Flim Boiling Condensation manual

EXPERIMENTAL MANUAL

MODEL: HE163

SOLUTION ENGINEERING SDN. BHD.NO.3, JALAN TPK 2/4, TAMAN PERINDUSTRIAN KINRARA,47100 PUCHONG, SELANGOR DARUL EHSAN, MALAYSIA.TEL: 603-80758000 FAX: 603-80755784E-MAIL: [email protected]: www.solution.com.my

SOLTEQ EQUIPMENT FOR ENGINEERING EDUCATION

230-0210-HE

FILM & DROPWISE

CONDENSATION

UNIT

FILM & DROPWISE

CONDENSATION

UNIT

SOLTEQ® FILM & DROPWISE CONDENSATION UNIT (Model: HE 163)

i

Table of ContentsPage

Table of Contents............................................................................................................................... iList of Figures……………………………………………………………………………………………….iii

1.0 INTRODUCTION..................................................................................................................1

2.0 GENERAL DESCRIPTION..................................................................................................22.1 Unit Assembly…………………………………………………………………………………22.2 Experimental Capabilities……………………………………………………………………..22.3 Specifications……………………………………………………………………………………32.4 Overall Dimensions……………………………………………………………………………42.5 General Requirements…………………………………………………………………………4

3.0 INSTALLATION AND COMMISSIONING ...........................................................................53.1 Temperature Sensors ....................................................................................................53.2 Heating Element.............................................................................................................53.3 Cooling Water Supply ....................................................................................................53.4 Cooling Water Drain.......................................................................................................53.5 Commissioning Procedures ...........................................................................................5

4.0 SUMMARY OF THEORY.....................................................................................................64.1 Mechanism of Condensation..........................................................................................64.2 Film-Condensation coefficient for vertical surfaces ........................................................7

5.0 GENERAL OPERATING PROCEDURES .........................................................................115.1 Electrical Connection ..................................................................................................115.2 Temperature Selection ................................................................................................115.3 Heater Setting .............................................................................................................115.4 Cooling Water Control..................................................................................................11

6.0 EXPERIMENTAL PROCEDURE .......................................................................................126.1 General Start Up Procedures.......................................................................................126.2 General Shut Down Procedures...................................................................................126.3 Experiment 1: DEMONSTRATION OF FILMWISE & DROPWISE

CONDENSATIION ........................................................................................................136.4 Experiment 2: THE FILMWISE HEAT FLUX & SURACE HEAT TRANSFER

COEFFICIENT DETERMINATION AT CONSTANT PRESSURE.................................146.5 Experiment 3: THE DROPWISE HEAT FLUX & SURACE HEAT TRANSFER

COEFFICIENT DETERMINATION AT CONSTANT PRESSURE.................................156.6 Experiment 4: THE EFFECT OF AIR INSIDE CHAMBER ...........................................16


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7.0 EQUIPMENT MAINTENANCE ..........................................................................................177.1 Heater ..........................................................................................................................177.2 Condenser ...................................................................................................................17

8.0 SAFETY PRECAUTIONS ..................................................................................................188.1 Warning........................................................................................................................188.2 Cautions.......................................................................................................................18

APPENDIX A Experimental Data SheetAPPENDIX B Typical Experimental ResultAPPENDIX C Sample CalculationAPPENDIX D Filmwise and Dropwise condensation


iii

List of FiguresPage

Figure 1 Unit Construction for Film & Dropwise Condensation Unit 2(Model: HE 163)

Figure 2 Film condensation on a vertical plate: a) increase in film thickness with 7Position, b) balance on element of condensate.


1

1.0 INTRODUCTION The use of steam both for power production to convey heat has a long history and its use in these fields is likely to continue into the foreseeable future.

In all applications, 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 aheating 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.

Steam may condense onto a surface in two distinct modes, known as the Filmwise and the Dropwise condensation. For the same temperature difference between the steam and the surface, dropwise condensation is several times more effective than filmwise, and for this reason the former is desirable although in practical plants, it seldom occurs for prolonged periods.

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 perform a few experiments to demonstrate both concepts.


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2.0 GENERAL DESCRIPTION2.1 Unit Assembly

Figure 1: Unit Construction for Film & Dropwise Condensation Unit (Model: HE 163)

1. Pressure Relief Valve 6. Separator

2. Indicators 7. Dropwise Condenser

3. Flowmeter 8. Filmwise Condenser

4. Discharge Valve 9. Coiled-Heater

5. Pressure Transmitter 10. Vacuum Ejector

1

2

3

6

5

7

9

4

8

10


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2.2 Experiment CapabilitiesVisual observation of filmwise and dropwise condensation, as well as nucleate boiling.

Determination of heat flux and heat transfer coefficients in both filmwise and dropwise condensation at different operating pressures.

Investigation on the relationship between saturation pressure and temperature for water up to 100 °C.

Study on the effect of air on heat transfer coefficient in the chamber.

2.3 Specifications2.3.1 Steam Chamber

Borosilicate Glass cylinder with flanged ends and coverso Outer Diameter : 105 mmo Height : 400 mmo Thickness : 5 mm

2.3.2 CondensersTwo water-cooled condensers fabricated from copper and brass.o Diameter : 12.7 mmo Length : 120 mmo Material :

Gold plated (dropwise condenser)Natural finish (filmwise condenser)

* Each condenser is fitted with 3 thermocouples to measure the mean surface temperature and 2 temperature sensors to measure the inlet and outlet water temperatures.

2.3.3 Heating ElementCoiled Heater with thermal protectiono Power : 3.0 kWo Control : Triac control between 0.4 to 3.0 kW

2.3.4 Air Extraction SystemAir cooler, separator, and water jet vacuum pump.


4

2.3.5 InstrumentationsTemperature sensors at all important points.

Pressure sensor to measure the chamber pressure.

Flowmeters to measure the water flow rate through the condensers:o Dropwise condenser : 0.4 – 4.0 LPMo Filmwise condenser : 0.1 – 1.0 LPM

2.3.6 Safety FeaturesPressure switch to turn off the heater when chamber pressure exceeds 1.50 Abs Bar.

Pressure relief valve to discharge at 1.50 Abs Bar.

2.4 Overall DimensionsHeight : 800 mmWidth : 900 mmDepth : 600 mm

2.5 General RequirementsElectrical : 230VAC/50Hz/25 AmpWater : Continuous water supply (Min 10LPM @ 2-3 Bar)


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3.0 INSTALLATION AND COMMISSIONINGEnsure that the main switch is switch off. Place the Film & Dropwise Condensation Unit on a bench.

3.1 Temperature SensorsFive temperature sensors are installed and each lead has a label. There are also 6 thermocouple wires installed. Ensure that all thermocouples and the lead are in good condition.

3.2 Cooling Water SupplyThe Film & Dropwise Condensation Unit requires a source of clean andconstant temperature (cold) water with flow approximately 4 - 5 LPM at 2 to 3 bar supply. The Film & Dropwise Condensation Unit comes with water inlet valves to control the water flow rates. Connect the water supply to the cold-water inlet.

3.3 Cooling Water DrainThe Film & Dropwise Condensation Unit comes with two drain tubes; one forthe condenser and one for the vacuum ejector. They should be secured properly so that it will not fall out during the experiment.

3.4 Commissioning ProceduresPush the reset button of the Earth Leakage Circuit Breaker (ELCB) inside the control panel after the main power supply is switched on. The ELCB should be kicked off, indicating that the ELCB is functioning properly. If not, have a trained wireman to inspect the trainer for any electrical leakage. The ELCB should be tested at least once a month. Switch on the main switch and check the indicators. They should display the measurements of all respective instruments. Fill the boiler chamber with distilled water from the bottom valve until the water level is sufficient to fully cover the heater element. Switch on the heater and observe the boiling. Then, slowly open the cooling water of both film and dropwise condensers. The flow indicators should display the respective flow rates. Switch off the heater, the unit is ready for use.

Note: Never operate the heater whenever the water level falls below the heater element as this will permanently damage the heater.


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4.0 SUMMARY OF THEORY4.1 Mechanism of Condensation

Condensation of a vapor to a liquid and vaporization of a liquid to a vapor both involve a change of phase of a fluid with large heat-transfer coefficients. Condensation occurs when a saturated vapor such as steam comes in contact with a solid whose surface temperature is below the saturation temperature, to form a liquid such as water.

Normally, when a vapor condenses on a surface such as a vertical or horizontal tube or other surface, a film of condensate is formed on the surface and flows over the surface by the action of gravity. It is this film of liquid between the surface and the vapor that forms the main resistance to heat-transfer. This is called filmwise condensation.

Another type of condensation, dropwise condensation, can occur, where small drops are formed on the surface. These drops grow and coalesce, and the liquid flows from the surface. During this condensation, large areas of tube are devoid of any liquid and are exposed directly to the vapor. Very high rates of heat-transfer occur on these bare areas. The average heat transfer coefficient for dropwise condensation is five to 10 times larger than the filmwisecoefficients.

Dropwise condensation can be promoted by making the surface non-wetting (via coating). However, dropwise condensation is difficult to maintain in industrial applications due to oxidation, fouling and degradation of coating, and eventually film condensation occurs. Therefore, condenser designs are often based on the assumption of filmwise condensation.


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4.2 Film-Condensation coefficients for vertical surfacesFilm-type condensation on a vertical wall or tube can be analyzed analytically by assuming laminar flow of the condensate film down the wall. The film thickness is zero at the top of the wall or tube and increases in thickness as it flows downward because of condensation. Nusselt assumed that the heat-transfer from the condensing vapor at Tsat, through this liquid film, and to the wall at Tw was by conduction. Equating this heat-transfer by conduction to that from condensation of the vapor, a final expression can be obtained for the average heat-transfer coefficient over the whole surfaces.

In Figure 2 (a), vapor at Tsat is condensing on a wall whose temperature is Tw.The condensate is flowing downward in laminar flow. Assuming unit thickness,

l in Figure 2 (b) is -y) (dx l.

The downward force on this element is the gravitational force minus the

buoyancy force, or -y)(dx)×( l- ) g is the density of the saturated

vapor. This force is balanced by the viscous-shear force at the plane y of l(dv/dy) (dx·1). Equating these forces;

dxdydgdxy ll (4.2-1)

Integrating and using the boundary condition that at y = 0;

2/2yyg l (4.2-2)

Figure 2: Film condensation on a vertical plate: a) increase in film thickness with position, b) balance on element of condensate.

The mass flow rate of film condensate at any point x for unit depth is;


8

0

2

02/ dyyygdym l

lll (4.2-3)

Integrating;

lll gm3

3

(4.2-4)

At the wall, for area (dx·1) m2, the rate of heat transfer is as follows if a linear temperature distribution is assumed in the liquid between the wall and the vapor;

wsatlylx TTdxkdydTdxkq0

1 (4.2-5)

In a dx distance, the rate of heat transfer is qx. Also, in this dx distance, the increase in mass from condensation is dm. Using Eq. (4.2-4);

lll

lll dggddm 23

3(4.2-6)

Making a heat balance for dx distance, the mass flow rate dm times the latent heat h fg must equal the qx from Eq. (4.2-5):

wsatllllfg TTdxkdgh 2

(4.2-7)

Integrating, with = 0 at s = 0 and = at x = x;

4/1

4

llfgwsatllgh TTxk

(4.2-8)

Using the local heat-transfer coefficient hx at x, a heat balance gives;

wsatlwsatx TTdxkTTdxh 11 (4.2-9)

This gives

lx kh (4.2-10)


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Combining Eqs. (4.2-8) and (4.2-10);

4/13

4 wsatllfgllx TTx kghh (4.8-17)

By integrating over the total length L, the average value of h is obtained as follows;

L Lxx hdxhLh0 3

41(4.2-11)

4/13

943.0 wsatllfgll TTL kghh (4.2-12)

However, for laminar flow, experimental data are about 20% above Eq. (4.2-12). Hence, the final recommended expression for vertical surfaces in laminar flow is shown as Eq. (4.2-13):

4/13

13.1 Tk LghkhLN llfgll

lNu (4.2-13)

where l is the density of liquid in kg/m3 and that of the vapor, g is 9.8066

m/s2, L is the vertical height of the surface or tube in m, l is the viscosity of

liquid in Pa·s, kl is the liquid thermal conductivity in W/m K, T = Tsat-Tw in K,

and h fg is the latent heat of condensation in J/kg at Tsat. All physical properties of the liquid except h fg are evaluated at the film temperature T f = (Tsat + Tw)/2.For long vertical surfaces the flow at the bottom can be turbulent. The Reynolds number is defined as;

llDmN 44Re (vertical tube, diameter D) (4.2-14)

llWmN 44Re (vertical plate, width W) (4.2-15)

where m is the total kg mass/s of condensate at tube or plate bottom and =m/ D or m/W. The NRe should be below 1800 for Eq. (4.2-13) to hold. The

reader should note that some references define NRe as / . Then this NReshould be below 450.

For turbulent flow for NRe 1800;


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4.0

Re

3/1

2

32

0077.0 NLgkhLN ll

lNu (4.2-16)

Solution of this equation is by trial and error, since a value of NRe must first be assumed in order to calculate h.


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5.0 GENERAL OPERATING PROCEDURES5.1 Temperature Reading

To read a particular temperature, use the temperature selector knob to select the desired reading. The knob indicates temperature T1 to T4. Tsurf of filmwiseand Tsurf of dropwise are indicated by individual digital displays.

5.2 Cooling Water Flow ReadingTo read a particular flow, use the flow selector knob to select the desired reading (FT1 or FT2).

5.3 Heater SettingTo turn on the heater, turn the heater switch to “ON” position. The power supply to the heater is controlled by turning the potentiometer clockwise to increase the value or anticlockwise to reduce the value. Use both coarse and fine regulators to obtain the desired heating power.

5.4 Cooling Water ControlThe cooling water flowrate can be controlled by simply turning the valve clockwise to reduce flow rate or turning the valve anti-clockwise to increase flow rate.


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6.0 EXPERIMENTAL PROCEDURE6.1 General Start-up Procedures

1. Ensure that the main switch is in the off position. 2. Turn the power regulator knobs fully anti-clockwise to set the power to

minimum.3. Check to ensure that valves V1 to V6 are closed.4. Fill the chamber 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 close the vent valve, V4.

5. Adjust the water flow rate to the condenser by controlling the control valve according to the experimental procedure.

6. Turn on the main switch and the heater switch. Set the heater power by rotating the power regulator clockwise to increase the heating power.

7. Observe the water temperature reading; it should increase when the water starts to heat-up.

8. Heat up the water to boiling point until the pressure reaches 1.02 – 1.10 bar. Immediately open valve V1 and follow by valve V5 for 1 minute to vacuum out the air inside the condenser. Then close both valves V1 and V5.

9. Let the system to stabilize. Then take all relevant measurements for experimental purposes. Make adjustment if required.6.2 General Shut-down Procedures

1. Turn the voltage control knob to 0 Volt position by turning the knob fully anti-clockwise. Keep the cooling water flowing for at least 5 minutes through the condensers to cold them down.

2. Switch off the main switch and power supply. Then, unplug the power supply cable.

3. Close the water supply and disconnect the cooling water connection tubes if necessary. Otherwise, leave the connection tubes for next experiment.

4. Discharge the water inside the chamber using the discharge valve.


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6.3 Experiment 1: DEMONSTRATION OF FILMWISE AND DROPWISE CONDENSATIONObjective:To demonstrate the filmwise and dropwise condensation

Procedures:1. Follow the basic procedure as written in section 6.1. Make sure that the

equipment is connected to the service unit.

Assignment:Describe the characteristics of filmwise and dropwise condensation and how it may affect the efficiency of the condensers.


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6.4 Experiment 2: THE FILMWISE HEAT FLUX AND SURFACE HEAT TRANSFER COEFFICIENT DETERMINATION AT CONSTANT PRESSUREObjective:To determine the filmwise heat flux and surface heat transfer coefficient at constant pressure

Procedures:1. Circulate cooling water through the filmwise condenser starting with a

minimum value of 0.1 LPM.2. Adjust the heater power to obtain the desired pressure at 1.01 bar.3. When the condition is stabilized, record the steam (Tsat) & surface

temperature (Tsurf), Tin (T1) & Tout (T2), and flowrate.

Assignment:1. Plot Heat Flux vs. Temperature Difference (Tsat - Tsurf

2. Plot a Surface Heat Transfer Coefficient vs. Temperature Difference (T).

sat -TsurfNote: Power is calculated using the heat removed from the cooling water

(

).

).


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6.5 Experiment 3: THE DROPWISE HEAT FLUX AND SURFACE HEAT TRANSFER COEFFICIENT DETERMINATION AT CONSTANT PRESSUREObjective:To determine the dropwise heat flux and surface heat transfer coefficient at constant pressure

Procedures:1. Circulate cooling water through the dropwise condenser starting with a

minimum value of 0.4 LPM.2. Adjust the heater power to obtain the desired pressure at 1.01 bar.3. When the condition is stabilized, record the steam ((Tsat) & surface

temperature (Tsurf), Tin (T3) & Tout (T4), and flowrate.

Assignment:1. Plot Heat Flux vs. Temperature Difference (Tsat - Tsurf

2. Plot Surface Heat Transfer Coefficient vs. Temperature Difference (T).

sat -Tsurf

3. Plot Heat Flux vs. Temperature Difference (T).

sat - Tsurf) for filmwise and dropwise condensation in a single graph. Plot also Surface Heat Transfer Coefficient vs. Temperature Difference (Tsat -Tsurf) for filmwise and dropwise condensation in a single graph. Compare and discuss the heat transfer coefficients between filmwise and dropwise condensation.


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6.6 Experiment 4: THE EFFECT OF AIR INSIDE CHAMBERObjective:To demonstrate the effect of air on heat transfer coefficient of condensation.

Procedures:1. Circulate cooling water through the filmwise condenser at the highest

flowrate until the pressure is reduced to below 1 bar.2. Open the discharge valve and let an amount of air to enter the chamber.Note: Increase of 0.01 bar indicates 1% of air is injected.4. Regulate the water flow rate to the condenser starting with a minimum

value of 0.4 LPM.5. Adjust the heater power to obtain the desired pressure at 1.01 bar.6. When the condition is stabilized, record the steam (Tsat) & surface

temperature (Tsurf

7. Repeat step 1-6 for dropwise condensation.), Tin (T3) & Tout (T4), and flowrate.

Assignment:1. Plot Surface Heat Transfer Coefficient vs. Temperature Difference (Tsat -

Tsurf

2. Plot Surface Heat Transfer Coefficient vs. Temperature Difference (T

) with the presence of air, for filmwise and dropwise condensation respectively.

sat -Tsurf

3. Describe the phenomena theoretically.

) with the presence of air and without presence of air in a single graph,for filmwise and dropwise condensation respectively. Compare and discuss the effect of air on heat transfer coefficients.


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7.0 EQUIPMENT MAINTENANCE7.1 Heater

Cool down the equipment before draining the water inside the glass vessel so that the heater will not be overheated when there is no water inside the vessel.

7.2 CondenserMake sure tap water used is free from any contamination to prevent blockage inside the condenser.


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8.0 SAFETY PRECAUTION8.1 Warning

High voltages exist and are accessible in the control panel. Return the unit to your supplier for any servicing.

8.2 Cautions1. Never splash water to the control panel. This will cause body injury and

damage to the equipment.2. Never use your bare hand to test the AC Power Supply. It may cause

hazardous injury.


APPENDIX AEXPERIMENTAL DATA SHEET

SOLTEQ® FILM & DROPWISE CONDENSATION UNIT (Model: HE 163)EXPERIMENT 2: THE FILMWISE HEAT FLUX AND SURFACE HEAT TRANSFER COEFFICIENT DETERMINATION AT CONSTANT PRESSURE

Flow rate(LPM) Power(W) Tin(degC) Tout(degC) Tsat(degC) Tsurf(degC) Tsat - Tsurf(degC) (degC) (W/m2 U(W/m) 2.K)

qx = Heater Power (W)Tsat = Saturation Temperature (K)Tsurf = Surface Temperature (K)

= Heat Flux (W/m2)U = Heat Transfer Coefficient (W/m2.K)

SOLTEQ® FILM & DROPWISE CONDENSATION UNIT (Model: HE 163)EXPERIMENT 3: THE DROPWISE HEAT FLUX AND SURFACE HEAT TRANSFER COEFFICIENT DETERMINATION AT CONSTANT PRESSURE

Flow rate(LPM) Power(W) Tin(degC) Tout(degC) Tsat(degC) Tsurf(degC) Tsat - Tsurf(degC) (degC) (W/m2 U(W/m) 2.K)



SOLTEQ® FILM & DROPWISE CONDENSATION UNIT (Model: HE 163)EXPERIMENT 4: THE EFFECT OF AIR INSIDE CHAMBER

Flow rate(LPM)FOR FILMWISE CONDENSER:

Power(W) Tin(degC) Tout(degC) Tsat(degC) Tsurf(degC) Tsat - Tsurf(degC) (degC) (W/m2 U(W/m) 2.K)



SOLTEQ® FILM & DROPWISE CONDENSATION UNIT (Model: HE 163)EXPERIMENT 4: THE EFFECT OF AIR INSIDE CHAMBER

Flow rate(LPM)FOR DROPWISE CONDENSER:

Power(W) Tin(degC) Tout(degC) Tsat(degC) Tsurf(degC) Tsat - Tsurf(degC) (degC) (W/m2 U(W/m) 2.K)



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Flim Boiling Condensation manual