### 6 Heat transfer is Where h is the heat transfer coefficient, q is the

Theory
Heat transfer is
‫ ݍ‬ൌ ݄‫∆ܣ‬
[1]
Where h is the heat transfer coefficient, q is the heat flow, A is the surface area and T is the
difference in temperature. To solve for the heat transfer coefficient, divide both sides by the
area and the temperature differences. Equation (1) then becomes equation (2)
௤
݄ ൌ ஺∆்
[2]
In the case that heat flow is not given, it can be calculated by measuring the mass, time, and
temperature. The specific heat value also needs to be known. Multiplying mass flow rate
times, change of temperature, and specific heat value, will give you heat flow rate as show in
equation [3].
‫ ݍ‬ൌ ∆ [3]
During this experiment, there will be two heat flow values. The first will be the energy used
by the equipment and the second will be the energy of the heated water. These two values
can be used to create an energy balance.
௜௡
ൌ [4]
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The energy in,
out,
௜௡
, is the watts measured that the appliance uses and Energy
ed.
, is the energy the water has after being heat
w
ill be lost in the
form of heat.
The coffee pot in the experiment has a tube that carries the heated water. To determine the
heat transfer coefficient, measure the watts the coffee pot uses, the initial and final
temperature of the water, and the surface area of the tube. The measurements then can be
used along with equation [2] to solve for the heat transfer coefficient in the coffee pot and
equation [4] for the energy balance.
The experiment using the hot plate involves beakers of water being heated on a hot plate
under three scenarios. The first is where the bottom of the beaker is dry, the second a thin
layer of water, and the third is a thin layer of oil. The objective of this part of the experiment
is to observe how water and oil can affect the energy loss of the overall system. In this part
of the experiment, surface area is defined by the area that comes into contact with the heat
plate.
Another part of the overall experiment was the use of the distillation column with an
unknown mixture and then with water in the reboiler. This part of the experiment involved
observing the surface area of the condenser at different input energies and different levels
of reflux. It also involves calculating the energy loss between the cooling water entering the
column and leaving the column. The energy of the water can be calculated with equation [3]
and the overall energy balance will be calculated using equation [4].
There are two types of systems that can be seen in this experiment. The first is open system
and the other is closed system.
7
Figure 1: Thermodynamic system.
Above is an image of a thermodynamic system. A system consists of a system, system
boundary, and surroundings. An open system allows energy to move across the boundary. A
closed system can have a rigid boundary and no energy can leave the system. [1]
8
Equipment
Figure 2: Coffee Pot
The coffee pot in figure 2 is a Mr. COFFEE. MR. COFEE is a SUNBEAM product. The model
number is PL12 W25VZ. It was made in Venezuela.
Figure 3: Kill A WATT
Figure 3 is a device used to measure the energy a device uses. The unit options are Volt,
Amp, Watt, Hz, and KWH. The device is plugged in an outlet and the device that one wants to
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know the energy being used is plugged into the KILL A WATT. The maximum voltage is 125
VAC and the maximum current is 15A. The maximum power is 1875VA. The serial number
is SAj64189. It was made in China.
Figure 4: Isotemp hotplate
Figure 4 is a hotplate. It also has magnets underneath the ceramic plate that will cause
stirring when used with magnetic stirring bars. It is made by Fisher Scientific and
erial number is 1886090806821.
assembled is Malaysia. The s
This image cannot currently be displayed.
Figure 5: ScoutPro scale
The model for the ScoutPro is SP401. The max is 400g and the accuracy is 0.1g.
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This image cannot currently be displayed.
Figure 6: Pelouze Scale
Above is a picture of the Pelouze scale used during the experiment. The model is Y50. The
maximum weight is 50lb and the accuracy is 2oz. It was made in China and the number is
54667. The serial number is 1200000565 and the date code is 1604.
Figure 7: Microwave
The microwave shown above is GoldStar Turntable. It was manufactured in September
1988 and model number MM101M.
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Figure 8: Maytag Microwave
It has a maximum 1025 output Watts and 120 Volts.
Figure 9: General Electric Microwave
The above image is a General Electric Microwave.
12
13
Procedure
Water Mixture
The weight of a beaker is measured and recorded, and this beaker is used for cold water
only. Fill the beaker with 100 mL of cold water. Measure and record the weight of the
beaker filled with water. The weight of the water is found by subtracting the weight of the
empty beaker from that of the full beaker. Repeat this process with a new beaker, except
hot water is used instead of cold water. One additional beaker is needed for the mixing of
the hot and cold water. The weight of this beaker should also be measured and recorded.
Using a thermometer, measure and record the initial temperatures of both the hot and cold
water. Mix the hot and cold water together in the empty beaker. After mixing, measure and
record the temperature and weight of the mixed sample. This process is repeated two more
times.
Heating with Coffee Pot
Measure and record the weight of a beaker (make sure it can hold at least 500 mL). Pour
500 mL of cold water into the beaker and weigh again. Using a thermometer, measure the
initial temperature of the water. Pour the water into the reservoir of the coffee pot. With
the coffee pot powered off, attach a digital wattmeter to the power cord to measure the
watts going into the coffee pot. Turn the coffee pot on and begin keeping the time the water
is in the coffee pot. While the water is heating up, record the average watts that the coffee
pot is using. When the water completely cycles through the coffee pot and the wattmeter
indicates its initial value again (close to zero), stop the timer and record the amount of time
the water was heated. Measure the temperature of the water as soon as possible. After the
temperature is measured, pour the water back into the same beaker used earlier and
measure the weight of the water and the beaker again.
Additionally, after the above experiment is performed, follow the same procedure up to
measuring the temperature of the water after it is cycled through the coffee pot. After the
temperature is measured, pour this hot water back in the coffee pot and once again follow
the procedure in the previous paragraph.
Heating with Microwave Oven
Measure and record the weight of a microwave safe container (e.g. a beaker). Pour cold
e a thermometer
water into the microwave safe container and measure the weight again. Us
14
to measure the initial temperature of the water. Attach a digital wattmeter to the
microwave oven while powered off. Place the water in the microwave oven and start the
microwave for thirty seconds. Record the average watts the microwave oven is using.
After heating, measure the temperature of the water as soon as possible. Measure the
weight of the water and container again after heating. Repeat this entire process for two
different microwave ovens.
Heating with Hot Plate
Measure and record the weight of a hot plate safe container. Pour cold water into this
container and measure the weight again. Using a thermometer, measure the initial
temperature of the water. Attach a digital wattmeter to the hot plate. Place the water on
top of the hot plate, turn the hot plate on and begin a timer. While the hot plate is heating
up, notice the readings on the wattmeter and their behavior. After the water has been on
the hot plate for 300 seconds, measure the temperature of the water and the weight of the
water and container. Repeat this same process two more times, except rub water and
glycerin (separately) on the bottom of the container during these trials.
Distillation Column
Set the input wattage on the desired amount and then record this value. Then record the
actual watts in the reboiler. Set the reflux to the desired value. Monitor the graph until
steady state is reached. If the solution in the reboiler is pure water, then the temperature in
all the trays at state will be close to 100˚C. Also observe the condenser to see how much
surface area is being used. When the reflux or wattage input is changed, record the mass
flow rate.
15
Results
Coffee Pot
From the experiment of heating water with a coffee pot, the change in temperature and
mass of the water was measured, and an energy balance could be performed for the system.
The energy balance for the system was found with the following equations:
E in = Watts × Time and E used = V × ρwater × C p × ∆T .
The first experiment used 500 mL of
water and was performed three times. Table 1 shows the results from this experiment.
Table 1: Results of Heating 500 mL in Coffee Pot
Heating with Coffee Pot
Initial (Cold)
Water
Trial
Volume of
water
(mL)
1
2
3
500
Final (Hot) Water
Energy
Time
Temp
Weight
Temp
Weight
(watts)
(s)
(°C)
(g)
(°C)
(g)
918
255
26
482.5
77.4
442.6
51.4
-39.9
918
250
27.9
487.3
78.2
442.1
50.3
-45.2
918
300
27.7
480.9
80.4
445.8
52.7
-
Δ Temp Δ Weight
35.1
From the results obtained, the temperature increases as it cycles through the coffee pot.
There is also a loss of water from initial to final as well. This loss results from water that
comes off as steam, or water that does not make it all the way from the reservoir to the
coffee pot. Energy balances can also be performed on the system from the data collected.
The results for the energy balance are shown in Table 2.
Table 2: Energy Balance for Heating 500 mL in Coffee Pot
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Trial
Energy in (kJ) Energy used (kJ)
1
234.09
104.7
2
229.5
102.5
3
275.4
107.3
The energy balance for heating up 500 mL of water with a coffee pot shows that not all the
energy that goes into the system through electricity is converted to heating up the water.
Some of the energy is lost. Figure 10 shows the comparison of energy in to energy used for
the system.
Heating 500 mL of Water in Coffee
Pot
300
250
kJ
200
150
Energy In
100
Energy Used
50
0
1
2
3
Trial
Figure 10: Energy Results for Heating 500 mL of Water in Coffee Pot
When 500 mL of water is added to the reservoir, less than half of the energy that goes into
the system through electricity comes out as heat added to the water, measured by
temperature. This experiment was also performed with samples of 300 mL and 100 mL of
water in the coffee pot. The results from these experiments are shown in Table 3.
Table 3: Results of Heating 300 and 100 mL of Water in Coffee Pot
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Heating with Coffee Pot
Initial
Final
Volume of
Energy
water
(mL)
(watts)
Time (s)
Temp (°C) Weight (g) Temp (°C) Weight (g)
Δ Temp
Δ Weight
91.3
920
115
5.7
91.3
57
75.1
51.3
-
100.7
920
151
11.6
100.7
55.5
66.5
43.9
-34.2
292.5
920
222
6.3
292.5
72.5
251.7
66.2
-40.8
308.3
930
220
10.2
308.3
78.6
262.7
68.4
-
16.2
45.6
From these results, there was a larger temperature change with a greater volume of water.
Energy balances were also performed on this set of data, and the results are shown in Table
4.
Table 4: Results of Energy Balance for Heating 300 and 100 mL of Water
Volume of water (mL)
Energy In (kJ) Energy Used (kJ)
204.6
85.9
204.24
78.9
100.7
138.92
18.0
91.3
105.8
19.1
308.3
292.5
The lower volumes of water used significantly less energy than the higher volumes of water.
Compiling all the data, an average energy in and energy used was computed for 500, 300,
and 100 mL of water. The results of this are shown in Figure 11.
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Heating Water in Coffee Pot
300
250
kJ
200
150
Energy In
100
Energy Used
50
0
500
300
100
mL of water
Figure 11: Energy Balance Results for Heating Water in Coffee Pot
From the results and graph, the more water that is put into the coffee pot results in more
electrical energy being put into the coffee pot in order to completely cycle the water
ver, when small amounts of water are put in the coffee pot (100 mL), very
through. Howe
little energy in comparison to what is put in the system is used for heating the water as it
cycles through.
Microwave Oven
Three different microwaves were used to heat water and collect data. The watts supplied to
the microwave, time heated in the microwave, initial and final temperature and weight
were recorded. The results for microwave 1 are shown in Table 5.
Table 5: Results of Heating Water in Microwave 1
Heating with
Trial
Microwave Oven #1
Energy (watts) Time (s) Temp (°C) Weight (g) Temp (°C) Weight (g) Δ Temp Δ Weight
19
1
180
30
25.9
136.1
49.7
135.1
23.8
2
180
30
25.1
134.1
48.1
134
23
3
180
30
25.6
136.1
50.2
135.1
24.6
1
-
0.1
-
1
-
Heating the water in the microwave showed very little change in weight from before and
after heating for thirty seconds. Table 6 shows the results from microwave 2.
Table 6: Results of Heating Water in Microwave 2
Heating with Microwave Oven #2
Trial Energy (watts) Time (s) Temp (°C) Weight (g) Temp (°C) Weight (g) Δ Temp Δ Weight
1
171
30
26.1
133.1
54.4
132.3
28.3
-0.8
2
171
30
26.3
139.6
54.4
137.9
28.1
-
3
171
30
27
138.9
55.5
138
28.5
-0.9
1.7
Microwave 2 shows similar results to microwave 1, with a slightly higher change in
temperature. The results for microwave 3 are shown in table 7.
Table 7: Results of Heating Water in Microwave 3
Heating with Microwave Oven #3
Trial Energy (watts) Time (s) Temp (°C) Weight (g) Temp (°C) Weight (g) Δ Temp Δ Weight
1
173
30
7.6
125.9
30.8
125.3
23.2
-
0.6
2
173
30
8.2
131.5
31.2
131.4
23
-
0.1
20
3
173
30
7.5
126.5
29.5
125.9
22
-0.6
From the data collected for each microwave, energy balances can be performed for the
system. The energy in refers to the energy supplied by electricity, where the energy used is
the energy used to heat the water. The results for this energy balance can be found in table
8.
Table 8: Results of Energy Balance for Heating Water in Microwave
Heating with Microwaves
Microwave
Energy In
Energy Used
1
5.40
5.41
2
5.13
6.72
3
5.19
4.55
The results of the energy balance show some strange behavior. In microwave 1 and 2, the
energy used is greater than the energy supplied by electricity. These results are shown
graphically in figure 12.
kJ
Heating with Microwaves
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
Energy In
Energy Used
1
2
3
Microwave
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Figure 12: Energy Balance Results for Heating Water in Microwave
One possible explanation for the energy used being greater than the energy in could be that
the energy balance was performed on an open system. That is to say, perhaps the water
already had a certain amount of energy that was unaccounted for before being placed in the
microwave. The additional energy added to the water from heating it could make the total
amount of energy used greater than the energy supplied by the microwave.
Distillation Column
Measurements of the amount of water exiting from the discharge of the distillation column
were taken, and the flow rate was calculated. Figure 13shows the flow rates at different
watts entering the distillation column.
Flow Rate (L/min)
9.2
9.0
L/min
8.8
8.6
8.4
8.2
8.0
7.8
7.6
1611
2330
2339
2345
Watts
Figure 13: Distillation Column Discharge Flow Rates for Various Watts
From the results obtained, the amount of watts for the range of 1600-2400 watts does not
have a patterned effect on the flow rate. Before all trays reach 100C the average the amount
of mass lost was calculated. Subtracting the cooling water supply from the cooling water
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return resulted in a mass gain of .01L/min. After all trays had reached 100C the average
gain was 4.9L/min. Please see the appendix for the raw data of the distillation column.
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Discussion
The first part of the experiment involved putting cold water into the microwave and
observing how much the temperature increases. In the first microwave the average
temperature increase in 30 s was 23.8 C. The average watts the microwave used was 180
Watts. The second microwave the average temperature increase was 28.3 C in 30s and it
used 171 watts. The third microwave had an average temperature increase of 22.7 C in 30s
and used 173 watts.
The second part of the experiment involved observing the amount of energy lost using a
coffee pot. Several experiments were performed involving a coffee pot. The first was
performed with cold water; the second with ice cold water, and the third was using the
On average the coffee pot took about 268 seconds to heat 500mL of water up with an
average increase of 51.5 C. The average amount of water lost was 40g. When 300 mL of
water was used, the coffee pot took about 221 seconds to heat up with an average
temperature increase of 67 C. The average amount of water lost during this part of the
experiment was 43.2 g. The third part of experiment used 100 mL of water. It took an
average of 133 seconds to heat the water, with
an increase in temperature by 47.6 C.
When using the heating plate the temperature increase was observed for 30s. However, the
watts supplied to the heating plate were cyclic and could not be measured accurately
enough to properly perform an energy balance on the system.
One of the objectives in this experiment was to observe and calculate the amount of energy
lost by the different systems. The microwave has the least amount of energy lost and the
The distillation column was observed at the following watts. The highest flow rate was at
2339 watts where the flow rate was 8.9 liters/ min with 0.5 uncertainty. The lowest flow
rate was at 2330 watts where the flow rate was observed at 8.2 liters/min with 1.2
uncertainty. At
the same reflux, but at 1600 watts, the flow rate was 8.5 liters/min.
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The condenser of the distillation column was observed at different refluxes and different
wattage. When 1500 watts and 100% reflux was used, all 12 coils on the condenser were
observed being used to condense. The least amount of surface area observed being used
was at 700 watts and 80% reflux; none of the 12 coils on the condenser were being used.
25
Conclusion
The amount of watts the microwave used did not correlate with the temperature increase of
the water. The amount of surface used by condenser is affected by the amount of reflux and
watts used. The higher the reflux and wattage the more surface area used. The flow rate of
the cooling water in the range of 1600-2400 watts does not have a pattern.
Recommendations
The experiment done with the coffee should be redone with a different coffee pot model.
Even though the experiment was done multiple times, a different model may yield different
mass loss and temperature increase.
References
Thermodynamic and Heat Transfer. Web. 14
tutorial.blogspot.com/2008/02/system-and-boundary-in-
[1] "System and Boundary in Thermodynamic."
Sept. 2011. <http://thermo-
thermodynamic.html>.
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Appendix A