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Boiling Film Experiment

The study of heat transfer with phase

change

Boiling Liquid Experiment

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Objectives

Determine the boiling Regimes as a function ofthe temperature difference (Tsurface-Tsat)

Determine the heat flux and heat transfer

Coefficient as a function of temperature difference

Determine the effect of pressure on the heat flux

and heat transfer Coefficient curves

Compare experimental values to predicted values

Examine the condensation overall heat transfer

Coefficient but not required

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Equipment

Tb

TS

Liquid is R141b

Heating rod is copper coated

with an area of 1.8x10-3 m2

(including the end)

System contained in a glass pipe with a coil

condenser with an area of 0.032 m2

Data taken: voltage and current, Temperature ofheating element surface, Pressure, Liquid temperature,

Vapor temperature, water temperature in and out, flow

rate, cycle time of heater (in film boiling), and

number of coils with condensate .

12.7 mm

42 mm

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Procedure

Turn on water to condenser and adjust to flow rateHigh first week for low pressure

Low second week for high Pressure (100 kPag)

Adjust voltage to 5 volts to observe convection

Increase voltage (5, 20, 5 volts) and observe Regimes

Second week, just look at nucleate to film, by

increaing by 20 volts until at 100 volts, control

pressure with water flow, start taking data.

Once into film boiling, reduce voltage to go back

nucleate (and then free convection)

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Equations

( )

( )

ooii

lmcoilC

lm

outsatinsat

inoutPC

satSeH

H

H

AhAhUTUAQ

T

Tn

TTT

TTTTTT

TTCmQ

TThThA

Q

A

QEIQ

111

condenserhout througHeat

Flux W/m

off)on/(onTimecycling,(IfsWatt

elementughinput throHeat

1

2

12

12

2

+==

=

==

=

==

+=

depends on number of coils being used

hi is small

ho is large

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Tsat= f(P)

Critical heat flux

Burnout point

Need atmospheric Pressure

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Predictive Equations

( )[ ]

( )

( )

( )( )12

21

21

12

12

3

2

2

2

278169

61

2

111

11

Pr

Pr

10-20Pr559.01

387.060.0

or

20.2Table11-20eqn

tubehorizontal-ConvectionNatural

TTTT

V

TV

TDg

Grk

C

GrRa

RaNu

CRaNu

Th

A

Q

Av

P

P

D

DD

n

DD

eH

=

+

=

=

==

=

+

+=

=

=

Must calculate

Chapter 7, p328

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Pressure Liq Density

40000 1260

70000 1235

100000 1215

110000 1210170000 1185

210000 1170

P/Liq Density

y = 1.80E-09x2 - 9.66E-04x + 1.29E+03

R2 = 9.98E-01

1160

1170

1180

11901200

1210

1220

1230

1240

1250

12601270

0 50000 100000 150000 200000 250000

Pressure (Pa)

Liq

Density(kg/m^3)

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Pressure Temperature

100 32

120 37

140 41.5

160 45.5

180 49

200 53

220 56

240 59.5

260 62.5

P/T chart

y = -0.0003x2 + 0.2984x + 5.4539

R

2

= 0.9996

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300

Pressure

Temperature

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( ) ( )

( )

( )( )

( ) ( )( )

21.74.0

62.0

09.0

FilmStable

21.618.0

PointCritical

21.5Pr

5-21eqnFluxNucleateRohsenow

413

41

2

min

41

2

3

7.1

21

+=

+

=

=

=

satSVo

ePVfgVLVV

VL

VLVfg

V

VLVfg

critical

fgsf

satSPLVLfgL

TTD

TChgkh

gh

A

q

gh

A

q

hC

TTCghA

q

Csf=0.013 or 0.007

Chapter 9, Table 9-2

Note: Te not needed nor is it known

Dont know TS

Or can calculate Csf

( ) Sexp

TfindtowithCombine satS TTh

A

q=

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Results

Log

Q/A

Log Te

Log Te

Logh

Log

Q/A

Log Te

@ 1 bar

@ 2 bar

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Significance

Nucleate boiling gives the highest heat flux

at low T. Operate near critical point but

with a margin of safety

Higher pressures extend region of nucleate

boiling at expense of higher temperature