UNIVERSITI TEKNOLOGI MARAFAKULTI KEJURUTERAAN KIMIA

THERMOFLUIDS LABORATORY (CGE536)

NAME : MUHAMAD ADNAN BIN ZAINAL ABIDIN (2015208916)GROUP : 3EXPERIMENT : LAB 6 : FILM BOILING CONDENSATIONDATE : 3RD MAY2016PROG/CODE : EH2433BNo Title Allocated Marks

(%)Marks

1 Abstract 52 Introduction 53 Objectives 54 Theory 55 Procedures/Methodology 106 Apparatus 57 Results 108 Calculation 109 Discussion 2010 Conclusion 1011 Recommendations 512 References 513 Appendices 5

TOTAL 100

Remarks:

Checked by: Rechecked by:

Date: Date:

1

ABSTRACT

This Film and Dropwise Condensation Unit is used to observe the process of heat

transfer during condensation, as well as gather experimental data for a better theoretical

understanding. The unit itself contained bench top unit, with an integrated steam generator

and air extraction system. The main components in the unit are the specially designed

condensers for the observation of both filmwise and dropwise condensation about the

differences of them. In this experiment, we want to study the heat transfer coefficient and

the heat flux. Besides that, we were study the effect of air inside the chamber. Condensation

occurs when vapor changes to liquid state with a large heat-transfer coefficient. Filmwise

condensation occurs on a vertical or horizontal plane when a film of condensate is formed

on surface and flows by action of gravity. Dropwise condensation occurs when small drops

formed on surface. The heat transfer coefficient can be calculated using Nussselt equation. .

Nusselt assumed that the heat transfer that occurs from the vapor through the film and to the

wall is conduction. Since the process is conduction is well known, therefore calculation on

the heat-transfer coefficients can be done. In this experiment, obtained data are for Tsat, Tsurf,

Tin and Tout.

2

INTRODUCTION

Filmwise and Dropwise are two forms of condensation. In filmwise condensation a

laminar film of vapor is created upon a surface. This film can then flow downwards, increasing

in thickness as additional vapor is picked up along the way. In dropwise then flow downwards,

accumulating static droplets below them along the way.

When the rate of condensation is low (e.g., a non-condensable gas is present) or when the

liquid does not "wet" the wall, dropwise condensation occurs. In most engineering components

where condensation is a required part of an industrial process film condensation is expected,

because of the large mass flux of condensed liquid per unit length of wetted area.

Dropwise condensation was first recognized by Schmidt et al. (1930), and much interest

was stimulated by their report that heat transfer coefficient are between 5 and 7 times those

found with film condensation. Over the years there have been a few demonstrations of successful

applications on an industrial scale. 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 power 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. Dropwise condensation

is difficult to sustain reliably; therefore, industrial equipment is normally designed to operate in

filmwise condensation mode.

In all application, the steam must be condensed as it transfers heat to a cooling medium

which could be cold water in a condenser of generating station, hot water in a heating calorifier,

sugar solution in a sugar refinery and etc. during condensation very high heat fluxes are possible

and provided that the heat can be quickly transferred from the condensing surface into the

cooling medium, the heat exchangers can be compact and effective.

The SOLTEQ Film & Dropwise Condensation Unit (Model: HE163) is designed to help

student to understand several key aspects in condensation topic, in particular the process of

filmwise and dropwise condensation. It allows students to visualize both phenomena and

3

perform a few experiments to demonstrate both concepts and how their applied and give benefit

in industry.

4

OBJECTIVES

1. To demonstrate the filmwise and dropwise condensation.

2. To describe filmwise and dropwise condensation

3. To demonstrate the effect of air on heat transfer coefficient of condensation

4. To demonstrate the filmwise heat flux and surface heat transfer coefficient ay constant

pressure.

5. To determine the dropwise heat flux and surface heat transfer coefficient at constant

pressure.

5

THEORY

Mechanism of Condensation

Condensation of a vapor to a liquid and vice versa, both involve a change of a fluid with

large heat-transfer coefficients. Condensation occurs when a saturated vapor such as steam

makes a contact with a solid whose surface temperature is below the saturation temperature, to

form a liquid such as water.

When a vapor condenses on a surface, for example vertical or horizontal tube or other

surface, a film of condensate is formed on the surface and flows over the surface because of

gravity. It is this film of liquid between the surface and the vapor that produce the main

resistance of heat transfer. This is called filmwise condensation.

Another type of condensation is dropwise condensation. Dropwise condensation occurs

when small drops are formed on the surface. These drops grow and mix together, and the liquid

flows from the surface. Large areas of tube are devoid of any liquid and are exposed directly to

the vapor during condensation. Very high rates of heat-transfer occur on these bare areas. The

average heat transfer coefficient for dropwise condensation is five to ten times larger than the

filmwise coefficient.

Dropwise condensation can be promoted by making the surface non-welting by coating.

However, dropwise condensation is difficult to maintain in industrial applications because of

oxidation, fouling and degrading of coating, and finally film condensation occurs. Therefore,

condenser designs are often based on the assumption of filmwise condensation.

Film-condensation coefficients for vertical surfaces

Film type condensation on a vertical wall or tube can be find analytically by assuming

laminar flow of the condensate film down the wall. The film thickness is zero at the top of the

6

wall or tube. It increases in thickness as it flows downward as a result of condensation. Nusselt

assumed that the heat transfer from the condensing vapor at Tsat, through this liquid film, and at

the wall at Tw, was by conduction. Equating this heat-transfer by conduction to that from

condensation of the vapor, final expression can be obtained for the average heat-transfer

coefficient over the whole surfaces.

7

APPARATUS

Equipment Prefer:

SOLTEQ MODEL: HE 163 (Film and Dropwise Condensation Unit)

8

PROCEDURE

General Start-up

1. The main switch is ensured in its off position.

2. The power regulator knobs are turned fully anti-clockwise to set the power to minimum.

3. Valves V1 to V6 are checked to ensure its closed.

4. The chamber is filled with distilled water until the water level stays between the hater and

baffles plates. The heater is ensured fully immersed in the water throughout the

experiment. The chamber is filled with water through the drain valve with the vent valve,

V4 opened. Then the vent valve V4 is closed.

5. The water flow rate to the condenser is adjusted by controlling the control valve

according to experimental procedure.

6. The main switch and the heater switch are turned on. The heater power is set by rotating

the power regulator clockwise to increase the hater power.

7. The water temperature reading is observed where the water temperature should increase

when its start heat-up.

8. The water is heated up to boiling point until the pressure reaches 1.02-1.10 bar.

Immediately valve V1 is opened and follow by valve V5 for 1 minute to vacuum out the

air inside condenser. Then both valve V1 and V5 is closed.

9. The system is let to stabilize. Then all relevant measurement is taken for experimental

purposes. Adjustment is made if required.

General shut-down

1. The voltage control knob is turned to 0 Volt position by turning the knob fully anti-

clockwise. The cooling water is kept flowing for at least 5 minutes through the condenser

to cold them down.

2. The main switch and power supply are switch off. Then, the power supply cable is

unplugged.

3. The water supply is closed and the cooling water connection tubes are disconnected if

necessary. Otherwise, the connection tubes are leaved for next experiment.

4. The water inside the chamber is discharged using the discharge valve.

9

A) Demonstration of filmwise and dropwise condensation

1. The basic procedure is followed as written in the general set-up. The equipment by make

sure connected to the service unit.

B) The filmwise heat flux and surface heat transfer coefficient determination at constant

Pressure

1. Cooling water is circulated through the filmwise condenser starting with a minimum

value of 0.1 LPM.

2. The heater power is adjusted to obtain the desired pressure at 1.01 bar.

3. When the condition is stabilized, the steam (T sat) and surface temperature (T surf ) , T ¿ (T1)

and T out (T2), and flowrate are recorded.

C) The dropwise heat flux and surface heat transfer coefficient determination at

Constant pressure

1. Cooling water is circulated through the dropwise condenser starting with a minimum

value of 0.4 LPM.

2. The heater power is adjusted to obtain the desired pressure at 1.01 bar.

3. When the condition is stabilized, the steam (T sat) and surface temperature(T surf ), T ¿ (T3),

T out (T4) and flowrate are recorded.

10

RESULTS

Experiment 1: Demonstration of filmwise and dropwise condensation

Figure 2: (Left) The Filmwise Condensation and (right) The Dropwise Condensation

11

Experiment 2:

Table 1: The filmwise heat flux and surface heat transfer coefficient determination at constant

pressure

Flowrat

e (LMP) Power (P)

Tin

( ̊ C)

Tout

( ̊ C)

Tsat

( ̊ C)

Tsurf

( ̊ C)

ΔTm

( ̊ C) q ɸ U

0.1 185 31.9 32.0 70.4 30.7 38.44 185 45826.11 1192.15

0.2 205 34.3 34.6 69.2 33.3 35.35 205 50780.28 1436.50

0.3 230 34.6 34.9 68.8 33.8 34.05 230 56973.00 1673.22

0.4 259 34.8 34.9 68.5 34.1 33.65 259 64156.55 1906.58

34.4 35 35.9 39.70

10000

20000

30000

40000

50000

60000

70000

Heat Flux vs Tsat-Tsurf

Tsat-Tsurf

Heat

Flu

x

Heat Flux vs. Tsat-Tsurf for filmwise without air

12

34.4 35 35.9 39.70

500

1000

1500

2000

2500

Heat Coefficient vs Tsat-Tsurf

Tsat-Tsurf

Heat

Coe

fficie

nt

Heat coefficient against Tsat-Tsurf for filmwise without air

13

Experiment 3:

Table 2: The dropwise heat flux and surface heat transfer coefficient determination at constant

pressure

Flowrate

(LMP)

Power

(P)

Tin

( ̊ C)

Tou

t

( ̊ C)

Tsat

( ̊ C)

Tsurf

( ̊ C)

ΔTm

( ̊ C) q ɸ U

0.4 347 34.6 35.7 68.8 41.6 33.65 347 85954.92 2554.38

0.8 365 34.9 35.9 72.2 44.2 36.80 365 90413.67 2456.89

1.2 487 35.1 35.9 71.8 45.2 36.30 487 120634.13 3323.25

1.6 588 34.4 36.1 70.2 46.6 34.94 588 145652.71 4168.65

23.6 26.6 27.2 280

20000

40000

60000

80000

100000

120000

140000

160000

Heat Flux vs Tsat-Tsurf

Tsat-Tsurf

Heat

Flu

x

Heat Flux vs. Tsat-Tsurf for dropwise without air

14

23.6 26.6 27.2 280

500

1000

1500

2000

2500

3000

3500

4000

4500

Heat Coefficient vs Tsat-Tsurf

Tsat-Tsurf

Heat

Coe

fficie

nt

Heat coefficient against Tsat-Tsurf for dropwise without air

15

Experiment 4:

Filmwise

Table 3: The effect of air inside chamber for filmwise

Flowrate

(LMP)

Power

(P)

Tin

( ̊ C)

Tout

( ̊ C)

Tsat

( ̊ C)

Tsurf

( ̊ C)

ΔTm

( ̊ C) q ɸ U

0.1 248 33.1 35.1 68.3 33.7 34.19 248 61431.76 1796.79

0.2 275 33.1 33.6 68.9 32.5 35.55 275 68119.89 1916.17

0.3 298 33.1 34.9 69.7 32.1 35.69 298 73817.19 2068.29

0.4 308 33.3 33.4 69.8 31.7 36.45 308 76294.28 2093.12

34.6 36.4 37.6 38.11600

1700

1800

1900

2000

2100

2200

Heat Coefficient vs Tsat-Tsurf

Tsat-Tsurf

Heat

Coe

fficie

nt

The heat coefficient vs Tsat-Tsurf for filmwise with 1% air

16

Dropwise

Table 4: The effect of air inside chamber for dropwise

Flowrate

(LMP)

Power

(P)

Tin

( ̊ C)

Tout

( ̊ C)

Tsat

( ̊ C)

Tsurf

( ̊ C)

ΔTm

( ̊ C) q ɸ U

0.4 323 33.4 34.3 71.3 32.6 37.45 323 80009.91 2136.45

0.8 559 33.4 34.4 70.5 32.6 36.60 559 138469.16 3783.31

1.2 571 33.6 34.5 71.7 32.9 37.65 571 141441.66 3756.75

1.6 685 33.8 34.9 72.3 33.3 37.95 685 169680.46 4471.16

37.9 38.7 38.8 390

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Heat Coefficient vs Tsat-Tsurf

Tsat-Tsurf

Heat

Coe

fficie

nt

The heat coefficient vs Tsat-Tsurf for dropwise with 1% air

DISCUSSIONS

17

In this experiment we are mostly investigate about the film boiling condensation

by using the SOLTEQ Film and Dropwise Condensation Unit (Model: HE 163). There are 4

objectives that must be accomplished. For the experiment 1, we have to demonstrate the filmwise

and dropwise condensation. From this experiment, we are able to describe the characteristics of

filmwise and dropwise condensation. In filmwise condensation, most materials used in the

construction of heat exchangers are “wettable” and during the condensation a film condensate

spreads over the surface. More vapour condenses onto the outside of this film will increases its

thickness and causes the flow downward and drip from the lowest points. The heat given up by

the vapour during condensation is conducted through the film. During filmwise condensation a

layer of condensate covers the cool surface and this will cause the resistance to the transfer of

heat. However, for the dropwise condensation the material used in the construction is “non-wet

table” .When the steam condenses, a large number of spherical forms on its surface. These beads

become larger and then the trickle downwards. The moving bead gathers all the static beads

along its downward path, becomes larger, accelerates and leaves a virtually bare surface in its

trail.

For experiment 2 and 3, theoretically there is a big difference from the graph for the

dropwise and filmwise condensation based on its heat transfer coefficient and temperature

difference. For dropwise there is a relatively larger area heat transfer coefficient that proposes a

larger value of heat transfer during condensation. As for filmwise there is a smaller value of heat

transfer and the larger area on the graph that shows the larger margin of heat transfer value are at

larger heat transfer value. But for the errors that has occur, they didn’t match for the desirable

data.

For experiment 4, theoretically, the clear difference between both heat transfer coefficient

and temperature difference for filmwise and dropwise condensation is for dropwise with the

present of air there is a larger value of heat transfer coefficient at a small temperature difference

rather than for filmwise that shows a smaller value of heat transfer coefficient and at a larger

difference of temperature. The analysis for the data collected is that heat flux shows a clear

difference due to the presence of air. With the presence of air the heat flux value is smaller.

Dropwise condensation is far more efficient for condensation process due to the specifications

18

for each plate surface. However, we are not able to achieve the desired outcome due to some

errors.

The errors involve that effect the results is due to fluid involve for the process of

condensation to occur. The impurities that contain within the fluid involve has effect the density

and boiling temperature that occur at a much lower temperature. Thus condensation occurs at a

less precise order and resulting in impairment data.

19

CONCLUSION

For experiment 2 and 3, we have concluded that the dropwise condensation heat flux and

surface heat transfer coefficient at constant pressure occur at a relatively larger value at smaller

temperature difference than for filmwise condensation. Thus efficient condensation

For experiment 4, we have demonstrated the effect of air on heat transfer coefficient of

condensation for dropwise and filmwise, it concluded that dropwise has a more stable and larger

heat transfer value for condensation process thus a more efficient condensation process.

RECOMMENDATIONS

1. Avoid error in taking readings and make sure eyes of observer are parallel to the meniscus

2. Make sure the valve were close tightly when the film condensation equipment is turn off.

3. Make sure all the valve close at the beginning of the experiment

4. Allow the cooling water to flow at the end of the experiment before the equipment is shut

down to avoid the cracking of cylindrical tube.

20

REFERENCES

1) Aksan, S. N. and Rose, J. W. (1973). Dropwise condensation—the effect of thermal

properties of the condenser material. Int. J. Heat Mass Transfer, 16, 461-467.

2) Blackman, L. C. F., Dewar, M. S. J. and Hampson, H. (1957). Compounds for promoting

dropwise condensation of steam. J. Appl. Chem., 7, 160-171.

21

Appendices

22

23