filmdropwise lab .docx

8/14/2019 filmdropwise lab .docx

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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


Tm =

=


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=

=36.95 C

Heat flux, =

=

=1555.52 w/m 2


=

=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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Tm =

=

=

=36.55 C

Heat flux, =

=

=2075.80 w/m 2


= =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


Tm =

=

=

.

Heat flux, =

=

= 864.45 w/m 2


=

=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


Tm =

=

=

=36.85 C

Heat flux, =

=

= 1037.84 w/m 2


=

=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


Tm =

=

=

=36.25 C

Heat flux, =

=

=7606.71 w/m 2


=


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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


Tm =

=

=

=34.91 C

Heat flux, =

=

=40436.18 w/m 2



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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


Tm =

=

=

=35.13 C

Heat flux, =

=


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=40081.97 w/m 2


=

=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


Tm =

=

=

=35.44 C


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=35.39 C

Heat flux, =

=

=45620.43 w/m 2


= =1289.08 w/m 2.K

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

0 5 10 15 20 25



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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


0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25



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Tm =

=

=

=30.90 C

Heat flux, =

=

= 16766.46 w/m 2


=

=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


Tm =

=

=

=31.38 C

Heat flux, =

=

= 19352.39 w/m 2


=

=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


Tm =

=

=

=35.12 C

Heat flux, =

=

=17108.28 w/m 2


= =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


Tm =

=

=

=35.59 C

Heat flux, =

=

=16598.03 w/m 2



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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


Tm =

=

=

=36.24 C

Heat flux, =

=

= 16417.21 w/m 2


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=

=453.01 w/m 2.K

16000

16500

17000

17500

18000

18500

19000

19500

0 5 10 15 20 25 30 35



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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


0

100

200

300

400

500

600

700

0 5 10 15 20 25 30 35



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Tm =

=

=

=37.49 C

Heat flux, =

=

=9286.08w/m 2


=

=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


Tm =

=

=

=36.04 C

Heat flux, =

=

=19699.16 w/m 2


=

=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


Tm =

=

=

=36.09 C

Heat flux, =

=

=21358.72 w/m 2


= =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


Tm =

=

=

=36.30 C

Heat flux, =

=

=24197.30 w/m 2


=


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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


Tm =

=

=

=36.10 C

Heat flux, =

=

=29032.31 w/m 2


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=

=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

filmdropwise lab .docx

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