IN HEAT AND MASS TRANSF~I~ 0094-4548/82/030221-06502.00/0 Vol. 9, pp. 221-226, 1982 © Pergamon Press Ltd. Printed in the United states

FURTHER EXPERIMENTS ON TRANSIENT SWELLING

DURING POOL BOILING

J,P. Gupta , A. ShaDma & D. Garg Chemical Engineering Department India~ Institute of Technolo~

Kanpur-208016, India

(Communicated by J.H. Whitelaw)

Pool boiling equipment are extensively use4 to produce

distilled water for boiler feed, to concentrate dilute solutloms, to

provide vapor reflux at the bottom of distillati~ column and,

lately, also as am emergency condenser for high pressure steam in

nuclear power plants. A large amount of space is arbitrarily left

above the liquid level for the dise~gagemeat uE the entrained liquid

droplets from the vapor. For the power plant reboilers, Kern [13

states that the liquid level is malntained at 50~ of the shell diame-

ter, while for the kettle reboilers, it is kept at approximately 60~,

the remainder of the space bei~ 'adequate' for the disengagement of

the entrained liquid dropletS.

The above rules-of-thumb were satisfactory for small units

used in the ¥1ftees when Kern wrote his famous book. However, with

larger sizes and high pressures currently in use, it is very important

that the units be slzed properly since the thickness of the shell

and hence its cost are related to the pressure and radius.

221

222 J.P. Gupta, A. Sha_rn~ and D. C~rg Vol. 9, No. 3

An importent factor which had ben ignored until veEy recently

is the signiflcant increase or swelli~ in the 2-phase level due to

the vapor generation. This cuts down the net available dlsengagement

spaae. In a poorly sized unit, the disengagement space may redt~e to

nil. Therefore the knowledge of swelling 18 important to properly

si -e up the hoiling ulp-ent [2J. singh [3] dmlo

the first set of relatiun8 add an iterati~e analytical prooedure to

calculate the swelled level° This has been verified experimer~allY

by T ~ o n ~, Gupte [ 4 ] us~.g water .

Since the publicatlon of [4], other researaheEs and equl~ent

designers have ~ked if the model would hold for other liquids

solutiun8 with viscosities and surface ter~|iun8 different than th~

of water. In this paper we report the results obtained by using

liquids of different densities, viscosities ~d surface tensiO~o It

turns out that indeed the model holds for them a~8o and hence Qaa~ be

used in design using any liquid or solution° This also cancludes our

curr~t experimental program in thl8 area,

The equil~er~ used has been described I~ detail by Tando~

& Gupta [4~. Briefly, it was a glass column calibrat Id in units

of OeOOS-m with a 2-kW immersion heater 8=rewed into the bottom

flange. Rest of the dimensions are shown in Fig.(I) of RIg.J4] °

The liquids used were salt and sugar solutions listed in

T a b l e l ,

Vol. 9, No. 3 TRANSII~XTf SHT~Z.TL',IG DURING POOL BO]XJ_h~ 223

Table I

PROPERTIES OF SOLUTIONS USED

CAll solutions made in distilled water. Percent composition in weight percent)

Solution

,~oncentrat ions

Boiling Point, B.P., C)

Density

~B.P. , , J ,

Vlscosity,-7 25C

( Zo3kg/m. e. ) "~ B.P.

Surf ace / 25(:: renslon

( 10 3N/m) S.P,

Sugar Solutions

10~

(100.5)

1135

1041 i

1.233

0.33

29.8

22.5

20~ 30~

(iO1.O) (102.O)

1172 1210

1075 1110

1.7 3.0

0.336 0.341

30.7 31.62

23.2 23.9

Salt (NaCI) Solutions

10~

(lO4.o)

1184

1083 i

m

0.337

31.5

23.5

21.8%

(107.O) ii

1256

1146

0.347

33,6

25.1

These solutions were chosen because cf their practical nature

since these are used in the manufacture cf iodized and free flowing

salt and in sugar production by evaporation In units where pool

boiling Is encountered. Besides, these cover a range of parameters

which represent a large number of other pure liquids and solutions

as well. All the solutions used were made in distilled water.

One solution1 at a time was filled into the glass colmun upto

a height of approximately o~e meter and heated by means of the

immersion heater. When the heating was started, the level increased

224 J.P. Oupta, A. Sharma and D. Garg Vol. 9, No. 3

due to decrease in density• The liquid level Just before boiling

was noted. The increase in the level due to the release of vapor

during boiling was thal noted. This level, due to the vary nature

of boiling, is not a steady value but has a range of a few centi-

meters. At times, a momentary spurt would temporarily raise the

2-phase level further by 0.015 to O.02-m. Experiments were repeated

by varying the initial height of the liquid. The proQedure for this

is glven in .

R e s u l t s

The mathematical modal given by Singh told Gt~pta ~3~ was used

to calculate the swelled height by the iterative tectmique described

therein •

For the liquids tested (Table 1), the results ace given in

Fig.( 1). The ope~ symbols denote the values calculated from the

model while the short vertical lines denote the experimental values

which, as discusse6 above, varied within a few centimeters. It

includes the O.015 to O•02-m sudden bursts scmet~es enco~altered in

the system.

The work reported here ind in Ref.[4] conclusively demonstrate

the usefulness of our mathematical model ~3~ in calculatlng the

swelled height c~ the 2-phase mixture in a pool boiling equil~ent.

This should give a new confidence to the designers who otherwise

find it difficult to calculate the exact dlseng~ement sp~e

available in a pool boiling equipment and end up doing a significant

overde s Ign.

Vol. 9, No. 3 TRANSI]~f SWELLII~DURING POOL BOILIk~ 225

Acknewleduemem:

H e l p provided by Dr.P.CoNigam• Chemistry Department, IoI.T.

Kanpur in measurements of eurfaos tensi~ Is gratefully acknowledged.

0

2.

3.

4,

D•Q.Kerne 'Prc~ess Heat Transfer' • McGraw-Hill• New York (1950).

K.J.Bella 'Heat Exchangers w~th phase change.• Invited Lecture• Int, S e m i n a r cm Advancements in Heat Exchangers, Dubrovnlk• Yugoslavia• September, 1981.

K°P.S~gh & J.P.Guptat 'Transient swelling cf llqu~ level during pool boiling in ml emergen~ condenser', Letters i~ Heat Mass Trarls~er, 8( I)• 25-33 ( 1981)o

Nears Tando~ & JoP,Gupta• 'Experiments oll transient swelZing during pool boiling'• Letters in Heat Mass T~ansf~r • 8( 3), 247-252 (1981).

226 J.P. Gupta, A. Sharma and D. Garg Vol. 9, No. 3

1-10

1.00

o 10°1o sugar solut ion

V 20°•0 sugar solution

A 30010 sugar solution

O 10°1o NoCI so lu t ion

o 21.8Olo NQCI solut ion

0.90

E 0.80 c

c

0.70

~n 0-60

0.50

0.40

0.30 " 0.30 0-40 0-50 0.60 0.70 0.80 0-90 1-00 1.10

In i t i a l height, m

FIG, 1

S w e l l e d H e i g h t v s . I n i t i a l H e i g h t f o r V a r i o u s 8 o l u t i o a e