the Emergency Stop button is released (pulled out).
9. Run the HT36 software and select the exercise required. Check that the
software reads ‘IFD OK’ in the bottom right-hand corner of the screen.
10. Select the mimic diagram in the software by clicking on the
icon.
11. Select the ‘Power On’ switch on the software mimic diagram.
12. Select the Hot Water Pump Control button. In the controller window, set the
controller to Manual and then set the Hot Water Pump Speed to 100% using
the Manual Control box in the right-hand pane of the window. The hot water
pump should begin to operate. Run the pump until the hot water circuit of the
heat exchanger has filled with water and all bubbles have been expelled from
the circuit. Top up the hot water tank with clean (preferably de-ionised or demineralised) water if the level drops below the tip of the level sensor.
13. Set the Hot Water Pump Speed back to 0%. The pump should cease
operation. Close the controller window.
14. Fully close the pressure regulator at the cold water inlet. On the mimic
diagram screen, set the Cold Water Valve to 100%. The valve should be
heard to operate. Gradually open the pressure regulator. Cold water should
begin to flow through the cold water circuit. Open the pressure regulator until
a flow rate of 4.9 L/min is reached, then lock the regulator setting. Allow water
to flow until any bubbles have been eliminated, then set the cold water valve
back to 0%.
The HT36 accessory is now installed and primed ready for use.
Refer to the HT30XC manual for further information on the service unit and its
operation.
Refer to the Operation section and Laboratory Teaching Exercises for more
information on the operation of the HT36 and the investigations that can be
performed using this Heat Exchanger. The Teaching Exercises are also available
from within the HT36 software Help Text.
11
Operation
Where necessary, refer to the drawings in the Equipment Diagrams section.
Operating the Software
Note: The diagrams in this section are included as typical examples and may not
relate specifically to the individual product described in this instruction manual.
The Armfield Software is a powerful Educational and Data Logging tool with a wide
range of features. Some of the major features are highlighted below, to assist users,
but full details on the software and how to use it are provided in the presentations
and Help text incorporated in the Software. Help on Using the Software or Using the
Equipment is available by clicking the appropriate topic in the Help drop-down menu
from the upper toolbar when operating the software as shown:
Before operating the software ensure that the equipment has been connected to the
IFD5 Interface (where IFD5 is separate from the equipment) and the IFD5 has been
connected to a suitable PC using a USB lead. For further information on these
actions refer to the Operation manual.
Load the software and wait for the presentation screen to open fully as shown:
Before proceeding to operate the software ensure that IFD: OK is displayed at the
bottom of the screen. If IFD:ERROR is displayed check the USB connection between
the IFD5 and the PC and confirm that the red and green LED’s are both illuminated.
If the problem persists then check that the driver is installed correctly (refer to the
Operation manual).
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Operation
Presentation Screen - Basics and Navigation
As stated above, the software starts with the Presentation Screen displayed. The
user is met by a simple presentation which gives them an overview of the capabilities
of the equipment and software and explains in simple terms how to navigate around
the software and summarizes the major facilities complete with direct links to detailed
context sensitive ‘help’ texts.
To view the presentations click Next or click the required topic in the left hand pane
as appropriate. Click More while displaying any of the topics to display a Help index
related to that topic.
To return to the Presentation screen at any time click the View Presentation icon
from the main tool bar or click Presentation from the dropdown menu as
shown:
For more detailed information about the presentations refer to the Help available via
the upper toolbar when operating the software.
Toolbar
A toolbar is displayed at the top of the screen at all times, so users can jump
immediately to the facility they require, as shown:
The upper menu expands as a dropdown menu when the cursor is placed over a
name.
The lower row of icons (standard for all Armfield Software) allows a particular
function to be selected. To aid recognition, pop-up text names appear when the
cursor is placed over the icon.
Mimic Diagram
The Mimic Diagram is the most commonly used screen and gives a pictorial
representation of the equipment, with continuously updated display boxes for all the
various sensor readings, calculated variables etc. directly in engineering units.
To view the Mimic Diagram click the View Diagram icon
or click Diagram from the View drop-down menu as shown:
from the main tool bar
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Armfield Instruction Manual
A Mimic diagram is displayed, similar to the diagram as shown:
In addition to measured variables such as Temperature, Pressure and Flowrate (from
a direct reading flowmeter), calculated data such as Motor Torque, Motor Speed and
Discharge / Volume flowrate (from pressure drop across an orifice plate) are
continuously displayed in data boxes with a white background. These are
automatically updated and cannot be changed by the user.
Manual data input boxes with a coloured background allow constants such as Orifice
Cd and Atmospheric Pressure to be changed by over-typing the default value, if
required.
The data boxes associated with some pressure sensors include a Zero button
alongside. This button is used to compensate for any drift in the zero value, which is
an inherent characteristic of pressure sensors. Pressing the Zero button just before
starting a set of readings resets the zero measurement and allows accurate pressure
measurements to be taken referenced to atmospheric pressure. This action must be
carried out before the motor is switched on otherwise the pressure readings will be
offset.
14
Operation
The mimic diagram associated with some products includes the facility to select
different experiments or different accessories, usually on the left hand side of the
screen, as shown:
Clicking on the appropriate accessory or exercise will change the associated mimic
diagram, table, graphs etc to suit the exercise being performed.
Control Facilities in the Mimic Diagram
A Power On button allows the motor to be switched off or on as required. The button
always defaults to off at startup. Clicking this button switches the power on (1) and off
(0) alternately.
A box marked Motor Setting allows the speed of the motor to be varied from 0 to
100% either stepwise, by typing in values, or using the up / down arrows as
appropriate. It is usual to operate the equipment with the motor initially set to 100%,
then reduce the setting as required to investigate the effect of reduced speed on
performance of the equipment.
When the software and hardware are functioning correctly together, the green LED
marked Watchdog Enabled will alternate On and Off. If the Watchdog stops
alternating then this indicates a loss of communication between the hardware and
software that must be investigated.
Details on the operation of any automatic PID Control loops in the software are
included later in this section.
Data Logging Facilities in the Mimic Diagram
There are two types of sampling available in the software, namely Automatic or
Manual. In Automatic logging, samples are taken regularly at a preset but variable
interval. In Manual logging, a single set of samples is taken only when requested by
the operator (useful when conditions have to be changed and the equipment allowed
to stabilize at a new condition before taking a set of readings).
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Armfield Instruction Manual
The type of logging will default to manual or automatic logging as appropriate to the
type of product being operated.
Manual logging is selected when obtaining performance data from a machine where
conditions need to stabilize after changing appropriate settings. To record a set of set
of data values from each of the measurement sensors click the
main toolbar. One set of data will be recorded each time the
icon from the
icon is clicked.
Automatic logging is selected when transients need to be recorded so that they can
be plotted against time. Click the
the
icon from the toolbar to start recording, click
icon from the toolbar to stop recording.
The type of logging can be configured by clicking Configure in the Sample dropdown menu from the upper toolbar as shown:
In addition to the choice of Manual or Automatic sampling, the parameters for
Automatic sampling can also be set. Namely, the time interval between samples can
be set to the required number of minutes or seconds. Continuous sampling can be
selected, with no time limit or sampling for a fixed duration can be set to the required
number of hours, minutes or seconds as shown:
Tabular Display
To view the Table screen click the View Table icon
click Table from the View dropdown menu as shown:
16
from the main tool bar or
Operation
The data is displayed in a tabular format, similar to the screen as shown:
As the data is sampled, it is stored in spreadsheet format, updated each time the
data is sampled. The table also contains columns for the calculated values.
New sheets can be added to the spreadsheet for different data runs by clicking the
icon from the main toolbar. Sheets can be renamed by double clicking on the
sheet name at the bottom left corner of the screen (initially Run 1, Run 2 etc) then
entering the required name.
For more detailed information about Data Logging and changing the settings within
the software refer to the Help available via the upper toolbar when operating the
software.
Graphical Display
When several samples have been recorded, they can be viewed in graphical format.
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Armfield Instruction Manual
To view the data in Graphical format click the View graph icon
tool bar or click Graph from the View drop-down menu as shown:
from the main
The results are displayed in a graphical format as shown:
(The actual graph displayed will depend on the product selected and the exercise
that is being conducted, the data that has been logged and the parameter(s) that has
been selected).
Powerful and flexible graph plotting tools are available in the software, allowing the
user full choice over what is displayed, including dual y axes, points or lines,
displaying data from different runs, etc. Formatting and scaling is done automatically
by default, but can be changed manually if required.
To change the data displayed on the Graph click Graph Data from the Format
dropdown menu as shown:
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Operation
The available parameters (Series of data) are displayed in the left hand pane as
shown:
Two axes are available for plotting, allowing series with different scaling to be
presented on the same x axis.
To select a series for plotting, click the appropriate series in the left pane so that it is
highlighted then click the appropriate right-facing arrow to move the series into one of
the windows in the right hand pane. Multiple series with the same scaling can be
plotted simultaneously by moving them all into the same window in the right pane.
To remove a series from the graph, click the appropriate series in the right pane so
that it is highlighted then click the appropriate left-facing arrow to move the series into
the left pane.
The X-Axis Content is chosen by default to suit the exercise. The content can be
changed if appropriate by opening the drop down menu at the top of the window.
The format of the graphs, scaling of the axes etc. can be changed if required by
clicking Graph in the Format drop-down menu as shown:
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Armfield Instruction Manual
For more detailed information about changing these settings refer to the Help
available via the upper toolbar when operating the software.
PID Control
Where appropriate, the software associated with some products will include a single
or multiple PID control loops whereby a function on the product can be manually or
automatically controlled using the PC by measuring an appropriate variable and
varying a function such as a heater power or pump speed.
The PID loop can be accessed by clicking the box labelled PID or Control depending
on the particular software:
A PID screen is then displayed as shown:
20
Operation
The Mode of operation always defaults to Manual control and 0% output when the
software is loaded to ensure safe operation of the equipment. If appropriate, the
operator can retain manual operation and simply vary the value from 0 to 100% in the
Manual Output box, then clicking Apply.
Alternatively, the PID loop can be changed to Automatic operation by clicking the
Automatic button. If any of the PID settings need to be changed from the default
values then these should be adjusted individually before clicking the Apply button.
The controller can be restored to manual operation at any time by clicking the
Manual button. The value in the Manual Output box can be changed as required
before clicking the Apply button.
Settings associated with Automatic Operation such as the Setpoint, Proportional
Band, Integral Time, Derivative Time and Cycle Time (if appropriate) can be
changed by the operator as required before clicking the Apply button.
Clicking Calculations displays the calculations associated with the PID loop to aid
understanding and optimization of the loop when changing settings as shown:
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Armfield Instruction Manual
Clicking Settings returns the screen to the PID settings.
Clicking OK closes the PID screen but leaves the loop running in the background.
In some instances the Process Variable, Control variable and Control Action can
be varied to suit different exercises, however, in most instances these boxes are
locked to suit a particular exercise. Where the variables can be changed the options
available can be selected via a drop-down menu.
Advanced Features
The software incorporates advanced features such as the facility to recalibrate the
sensor inputs from within the software without resorting to electrical adjustments of
the hardware. For more detailed information about these advanced functions within
the software refer to the Help available via the upper toolbar when operating the
software.
Operating the Equipment
Before operating the equipment, ensure that the HT36 Extended Tubular Heat
Exchanger and the HT30XC base unit have been assembled and installed as shown
in the separate Installation section.
Connecting the heat exchanger to the service unit
The connections required are as follows:
22
Operation
The connectors are colour coded on both the service unit and the heat exchanger
accessory, with blue for cold water and red for hot water.
Configuring the heat exchanger for countercurrent and cocurrent flow
The cold water supply always enters the heat exchanger at the same end. The hot
water supply may be configured to enter at the same end as the cold water flow
(cocurrent flow), or at the opposite end (countercurrent flow). The direction of the hot
water flow is set by the direction of the hot water pump. This is controlled by the
software, and thus countercurrent flow may be set by selecting a ‘Countercurrent’
software exercise and cocurrent flow by selecting a ‘Cocurrent’ exercise.
Configuring the number of active heat exchanger tubes
The heat exchanger may be used with one, two, three or four active sections. To
configure the exchanger, close each manual valve on the heat exchanger (but NOT
the valves on the HT30XC service unit) by turning the handle at right-angles to the
tube. Then open the appropriate valve as follows:
4 tubes
Open the lower right valve on the exchanger (turn handle in line with tube)
3 tubes
Open the lower left valve on the exchanger
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Armfield Instruction Manual
2 tubes
Open the upper right valve on the exchanger
1 tube
Open the upper left valve on the exchanger
If you are uncertain as to the correct valve settings, run the software and select the
number of active tubes you require. The software will then show an image with the
correct valve settings on the display screen.
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Operation
Configuring the software to match the number of active tubes
The cocurrent and countercurrent exercises in the software (not the Project Work
exercises) include a panel on the left when the number of active sections may be
selected. When one of these options is selected, the software screen displays the
manual valve settings for the cold water circuit, and the inactive outer annuli (i.e.
those through which the cold water does not flow) are dimmed on the display.
Priming the hot water circuit
The hot water circuit should be filled with deionised or demineralised water if
possible, to minimise scale and reduce the need for cleaning. If this is not available
then the water used should be clean. To prime the hot water circuit, fill the hot water
vessel on the HT30XC service unit with water by carefully removing the lid (without
damaging the level sensor attached to it) and pouring in the water. The vessel should
be filled until it covers the tip of the level sensor mounted on the lid of the vessel.
Check that the accessory has been connected to the service unit as described
above, and that the service unit is connected to a suitable PC. Switch on the service
unit using the mains switch on the front of the unit.
Run the HT36 software (any exercise). Switch the service unit from standby to on by
selecting the ‘Power On’ switch on the software mimic diagram screen.
Select the hot water flow rate control button. In the controller window, set the
controller to ‘Manual’ and gradually increase the manual control setting to 100%
using the arrow buttons. Check that the pump starts to operate and water begins to
flow through the hot water system. The hot water vessel may need topping up as
water enters the rest of the system, to keep the tip of the level sensor covered.
Select the heater control button, and set the controller to Automatic with a Set Point
of 80°C (maximum operating temperature- do not operate at this temperature for
more than a few minutes, as prolonged high temperatures may cause softening and
warping of the acrylic outer heat exchanger tube). The heater should begin to
operate. As the water heats, dissolved air will be released from the hot water. The
resulting bubbles, along with any air still remaining in the system after the initial
priming process, will be gradually flushed from the system and into the hot water
vessel as hot water continues to flow through the system. They may be encouraged
to move by gently squeezing the flexible tubing.
Controlling the cold water flow
DO NOT re-adjust the pressure regulator to vary the flow of cold water through the
heat exchanger.
The cold water flow should be adjusted using the cold water flow control valve, which
can be set using the control box on the software screen.
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Armfield Instruction Manual
Controlling the hot water flow
The hot water flow rate can be controlled using the hot water pump, which can be set
using the PID controller in the software. To adjust the controller Set Point or PID
values, click on the hot water ‘Flow’ button on the software screen to open the
controller window, and select ‘Automatic’. For approximate default values of the
controller settings, the Proportional Band may be set to 100%, with an Integral time
of 3s and Derivative time of 0s (these values are set by default and in most cases the
flow rate can be controlled by simply entering the required flow rate in the Set Point
box). The settings required for the exercises included in this manual described in the
individual Laboratory Teaching Exercises and in the software Help Text.
Setting the hot water temperature controller
The hot water temperature can be controlled using the heater (SSR drive) in the hot
water vessel, which is operated using the ‘Heater’ controller in the software.
Selecting this controller button opens the controller window, and the controller should
then be set to Automatic. The Proportional Band should be set to 100%, with Integral
and Derivative times of 0s. The Set Point value (i.e. the required temperature) should
then be entered in the appropriate box.
By default, the heater controller compares the Set Point value to the inlet
temperature of the hot water stream as it enters the heat exchanger, and adjusts the
proportion of heating time until the inlet temperature matches the required Set Point.
The hot water stream always flows through every section of tubing, but depending on
the configuration of the cold water supply, not every section of the heat exchanger
will be part of the heat exchange process. In cocurrent flow, the point at which the hot
water enters the active section of the heat exchanger will differ depending on the
number of active tubes. By default, the controller is set to monitor the temperature T5
(the initial inlet point), which will give reasonable accuracy. However, for greater
accuracy the controller may be reconfigured to monitor the inlet temperature for the
active section of the heat exchanger. To change the temperature monitored, open
the controller window and select the required thermocouple from the ‘Process
Variable’ drop-down list.
Measuring the water temperatures
The water temperatures are displayed on the mimic diagram screen. The values
displayed reflect the configuration selected, i.e. the number of tubes through which
the hot and cold water streams are flowing. The correct number of tubes should be
selected in order to display the relevant temperatures.
Prevention of bubbles in the hot water circuit
Before taking results, ensure that all air bubbles have been expelled from the water
via the priming vessel. Note that as the water is heated for the first time the air
dissolved in the water will continue to be released. It is therefore sensible to heat the
water to the maximum intended operating temperature before carrying out tests at
lower temperatures, as described in Priming the Hot Water Circuit.
The hot water vessel is equipped with a level sensor, which will cut electrical power
to the heating element and pump until the system is primed.
26
Operation
Effect of cold water temperature on heat exchange
The temperature of the water entering the equipment from the mains cold water
supply will affect the range of range of hot and cold water flowrates and/or the
temperature of the hot water that can be achieved when using the equipment.
The heater in the hot water circulator has a nominal rating of 2 kW, limiting the heat
exchange from the hot water stream to the cold water stream to this value. If the
temperature of the hot water will not reach the value set on the PID controller with the
controller providing full power to the heater then this indicates that the limit of the
heater power has been reached. This is not a problem and simply requires an
adjustment to the settings on the equipment.
To operate with the same flowrates then a lower hot water temperature must be
accepted (reduced differential temperature between the two fluid streams). To
operate with an elevated hot water temperature then one or both of the flowrates
must be reduced until the demand on the heater is less than 2 kW.
Some of the settings in the practical training exercises may be affected in this way.
An excessively warm mains water supply will not present any problems since the
temperature difference between the two fluid streams will be reduced. This would
allow the hot water stream to be increased to even higher temperatures than quoted.
An excessively cold mains water supply may mean that the hot water temperature
quoted cannot be achieved because of the increased temperature difference
between the two fluid streams. Operation at reduced hot water temperature or
reduced flowrate must then be accepted.
Connecting HT30X or HT30XC to a PC
The USB port on the right hand side of the console allows the voltage signals from
the sensors, valve and pump to be sent to the USB port of a suitable PC. The
WindowsTM based HT36 software allows control of the HT30XC service unit, and
logging of the sensor outputs from the heat exchanger. The software should be
installed on a PC running Windows™ 98 or later, which must have an available USB
port for connection to the Ht30XC. The software MUST be installed before
connecting the PC to the service unit- installation is described in the product
Installation section.
Once the software has been installed and the PC has been connected to the service
unit with the HT36 accessory in place and connected as described in the Installation
section, the HT36 software should be run (Select Armfield Heat Exchanger Software
from your Start menu and select HT36). The software will then present a selection of
exercises to choose from. The Laboratory Teaching Exercises provided in this
manual describe the appropriate exercise to pick (either Countercurrent or
Cocurrent). If performing independent study work or other project work that does not
use a standard configuration then one of the two Project Work exercises may be
chosen instead.
Use of the software for controlling the equipment and logging the sensor data is
described in the Laboratory Teaching Exercises. This information is also available in
the Software Help Text, accessible from within the software. It is recommended that
students perform at least a representative selection of the Laboratory Teaching
Exercises, to become familiar with the equipment and the use of the software, before
attempting independent project work.
27
Armfield Instruction Manual
Operation of Guest push fittings
Guest push fittings are used on the equipment for convenience when changing the
configuration or removing items for cleaning. The diagrams below show the simple
operation of these fittings:
To connect to a quick release fitting
Align the parallel section of the rigid tube with the loose collet on the quick release
fitting…
and push firmly until the tube stops.
An 'O' ring inside the fitting provides a leak-proof seal between the tube and the
fitting. The collet grips the tube and prevents it from being pulled out from the fitting.
To disconnect from a quick release fitting
Push the loose collet against the body of the quick release fitting while pulling the
tube firmly.
The tube will slide out from the fitting. The tube/fitting can be assembled and
disassembled repeatedly without damage.
28
Equipment Specifications
I/O Port Pin Connections
To allow access to the measurement signals in applications other than when using
the apparatus with an Armfield data logger interface and associated software, the
connections to the 50 way connector are listed below for information:
Pin No
Channel No
Signal Function
Analog Inputs (0-5 V dc):
1
Ch 0
Temperature 1 (0-200°C)
2
Ch 1
Temperature 2 (0-200°C)
3
Ch 2
Temperature 3 (0-200°C)
4
Ch 3
Temperature 4 (0-200°C)
5
Ch 4
Temperature 5 (0-200°C)
6
Ch 5
Temperature 6 (0-200°C)
7
Ch 6
Temperature 7 (0-200°C)
8
Ch 7
Temperature 8 (0-200°C)
9
Ch 8
Temperature 9 (0-200°C)
10
Ch 9
Temperature 10 (0-200°C)
11
Ch 10
Flow F1 (0-3 L/min)
12
Ch 11
Flow F2 (0-1.5 L/min)
13-21
Not used
Analog Outputs (0-5V dc):
22
Not used
23
Ch 0
Hot water pump speed
24
Ch 1
Cold water valve setting
25
Not used
29
Armfield Instruction Manual
Digital Inputs (0-5V dc):
26-27
Not Used
30
Ch 2
21-32
Not used
33
Ch 4
34-37
Not used
Level Monitor
Thermostat Monitor
Digital Outputs (0-5V dc):
38
Ch 0
Power On
39
Ch 1
Watchdog pulse
40
Ch 2
SSR drive
41
Ch 3
Pump direction
42
Digital Ground
43
Ch 4
Stirrer on
44
Ch 5
Aux heater on
47-48
Digital Ground
49-50
Not Used
USB Channel Numbers
The HT36 includes Windows™-compatible software for full remote operation of the
equipment and data logging of all output signals. However, users may prefer to write
their own software for control and data logging, and for the convenience of those
wishing to do so, Armfield has provided additional USB drivers allowing operation of
the equipment via the USB socket on the HT30XC console. The relevant channel
numbers for the HT36 are as follows:
Channel No
Signal Function
Analog Inputs (0-5 V dc):
Channel 0
Temperature T1 (0 to133°C = -5 to +5 V)
Channel 1
Temperature T2 (0 to133°C = -5 to +5 V)
30
Equipment Specifications
Channel 2
Temperature T3 (0 to133°C = -5 to +5 V)
Channel 3
Temperature T4 (0 to133°C = -5 to +5 V)
Channel 4
Temperature T5 (0 to133°C = -5 to +5 V)
Channel 5
Temperature T6 (0 to133°C = -5 to +5 V)
Channel 6
Temperature T7 (0 to133°C = -5 to +5 V)
Channel 7
Temperature T8 (0 to133°C = -5 to +5 V)
Channel 8
Temperature T9 (0 to133°C = -5 to +5 V)
Channel 9
Temperature T10 (0 to133°C = -5 to +5 V)
Channel 10
Hot water flow F hot (0 to 25 L/min = 0 to 5 V)
Channel 11
Cold water flow F cold (0 to 5 L/min = 0 to 5 V)
Analog Outputs (0-5V dc):
Channel 0
Hot water pump speed
Channel 1
Cold water valve setting
Digital Inputs (0-5V dc):
Channel 0
Not Used
Channel 1
Not Used
Channel 2
Level monitor
Channel 4
Thermostat monitor
Digital Outputs (0-5V dc):
Channel 0
Power on required
Channel 1
Watchdog pulse
Channel 2
SSR drive
Channel 3
Pump direction
(1 = on)
(1 pulse every 5 seconds)
(1 = on)
(1 = cocurrent)
Environmental Conditions
This equipment has been designed for operation in the following environmental
conditions. Operation outside of these conditions may result reduced performance,
damage to the equipment or hazard to the operator.
31
Armfield Instruction Manual
a. Indoor use;
b. Altitude up to 2000 m;
c. Temperature 5 °C to 40 °C;
d. Maximum relative humidity 80 % for temperatures up to 31 °C, decreasing
linearly to 50 % relative humidity at 40 °C;
e. Mains supply voltage fluctuations up to ±10 % of the nominal voltage;
f.
Transient over-voltages typically present on the MAINS supply;
Note: The normal level of transient over-voltages is impulse withstand (overvoltage) category II of IEC 60364-4-443;
g. Pollution degree 2.
Normally only nonconductive pollution occurs.
Temporary conductivity caused by condensation is to be expected.
Typical of an office or laboratory environment
32
Routine Maintenance
Responsibility
To preserve the life and efficient operation of the equipment it is important that the
equipment is properly maintained. Regular maintenance of the equipment is the
responsibility of the end user and must be performed by qualified personnel who
understand the operation of the equipment.
General
In addition to regular maintenance the following notes should be observed:
1. The HT30XC service unit should be disconnected from the electrical and
water supplies when not in use.
2. Water should be drained from the inner tubes and outer annulus of the HT36
heat exchanger after use to minimise build up of scale or fouling on the heat
exchange surfaces.
The water can be drained by simply disconnecting the four flexible tubes
connecting the exchanger to the HT30XC service unit.
3. Any build up of scale inside the heat exchanger can be removed by passing a
mild descaler through the exchanger then flushing thoroughly with clean
water.
Any stubborn deposits can be eliminated by manual cleaning having carefully
removed the inner tube from the outer annulus. To remove the metal tube for
cleaning, disconnect the quick release fittings from each end of the metal tube
then pull the tube out of the assembly taking care not to damage the 'O' ring
seals. After cleaning, lubricate the 'O' ring seals with a small amount of wetting
agent before re-inserting the metal tube and replacing the quick release
fittings.
Note: The PVC housing at each end of the acrylic tube is bonded to the acrylic
tube and cannot be removed.
If it is necessary to replace the 'O' ring seals the replacements should have the
following specification:
Material Nitrile rubber
Diameter To suit 3/8" shaft
Section 0.103" section
For reference the Dowty part number is 200-110-4470
33
Laboratory Teaching Exercises
Index to Exercises
Exercise A - Indirect Heating/Cooling Demonstration
Exercise B - Energy Balance and Overall Efficiency
Exercise C - Cocurrent and Countercurrent Flow
Exercise D - Overall Heat Transfer Coefficient
Exercise E: Effect of Flow Rate
Exercise F: Driving Force
Exercise G: Project Work
Nomenclature
Name
Symbol SI Unit
Notes/Calculation
ID of tube
di
m
0.0083
OD of tube
do
m
0.0095
ID of shell
ds
m
0.014
Arithmetic mean diameter of tube
dm
m
Heat transmission length
L
m
0.330 per tube
Heat transfer area
A
m2
 . dm . L
Specific Heat Capacity hot fluid
Cp hot
kJ/kg°K
From table 1
Specific Heat Capacity cold fluid
Cp cold
kJ/kg°K
From table 1
Hot fluid inlet temperature
T1
(°C)
T5 Cocurrent
Hot fluid intermediate temperature 1
T2
(°C)
T4 Cocurrent
Hot fluid intermediate temperature 2
T3
(°C)
Hot fluid intermediate temperature 3
T4
(°C)
T2 Cocurrent
34
Laboratory Teaching Exercises
Hot fluid outlet temperature
T5
(°C)
Cold fluid inlet temperature
T6
(°C)
Cold fluid intermediate temperature 1
T7
(°C)
Cold fluid intermediate temperature 2
T8
(°C)
Cold fluid intermediate temperature 3
T9
(°C)
Cold fluid outlet temperature
T10
(°C)
T1 Cocurrent
Decrease in hot fluid temperature
°C
T1 – T5 (Counter)
Increase in cold fluid temperature
°C
T6 – T10
Driving force, inlet
°C
T1 – T10
Driving force, outlet
°C
T5 – T6
Logarithmic Mean Temperature Difference
°C
Volume flowrate (hot fluid)
qv hot
m3/s
From F hot (litres/min)
Volume flowrate (cold fluid)
qv cold
m3/s
From F cold (litres/min)
Density of hot fluid
 hot
kg/m3
From table 2
Density of cold fluid
 cold
kg/m3
From table 2
Mass flow rate hot fluid
qm hot
kg/s
qv hot x  hot
Mass flow rate cold fluid
qm cold
kg/s
Qv cold x  cold
Heat power emitted from hot fluid
Qe
W
qm h .(Cp) h (T1 – T5)
Heat power absorbed by cold fluid
Qa
W
qm c .(Cp) c (T6 – T10)
Heat power lost (or gained)
Qf
W
Qe - Qa
35
Armfield Instruction Manual
Overall Efficiency

%
Temperature Efficiency hot fluid
 hot
%
Temperature Efficiency cold fluid
 cold
%
Mean Temperature Efficiency
 mean
%
Overall Heat Transfer Coefficient
U
W/m2°C
Reference Tables
Table 1
Specific Heat Capacity of Water (Cp kJ/kg°K)
Table 2
Density of Water ( kg/m3)
36
Laboratory Teaching Exercises
Calculating Reynolds Number
For tubular heat exchangers, when using Reynold’s Number to describe the
characteristics of the exchanger it is usual to calculate it for the process fluid, which
is generally the fluid flowing through the inner tube. It is also possible to calculate a
Reynold’s Number for fluid flowing through the outer shell. This may sometimes be of
interest, for example in systems where one fluid has a high viscosity, which may
provide more efficient heat exchange when directed through the outer shell if the flow
is sufficiently turbulent.
Reynold’s Number for a tubular heat exchanger may be calculated as follows:
For the Inner Tube (hot fluid if configured as described in the manual):
Where  t = Density of fluid in inner tube at temp T tave (kg/m³)
u t = Fluid velocity in the inner tube (m/s)
d i = Tube ID = Inner diameter of tube (m)
= 892.5 x 10-6 m (see dimensions below)
 t = Dynamic viscosity of fluid in inner tube at temp T tave (10-3 m2/s )
where
T tave = Average temperature of fluid within inner tube (K)
For the Outer Tube (cold fluid if configured as described in the manual):
Where  s = Density of fluid in outer shell at temp T save (kg/m³)
37
Armfield Instruction Manual
u s = Fluid velocity in the outer shell (m/s)
d e = Equivalent diameter of shell (m)
(see dimensions below)
= 111.875 x 10-6 m
 t = Dynamic viscosity of fluid in outer shell at temp T save (10-3 m2/s )
where T save = Average temperature of fluid within outer shell (K)
For the HT36, exchanger dimensions are as follows:
Tube ID = 8.925 mm = 0.0008925 m
Tube OD = 9.525 mm = 0.0009525 m
Shell ID = 14 mm = 0.0014 m
The HT36 software calculates Reynold’s number for the hot and cold streams using
the above equation. The software also automatically calculates the density and
kinematic viscosity of the hot and cold fluid streams using the temperature of the
relevant stream averaged over the entire length of the heat exchanger.
38
Exercise A: Indirect Heating/Cooling Demonstration
Objective
To demonstrate indirect heating or cooling by transfer of heat from one fluid stream
to another when separated by a solid wall (fluid to fluid heat transfer)
Method
By measuring the changes in temperature of two separate streams of water flowing
through the inner tube and outer annulus of a tubular (concentric double pipe) heat
exchanger
Equipment Required
HT30XC Computer Compatible Heat Exchanger Service Unit
HT36 Extended Tubular Heat Exchanger
PC running MicrosoftTM Windows 98 or XP with available USB port
Equipment set-up
Before proceeding with the exercise, ensure that the equipment has been prepared
as follows:
Locate the HT36 Extended Tubular Heat Exchanger on the HT30XC Service Unit
and secure it using the knurled fixings.
Connect the ten thermocouples on the heat exchanger to the appropriate sockets on
the front of the HT30XC plinth (labelled T1 – T10).
Connect the hot and cold water supplies as follows:
Ensure that a cold water supply is connected to the inlet of the pressure regulating
valve.
Ensure that the service unit is connected to an electrical supply.
Switch on the front Mains switch.
39
Armfield Instruction Manual
Ensure that the service unit is connected to a suitable PC, and run the HT36
software. Select the Countercurrent exercise.
Switch the service unit from Standby to On by selecting the Power On switch on the
mimic diagram screen.
Prime the hot and cold water circuits as described in the Operation section.
Open the cold water configuration valve for 4 tube configuration.
To open the valve, turn the black valve handle in line with the tube/valve body. Close
the other three cold water configuration valves. To close the valve, turn the black
handle at 90° to the tube/valve body.
Theory/Background
Any temperature difference across the metal tube wall will result in the transfer of
heat between the two fluid streams. The hot water flowing through the inner tube will
be cooled and the cold water flowing through the outer annulus will be heated.
Note: For this demonstration the heat exchanger is configured with the two streams
flowing in opposite directions (countercurrent flow).
Procedure
(Refer to the Operation section if you need details of the instrumentation and how to
operate it.)
In the software, in the ‘Number of Tubes’ box on the left, select ‘4’.
40
Exercise A
Set a cold water flow rate of approximately 1 l/min by adjusting the arrows on the
side of the cold water flow rate display box.
Check the cold water inlet temperature T6 (shown in a display box on the mimic
diagram screen).
Set the temperature controller to a set point approximately 30oC above the cold water
inlet temperature (e.g. if T6 is 15°C then choose a Set Point of 45°C). Check that the
Proportional Band is set to 100, the Integral Time to 3 and the Derivative Time to 0,
and change them accordingly if they do not match these values.
Click on the Heater control box. In the heater controller window, type in the required
value for the Set Point, and then select Automatic control from the selection on the
top right of the window. Check that the Proportional Band is set to 5, the Integral
Time to 200 and the Derivative Time to 0, and change them accordingly if they do not
match these values. Click on ‘Apply’ and then ‘OK’ to close the window.
Set the hot water flow controller to give 3 l/min: click on the ‘Flow’ controller box, and
type the required Set Point (3.0 l/min) into the Set Point box. The Proportional Band
should be 100% and the Integral time should be 3s. The Derivative time should be
0s. Select ‘Automatic’ in the top right of the controller window, then ‘Apply’. Select
‘OK’ to close the controller window.
Allow the heat exchanger to stabilise (monitor the temperatures on the mimic
diagram display).
When the temperatures are stable select the
following:
icon on the top toolbar to record the
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, F hot , F cold .
Adjust the cold water control valve to give 2 litres/min, using the arrow buttons on the
side of the display box.
Create a new results sheet using the
icon.
Check that the correct number of tubes is still selected on the mimic diagram.
Allow the heat exchanger to stabilise then repeat the above readings by selecting the
icon.
If there is ample time in which to take results, then other combinations of hot and cold
water flow rates may be investigated. Remember to create a new results sheet for
each set of results by selecting the
icon.
Open the heater controller window and adjust the controller from ‘Automatic’ to ‘Off’.
Open the hot water pump controller window and change the set point to 0 l/min. Set
the cold water flow control valve to 0%.
Close the manual flow valve for four tube configuration and open the valve for three
tube configuration:
41
Armfield Instruction Manual
In the ‘Number of Tubes’ box on the left of the software screen, select 3.
Repeat the above procedure with the heat exchanger configured for three tubes
(leave the software set to 3 tubes).
Remember to create a new results sheet for each set of results. The software will
record all ten thermocouple outputs, but will use only the sensors on the active
sections for performing calculations.
Set the heater, hot water pump and cold water valve to 0. Close the manual flow
valve for three tubes, and open the valve for two tubes:
Repeat the procedure as before, remembering to create a new results sheet and to
select the correct number of tubes in the software.
Finally, configure the accessory for operation with a single tube:
42
Exercise A
Repeat the above procedure.
Set the heater, pump and cold water flow valve to 0, then select the Power On switch
to set the HT30XC service unit to Standby.
Results and Calculations
For each set of readings your raw data is presented in a table using the following
headings:
Hot fluid volume flowrate
qv hot
(m3/s)
Hot fluid inlet temperature
T1
(°C)
Hot fluid mid temperature 1
T2
(°C)
Hot fluid mid temperature 2
T3
(°C)
Hot fluid mid temperature 3
T4
(°C)
Hot fluid outlet temperature
T5
(°C)
Cold fluid volume flowrate
qv cold
(m3/s)
Cold fluid inlet temperature
T6
(°C)
Cold fluid mid temperature 1
T7
(°C)
Cold fluid mid temperature 2
T8
(°C)
Cold fluid mid temperature 3
T9
(°C)
Cold fluid outlet temperature
T10
(°C)
From F hot (litres/min)
From F cold (litres/min)
You should also estimate and record the experimental errors for these
measurements.
43
Armfield Instruction Manual
For each set of readings your derived results are also tabulated under the following
headings:
Reduction in hot fluid temperature
= T1 – T5 (oC)
Increase in cold fluid temperature
= T10 – T6 (oC)
Estimate the cumulative influence of the experimental errors on your calculated
values for
and
.
Compare the changes in temperature at the different flowrates.
Conclusion
You have demonstrated how, using a tubular heat exchanger, a stream of cold fluid
can be heated by indirect contact with another fluid stream at a higher temperature
(the fluid streams being separated by a wall which conducts heat). This transfer of
heat results in a cooling of the hot fluid.
and
when the flow of cold water is
Comment on the changes in
increased. The consequence of these changes will be investigated in a later
exercise.
Comment on the effect of differing numbers of tubes (and therefore differing lengths
of tubular heat exchanger).
Note: To save time Exercise B can be carried out using the readings obtained from
this exercise.
44
Exercise B: Energy Balance and Overall Efficiency
Objective
To perform an energy balance across a Tubular Heat Exchanger and calculate the
Overall Efficiency at different fluid flowrates.
Method
By measuring the changes in temperature of the two separate fluid streams in a
tubular heat exchanger and calculating the heat energy transferred to/from each
stream to determine the Overall Efficiency.
Equipment Required
As Exercise A.
Optional Equipment
As Exercise A.
Equipment set-up
If using the results from Exercise A then the equipment is not required.
If previous results are not available refer to the Set-up and Procedure sections of
Exercise A.
Theory/Background
Note: For this demonstration the heat exchanger is configured for countercurrent
flow (the two fluid streams flowing in opposite directions).
Mass flow rate (qm) = Volume flow rate (qv) x Density of fluid () (kg/s)
Heat power (Q) = Mass flow rate (qm) x specific heat (Cp) x change in temperature
(W)
Therefore:
Heat power emitted from hot fluid Q e = qm h .(Cp) h (T1 – T5) (W)
Heat power absorbed by cold fluid Q a = qm c .(Cp) c (T6 – T10) (W)
Heat power lost (or gained) Q f = Q e - Q a (W)
Overall Efficiency
(%)
Theoretically Q e and Q a should be equal. In practice these differ due to heat losses
or gains to/from the environment.
Note: In this exercise the cold fluid is circulated through the outer annulus, if the
average cold fluid temperature is above the ambient air temperature then heat will be
lost to the surroundings resulting in <100%. If the average cold fluid temperature is
below the ambient temperature then heat will be gained resulting in >100%.
45
Armfield Instruction Manual
Procedure
Use the results obtained from Exercise A.
Results and Calculations
For each set of readings your raw data is presented in a table using the following
headings:
Hot fluid volume flowrate
qv hot
(m3/s)
Hot fluid inlet temperature
T1
(°C)
Hot fluid mid temperature 1
T2
(°C)
Hot fluid mid temperature 2
T3
(°C)
Hot fluid mid temperature 3
T4
(°C)
Hot fluid outlet temperature
T5
(°C)
Cold fluid volume flowrate
qv cold
(m3/s)
Cold fluid inlet temperature
T6
(°C)
Cold fluid mid temperature 1
T7
(°C)
Cold fluid mid temperature 2
T8
(°C)
Cold fluid mid temperature 3
T9
(°C)
Cold fluid outlet temperature
T10
(°C)
From F hot (litres/min)
From F cold (litres/min)
You should also estimate and record the experimental errors for these
measurements.
For each set of readings, the software calculates the following variables. These may
also be obtained from the Reference Tables:
Specific heat of hot
fluid
Cp h
kJ/kg°K (From table 1 using average hot water
temperature)
Specific heat of cold
fluid
Cp c
kJ/kg°K (From table 1 using average cold water
temperature)
Density of hot fluid
h
kg/m3 (From table 2 using average hot water
temperature)
Density of cold fluid
c
kg/m3 (From table 2 using average cold water
temperature)
46
Exercise B
For each set of readings, your derived results are also tabulated under the following
headings:
Mass flow rate (hot fluid)
qm h
(kg/s)
Mass flow rate (cold fluid)
qm c
(kg/s)
Heat power emitted
Qe
(W)
Heat power absorbed
Qa
(W)
Heat power lost
Qf
(W)
Overall Efficiency

(%)
Estimate the cumulative influence of the experimental errors on your calculated
values for Q e , Q a , Q f and .
Compare the heat power emitted from/absorbed by the two fluid streams at the
different flowrates.
Conclusion
Explain any difference between Q e and Q a in your results.
Comment on the effects of the increase in the cold fluid flowrate.
Exercise C should be carried out on completion of this exercise.
47
Exercise C: Cocurrent and Countercurrent Flow
Objective
To demonstrate the differences between cocurrent flow (hot and cold flows in same
direction) and countercurrent flow (hot and cold flows in the opposite direction) and
the effect on the heat transferred, temperature efficiencies and temperature profiles
through a Tubular Heat Exchanger.
Method
By measuring the temperatures of the two fluid streams. Using the temperature
changes and differences, to calculate the heat energy transferred and the
temperature efficiencies.
Equipment Required
HT30XC Computer Compatible Heat Exchanger Service Unit
HT36 Extended Tubular Heat Exchanger
PC running MicrosoftTM Windows 98 or XP with available USB port
Equipment set-up
Before proceeding with the exercise, ensure that the equipment has been prepared
as follows:
Locate the HT36 Extended Tubular Heat Exchanger on the HT30XC Service Unit
and secure it using the knurled fixings.
Connect the ten thermocouples on the heat exchanger to the appropriate sockets on
the front of the HT30XC plinth (labelled T1 – T10).
Connect the hot and cold water supplies as follows:
Ensure that a cold water supply is connected to the inlet of the pressure regulating
valve.
Ensure that the service unit is connected to an electrical supply.
48
Exercise C
Switch on the front Mains switch.
Ensure that the service unit is connected to a suitable PC, and run the HT36
software. Select the Countercurrent exercise.
Switch the service unit from Standby to On by selecting the Power On switch on the
mimic diagram screen.
Prime the hot and cold water circuits as described in the Operation section.
Open the cold water flow control valve to give a 4 tube configuration (turn the black
valve handle in line with the tube/valve body).
Close the other three manual valves on the accessory configuration (turn the black
valve handles at right angles to the tube/valve body).
Theory/Background
Countercurrent operation
When the heat exchanger is operated with countercurrent flow, the hot and cold fluid
streams flow in opposite directions across the heat transfer surface (the two fluid
streams enter the heat exchanger at opposite ends).
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Armfield Instruction Manual
From the previous exercises:
Reduction in hot fluid temperature
= T1 – T5 (°C)
Increase in cold fluid temperature
= T10 – T6 (°C)
Heat power emitted from hot fluid Q e = qm h .Cp h (T1 – T5) (W)
A useful measure of the heat exchanger performance is the temperature efficiency of
each fluid stream. The temperature change in each fluid stream is compared with the
maximum temperature difference between the two fluid streams giving a comparison
with an exchanger of infinite size.
(%)
Temperature efficiency for hot fluid
(%)
Temperature efficiency for cold fluid
Mean Temperature Efficiency
(%)
Cocurrent operation
When the heat exchanger is connected for cocurrent operation the hot and cold fluid
streams flow in the same direction across the heat transfer surface (the two fluid
streams enter the heat exchanger at the same end).
50
Exercise C
Reduction in hot fluid temperature
= T5 – T1 (°C)
Increase in cold fluid temperature
= T10 – T6 (°C)
Heat power emitted from hot fluid Q e = qm h .Cp h (T5 – T1)(W)
(%)
Temperature efficiency for hot fluid
(%)
Temperature efficiency for cold fluid
Mean Temperature Efficiency
(%)
Procedure
(Refer to the Operation section if you need details of the instrumentation and how to
operate it.)
In the software, in the ‘Number of Tubes’ box on the left, select ‘4’.
Set a cold water flow rate of 1 l/min by adjusting the arrows on the side of the cold
water flow rate display box.
Check the cold water inlet temperature T10 (shown in a display box on the mimic
diagram screen).
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Armfield Instruction Manual
Set the temperature controller to a set point approximately 30oC above the cold water
inlet temperature (e.g. if T10 is 15°C then choose a Set Point of 45°C):
Click on the Heater control box. In the heater controller window, type in the required
value for the Set Point, and then select Automatic control from the selection on the
top right of the window. Check that the Proportional Band is set to 5, the Integral
Time to 200 and the Derivative Time to 0, and change them accordingly if they do not
match these values. Click on ‘Apply’ and then ‘OK’ to close the window.
Set the hot water flow controller to give 2 l/min: click on the ‘Flow’ controller box, and
type the required Set Point (2.0 l/min) into the Set Point box. The Proportional Band
should be 100% and the Integral time should be 3s. The Derivative time should be
0s. Select ‘Automatic’ in the top right of the controller window, then ‘Apply’. Select
‘OK’ to close the controller window.
Allow the heat exchanger to stabilise (monitor the temperatures on the mimic
diagram display).
When the temperatures are stable select the
following:
icon on the top toolbar to record the
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, F hot , F cold .
Open the heater controller window and adjust the controller from ‘Automatic’ to ‘Off’.
Open the hot water pump controller window and change the set point to 0 l/min. Set
the cold water flow control valve to 0%.
Save your results sheet by selecting ‘Save’ from the ‘File’ menu of the software. Save
it with a file name such as ‘HT36 Exercise C Countercurrent’.
If a printer is available then you may find it useful to print a graph of the hot and cold
water temperatures against the distance from the hot water inlet (the default graph
for the software). To print a graph, select the graph icon (
), then the print icon.
Select ‘Load New Experiment’ from the ‘File’ menu, and select the Cocurrent
exercise.
In the ‘Number of Tubes’ box on the left, select ‘4’.
Set a cold water flow rate of 1 l/min, a hot water flow rate of 2 l/min, and the same hot
water temperature set point as for the countercurrent part of this exercise.
When the temperatures are stable select the
following:
icon on the top toolbar to record the
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, F hot , F cold .
Print a graph of the cocurrent results, and save your results sheet with a title such as
‘HT36 Exercise C Cocurrent’.
If time permits, the exercise may be repeated with 3, 2 and 1 heat exchanger tubes
by adjusting the manual flow valves (as described in the Operation section).
Remember to select the correct number of tubes within the software to match the
valve configuration on the hardware.
52
Exercise C
Results and Calculations
For each set of readings your raw data is presented in a table using the following
headings:
Hot fluid volume flowrate
qv hot
(m3/s)
From F hot (l/min)
Hot fluid inlet temperature
T1
(°C)
(T5 Cocurrent)
Hot fluid intermediate temperature 1
T2
(°C)
(T4 Cocurrent)
Hot fluid intermediate temperature 2
T3
(°C)
Hot fluid intermediate temperature 3
T4
(°C)
(T2 Cocurrent)
Hot fluid outlet temperature
T5
(°C)
(T1 Cocurrent)
Cold fluid volume flowrate
qv cold (m3/s)
Cold fluid inlet temperature
T6
(°C)
Cold fluid intermediate temperature 1
T7
(°C)
Cold fluid intermediate temperature 2
T8
(°C)
Cold fluid intermediate temperature 3
T9
(°C)
Cold fluid outlet temperature
T10
(°C)
From F cold (l/min)
Note: In cocurrent flow T1 is the hot fluid outlet temperature and T5 is the hot fluid
inlet temperature.
You should also estimate the experimental errors for these measurements.
For each set of readings plot the temperatures at inlet, mid positions and outlet
against position then estimate the profile of each stream through the exchanger.
For each set of readings, the software obtains the following variables. These may
also be obtained from the Reference Tables:
Specific heat of hot fluid
Cp h kJ/kgoK (From table 1 using average temperature)
Density of hot fluid
h
kg/m3 (From table 2 using average temperature)
For each set of readings your derived results are also tabulated; the following
headings are used:
Reduction in hot fluid temperature
(oC)
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Armfield Instruction Manual
(oC)
Increase in cold fluid temperature
Heat power emitted from hot fluid
Qe
(W)
Temperature efficiency for hot fluid
h
(%)
Temperature efficiency for cold fluid
c
(%)
Mean temperature efficiency
m
(%)
Estimate the cumulative influence of the experimental errors on your calculated
values for each of the above temperature differences and efficiencies.
Compare each set of calculated values.
Conclusion
Your results from this exercise should indicate clearly the basic differences between
Cocurrent and Countercurrent flow through the tubular heat exchanger. The selection
of the best arrangement for a particular application depends on many parameters
such as Overall Heat Transfer Coefficient, Logarithmic Mean Temperature
Difference, Fluid Flowrate etc. These will be explained and investigated in later
exercises.
Comment on the change in
and
from cocurrent to countercurrent operation.
when the heat exchanger is converted
Comment on the differences between the hot and cold fluid temperature efficiency for
any given configuration and explain the changes in efficiency when the configuration
is changed from cocurrent to countercurrent operation.
Note: To save time Exercise D can be carried out using the readings obtained from
this exercise.
54
Exercise D: Overall Heat Transfer Coefficient
Objective
To determine the Overall Heat Transfer Coefficient for a Tubular Heat Exchanger
using the Logarithmic Mean Temperature Difference to perform the calculations (for
cocurrent and countercurrent flow).
Method
By measuring the temperatures of the two fluid streams and calculating the LMTD
from which the overall heat transfer coefficient can be calculated for each flow
configuration.
Equipment Required
As Exercise C.
Optional Equipment
As Exercise C
Equipment set-up
If using the results from Exercise C then the equipment is not required.
If previous results are not available refer to the Set-up and Procedure sections of
Exercise C.
Theory/Background
Countercurrent Flow
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Armfield Instruction Manual
Cocurrent Flow
Heat power emitted from hot fluid Q e = qm h .Cp h (T1 – T5) (W)
Note: To eliminate the effect of heat losses/gains in the cold water stream the heat
emitted from the hot fluid stream will be used in the calculations.
Because the temperature difference between the hot and cold fluid streams varies
along the length of the heat exchanger it is necessary to derive an average
temperature difference (driving force) from which heat transfer calculations can be
performed. This average temperature difference is called the Logarithmic Mean
Temperature Difference (LMTD)
.
where
LMTD
= (T1 – T10)
= (T5 – T6) (oC)
Note: This equation cannot produce a result for the case where
=
.
(oC)
LMTD
In this example the equation for LMTD is the same for both countercurrent and
cocurrent operation because the temperature measurement points are fixed on the
exchanger. Two different equations will result if the temperature points are related to
fluid inlets and outlets.
The heat transmission area in the exchanger must be calculated using the arithmetic
mean diameter of the inner tube.
(m)
Arithmetic mean diameter
Heat transmission length
Heat transmission area
L
(m)
A =  . dm . L (m2)
(d m can be used since r2/r1<1.5 otherwise the logarithmic mean radius d lm must be
used)
Overall Heat Transfer Coefficient
Procedure
Use the results obtained from Exercise C.
56
(W/m2K)
Exercise D
Results and Calculations
Technical data:
Inner tube inside diameter
d i = 0.0083
(m)
Inner tube outside diameter
d o = 0.0095
(m)
Heat transmission length
L = 0.330 per tube(1.32 total)
(m)
Your raw data is presented in a table using the following headings:
Hot fluid volume flowrate
qv hot
(m3/s)
From F hot (l/min)
Hot fluid inlet temperature
T1
(°C)
(T5 Cocurrent)
Hot fluid intermediate temperature 1
T2
(°C)
(T4 Cocurrent)
Hot fluid intermediate temperature 2
T3
(°C)
Hot fluid intermediate temperature 3
T4
(°C)
(T2 Cocurrent)
Hot fluid outlet temperature
T5
(°C)
(T1 Cocurrent)
Cold fluid volume flowrate
qv cold (m3/s)
Cold fluid inlet temperature
T6
(°C)
Cold fluid intermediate temperature 1
T7
(°C)
Cold fluid intermediate temperature 2
T8
(°C)
Cold fluid intermediate temperature 3
T9
(°C)
Cold fluid outlet temperature
T10
(°C)
Arithmetic mean diameter
dm
(m)
Heat transmission area
A
(m2)
From F hot (l/min)
Note: In cocurrent flow T1 is the hot fluid outlet temperature and T5 is the hot fluid
inlet temperature.
You should estimate the experimental errors for these measurements.
For each set of readings, the software calculates the following variables. These may
also be obtained from the Reference Tables:
Specific heat of hot fluid
Cp h kJ/kg°K (From table 1 using average temperature)
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Armfield Instruction Manual
Density of hot fluid
h
kg/m3 (From table 2 using average temperature)
For each set of readings, your derived results are tabulated; the following headings
are used:
Temperature difference
(oC)
Temperature difference
(oC)
Mass flow rate (hot fluid)
qm h
(kg/s)
Heat power emitted from hot fluid
Qe
(W)
LMTD
(°C)
Overall heat transfer coefficient
U
(W/m2K)
Estimate the cumulative influence of the experimental errors on your calculated
values for
and U.
Compare your calculated values for
and U for each set of readings.
Conclusion
You have now been introduced to the method for calculating the Overall Heat
Transfer Coefficient for a heat exchanger. This is the most important characteristic of
a heat exchanger. The effect of fluid flowrates and temperature differences between
the hot and cold fluid streams will be investigated in later exercises.
Comment on the differences in
and
when the heat exchanger is configured
for cocurrent and countercurrent flow. Comment on the resulting values for
its effect on U.
and
Comment on any difference between the Overall Heat Transfer Coefficient for the
same heat exchanger in cocurrent and countercurrent flow (with all other variables
the same).
If you have conducted a similar exercise using a plate heat exchanger (HT32) or
shell and tube heat exchanger (HT33) compare the performances and comment on
the differences.
Exercise E should be carried out on completion of this exercise.
58
Exercise E: Effect of Flow Rate
Objective
To investigate the effect of changes in hot and cold fluid flow rate on the
Temperature Efficiencies and Overall Heat Transfer Coefficient.
Method
By measuring the fluid temperatures at different combinations of hot and cold fluid
flowrate then calculating the corresponding Overall Heat Transfer Coefficient.
Equipment Required
HT30XC Computer Compatible Heat Exchanger Service Unit
HT36 Extended Tubular Heat Exchanger
PC running MicrosoftTM Windows 98 or XP with available USB port
Equipment set-up
Before proceeding with the exercise, ensure that the equipment has been prepared
as follows:
Locate the HT36 Extended Tubular Heat Exchanger on the HT30XC Service Unit
and secure it using the knurled fixings.
Connect the ten thermocouples on the heat exchanger to the appropriate sockets on
the front of the HT30XC plinth (labelled T1 – T10).
Connect the hot and cold water supplies as follows:
Ensure that a cold water supply is connected to the inlet of the pressure regulating
valve.
Ensure that the service unit is connected to an electrical supply.
Switch on the front Mains switch.
Ensure that the service unit is connected to a suitable PC, and run the HT36
software. Select the Countercurrent exercise.
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Armfield Instruction Manual
Switch the service unit from Standby to On by selecting the Power On switch on the
mimic diagram screen.
Prime the hot and cold water circuits as described in the Operation section.
Open the cold water flow control valve to give a 4 tube configuration (turn the black
valve handle in line with the tube/valve body).
Close the other three manual valves on the accessory configuration (turn the black
valve handles at right angles to the tube/valve body).
Theory/Background
Refer to Teaching Exercises C & D for details of the relevant theory relating to the
calculation of the Temperature efficiencies and Overall Heat Transfer Coefficients.
Procedure
(Refer to the Operation section if you need details of the instrumentation and how to
operate it.)
In the software, in the ‘Number of Tubes’ box on the left, select ‘4’.
Set a cold water flow rate of 1 l/min by adjusting the arrows on the side of the cold
water flow rate display box.
Check the cold water inlet temperature T10 (shown in a display box on the mimic
diagram screen).
Set the temperature controller to a set point approximately 30oC above the cold water
inlet temperature (e.g. if T10 is 15°C then choose a Set Point of 45°C):
Click on the Heater control box. In the heater controller window, type in the required
value for the Set Point, and then select Automatic control from the selection on the
top right of the window. Check that the Proportional Band is set to 5, the Integral
Time to 200 and the Derivative Time to 0, and change them accordingly if they do not
match these values. Click on ‘Apply’ and then ‘OK’ to close the window.
Set the hot water flow controller to give 1 l/min: click on the ‘Flow’ controller box, and
type the required Set Point (1.0 l/min) into the Set Point box. The Proportional Band
should be 100% and the Integral time should be 3s. The Derivative time should be
0s. Select ‘Automatic’ in the top right of the controller window, then ‘Apply’. Select
‘OK’ to close the controller window.
60
Exercise E
Allow the heat exchanger to stabilise (monitor the temperatures on the mimic
diagram display).
When the temperatures are stable select the
following:
icon on the top toolbar to record the
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, F hot , F cold .
Select the
icon to create a new results sheet.
Repeat the above for different settings of the hot and cold fluid volume flowrate as
follows. Remember to create a new results sheet for each set of results, and to check
that the software is still configured for the correct number of heat exchanger tubes.
F hot (litres/min)
F cold (litres/min)
2
1
3
1
2
2
1
2
1
3
Note: The above results are all obtained with turbulent flow through the heat
exchanger (Reynolds number >2000). If time permits, the effect of laminar flow can
be investigated by operating the heat exchanger with flowrates below 0.4 litres/min.
As the flow measurement will not be as accurate at these settings it is suggested that
the volume flowrate is checked using a measuring cylinder and stopwatch (to
intercept the flow to drain).
Open the heater controller window and adjust the controller from ‘Automatic’ to ‘Off’.
Open the hot water pump controller window and change the set point to 0 l/min. Set
the cold water flow control valve to 0%.
Save your results sheet by selecting ‘Save’ from the ‘File’ menu of the software. Save
it with a file name such as ‘HT36 Exercise E Countercurrent’.
If a printer is available then you may find it useful to print a graph of the hot and cold
water temperatures against the distance from the hot water inlet for each set of
results. To print a graph, select the graph icon (
), then the graph configuration
icon (
). Highlight the results on the right and move them all to the left using the
red arrow key. Select the first set of results (run 1 hot and cold), and move them back
onto the y-axis plot with the arrow key. ‘Apply’ and close the print configuration
window, then select the print icon. Repeat this process for each set of results.
Select ‘Load New Experiment’ from the ‘File’ menu, and select the Cocurrent
exercise.
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Armfield Instruction Manual
In the ‘Number of Tubes’ box on the left, select ‘4’.
Set a cold water flow rate of 1 l/min, a hot water flow rate of 1 l/min, and the same hot
water temperature set point as for the countercurrent part of this exercise.
When the temperatures are stable select the
the following:
icon on the top toolbar to record
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, F hot , F cold .
Select the
icon to create a new results sheet.
Repeat the above for different settings of the hot and cold fluid volume flowrate as
follows. Remember to create a new results sheet for each set of results and to check
that the software is still configured for the correct number of tubes.
F hot (litres/min)
F cold (litres/min)
2
1
3
1
2
2
1
2
1
3
Note: The above results are all obtained with turbulent flow through the heat
exchanger (Reynolds number >2000). If time permits, the effect of laminar flow can
be investigated by operating the heat exchanger with flowrates below 0.4 litres/min.
As the flow measurement will not be as accurate at these settings it is suggested that
the volume flowrate is checked using a measuring cylinder and stopwatch (to
intercept the flow to drain).
Open the heater controller window and adjust the controller from ‘Automatic’ to ‘Off’.
Open the hot water pump controller window and change the set point to 0 l/min. Set
the cold water flow control valve to 0%. Set the HT30XC service unit back to Standby
by selecting the Power On switch on the mimic diagram.
Save your results sheet by selecting ‘Save’ from the ‘File’ menu of the software. Save
it with a file name such as ‘HT36 Exercise E Cocurrent’.
Print your results as for the countercurrent section of this experiment.
If time permits, the exercise may be repeated with 3, 2 and 1 heat exchanger tubes
by adjusting the manual flow valves (as described in the Operation section).
Remember to select the correct number of tubes to match the configuration of the
valves on the hardware.
62
Exercise E
Results and Calculations
Technical data:
Inner tube inside diameter
d i = 0.0083
(m)
Inner tube outside diameter
d o = 0.0095
(m)
Heat transmission length
L = 0.330 per tube (1.32 total)
(m)
For each set of readings your raw data is presented in a table using the following
headings:
Hot fluid volume flowrate
qv hot
(m3/s)
From F hot (l/min)
Hot fluid inlet temperature
T1
(°C)
(T5 in cocurrent)
Hot fluid intermediate temperature 1
T2
(°C)
(T4 in cocurrent)
Hot fluid intermediate temperature 2
T3
(°C)
Hot fluid intermediate temperature 3
T4
(°C)
(T2 in cocurrent)
Hot fluid outlet temperature
T5
(°C)
(T1 in cocurrent)
Cold fluid volume flowrate
qv cold
(m3/s)
From F cold (l/min)
Cold fluid inlet temperature
T6
(°C)
Cold fluid intermediate temperature 1
T7
(°C)
Cold fluid intermediate temperature 2
T8
(°C)
Cold fluid intermediate temperature 3
T9
(°C)
Cold fluid outlet temperature
T10
(°C)
Note: In cocurrent flow T1 is the hot fluid outlet temperature and T5 is the hot fluid
inlet temperature.
You should estimate the experimental errors for these measurements.
For each set of readings, the software calculates the following variables. These may
also be obtained from the Reference Tables:
Specific heat of hot
fluid
Cp h
kJ/kg°K (From table 1 using T2 as the average
temperature)
Density of hot fluid
h
kg/m3 (From table 2 using T2 as the average
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Armfield Instruction Manual
temperature)
For each set of readings your derived results are also tabulated; the following
headings are used:
Mass flow rate (hot fluid)
Qm h
(kg/s)
Heat power emitted from hot fluid
Qe
(W)
LMTD
(°C)
Overall Heat Transfer Coefficient
U
(W/m2°C)
Temperature efficiency for hot fluid
h
(%)
Temperature efficiency for cold fluid
c
(%)
Mean temperature efficiency
m
(%)
Estimate the cumulative influence of the experimental errors on your calculated
values for
, U and the temperature efficiencies.
Compare the results for U and the temperature efficiencies at the different hot and
cold fluid flowrates.
Conclusion
Your results from this exercise should indicate clearly the different effects of hot and
cold flowrate on the Overall Heat Transfer Coefficient and temperature efficiencies.
Comment on the effects of changing the hot and cold fluid flowrates.
If additional results were obtained at very low cold fluid flowrate, comment on the
effect of laminar flow through the annulus.
If additional results for 1, 2 and 3 tubes were obtained, compare the results for
differing lengths of heat exchanger.
If you have conducted a similar exercise using a plate heat exchanger (HT32) or
shell and tube heat exchanger (HT33) compare the performances and comment on
the differences.
Exercise F should be carried out on completion of this exercise.
64
Exercise F: Driving Force
Objective
To investigate the effect of driving force with cocurrent and countercurrent flow.
Method
By measuring the fluid temperatures at different hot fluid inlet temperatures then
calculating the corresponding Temperature Efficiencies and Overall Heat Transfer
Coefficients to determine the effect of the driving force.
Equipment Required
HT30XC Computer Compatible Heat Exchanger Service Unit
HT36 Extended Tubular Heat Exchanger
PC running MicrosoftTM Windows 98 or XP with available USB port
Equipment set-up
Before proceeding with the exercise, ensure that the equipment has been prepared
as follows:
Locate the HT36 Extended Tubular Heat Exchanger on the HT30XC Service Unit
and secure it using the knurled fixings.
Connect the ten thermocouples on the heat exchanger to the appropriate sockets on
the front of the HT30XC plinth (labelled T1 – T10).
Connect the hot and cold water supplies as follows:
Ensure that a cold water supply is connected to the inlet of the pressure regulating
valve.
Ensure that the service unit is connected to an electrical supply.
Switch on the front Mains switch.
Ensure that the service unit is connected to a suitable PC, and run the HT36
software. Select the Countercurrent exercise.
65
Armfield Instruction Manual
Switch the service unit from Standby to On by selecting the Power On switch on the
mimic diagram screen.
Prime the hot and cold water circuits as described in the Operation section.
Open the cold water flow control valve to give a 4 tube configuration (turn the black
valve handle in line with the tube/valve body).
Close the other three manual valves on the accessory configuration (turn the black
valve handles at right angles to the tube/valve body).
Theory/Background
Refer to Teaching Exercises C and D for details of the relevant theory relating to the
calculation of the Temperature Efficiencies and Overall Heat Transfer Coefficients.
Procedure
(Refer to the Operational section if you need details of the instrumentation and how
to operate it.)
In the software, in the ‘Number of Tubes’ box on the left, select ‘4’.
Set a cold water flow rate of 1 l/min by adjusting the arrows on the side of the cold
water flow rate display box.
Check the cold water inlet temperature T10 (shown in a display box on the mimic
diagram screen).
Set the temperature controller to a set point approximately 15oC above the cold water
inlet temperature (e.g. if T10 is 15°C then choose a Set Point of 30°C):
Click on the Heater control box. In the heater controller window, type in the required
value for the Set Point, and then select Automatic control from the selection on the
top right of the window. Check that the Proportional Band is set to 5, the Integral
Time to 200 and the Derivative Time to 0, and change them accordingly if they do not
match these values. Click on ‘Apply’ and then ‘OK’ to close the window.
Set the hot water flow controller to give 2 l/min: click on the ‘Flow’ controller box, and
type the required Set Point (2.0 l/min) into the Set Point box. The Proportional Band
should be 100% and the Integral time should be 3s. The Derivative time should be
0s. Select ‘Automatic’ in the top right of the controller window, then ‘Apply’. Select
‘OK’ to close the controller window.
66
Exercise F
Allow the heat exchanger to stabilise (monitor the temperatures on the mimic
diagram display).
When the temperatures are stable select the
following:
icon on the top toolbar to record the
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, F hot , F cold .
Select the
icon to create a new results sheet.
Repeat the above at different Set Points for the hot water temperature controller,
increasing in steps of 5oC until the limit on the heater/controller is reached
(Approximately 50°C depending on the cold fluid inlet temperature).
Open the heater controller window and adjust the controller from ‘Automatic’ to ‘Off’.
Open the hot water pump controller window and change the set point to 0 l/min. Set
the cold water flow control valve to 0%.
Save your results sheet by selecting ‘Save’ from the ‘File’ menu of the software. Save
it with a file name such as ‘HT36 Exercise E Countercurrent’.
If a printer is available then you may find it useful to print a graph of the hot and cold
water temperatures against the distance from the hot water inlet for each set of
results. To print a graph, select the graph icon (
), then the graph configuration
icon (
). Highlight the results on the right and move them all to the left using the
red arrow key. Select the first set of results (run 1 hot and cold), and move them back
onto the y-axis plot with the arrow key. ‘Apply’ and close the print configuration
window, then select the print icon. Repeat this process for each set of results.
If there is plenty of time then the procedure may be repeated for different flow rates,
different hot water Set Point temperatures, and (if available) different cold water inlet
flow temperatures. The maximum cold water outlet temperature achievable is limited
by the maximum heater power input, and will depend on the combination of fluid flow
rates, cold water inlet temperature, and the number of heat exchanger tubes used.
With four tubes at maximum cold water flow rate, the maximum temperature gain in
the cold fluid may be as low as 5 to 10°C.
Select ‘Load New Experiment’ from the ‘File’ menu, and select the Cocurrent
exercise.
In the software, in the ‘Number of Tubes’ box on the left, select ‘4’.
Set a cold water flow rate of 1 l/min, a hot water flow rate of 2 l/min, and the same
initial hot water temperature set point as for the countercurrent part of this exercise.
When the temperatures are stable select the
following:
icon on the top toolbar to record the
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, F hot , F cold .
Repeat the above for different settings of the hot water temperature controller,
increasing in steps of 5oC until the limit on the heater controller is reached.
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Armfield Instruction Manual
If there is plenty of time then the procedure may be repeated for different flow rates,
different hot water Set Point temperatures, and (if available) different cold water inlet
flow temperatures. Similar but not identical limitations apply to the maximum
attainable heat exchange when operating under cocurrent flow. Students may wish to
investigate how these limitations compare to those in countercurrent flow.
The exercise can also be repeated with 1, 2, and 3 heat exchanger tubes used.
Remember to set the appropriate number of tubes within the software to suit the
valve settings on the hardware.
Results and Calculations
Technical data:
Inner tube inside diameter d i = 0.0083
(m)
Inner tube outside diameter d o = 0.0095 (m)
Heat transmission length L = 0.330 per tube (1.32 total) (m)
For each set of readings your raw data is presented in a table using the following
headings:
Hot fluid volume flowrate
qv hot
(m3/s)
From F hot (l/min)
Hot fluid inlet temperature
T1
(°C)
(T5 in cocurrent)
Hot fluid intermediate temperature 1
T2
(°C)
(T4 in cocurrent)
Hot fluid intermediate temperature 2
T3
(°C)
Hot fluid intermediate temperature 3
T4
(°C)
(T2 in cocurrent)
Hot fluid outlet temperature
T5
(°C)
(T1 in cocurrent)
Cold fluid volume flowrate
qv cold (m3/s)
Cold fluid inlet temperature
T6
(°C)
Cold fluid intermediate temperature 1
T7
(°C)
Cold fluid intermediate temperature 2
T8
(°C)
Cold fluid intermediate temperature 3
T9
(°C)
Cold fluid outlet temperature
T10
(°C)
From F cold (l/min)
Note: In cocurrent flow T1 is the hot fluid outlet temperature and T5 is the hot fluid
inlet temperature.
You should also estimate the experimental errors for these measurements.
68
Exercise F
For each set of readings, the software calculates the following variables. These may
also be obtained from the Reference Tables:
Specific heat of hot
fluid
Cp h
kJ/kg°K (From table 1 using average hot water
temperature)
Density of hot fluid
h
kg/m3 (From table 2 using T2 average hot water
temperature)
For each set of readings your derived results are also tabulated; the following
headings are used:
Mass flow rate (hot fluid)
Qm h
(kg/s)
Heat power emitted from hot fluid
Qe
(W)
LMTD
(°C)
Overall Heat Transfer Coefficient
U
(W/m2oC)
Temperature efficiency for hot fluid
h
(%)
Temperature efficiency for cold fluid
c
(%)
Mean temperature efficiency
m
(%)
Estimate the cumulative influence of the experimental errors on your calculated
values for
, U and the temperature efficiencies.
Compare your derived results at the various differential fluid temperatures.
Conclusion
Your results from this exercise should indicate clearly the effect of driving force
(temperature difference between the hot and cold fluid streams) on the Overall Heat
Transfer Coefficient and Temperature Efficiencies.
If you have conducted a similar exercise using a plate heat exchanger (HT32) or
shell and tube heat exchanger (HT33) compare the performances and comment on
the differences.
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Exercise G: Project Work
To Investigate Heat Loss from the Tubular Heat Exchanger
Practical Teaching Exercises A to F are performed with hot water flowing through the
inner tube and cold water flowing through the outer annulus. This arrangement
minimises the loss of heat from the heat exchanger because the temperature
difference between the cold water stream and the ambient air is relatively small. (If
the ambient air temperature is higher than the average temperature of the cold water
stream then a small gain in heat can occur.)
An investigation of heat loss from the heat exchanger when the hot water flows
through the outer annulus would provide a suitable project for students who have
completed the previous training exercises. The quick release fittings between the
heat exchanger and the service unit will allow the hot and cold fluid streams to be
interchanged.
By comparing the heat power emitted from the hot water with the heat power
absorbed by the cold water, the heat loss from the exchanger to the surroundings
can be determined. Details of the necessary measurements and calculations are
given in Teaching Exercise B.
Note: As the outer annulus of the heat exchanger is manufactured using clear acrylic
tube, the hot water flowing through the outer annulus should be limited to 65°C to
minimise softening of the tube. Similarly, the heat exchanger should not be operated
with hot water in the outer annulus for long periods of time.
To Investigate Reduction in Heat Transfer Coefficient due to Fouling of
the Heat Transfer Surfaces
The effect of fouling of the heat transfer surfaces can provide an interesting project
for students who have completed the previous training exercises.
The construction of the heat exchanger using ‘O’ ring seals allows the inner tubes to
be easily removed and replaced with alternative tubes, the inside surface of which
the have been pre-fouled.
Metal tubes 9.5mm (3/8”) outside diameter and 380 mm long (not supplied) should
be provided for the student to foul by coating the inside diameter with a suitable
insulating layer.
Note: The action of pushing the metal tube through an ‘O’ ring prevents the
application of fouling to the outer surface of the metal tube.
If alternative tubing is not available then the existing tubes can be fouled but it will be
necessary to remove the fouling before using the heat exchanger for normal
measurements.
To remove the inner metal tube from the heat exchanger, disconnect the quick
release fittings from each end of the tube then pull the tube out of the assembly
taking care not to damage the ‘O’ ring seals. Before re-inserting the metal tube, or
installing an alternative tube with fouling on the inner surface, lubricate the ‘O’ ring
seals with a small amount of wetting agent.
Note: The PVC housing at each end of the acrylic tube is bonded to the acrylic tube
and cannot be removed.
70
Exercise G
Designing an Alternative Heat Exchanger
An interesting project for students who have completed the previous training
exercises is to build and test a heat exchanger of their own design. Provided that the
alternative heat exchanger is constructed with inlet and outlet connections to suit the
quick release fittings on the HT36 Extended Tubular Heat Exchanger, then the
fittings used on the HT36 may be transferred directly, complete with the temperature
sensors fitted. The alternative heat exchanger can then be connected directly to the
HT30XC Service Unit for evaluation.
The inlet and outlet tubes should be 9.5mm (3/8”) outside diameter to allow direct
connection to the fittings supplied with the HT36 Extended Tubular Heat Exchanger.
If using the temperature sensors only from the HT36 then the tappings for the
temperature sensors should be 9.5mm (3/8”) inside diameter.
Teaching Exercises A to F may be applied to the students’; own design of heat
exchanger as appropriate.
Typical projects might include:
A tubular heat exchanger constructed with different internal dimensions.
A tubular heat exchanger constructed using different materials.
A tubular heat exchanger incorporating a helical spacer in the outer annulus to
increase the local velocity of the cold water relative to the metal tube.
71
Contact Details for Further Information
Main Office:
Armfield Limited
Bridge House
West Street
Ringwood
Hampshire
England BH24 1DY
Tel: +44 (0)1425 478781
Fax: +44 (0)1425 470916
Email: sales@armfield.co.uk
support@armfield.co.uk
Web: http://www.armfield.co.uk
US Office:
Armfield Inc.
436 West Commodore Blvd (#2)
Jackson, NJ 08527
Tel: (732) 928 3332
Fax: (732) 928 3542
Email: info@armfieldinc.com
72
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