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RESULT EXPERIMENT 1 : DEMONSTRATION OF FILMISE AND DROPWISE Type of Condensation Characteristic Observation Filmwise Low rate of condensation The water doplets flow Directly to the bottom Dropwise High rate of condensation The water droplet flow drop by drop to the bottom Table 1 10
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film boilng condensation

Aug 22, 2014

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Page 1: film boilng condensation

RESULT

EXPERIMENT 1 : DEMONSTRATION OF FILMISE AND DROPWISE

Type of Condensation Characteristic Observation

Filmwise Low rate of condensation The water doplets flowDirectly to the bottom

Dropwise High rate of condensationThe water droplet flow

drop by dropto the bottom

Table 1

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EXPERIMENT 2 : THE FILMWISE HEAT FLUX AND SURFACE HEAT TRANSFER COEFFICIENT DETERMINATION AT CONSTANT PRESSURE

Reading Power(W)

WaterFlowrate(LPM)

Steam, Tsat

Surface temperature,

Tsurf

∆T(Tsat – Tsurf)

Tin, T1 Tout, T2 Flowrate

1 -1803.19 0.1 71.3 83.9 -12.6 31.1 60.9 24.02 -372.09 0.2 71.5 72.8 -1.3 31.3 47.0 24.03 1373.86 0.3 71.4 68.2 3.2 31.2 41.8 24.04 4980.25 0.4 71.1 62.4 8.7 31.3 39.3 24.05 7942.65 0.5 71.6 60.5 11.1 31.2 38.2 24.06 11333.75 0.6 71.1 57.9 13.2 31.2 37.0 24.07 15527.52 0.7 71.4 55.9 15.5 31.2 36.2 24.08 19119.6 0.8 71.0 54.3 16.7 31.2 35.5 24.09 22667.48 0.9 71.3 53.7 17.6 31.2 35.2 24.010 26046.16 1.0 71.1 52.9 18.2 31.2 34.6 24.0

Table 2

Reading Heat Flux, q’’ Surface Heat Transfer Coefficient, h1 -1423.45 11.972 -293.72 228.953 1084.54 338.924 3931.46 451.895 6270.00 564.866 8947.46 677.847 12257.57 790.818 15093.19 903.789 17893.92 1016.7610 20561.08 1120.73

Table 3

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Graph 1

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Graph 2

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EXPERIMENT 3 : THE DROPWISE HEAT FLUX AND SURFACE HEAT COEFFICIENT AT CONSTANT PRESSURE

Reading WaterFlowrate(LPM)

Steam, Tsat

Surface temperature,

Tsurf

∆T(Tsat – Tsurf)

Tin, T1 Tout, T2 Flowrate Power(W)

1 0.4 71.2 67.0 4.2 31.2 39.9 24.0 2404.26092 0.8 71.2 61.5 9.7 31.2 36.6 24.0 11105.39593 1.2 71.1 58.0 13.1 31.1 35.0 24.0 22497.01364 1.6 71.6 57.6 14.0 31.1 33.9 24.0 32056.8132

Table 5

Reading Heat Flux, q’’ Surface Heat Transfer Coefficient, h1 1897.9459 451.892 8766.7027 903.783 17759.3514 1355.684 25305.9460 1807.57

Table 6

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Graph 315

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Graph 4

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Graph 5

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Graph 6

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EXPERIMENT 4 : THE EFFECT OF AIR INSIDE CHAMBER

Filmwise

Reading Pressure (atm)

WaterFlowrate(LPM)

Steam, Tsat

Surface temperature,

Tsurf

∆T(Tsat – Tsurf)

Tin, T1 Tout, T2 Flowrate Power(W)

1 1.01 0.1 71.0 74.3 -3.3 31.4 53.6 24.0 -472.26552 1.01 0.2 71.4 64.0 7.4 31.5 43.7 24.0 2118.03943 1.01 0.3 71.3 58.4 12.9 31.4 39.2 24.0 5538.38694 1.01 0.4 71.3 55.3 16.0 31.4 37.6 24.0 9159.08955 1.01 0.5 71.2 55.0 16.2 31.4 36.6 24.0 11592.09926 1.01 0.6 71.2 51.4 19.8 31.4 35.4 24.0 17001.55977 1.01 0.7 71.2 50.3 20.9 31.4 32.1 24.0 20937.1062

Table 7

Reading Heat Flux, q’’ Surface Heat Transfer Coefficient, h1 -372.8108 112.972 1672.0000 225.963 4372.0541 338.924 7230.2703 451.895 9150.9108 564.866 13421.1891 677.847 16527.9460 790.81

Table 8

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Dropwise

Reading Pressure (atm)

WaterFlowrate(LPM)

Steam, Tsat

Surface temperature,

Tsurf

∆T(Tsat – Tsurf)

Tin, T1 Tout, T2 Flowrate Power(W)

1 1.01 0.4 71.5 54.2 17.3 31.3 36.0 24.0 9903.26542 1.01 0.8 71.3 51.0 20.3 31.3 34.2 24.0 23241.18953 1.01 1.2 71.2 49.6 21.6 31.3 33.3 24.0 37094.31244 1.01 1.6 71.2 48.7 22.5 31.3 33.1 24.0 51519.8783

Table 9

Reading Heat Flux, q’’ Surface Heat Transfer Coefficient, h1 7817.7297 451.892 18346.8108 903.783 29282.5946 1355.684 40670.2703 1807.57

Table 10

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Filmwise

Graph 7

Dropwise

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Graph 8

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Filmwise

Graph 9

Dropwise

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Graph 10

CALCULATIONS

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Sample calculations

Heat flux

Q " = Q/A

Surface heat transfer coefficient

h= Q____

A.dT

Q= heat flow in input or lost heat flow , J/s=W

h=heat transfer coefficient, W/(m2K)

A= heat transfer surface area, m2

dT = difference in temperature between the solid surface and surrounding fluid are, K

Example

Heat flux

Q”= 1373.86/ 1.26677

= 1084.5405

Surface Heat transfer

Area condenser tube= πd2/4= 1.26677m2

h = 1373.86/(1.26677 x 3.2)

=338.92 W/(m2K)

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DISCUSSION

Experiment 1 : demonstration of film wise and drop wise condensation

The objective to demonstrate the film wise and drop wise condensation is achieved. The

characteristic of film wise at low rate condensation shows that the water droplets flow directly to

the bottom while drop wise at high rate of condensation shows that the water droplets flow drop

by drop to the bottom. This is because film wise condensation on vertical surfaces occurs when

the liquid phase fully wets the surface, whereas in drop wise condensation the liquid

incompletely wets the solid surfaces.

The condensation process begins with vapour condensing directly on the wall surface. However,

in contrast with drop wise condensation after the wall is initially wetted, it remains covered by a

thin film of condensate. Thus, the condensation rate is directly a function of the rate at which

heat is transported across the liquid film from the liquid-vapor interface to the wall.

Figure above shows three distinct regimes of film wise condensation on the vertical wall. These

regimes are proceeding in order from the top wall (x=0) that is laminar, wavy and turbulent. At

the top of the wall, where the film is thinnest, the laminar regime is exist. As the condensation

process proceeds, more and more condensation appears on the surface and the liquid condensate

is pulled downward by gravity. As the condensate moves downward, the film becomes thicker.

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Finally, if the film thickness becomes so great that irregular ripple in both time and space will

appear which is identified as turbulent flow regime.

Experiment 2 and 3

The cooling water is circulated through the film wise condenser starting with a minimum

value of 0.1 LPM.to attain the desired pressure at1.01 bar, the heater power is adjusted. When

the condition is stabilized, the steam at temperature saturated surface temperature at temperature

surface, temperature in and out and flow rates are jotted. Graph 2 shows that the heat flux

increases with temperature differences increases at constant steam pressure. While graph of drop

wise show that it increases more than the film wise graph. This can be explained in terms of how

the condensation forms in the condenser. The vapour drops in dropwise condensation are discrete

and are continually formed and released which means that the surface of the condenser is also

continually being exposed. In comparison, the film created in film wise condensation always

covers the surface of the condenser at film wise. As a relatively poor conductor of heat, this film

creates a thermal resistance which is the reason why the value for heat flux for film wise is lower

than the drop wise condensation.

To check the accuracy of the experiment, the values for the heat transfer coefficient in the film

wise condenser were compared to the values which are obtained theoretically using the heat

transfer coefficient equation:

h= Q____ A.dT

Q= heat flow in input or lost heat flow , J/s=Wh=heat transfer coefficient, W/(m2K)A= heat transfer surface area, m2

dT = difference in temperature between the solid surface and surrounding fluid are, K

Experiment 4: the effect of air inside chamber

The effect of a non condensable gas in the steam vapour is presented in the graph 7 until

10 show 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

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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

is consistently low.

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.

APPLICATION

During winter, the inside of windows will undergo fog, moisture or sweating. That fog or

moisture occurs when humid air comes in contact with a surface that is cooler than the air. This

happens when doors and windows are kept closed, hence holding in the moisture-filled air. A

thin film of dew or frost on your windows is normal and will not damage them

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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.

RECOMENDTION

1. Always opened the overflow valve to maintain or lower its pressure.

2. Make sure that the valve is closed tightly to ensure no leaking of water during

experiment.

3. Make sure that the pressure switch to turn off the heater when chamber pressure exceeds

1.20 abs bar, pressure relief valve to discharge at 1.5 abs bar

4. Make sure that when taking the reading of the flow rate, the eye level must be

perpendicular with the water inside the chamber.

5. Do not directly touch the over flow water that might have high temperature that can

blistered.

REFERENCES

Advanced Heat and Mass Transfer ,By Amir Faghri, Amir Faghri, Yuwen Zhang, John Howell, Yuwen Zhang, John Howell

W.W. Akers, S.H. Davis, Jr and J.E. Crawford, "Condensation of a Vapor in the Presence of a Noncondensing Gas," Chemical Engineering Progress Symposium Series, No 30, Vol 56, pp 139-144, 1960.

H.K. Al-Diwany and J.W. Rose, "Free Convection Film Condensation of Steam in the Presence of Noncondensing Gases," Int J Heat Mass Transfer, Vol 16, pp 1359-1369 1973.

K. Almenas and U. Lee, "A Statistical Evaluation of the Heat Transfer Data Obtained in the HDR Containment Tests," University of Maryland, 1984.

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K. Asano and Y. Nakano, "Forced Convection Film Condensation of Vapors in the Presence of Noncondensable Gas on a Small Vertical Flat Plate," J of Chem Engr of Japan , 1978.

APPENDIX

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