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M. 1 INTRODUCTION A loss of coolant accident (LOCA) and subsequent rewetting and ref- looding phenomena in a nuclear reactor constitute another important phases of the nuclear reactor accident. In this case, large amount of vapor is generated and high quality two-phase flow often encountered. Powerlevels under these accidents are relatively low (decay heat level) and the transient process is slow. Under these circumstances, the boiling and two-phase flow phenomena are not localized , but depend on the upstream conditions. In the nuclear reactor core, the heated length is considerably long extending to several meters. Therefore, the boiling and two-phase flow phenomena involved are those for large length to diameter ratio, 2/dhe' The heat and mass transfer mechanisms are considered to be quite different from those for small 2/dhe which have been studied in the previous chapters. The transient and steady state boiling phenomena under these large 2/dhe conditions are basically determined by the mass, momentum and energy transfer processes of annular or annular dispersed flowswhich are usually observed in high quality two-phase flow. Therefore, in this chapter and succeeding two chapters (Chapter 1V and V), the hydrodynamic characteristics' of annular or annular dispersed flow are studied. Several practical correlations which are ne- cessary to the analyses of nuclear reactor accidents have been developed. Firstly, the droplet size and its distribution are analysed in this chapter. An accurate knowledge of the mean droplet size and droplet size distribution is essential to the detailed analyses of droplet or annular dispersed flow. The inception of droplet entrainment from the liquid film significantly changes the mechanisms of mass, momentum and energy transfer [1,2]. The avail- able Interfacial area and droplet transport depend on the amount of entrainment and droplet size. Therefore, in order to accurately model and predict a number-of important physical phenomena in annular dispersed flow, an under- standing of mechanisms of entrainment, generation of droplets and size distribution are prerequisite. In particular, the relative velocity and droplet carryover, the dryout and post dryout heat transfer [3-7] and the effective- ness of the emergency core cooling in light water reactors [8-11] are signif- 155
icantly influenced by the amount of entrainment and droplet size. In view of its importance, a detailed modeling of amount of entrained droplet has been carried out recently [2] by considering the entrainment mechanism of the shearing off of roll-wave crests by streaming gas flow: However, there have been no satisfactory correlations for the prediction of the mean droplet size and size distribution for annular dispersed flow. The lack of such a correlation has been one of the main difficulties of analyzing various important phenomena in annular flow. The principal objective of this study, therefore, is to develop a reliable and simple predictive method for the mean droplet size as well as the droplet size distribution. A certain mechanistic modeling which are consistent with the reviously developed onset of entrainment criterion and correlation for the amount of entrainment has been adopted here to obtain a general correlation with wide ranges of applicability. Hence, the main mechanism of droplet generation considered here is the shearing off of the roll-wave crest by gas flow. In addition to the prksent model based on entrainment mechanism, several existing droplet size criteria based on droplet disintegration have been re- viewed in this study. As it becomes evident, the standard Weber number criterion expressed in terms of the relative velocity between gas and droplet gives far too large droplet sizes in annular.flow. This also indicates that . the droplet size in annular flow is mainly determined at the time of entrainment. 156
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TRANSIENT BOILING AND TWO-PHASE FLO
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ACKNOWLEDGEMENTS I would like to ex
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parallel to the water flow. The eff
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entrance and developed region of th
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vni
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II.3 II .2 II.4 II.5 II.6 II.7 II.8
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VI.3 VI.4 VI.2.1 VI.2.2 VI.2.3 VI.2
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high. The boiling phenomena under v
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• under zero liquid flow rate ( i
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CHAPTER I FORCED CONVECTIVE BOILING
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There have been two groups of works
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no direct interaction between the o
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On the other hand,the instantaneous
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- The properties were taken at film
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In Fig.9(a) is shown the effect of
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in a 19 mm i.d. tube with water and
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long heater. The transient non-boil
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shifts towards higher wall superhea
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Figures 27(a) and (b) show the effe
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where E is given by Eq.(8-2) E = 0
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decreasing period and increased wit
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gmax ,0 gmax ,st gmax ,st00 gmax ,t
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REFERENCES 1. Rosenthal,M.W.,"An ex
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(1954). 21. Kutateladze,S.S., Heat
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0 obtained by consulting a text boo
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o Cooling Water Storage Tank Pump S
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Fig.3 Z 10 Comparative coefficient
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0 E N lo' 106 105 Fig.4(b) The effe
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E N 107 106 105 1 Fig.4(d) P = 0.14
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Z N. m a) EX m 10 Fig.5 O 0 Compara
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0 N E X as E O' 15 0 0 Fig.6(b) 0.2
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N E 2 E 0 0 Fig.6(d) 0.396 MPa 1,2
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X Ln '-S N E }---..... } 2 E 0 0 Fi
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Ui rn 1 N E X m E Q' 0 Fig.7(d) 1 T
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x Ln Co N E ro E 0 Fig.8(b) 1 The v
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0 (N E x b E cr 15 10 0 0 Fig.9(a)
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j V c G 14 12 10 Fig .10 The variat
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E rn N rd E Cr Fig.12 7 6 5 4 3 2 1
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'.9 fS ~; x~ Photo.1 Steady state b
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^ CO TA 7 z D Z 10 1 0.1 \(1) (2) (
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" E cr Fig.16(b) 107 106 1o5 1 The
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N V 1 o 7 106 105 Fig.17(b) 1 10100
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E N 1 106 105 2 Fig.18(a) P=0.396 M
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iv 15 E x E (710 0 0.0 01 A Fig.19(
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2 X CO 20 cy 15 ro E °10 5 0 0.001
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• CO 0 cv 15 E ' E °'10 0.001 Fi
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03 N E 2 rd E o- Fig.20(a) The and
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00 E15 x rtl E 0'10 20 5 0 0.001 Fi
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00 2 co E o- Fig,20(e) The variatio
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00 CO I' rd 20 15 cr 10 5 0.0 01 Fi
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0 20 c+ 15 E x rd oor 10 5 01------
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Ni C15 2 20 x ro E o10 5 0 0.001 Ty
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20 N 15 E 2 E °r10 5 0 0.0 01 Fig.
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CN 20 (C" 15 E x CT 10 5 0t- 0.001
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CO Fig.24(d) The variation and velo
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0 0 0.001 Fig.25(b) 0.01 The variat
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O N N E 2 X rd' E 0 20 15 10 5 0 U.
Page 121 and 122: 0E 0 -P- N 2 x g E 0' 20 15 10 0 5
Page 123 and 124: • O 0' N E 2 rd E ET' 20 0.01 Fig
Page 125 and 126: • F-' O m 0 o0.1 QIQ rd CT 4- I c
Page 127 and 128: 110
Page 129 and 130: 112
Page 131 and 132: of these works, the transient heat
Page 133 and 134: Y pendicular to the flat plate. v i
Page 135 and 136: One assumes temperature distributio
Page 137 and 138: u for x*>t*h* = -------------------
Page 139 and 140: value oft and is given by solving f
Page 141 and 142: v v Here, S is a thickness of veloc
Page 143 and 144: *1.5* for -ln[1-{1-exp(-5.67Pr x )}
Page 145 and 146: previous cases St =)76{ 1 - exp(-t*
Page 147 and 148: ' u = (i)l/7 u~ S 1.7(69) T -TT= 1
Page 149 and 150: Equation (79) was derived based on
Page 151 and 152: The asymptotic value of the transie
Page 153 and 154: the transient heat flux attains the
Page 155 and 156: Greek Letters dtThermal boundarylay
Page 157 and 158: 10. 11. 12. 13. 14. 15. 16. 17. 18
Page 159 and 160: C a) . V F-- 4- 3 ~~U -~xL . (1.;L
Page 161 and 162: s 10 - s \ 6- 4- 2- 0- 0.01 Slug Fl
Page 163 and 164: ON Fig.5 3 2 1 0 0.01 Thermal bound
Page 165 and 166: 00 * s Fig. 6 5 4 3 2 1 0 0.01 Lami
Page 167 and 168: ln 0 * Fig.9 J 6 P. 4 3 2 1 0 Turbu
Page 169 and 170: Ln N N O I X a) CC Ln N O X (0 CD N
Page 171: 154
Page 175 and 176: Substituting Eqs. (3) and (4) into
Page 177 and 178: ]]I. 3 DROPLET GENERATION BY ENTRAI
Page 179 and 180: In the entrainment regime of entrai
Page 181 and 182: Ia. 4 MEAN DROPLET SIZE AND SIZE DI
Page 183 and 184: and the volume fraction oversize A
Page 185 and 186: p-1/3u2/3 We(D ~) = 0.0099 Reg/3pgu
Page 187 and 188: a a. 1 a. 1W Ad A. iw CD C g C w D
Page 189 and 190: 1. 2. 3. 4. 5. 6. 7- 8. 9. 10. 11.
Page 191 and 192: 34. Mugele, R. A. and Ind. Eng. Che
Page 193 and 194: n WAVE REG Ti 0' r ION VOLUME Vw SU
Page 195 and 196: I pr) M M \ N CO a) a) 100 10-2 10-
Page 197 and 198: N Io° - J 10-1 M N CO M iCI_ CT ;:
Page 199 and 200: N C\J C311 us-- N) QQ CS' I 1.4 C\J
Page 201 and 202: C '14- cacri N C:51 N CC I0~ 10-I 1
Page 203 and 204: • N ~-1 M J,~-- ~ I Q. M N a) C C
Page 205 and 206: M rr) ..I~ N IQ Cr) CD Fig. 14. 100
Page 207 and 208: B I 00 NA D vm D max *_ D 10' D 20'
Page 209 and 210: 192
Page 211 and 212: IV. 2 PREVIOUS WORKS In annular two
Page 213 and 214: it has been thought that a sufficie
Page 215 and 216: C = pf j Jfevq1 gvfe+ ifevg(10) or
Page 217 and 218: IV. 4 ENTRAINMENT RATE CORRELATION
Page 219 and 220: • E= 0 .022 pfjfRef-0.26E0.74_(26
Page 221 and 222: • uD= 6.6 x 10-7 Re0.74 Re0.185 W
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where the equilibrium rate is given
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f uD= 1.2 x 103RefReff..Reffm-0.25W
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f Figures 8 through 12 show the com
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droplet impingements and deposition
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where E is given by For The E = tan
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a W C C D E E ., g jf 'fe Jg k Ref
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1 2 3 4 5. 6. 7. 8. 9. 10 11 12 13
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29. Brodkey, R. S., "The Phenomena
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N 9 W 'W C) 67 -z 10 103 -4 10 105
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•W 0.1 0.01 0 0 0.2 Fig. 3. Entra
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s •w 10 1 0.1 0.01 0 0 a 0.2 Fig.
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.W 10 I o .) L1I 0 0.2 0.4 E/Em Fig
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I. _ I J w W a W 4 '4d 0.1 0.01 Fig
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4 E•- 1- U.! CC w w CL X w 'W I0
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w w 9 1.0 0.8 0.6 0.4 0.2 0.0 I.0 0
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1.0 0.8 0.6 04 0.2 8 0.0 1.0 0.8 0.
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1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 0.6
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1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 8 0
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1.0 0.8 0.6 0.2 0.4 I.0 0.8 8 0 .6
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LO 0.8 0.6 0.4 0.2 0.0 1.0 0.8 8 0.
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1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 8 0
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. 1.0 0.8 0.4 0.2 1.0 0.8 8 0 .6 0.
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w 8 2.0 L8 1.6 I.4 1.2 1 .0 0.8 0.6
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252
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254
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satisfactory correlations which pre
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a j* 99 =jagOp1/4(3) 2 pg where a,
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P Then where Dc r 4j p)2]1/3 g the
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o Droplets ejected from the interfa
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height from the pool surface. Howev
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Substituting Eqs. (32) through (35)
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dv pfD a€-f = Ti - opgD ,(43) whe
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liquid level is very low, i.e., 5-6
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Substituting Eq. (63) into Eq. (54)
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and Y jr (vr+j g )dt (72) Equation
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Equation where vh vh (79) 0 2h* can
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On is the other hand, in annular-di
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In Fig. 6, the general trend of the
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* ~ • This Efg(h,jg) = 2.213 N1.5
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f(DJj) =C1()fl5j*1.5 D*0.5(105) gp3
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-4 *3 0.5p ()_1.0 Efg(h,jg) = 7.13
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h* = 1.038 x 103 jgN095 0.23 DH0.42
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E fg (h,jg ) =2. 213 N1.5D*1 jigH .
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(1) Total Droplet Flux- In this wor
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intermediate gas flux regimes given
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g(v. h h* hm h+ m d *qc jfe jf 'fd
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REFERENCES 1. Ishii, M. and Grolmes
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30. 31. 32. 33. 34. 35. 36. 37. 38.
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61 62 63 64 65 66 67 68 69 70 71 72
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and Here pool and Equation gas phas
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0 0 uJ -3 I0 -4 10 -5 10 -6 I0 104
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* N vt v- M Sc CP } 10 4 103 2 I0 0
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ca._ a cri E cl:- cv ._ > 1 .2 1 .0
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w Cn Cn I0 -2 -3 10 I0 -4 -5 I0 -4
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U../ -2 10 -3 10 -4 10 -5 I0 -4 10
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W -2 10 -3 10 -4 10 I05 Fig. 11. Co
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CP Q1 .4w I0 -2 -3 10 -4 I0 105 Fig
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Q, v CT W 10 I0 -2 -3 -4 I0 -5 I0 -
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w CP CP -2 10 I0 I0 -3 -4 -6 10 Fig
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• • Fig. 19. M 0 CL. a 101 100
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N CD -2 I0 -3 177'10 c, -4 0 cn -5
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w co Table II. Summary of Various E
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330
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equations. However, the same approa
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The U. = ui/uo Li = t./to T = t U0i
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where ai' asi' ted perimeter di = 4
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uoRu uom opqoR(pCp =gaoR2 R doR'OR(
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In contrast to the design parameter
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• R _Hydraulic Diameter Ratio diR
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• For A scale model can be design
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The similarity criteria based on th
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m where the total flux j is given b
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By assuming an axially uniform heat
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t _ 0 to density change. In two-pha
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Negligible Effects of Viscosity Rat
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SR gRQR d = 1 R uR (AHsub)R 1 .(102
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It is noted that the above conditio
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In the present study, only general
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Pr P qs Qs q„ c R Re St t T Ts Ts
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1. 2. 3 4 5 6 7 8. 9. • • • 1
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W 01 DOWN 1COMMER PUMP ,-. P1 SINGL
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L FROM PUMP H DOWN - COMMER UPPER C
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370
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Concerning a LOCA and subsequent re
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turbulent flow regime. For a two-ph
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