Design and Fabrication of Multi Pass Multi Rack Solar Dryer

Design and Fabrication of Multi Pass Multi Rack Solar Dryer
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
Design and Fabrication of Multi Pass Multi Rack Solar Dryer
Hari Om Krishna1, Jihin C2, Thoufeer K. V3, Mohammed Dhervish P. N. M4, Sujith Raj P5, Shoukathali K6,
Muhammed saeed K7
1, 2, 3,4,5,6
Graduate students, 7Asst.Professor, Department of Mechanical Engineering, A W H Engineering College, Calicut,
Kerala, India
Traditional drying which is frequently done on the
ground in the open air is most widespread method used in
developing countries because it is the simplest and cheapest
method of conserving food stuffs.
Some disadvantage of open air drying are exposure of
food stuff to rain and dust, uncontrolled drying, exposure to
direct sunlight which is undesirable for some food stuffs,
infestation by insects, effect by animals etc.
Abstract—Aim of this paper is to design and fabricate a
solar dryer meant for drying fruits. The solar dryer has two
units: a solar collector and a drying chamber where product
to be dried is placed. In this dryer heat will be stored in an
absorber made of granite which will be covered with
aluminium sheet. The required angle of tilt will be provided
for the collector section depending on solar incident ray for
the effective heating on absorber. A blower will be deployed at
the inlet of the collector for air flow meant for forced
convection of heat to the drying chamber. Finally solar dryer
will be compared with open sun drying.
Air can take up moisture, but up to a limit, this limit is
the absolute (max) humidity and it is temperature
dependent. When air passes over a moist food it will take
moisture until it is virtually fully saturated, i.e. until
absolute humidity has been reached. But capacity of air for
taking up this moisture is dependent on its temperature.
The higher the temperature, the higher the absolute
humidity and larger uptake of moisture in it remains the
same, but the relative humidity falls and the air is enabled
to take up more moisture from surrounding. [15]
Keywords—Food processing, solar collector.
In many countries, the use of solar thermal system in the
agricultural area is to conserve vegetable, fruits, coffee and
other crops has shown to be practical, economical and the
responsible approach environment solar heating system to
dry food and other crops can improve the quality of the
product, food processing engineers and scientists have
found that by reducing the moisture content of food from
15% to 20%. Drying and presentation of agricultural
products have been one of the oldest uses of solar energy.
The traditional method still widely used throughout the
world, is open sun drying where diverse crops such as
fruits, vegetable, tobacco etc. are used and spread on the
ground and turned regularly until sufficiently dried.
Solar dryer is simply a device to heat air by utilizing
solar energy and it is employed in moving application
requiring low to moderate temperature below 80oc, such as
crop drying and space heating. They are defined as a
process of moisture removal due to simultaneous heat and
mass transfer. According to ikejiofor (1985) two type of
water are present in food items. The chemical bound water
and physically held water.
In drying, it is only physically held water that is
removed. The most important reason for the popularity of
dried products are longer shelf life, product diversity as
well as substantial volume reduction, this could be
expanded further with improvements in product quality and
process application.
1. Design and fabricate a solar dryer.
2. To compare fabricated solar dryer with open sun drying.
3. Comparing the rate of drying when the grapes are kept in
a single tray with that to the drying rate when it is kept
in multiple trays.
4. Thermal performance of solar dryer.
5. Studying the efficiency of solar dryer.
The performance of the solar dryer system is highly
influenced by the performance of the collector. Therefore
several studies have been conducted in order to improve the
performance of the solar dryer.
Bukola O. Bolaji, TajudheenM.AOlayangu and Taiwo
O. Falade [1] evaluated the performance of a solar wind
ventilated cabinet drier. It was designed, constructed and
tested in Nigeria on latitude 7.5ON. The result obtained
showed the temperature inside the drier and air heater was
higher than ambient temperature during most hours of the
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
During the period of test, the average air velocity
through solar drier was 1.62 m/s and the average daylight
efficiency of system was 46.7%. Chandrakumar B Pardhi
[2] used a forced convection mixed mode solar dryer in
performing the experiments on grapes. The experiments are
used to compare the performance of the smooth and
roughed plate collector. By providing artificial rib
roughness on the underside of the absorber plate has
enhanced the heat transfer. A.Fudholi, M.Y.Othman,
M.H.Ruslan, M.Yahya, A.Zaharin and K.Sopian [3]
designed and tested a solar drier for drying kinetics of
seaweed in Malaysia. The initial and final moisture content
of the seaweed are 94.6 %( wet basis) and 10 %( product
basis) respectively. The drying time was about 7 hours at
average solar radiation of about 600 W/m2 and air flow
rate 0.0613 kg/s. Three drying models were compared with
experiment data at average temperature and relative
humidity about 50°C and 20% respectively. The most
suitable model was selected to best describe the drying
behavior of seaweed. N.Rajeshwari and A.Ramalingam [4]
conducted a study to construct effective box type solar drier
using low cost material. Temperature inside the solar box
drier and grapes moisture with drying efficiencies of grapes
cluster dried in the solar box drier have been investigated.
A prototype of the drier was constructed to specification.
Theminimum of 0.045m2 of solar collector area according
to the design was required, an expected drying efficiency of
69.6% under average ambient conditions of 30°C and
76.1% relative humidity with average solar radiation of 650
W/m2, the average efficiency was evaluated as 69%.
S.Janjal, C.Phusampao, W.Nilnant, and P.Pankaew [5]
conducted experimental performance and modelling of a
greenhouse solar drying macadamia nuts. The drier consists
of a parabolic roof structure covered by polycarbonate
sheets on a concrete floor. The drier used to dry six batches
of macadamia nuts. Results obtained from this
investigation showed that drying temperature in the drier
varied from 30°Cto 65°C .The simulation result agreed
well with the experimental data for solar drying of the
macadamia nuts. The estimated of payback period of the
drier is 1 year. Rajeev Kumar Aggarwal [6] designed an
indirect solar dryer with electric backup system, in this
journal 25kg product is to be used and he proposed solar
cell and fan for the purpose of air heating during cloud
evening and morning for faster drying & reducing drying
time. Punic agrantum turmeric redchilies are the products
used for this experiment these are dried in open, solar,
Owen drying apparatus. The values are compared on the
basis of moisture content, color, sugar percentage etc. The
market value of dried product has also been compared.
R.J.Fuller [7] conducted a study in solar drying for the
sustainable agriculture and food production. Advances in
design methods, absorber and glazing materials are
discussed for the improvement of technical performance of
solar drier. O.A.Lasode [8] designed and constructed a
solar cabinet drier with convective heat flow. The design is
of the direct radiation type with double glass sheet collector
to enhance heat collection and increase the temperature
attainable in drying chamber. The drying chamber is
provided with adjustable vent holes for ventilation
depending on the desired rate of drying. The dryer was
constructed from local raw materials with overall
dimensions of 520mm x 370mm x420mm. Umesh
Toshniwal and S.R.Karale [9] reviewed a paper on solar
drier. Various design of solar drier is reported such as
combination of fuel burning with energy of sun, thus
reducing fossil fuel consumption. K.S.Tonui, EBK Mutai,
D.A MutuliMbuge [10] designed and constructed a solar
grain dryer integrated with a simple biomass burner using
locally available materials. The dryer is composed of solar
collector, drying chamber, backup heater and air flow
system. A minimum of 3.77m2 solar collector area was
required to dry a batch of 100kg maize grain in 6h with
natural convection from initial moisture content of 21% to
final moisture content of 13% wet basis. The thermal
efficiencies of the solar and solar assisted dryer were
39.9% and 57.7% respectively. The backup heating system
improved the efficiency of dryer by 17.8% and reduced
drying time substantially. N.A.Vlanchos, T.D Karapantsios,
A.I.Balouktsis [11] designed and tested a solar tray dryer.
The design was based on energy balances and on an hourly
averaged radiation data reduction procedure for tilted
surfaces. Detailed diagnostic experiments were carried out
with no drying material on the trays. Next a number of
experiments were conducted using a controlled reference
material whose reproducible dehydration pattern allows
comparison among nuns. For all employed conditions the
material gets completely dehydrated at a satisfactory rate
and with encouraging systems efficiency. James stiling,
Simon Li, Pieter Stoeve [12] evaluated the performance
comparison between two mixed mode solar dryers. The
dryers were identically constructed however one of the
dryer utilized mobile and easily adjustable flat
concentrating solar panels to maximize incident solar
energy on the dryer. The concentrating solar panels showed
a considerable increase in drying rate on sunny days, with a
27% decrease in total drying time as compared to the
normal dryer to reach the target dimensionless moisture
content of 0.2.
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
The faster drying rate achieved in the dryer utilizing
solar concentrators under both sunny and simulated cloudy
conditions demonstrates the ability to dry produce to an
acceptable moisture content in a reasonable time with the
objective of reducing post-harvest loss and preventing
spoilage. Gokhangurleknecdetozbalta [13] conducted solar
drying experiments of tomato. In this, new type tunnel solar
drier was designed and manufactured. Heated air in solar
air collector was forced through the tomatoes by a blower.
Drying time was examined with mass ratio as exponential
and polynomial correlation. Twelve different mathematical
models available in literature were compared using their
coefficient of determination of estimated solar drying
curves. Shahidul Islam Khan and Asif Islam [14] analyzed
the performance of solar water heater. Two solar water
heaters of 100 and 200 liters were installed on roof top of a
building. The data of 12 months have been collected and
analyzed. It was found that the incoming hot tap water was
about 30oc higher than the room temperature during day
time of winter months. N V vadar [16] conducted case
study on the basis of solar heating in food processing. case
study 1 is the solar dryer for banana slices using parabolic
solar collector dish here banana contains 80% of water
when heated up to70°C moisture content reduces to 10% he
conducted second case study on a solar dryer[Owen] for
cashew nut roasting they installs the cabinet for loading the
material on roof top while collector panels laid on south
side towards ground and shows the result that in roasting
application solar ovens are better suited for baking and
roasting application than concentrators uniform baking and
roasting in solar ovens. Muhammad Hanif Khalil [17]
developed and Evaluated a solar thermal collector designed
for drying grain. The performance of this collector was
evaluated at different convective flow rate of air. The
statistical analysis showed that increase in mass flow rate
significantly increases the performance of a solar collector.
It was concluded that the drying of grains the solar
collector must be operated at high mass flow rates of air
from 9am to 4pm to get maximum performance from the
solar thermal collector.
Thermo Cole is used as the insulation material for both
collector as well as drying chamber.
Based on design calculation length, width and height of
the solar collector is given as 70cm, 40cm and 25cm
respectively, area of the drying chamber is determined as
1.6m2 excluding the dimension for insulation. The absorber
is placed inside the solar collector; here aluminum sheet
painted black is used as absorber below absorber plate
granite plate of dimension 8mm is placed for storing
sensible heat. At the top of the absorber glass sheet is
placed which transmit maximum solar radiation falling on
it. A blower is used for continues blowing of air from
outside to the solar collector, the air is heated and heated
air is taken to drying chamber. Calibrated thermocouple is
fixed on granite plate, aluminum sheet, drying chamber and
collector for measuring the temperature.
A. Absorber
The absorber which is 70cm X 40cm black painted
aluminium sheet, fixed in the middle of solar collector. The
absorber was implicit to be a perfect black body and
greatest heat capacity. The aluminium sheet was used for
fabrication of the absorber because it has a high value of
adsorption (88%) and high heat capacity.
It is low cost, high melting point, inflammable and easily
available in the local market
B. Covering
The cover material or the glazing was 75cm X 45cm X
4mm thick glass sheet is placed at the top of the solar
collector box. Glass was used as glazing so that it shelter
the absorber from wind and allow solar radiation to reach
the absorber, it is also easily available, low cost , has high
value of transmittance for long and short wave radiations
(80%), not flammable and have high melting point.
C. Inlet And Outlet Duct
The inlet is 0.3m diameter made up of PVC fixed at the
bottom of the collector due to the fact that the air enters
from lower side at lower temperature. The outlet has the
top and cold air comes from lower side to replace the hotter
D. Supporting Frame
The collector was supported and fitted with the help of a
frame made up of angle iron, the frame was built with four
legs in such a way that the front two legs have a height of
0.2m and rear legs have a height of 0.6m thus makes the
required angle for the inclination of the supporting frame.
The experimental setup consist of a solar collector
consisting of an aluminum sheet as absorber plate ,granite
as thermal storage medium. A drying chamber consisting of
4 perforated trays held in two on each side of partition wall
pattern is used to accommodate the grapes for drying.
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
Table: 1
List of materials
E. Collector Orientation And Tilt Angle
The collector was oriented facing North-East axis,
having a tilt angle of 26.25O with horizontal. It was done to
normal the angle of maidens of solar radiation coming from
the sun on the collector surface.
Sl .No
To start with, the product to be dried may be washed and
or preheated as per requirements. The product is then
loaded in the trays. The trays must be filled with the grapes
and at no place should the bottom of tray be visible.
Otherwise, the hot air will flow through that area and
bypass the product, resulting in the reduction of the thermal
efficiency. It may be noted that if the product to be dried is
less than the capacity of the dryer, the loading of the
product should be done only in the top trays and the lower
trays may be left empty. The drying of the product is done
on batch mode. In the batch mode, the fresh product is
loaded only after removing the dried product of the
previous batch.
Multi pass multi rack, solar dyer was fabricated in
Calicut on latitude of 11.75ON using materials that are
easily obtainable from the local market.
Solar collector
Drying chamber
Supporting frame
Drying tray
GI sheet
GI sheet
Cast iron
Heat absorbed by the absorber will be transferred to the
storage medium and this heat will be dissipated and sent to
the drying chamber via duct by blowing ambient air sucked
by blower through an intermediate duct. Air runs in a six
pass inside the solar collector in a Z flow path with three
pass below the storage medium and rest of three above the
storage medium. This heated air will be passed through the
trays inside the drying chamber and finally escapes out to
the exit.
Fig: 2 Solar dryer
Fig: 1 Solar Dryer (Cad drawing)
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
Theoretically we are finding the quantity of heat needed
to evaporate the water, quantity of heat needed to evaporate
the water, average drying rate, mass of air needed for
drying, quantity of heat added to the air, area of the
collector etc.
1) To find the amount of moisture in kilogram to be
removed from the product was calculated using the
following equation: [18]
Where MP is the initial mass of product being dried; Mi
is the initial moisture content of grapes;Mf is the final
moisture content of grapes.
2) To find the Quantity of heat needed to evaporate the
water, [19]
Where Mw is the amount of moisture to be removed
from grapes; hfg is the latent heat of vaporization.
3) To find the Latent heat of vaporization, we can use the
general equation,[20]
Fig: 3 Dried product
Table: 2
Design considerations
Drying period
March 2015
Drying material quantity
1 Kg
No of trays
Load rating
Initial moisture content
81.4% wet basis
Final moisture content
18.6% wet basis
Ambient air temperature
33OC(Average for march)
4) To find the quantity of heat needed for vaporization [21]
Where Ma is the mass flow rate air, kg/h; hf and hi is the
final and initial enthalpy of drying and ambient air,
respectively, Kj/kg read using psychometric charts.
5) To find the Average drying rate,
6) To find the Mass of air needed for drying,
Maximum allowable
64 C
Drying time (Sunshine
Flat plate medium
Aluminium flat plate
Heat storage medium
Granite sheet
Test collector size
75cm long and 45cm wide
7) To find volumetric flow rate,
Va =mass flow rate /density
8) To find the Area of the collector,
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
Where I is the intensity of solar radiation in MJ, η
efficiency of solar collector.
9) To find area of drying chamber, [22]
The result obtained in a drying of a fresh sample of seed
less grapes in the cabinet dryer and in the open air
simultaneously are shown in fig:4.
In this case it was observed that the products in the
cabinet dryer dried faster than the open air drying, it takes
the grape in the cabinet solar dryer 32hr to achieve
moisture content of 18.6% and in the open air it takes 38hr
to achieve this.
Where Ww is the mass of the crop to be dried is Kg; h L is
the layer drying bed thickness, is the crop porosity;
the loading bed void fraction;
a bulk density of crop on
wet basis in Kg/m3.
Determination of drying rate in each tray
Here initial weight of the grapes was measured and dryer
was loaded with equal mass in each trays. Weights of the
grapes in each tray were measured at the end of the day and
the experiment continued up to a stage when the moisture
content in grapes reduced to 18.6%.
Comparison of solar drying V/S open sun drying
The initial weights of the grapes were measured and
dryer was loaded with equal mass in each trays. Weights of
the grapes in each tray were measured at regular interval of
1hr between 09:00 to 14:00 local time. Also the
temperatures at solar absorber, heat storage medium
(granite), covering and drying chamber were measured
using thermocouples attached to them by multimeter. After
measuring the weight and temperature position of each tray
were changed as to achieve uniform heating rate.
Contemporarily, open sun drying was done and weight
of the grapes were measured at regular interval of 1 hr. this
procedure was continued up to a stage when the moisture
content in the grapes reduced to 18.6%.
Mass of product (grams)
Open sun drying
Day 1
Solar dryer
Day 2
Tray 1
Day 3
Tray 2
Day 4
Day 5
Tray 3
Tray 4
Day 6
Fig: 5 drying rate on trays
Fig: 5 shows drying rate of each tray with mass of
grapes on y axis and number of days in x axis, as the days
pass by the mass of grapes in the trays decreases i.e.
moisture content decreases, in such a manner that, drying
rate decreases from tray1 to tray 4.
The hourly variation of temperature in solar collector
and drying chamber compared to the ambient temperature
for 6 days are shown in figures 4 to 9.
Time (hours)
Fig: 4 Comparison of drying rate
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
The dryer is hotter at mid-day when the sun is usually
overhead. The temperature inside the drying chamber and
collector are much higher than the ambient air-temperature
during most hours of the day light. This indicates prospect
for better performance than open air drying.
Temperature V/S Time (Day 3)
Temperature V/S Time (Day 1)
10:00 AM 11:00 AM 12:00 PM
10:00 AM 11:00 AM 12:00 PM
1:00 PM
2:00 PM
Granite sheet
Drying chamber
Ambient temperature
1:00 PM 2:00 PM
Granite sheet
Fig: 8 Variation of temperature day 3
Drying chamber
Ambient temperature
Temperature V/S Time (Day 4)
Fig: 6 Variation of temperature day1
Temperature V/S Time (Day 2)
10:00 AM 11:00 AM 12:00 PM
10:00 AM 11:00 AM 12:00 PM
1:00 PM 2:00 PM
Granite sheet
1:00 PM
2:00 PM
Granite sheet
Drying chamber
Ambient temperature
Drying chamber
Fig: 9 Variation of temperature day 4
Ambient temperature
Fig: 7 Variation of temperature day 2
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
Peak temperature was attained in the mid-day between
11am to 12pm. At day1 the absorber attained a temperature
between 60OC to 65OC, 50OC was recorded in the granite
sheet. While glass sheet was measured 46OC, drying
chamber was measured with 45OC temperature. Ambient
air temperature was measured as 32OC.
Temperature V/S Time (Day 5)
Samples of open sun drying and solar dryer dried grapes
were subjected to nutrition testing, the fat content in both
cases were almost same but carbohydrates and protein were
more in solar dryer dried grapes than open sun drying. The
table below shows nutrition distribution for both open sun
drying and solar dryer dried grapes.
10:00 AM 11:00 AM 12:00 PM
1:00 PM
Table: 3
Nutrition values of grapes
2:00 PM
Granite sheet
Drying chamber
Ambient temperature
Fig: 10 Variation of temperature day 5
Temperature V/S Time (Day 6)
Open Sun
Solar Drying
Crude protein
Total fat
Total carbohydrate
In this work, the practical way of cheaply and sanitarily
preserving food items by the use of solar dryer has been
demonstrated. The fabrication of the dryer does not require
high technology. At once installed the maintenance cost is
minimal the dryer was tested and the following conclusion
can be drawn based on result obtained.
 The maximum temperature on the absorber was
recorded on 65OC.
 The nutrition content in the grape which were dried in
the drying chamber were better than grapes dried in
open sun drying process.
 Drying rate was more in solar dryer than open sun
drying process.
 While performing experiment without changing the
position of trays it was concluded that the tray which
was first to be in contact with the incoming hot air
had the highest drying rates than other trays.
10:00 AM 11:00 AM 12:00 PM
1:00 PM
2:00 PM
Granite sheet
Drying chamber
Ambient temperature
Fig: 11Variation of temperature day 6
Fig 6,7,8,9,10,11 shows the temperature variation for
days 1,2,3,4,5,6 respectively at a regular interval of 1hour
from each elements of solar dryer.
International Journal of Emerging Technology and Advanced Engineering
Website: (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
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