filmdropwise lab .docx
TRANSCRIPT
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UNIVERSITI TEKNOLOGI MARAFAKULTI KEJURUTERAAN KIMIA
Chemical Engineering Laboratory I (CHE465)
NO. Title Allocated Marks (%) Marks1 Abstract 52 Introduction 53 Aims 5
4 Theory 55 Apparatus 56 Methodology/Procedure 107 Results 108 Calculations 109 Discussion 20
10 Conclusion 1011 Recommendations 512 Reference 5
13 Appendix 5TOTAL MARKS 100
Remarks:Checked by:
-------------------------------Date:
NAME : LUQMAN BIN MOHD IDRISSTUDENT NO : 2012625202GROUP : EH2202B
EXPERIMENT : FILM AND DROPWISE CONDESATION UNITDATE PERFORMED : 20 th MAY 2013SEMESTER : 2PROGRAMME CODE: EH220SUBMIT TO : DR. ABDUL HADI
http://i-learn.uitm.edu.my/Course/courseframe.php?cid=CHE465&module=informationhttp://i-learn.uitm.edu.my/Course/courseframe.php?cid=CHE465&module=information -
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Abstract
The equipment that is used is Film and Dropwise Condensation Unit (Model: NE 163).
There are about four experiments that should be run to achieve the objective of the experiment.
The student must be observed the process of heat transfer during condensation, as well as gather
experimental data for a better theoretical understanding. The main components in the unit are the
specially designed condensers for the observation of both filmwise and dropwise condensation.
Introduction
Filmwise and Dropwise are two form of condensation. In filmwise condensation a laminar
film vapour is created upon a surface. This film can then flow downward, increasing in thickness
as additional vapour is picked up along the way. In dropwise condensation vapour droplets form
at an acute angle to a surface. These droplets then flow downwards, accumulating static droplets
below them along the way.
The objective of this experiment is to investigate the difference in heat flux between the two
forms of condensation for the same conditions. The next objective is to investigate what effect
the presence of air in the condenser has on the heat flux and surface heat transfer coefficient.
This experiment would be used in by any industry which is trying to increase the efficiency of
heat transfer. An example of this is any vapour cycle such as the Rankine cycle. By increasing
the efficiency of the condenser, its operational pressure can be reduced and the overall efficiency
of the cycle can be increased.
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Aims
To demonstrate the filmwise and dropwise condensation To determine the filmwise heat flux and surface heat transfer coefficient at constant
pressure
To determine the dropwise heat flux and surface heat transfer coefficient at constant
pressure
To determine the effect of air on heat transfer coefficient of condensation
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Theory
Condensation of steam on the surface of a condenser causes heat to transfer from the
steam into the cooling medium flowing through the condenser. This type of heat transfer may
occur at very high fluxes depending on the conditions at the condenser surface. Steam may
condense in two different manners filmwise or dropwise. For the same operating conditions,
dropwise condensation exhibits a much higher and efficient heat transfer compared to filmwise
condensation. Although dropwise condensation is always desirable, it seldom occurs in practice
for a continuous period of time.
In filmwise condensation, most heat transfer surfaces on a heat exchanger are made of
wet table materials. During condensation, a film of condensate spreads over these surfaces. Asmore vapour condenses on the outside of the film, its thickness increases and the film will start
flowing downwards due to its weight. Heat transfer occurs through this film of condensate to the
surface material beneath, then to the cooling medium. The liquid film is generally a poor
conductor of heat, contributing much to the thermal resistance and inefficiency of this mode of
condensation.
In dropwise condensation, If the heat transfer surfaces are treated to become
nonwettable, the condensate that forms o n the surface will be shaped like spherical beads.
These beads adheres together to become larger as condensation proceeds. The bigger beads will
then start to flow downwards due to their weight, thus collecting all other static beads along the
way. As the beads increase in size, the velocity increases, finally leaving a trail of bare surface
free from liquid film. This bare surface offers very little resistance to the transfer of heat.
Therefore, very high heat fluxes are possible.
Formula used for log mean temperature difference:
Tm = (equation 1)
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Formula used for heat flux:
Heat flux, = (equation 2)
Formula for heat transfer coefficient :
Heat transfer coefficient, U = (equation 3)
Formula for heat remove from condensation:
Qx = C T (equation 4)
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Apparatus
Film boiling condensation
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Procedure
1.1: General start-up procedure
1. Main switch was ensured in the off position.
2. The power regulator knob is turned fully anticlockwise to set the power to minimum.
3. Ensured valve one and valve six was closed.
4. The chamber was filled with distilled water until the water level stays between the heater
and baffle plates. Always make sure that the heater is fully immersed in the water
throughout the experiment, water could be filled into the chamber through the drain valve
with the vent valve, V4 opened. Then closed the vent valve,V4.
5. The water flow rate was adjusted to the condenser by controlling the control valveaccording to the experimental procedure.
6. The main and heater switch was turned on. The heater power was set by rotating the
power regulator clockwise to increase the heating power.
7. The water temperature reading was observed, it should increase when the water starts to
heat up.
8. The water was heated up until to boiling point until the pressure reaches 1.02-1.10 bar.
Valve V1 was immediately opened and follow by valve V5 for 1 minute to vacuum out
the air inside the condenser. Then valve V1 and valve V5 was closed
9. Let the system to stabilize. Then all relevant measurements for experimental purpose
were takes. Make adjustment if required.
1.2 : General shut down procedure
1. The voltage control knob was turned to 0 volt position by turning the knob anticlockwise.
Keep the cooling water flowing for at least 5 minutes through the condenser to cold them
down.
2. The main switch and power supply was switched off. Then, unplug the power supply
cable
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3. The water was closed and disconnected the cooling water connection tubes if necessary.
Otherwise, leave the connection tubes for next experiment.
4. The water inside the chamber was discharged using the discharge valve.
Experiment 1: Demonstration of Filmwise and Dropwise condensation
1. The basic procedure was followed as written in section 1.1. Make sure that the equipment
is connected to the service unit.
Experiment 2: The Filmwise Heat Flux and Surface Heat Transfer Coefficient
Determination at Constant Pressure
1. Cooling water was circulated through the filmwise condenser starting with a
minimum value of 0.1LPM
2. The heater power was adjusted to obtain the desired pressure at 1.01bar.
3. The steam(T sat) and surface temperature(T surf ), T in(T1) and T out(T2), and flowrate was
recorded.
Experiment 3: The dropwise Heat Flux and Surface Heat Transfer Coefficient Determination at
Constant Pressure
1. Cooling water was circulated through the dropwise condenser starting with a
minimum value of 0.4LPM
2. The heater power was adjusted to obtain desired pressure at 1.01bar.
3. The steam(T sat) and surface temperature(T surf ), T in(T3) and T out(T4), and flowrate was
recorded.
Experiment 4: The Effect of Air Inside Chamber
1. Cooling water was circulated through the filmwise condenser at the highest flowrate
until the pressure was reduced to below 1bar.
2. The discharged was opened and let an amount of air to enter the chamber.
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3. The water flowrate was regulated to the condenser starting with a minimum value of
0.4LPM.
4. The heater power was adjusted to obtain the desired pressure at 1.01bar.
5. The steam(T sat) and surface temperature(T surf ), Tin(T 3) and T out(T4) and flowrate was
recorded.
6. Step 1-5 was repeated for dropwise condensation.
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Result
Experiment 1: Demonstration of filmwise and dropwise condensation
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Experiment 2: The filmwise heat flux and surface heat transfer coefficient determination atconstant pressure.
Flowrate
(LPM)
Power
(W)
T in
C)
Tout
Tsat
Tsurf
Tsat-
Tsurf
Tm
(w/m 2)
U
(w/m 2.k)
%
0.1 73 34.5 37.7 71.3 38.3 33.0 35.2 5531.02 157.13 3
0.2 79 34.3 35.0 70.5 34.7 35.8 35.8 2419.98 67.60 7
0.3 97 34.1 34.4 71.2 34.1 37.1 36.9 1555.52 42.10 10
0.4 102 34.0 34.3 70.7 33.7 37.0 36.6 2075.80 56.79 15
0.5 240 34.0 34.1 71.0 33.4 37.6 36.1 864.45 23.40 19
0.6 280 34.0 34.1 70.9 33.5 37.4 36.9 1037.84 28.16 22
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Experiment 3: The dropwise heat flux and surface heat transfer coefficient determination at
constant pressure
Flowrate
(LPM)
Power
(W)
T in
Tout
Tsat
Tsurf
Tsat-
Tsurf
Tm
(w/m 2)
U
(w/m 2.k)
%
0.4 167 33.9 35.0 70.7 63.4 8.3 36.25 7606.71 209.84 19
0.6 256 34.6 38.5 71.5 57.8 13.7 34.91 40436.18 1158.30 23
0.8 260 34.5 37.4 71.1 52.0 19.1 35.13 40081.97 1140.96 30
1.0 265 34.6 37.1 71.3 51.1 20.2 35.44 43210.36 1219.25 35
1.2 273 34.7 36.9 71.2 51.5 19.7 35.39 45620.43 1289.08 40
Experiment 4: The effect of air inside chamber
For filmwise condenser
Flowrate
(LPM)
Power
(W)
Tin
Tout
Tsat
Tsurf
Tsat-
Tsurf
Tm
(w/m 2)
U
(w/m 2.k)
%
0.1 267 34.9 44.6 70.9 53.1 17.8 30.90 16766.46 542.60 3
0.2 310 34.5 40.1 71.2 45.9 25.3 31.38 19352.39 616.71 70.3 314 34.3 37.6 71.1 43.2 27.9 35.12 17108.28 487.14 11
0.4 333 34.2 36.6 71.0 42.0 29.0 35.59 16598.03 466.37 15
0.5 355 34.1 36.0 71.3 40.6 30.7 36.32 16417.21 453.01 20
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For dropwise condenser
Flowrate
(LPM)
Power
(W)
Tin
Tout
Tsat
Tsurf
Tsat-
Tsurf
Tm
(w/m 2)
U
(w/m 2.k)
%
0.4 267 34.1 36.5 72.8 42.5 30.3 37.49 9286.08 247.69 20
0.6 269 34.1 36.0 71.1 40.2 30.9 36.04 19699.16 546.59 25
0.8 272 34.1 35.7 71.0 39.3 31.7 36.09 21358.72 591.82 30
1.0 274 34.1 35.5 71.1 38.8 32.3 36.30 24197.30 666.59 37
1.2 275 34.3 35.7 71.1 38.7 32.4 36.10 29032.31 804.22 43
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Calculation
Experiment 2:
Volumetric flowrate
= 0.10LPM=0.1 L
=
=1.667 g/s
Power, q x
Qx=C T
. g s . g. . - .
=22.33 W
Log mean temperature difference:
Tm =
=
=
=35.2 C
Heat flux, =
=
= 5531.02 w/m 2
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=
= 2419.98 w/m 2
Heat transfer coefficient, U =
=
=67.6 w/m 2.K
Volumetric flowrate
= 0.30LPM
=0.3 L
=
=5 g/s
Power, q x
Qx=C T
=5 g/s4.186kJ/kg.K(34.4-34.1
= 6.28 W
Log mean temperature difference:
Tm =
=
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=
=36.95 C
Heat flux, =
=
=1555.52 w/m 2
Heat transfer coefficient, U =
=
=42.1 w/m 2.K
Volumetric flowrate
= 0.40LPM
=0.4 L
=
=6.67 g/s
Power, q x
Qx=C T
=6.67 g/s4.186kJ/kg.K(34.3-34.0
= 8.38 W
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Log mean temperature difference:
Tm =
=
=
=36.55 C
Heat flux, =
=
=2075.80 w/m 2
Heat transfer coefficient, U =
= =56.79 w/m 2.K
Volumetric flowrate
= 0.50LPM
=0.5 L
=
=8.333 g/s
Power, q x
Qx=C T
. g s . g. . - .
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=3.49 W
Log mean temperature difference:
Tm =
=
=
.
Heat flux, =
=
= 864.45 w/m 2
Heat transfer coefficient, U =
=
=23.4 w/m 2.K
Volumetric flowrate
= 0.60LPM=0.6 L
=
=10.0 g/s
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Power, q x
Qx=C T
. g s . g. . - .
= 4.186 W
Log mean temperature difference:
Tm =
=
=
=36.85 C
Heat flux, =
=
= 1037.84 w/m 2
Heat transfer coefficient, U =
=
=28.16 w/m 2.K
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Experiment 3:
0
20
40
60
80
100
120
140
160
180
32 33 34 35 36 37 38
Surface heat transfer coefficient vs. Temperature difference
0
1000
2000
3000
4000
5000
6000
32 33 34 35 36 37 38
Heat flux vs. Temperature difference
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Volumetric flowrate
= 0.40LPM
=0.4 L
= =6.67 g/s
Power, q x
Qx=C T
=6.67 g/s4.186kJ/kg.K(35.0-33.9
= 30.71 W
Log mean temperature difference:
Tm =
=
=
=36.25 C
Heat flux, =
=
=7606.71 w/m 2
Heat transfer coefficient, U =
=
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=209.84 w/m 2.K
Volumetric flowrate
= 0.60LPM
=0.6 L
=
=10.0 g/s
Power, q x
Qx=C T
=10.0 g/s4.186kJ/kg.K(38.5-34.6 = 163.25 W
Log mean temperature difference:
Tm =
=
=
=34.91 C
Heat flux, =
=
=40436.18 w/m 2
Heat transfer coefficient, U =
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=
=1158.30 w/m 2.K
Volumetric flowrate
= 0.80LPM
=0.8 L
=
=13.33 g/s
Power, q x
Qx=C T
=13.33 g/s4.186kJ/kg.K(37.4-34.5
= 161.82 W
Log mean temperature difference:
Tm =
=
=
=35.13 C
Heat flux, =
=
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=40081.97 w/m 2
Heat transfer coefficient, U =
=
=1140.96 w/m 2.K
Volumetric flowrate
= 1.0LPM
=1.0 L
=
=16.67 g/s
Power, q x
Qx=C T
. g s . g. . - . = 174.45 W
Log mean temperature difference:
Tm =
=
=
=35.44 C
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=35.39 C
Heat flux, =
=
=45620.43 w/m 2
Heat transfer coefficient, U =
= =1289.08 w/m 2.K
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
0 5 10 15 20 25
Heat flux vs. Temperature difference
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Experiment 4:Filmwise condenser
Volumetric flowrate
= 0.10LPM
=0.1 L
=
=1.667 g/s
Power, q x
Qx=C T=1.667 g/s4.186kJ/kg.K(44.6-34.9
=67.69 W
Log mean temperature difference:
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25
Surface heat transfer coefficient vs. Temperature difference
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Tm =
=
=
=30.90 C
Heat flux, =
=
= 16766.46 w/m 2
Heat transfer coefficient, U =
=
=542.60 w/m 2.K
Volumetric flowrate
= 0.20LPM
=0.2 L
=
=3.333 g/s
Power, q x
Qx=C T
=3.333 g/s4.186kJ/kg.K(40.1-34.5
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= 78.13 W
Log mean temperature difference:
Tm =
=
=
=31.38 C
Heat flux, =
=
= 19352.39 w/m 2
Heat transfer coefficient, U =
=
=616.71 w/m 2.K
Volumetric flowrate
= 0.30LPM
=0.3 L
=
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=5 g/s
Power, q x
Qx=C T
=5 g/s4.186kJ/kg.K(37.6-34.3
= 69.07 W
Log mean temperature difference:
Tm =
=
=
=35.12 C
Heat flux, =
=
=17108.28 w/m 2
Heat transfer coefficient, U =
= =487.14 w/m 2.K
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Volumetric flowrate
= 0.40LPM
=0.4 L
=
=6.67 g/s
Power, q x
Qx=C T
=6.67 g/s4.186kJ/kg.K(36.6-34.2
= 67.01W
Log mean temperature difference:
Tm =
=
=
=35.59 C
Heat flux, =
=
=16598.03 w/m 2
Heat transfer coefficient, U =
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=
=466.37 w/m 2.K
Volumetric flowrate
= 0.50LPM
=0.5 L
=
=8.333 g/s
Power, q x
Qx=C T
=8.333 g/s4.186kJ/kg.K(36.0-34.1
=66.28 W
Log mean temperature difference:
Tm =
=
=
=36.24 C
Heat flux, =
=
= 16417.21 w/m 2
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Heat transfer coefficient, U =
=
=453.01 w/m 2.K
16000
16500
17000
17500
18000
18500
19000
19500
0 5 10 15 20 25 30 35
Heat flux vs. Temperature difference
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Experiment 4:Dropwise condenser
Volumetric flowrate
= 0.40LPM
=0.4 L
=
=6.67 g/s
Power, q x
Qx=C T
=6.67 g/s4.186kJ/kg.K(36.5-34.1 = 67.01 W
Log mean temperature difference:
0
100
200
300
400
500
600
700
0 5 10 15 20 25 30 35
Surface heat transfer coefficient vs. Temperature difference
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Tm =
=
=
=37.49 C
Heat flux, =
=
=9286.08w/m 2
Heat transfer coefficient, U =
=
=247.69 m 2.K
Volumetric flowrate
= 0.60LPM
=0.6 L
=
=10.0 g/s
Power, q x
Qx=C T
. g s . g. . - .
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= 79.53 W
Log mean temperature difference:
Tm =
=
=
=36.04 C
Heat flux, =
=
=19699.16 w/m 2
Heat transfer coefficient, U =
=
=546.59 m 2.K
Volumetric flowrate
= 0.80LPM
=0.8 L
=
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=13.33 g/s
Power, q x
Qx=C T
=13.33 g/s4.186kJ/kg.K(35.7-34.1
= 89.23 W
Log mean temperature difference:
Tm =
=
=
=36.09 C
Heat flux, =
=
=21358.72 w/m 2
Heat transfer coefficient, U =
= =591.82w/m 2.K
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Volumetric flowrate
= 1.0LPM
=1.0 L
= =16.67 g/s
Power, q x
Qx=C T
=16.67 g/s4.186kJ/kg.K(35.5-34.1
= 97.69 W
Log mean temperature difference:
Tm =
=
=
=36.30 C
Heat flux, =
=
=24197.30 w/m 2
Heat transfer coefficient, U =
=
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=666.59 w/m 2.K
Volumetric flowrate
= 1.2LPM
=1.2 L
=
=20 g/s
Power, q x
Qx=C T=20 g/s4.186kJ/kg.K(35.7-34.3
= 117.21 W
Log mean temperature difference:
Tm =
=
=
=36.10 C
Heat flux, =
=
=29032.31 w/m 2
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Heat transfer coefficient, U =
=
=804.22w/m2
.K
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0
5000
10000
15000
20000
25000
30000
35000
30 30.5 31 31.5 32 32.5 33
Heat flux vs. temperature difference
0
100
200
300
400
500
600
700
800
900
30 30.5 31 31.5 32 32.5 33
Heat traansfer coefficient vs. Temperature difference
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0
10000
20000
30000
40000
50000
60000
36 36.5 37 37.5 38 38.5
U ( W / m 2 )
Temperature Difference (K)
Heat Flux vs. Temperature Difference
Filmwise
Dropwise
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Discussion
Heat flux increases with steam pressure and the temperature difference between the
steam and the condenser surface and that the values for Heat flux for each set value of pressure is
higher using dropwise condensation that by using filmwise condensation in the same conditions.
The final observation is confirmed in the which quotes that at atmospheric pressure, the Heat
Flux in dropwise condensation can be more than twenty times larger than in filmwise. This can
be explained in terms of how the condensation forms on the condenser.
The vapour drops indropwise condensations are discrete and are continually formed and
released which means that the surface of the condenser is also continually exposed. In
comparison, the film created in filmwise condensation always covers the surface of the
condenser. As a relatively poor conductor of heat, this film creates a thermal resistance which isthe reason why the value for Heat Flux is lower for filmwise in comparison to dropwise
condensation.
To check the accuracy of the experiment, the values for the Heat Transfer Coefficient in
the filmwise condenser were compared to the values which are obtained theoretically using the
Nusselt equation. One explanation for this is the presence of non-condensable gases in the steam
vapour. The graph shows that for a certain temperature difference, the Heat Flux for a condenser
using steam mixed with 5% of air is significantly smaller than pure steam, and the magnitude of
this difference increases with temperature difference. In the case of Heat Transfer Coefficients,
the value for both steam and steam with air approaches zero, but when the steam is mixed with
air it consistently slows.
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Conclusion
In conclusion, dropwise condensation is a more effective method of heat transfer than
filmwise condensation and the presence of air in steam vapour significantly reduces the heat
transfer. This result is based on the data that is collected and the observation in the graph. The
heat flux and the heat transfer coefficient of dropwise condensation is higher compared to
filmwise condensation. Filmwise is poor conductor of heat which creates thermal resistance that
causes heat flux and heat transfer coefficient is lower than dopwise condensation.
Recommendation
The most important thing in this experiment is student should make sure that heater always
immersed in water during the experiment. If not the experiment should not be carry on. Next, the
equipment that is used in the experiment must be in best condition before starting the
experiment. Students should ask the technician that is responsible for that equipment if there
issomething wrong with it. When student take the result, ensure that the reading pressure is at
1.01 bar, where it is stabilized.
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Reference
1) Mayhew, Y, Rogers, G. (1992). Engineering thermodynamics: Work & Heat Transfer 4th ed.
Prentice Hall.
2) J.W. Rose, Condensation Heat Transfer Fundamentals, Transactions of the IChemE,
vol.76(A), pp. 143 152, 199
3) Incropera, F, DeWitt, D. (1996).Fundamentals of heat and mass transfer. 4thed. Wiley
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Appendix