EG Modeling of Direct Contact Wet Cooling Tower in ETRR-2

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1 EG Modeling of Direc Conac We Cooling Tower in ETRR-2 H.H. El Khaib, A.L. Isil, M. E. ElRefaie* Reacors Deparmen, NRC, AEA, P. No , Cairo, Egyp *Al Azhar Universiy, Cairo, Egyp ABSTRACT The Egypian Tesing and Research Reacor no.2 (ETRR-2) was commissioned a 1997 wih ximum power 22MW for research purposes; an induced draf we cooling ower (couner flow ype) was pued in operaion in 2003 insead of he firs one. Invesigaions are achieved o evaluae cooling ower perfornce o guaranee ha he cooling ower capable o dissipae hea generaed in reacor core. Merkel and Poppe analysis was applied o simulae his cooling ower packing. Merkel analysis was applied o predic waer oule emperaure from cooling ower and also o show he effec of ambien condiions on his emperaure. Poppe analysis was applied o predic Merkel number which evaluae cooling ower. The Runge-Kua numerical mehod was applied o solve he differenial equaions in his model and an engineering equaion solver (EES) is he language used o model he cooling ower. This research illusraes ha he cooling ower achieves good perfornce in various sever ambien condiion a ximum operaing condiion of reacor power. The resuls show ha a severe summer condiion of we bulb emperaure equals 24ºc and ower inle emperaure equals 37 ºc, he oule waer emperaure equals.4ºc from cooling ower, while he Merkel number is be found Key Words: Cooling Tower / Research Reacor / Cooling sysem INTRODUCTION The cooling ower is a sysem in which recirculaing cooling waer from a condenser or hea exchangers is evaporaively cooled by conac wih amospheric air. Two modes of hea ransfer are involved in cooling owers: evaporaion and convecion. The rae of hea ransfer by boh convecion and evaporaion increases wih an increase in air-o-waer inerfacial surface, relaive velociy, conac ime and emperaure difference. Packing serves o increase he inerfacial surface area; he ower chimney or fans creae he relaive air-o-waer velociy; and conac ime is a funcion of ower size. These hree facors are influenced by he ower design. The abiliy of a ower o saisfy is funcion is measured by how close i brings he cooling waer emperaure o he we-bulb emperaure of he surrounding air. Classificaion of cooling ower Mos cooling owers used in refrigeraion plans for commercial buildings or indusrial applicaions are mechanical draf cooling owers uses fans o exrac amospheric air. A cooling ower consiss of a fan o exrac inake air, a hea ransfer medium or packing, a waer basin, a waer disribuion sysem, and an ouer casing. According o he locaion of he fan corresponding o he packing and o he flow arrangemens of air and waer, curren widely used mechanical draf cooling ower for HVAC and indusrial applicaions can be classified ino he following caegories (1) : 1-Naural-circulaion cooling owers, 2-Couner flow induced draf cooling owers, 3-Cross flow induced draf cooling owers; and 4-Couner flow forced draf cooling owers. 3-Cross flow induced draf cooling owers; and 4-Couner flow forced draf cooling owers.

2 In he couner flow induced draf cooling ower which exiss in ETRR-2, as shown in Fig. (1) The fan is locaed downsream from he packing a he air exi. Amospheric air is drawn by he fan hrough he inake louver or, more simply, an opening covered by wire mesh and discharged a a higher velociy from he op fan oule. Cooling waer from he condenser or recalculaing waer from Air oule Waer in le Packin g Air in Basin Air in Waer ou Fig. (1): Couner flow induced draf cooling ower. Reacor pool Reacor core Mx5 T 2b = T 2c = T 2c = T o Ho sream circui Cold sream circui T ci Air oule 2a T i [ C] 14 2c Mx1 2b i o T 14 T 2c T 2b T 12 Core H.X2 Core H.X1 T T 6 T 5 Mx2 6 5 T Cooling ower i Mx3 T T 9 T 8 Pool HX T 10 T 2d 2 3 To he pool 10 2d T o [ C] i (0), RH (0) Mx4 Fig. (2): Cooling sysem diagram. Air inle

3 he coil or hea exchanger or combinaion of all is evenly sprayed or disribued over he packing and falls down ino he waer basin. Air is exraced across he packing and comes in direc conac wih he waer film. Because of he evaporaion, a sll porion of he cooling waer, usually abou 1 percen of he waer flow is loss; he emperaure of he waer gradually decreases as i falls down hrough he packing counercurren o he exraced air. Evaporaed waer vapor is absorbed by he air sream. Large waer droples enrained in he air sream are colleced by he drif eliminaors. Finally, he air sream and drif are discharged a he op exi. Drif, or carryover, is he minue waer droples enrained in he air sream discharged ou of he ower. The evaporaively cooled waer falls ino he waer basin and flows o he hea exchanger. Effeciveness models have been presened for cooling owers and cooling coils (2), he models uilized exising effeciveness relaionships developed for sensible hea exchangers wih modified definiions for number of ransfer unis and he capaciance rae raio. Simple mehods were also developed for esiing he waer loss in cooling owers and he perfornce of cooling coils having boh we and dry porions. Sudies of a we cooling owers and is applicaion for once-hrough cooling a river side power-plan sies (3) where he permissible river hea assimilaion capaciy is inadequae o absorb all of he wase hea. A comprehensive compuer model is presened giving a hermodynamic analysis, economic assessmen, and opimum design of once-hrough/we ower hybrid cooling sysems. A compuer program (4) is presened o simulae he herl behavior of a nuclear reacor. I prediced he cooling capaciy of he nuclear reacor while aking ino accoun he curren clie condiions, and also moniors he behavior of he herl equipmens involved in his process and his for differen levels of power. The program gave all he characerisics of air a he exi of he cooling owers and he loss of waer due o he cooling process. MATHEMATICAL MODEL A scheic diagram of couner flow cooling ower is shown in he Fig. (3), which illusraes he mechanism of hea ransfer inside cooling ower according o Merkel mehod, waer inle cooling ower a emperaure T i and exi a emperaure T o, while he air which is source of cooling eners cooling ower wih enhalpy i (0) and exi a enhalpy i (o). T i Waer Temperaure T o i (0) Air-vapor i (o) X Fig. (3): Scheic diagram of couner flow cooling ower.

4 Merkel analysis (5), was used o define and describe he cooling ower heory, and illusraes he following differenial equaions applied on he cooling ower packing, di NTU = (i i ) dv VT (1) di m a dt dv m a NTU = = ( (i i )) dv V m w *c m w *c T Where, NTU is he number of ransfer uni, i = he air vapor mixure enhalpy, i = he air vapor sauraed enhalpy, and V = he cooling ower packing volume. m a =air ss flow rae. m w =waer ss flow rae. T =ower oule emperaure, and c =waer specific hea a consan pressure. (2) Air m a,ω,o,i,o Waer m w,i,t w,i ω a + d ω i a + di m w + dm w dv ω,i m w,t w v m a,ω,i, i,i Air m w,t w,o Waer Fig. (4): cooling ower packing conrol volume. For Poppe analysis showed by Klopper, e.al. (6), he differenial equaions ha describe he cooling ower packing are as follows: dω = dt c (m w / m a )( ω ω) ( Le 1) [ i i ( ω ω) i ] ( ω ω) [ i i + c T ] f v (3)

5 di dt mw c = m a 1+ ( ω ω) ct ( Le 1) [ i i ( ω ω) i ] ( ω ω) [ i + ] i f v ct (4) dme dt p = [ i i + ( Le 1) [ i i ( ω ω) i ] ( ω ω) c T ] Where, ω Is he humidiy raio of air vapor mixure inside ower packing, Me p is he Merkel number of he ower. Solving he above differenial equaions using Runge-Kua numerical mehod applied on he conrol volume illusraed in Fig (4) will predic he cooling ower oule emperaure, and also illusraes he effec of ambien on his emperaure, he ambien condiion appears in iniial condiion of enhalpy of air eners he cooling ower, also a Merkel number by Poppe mehod can be prediced from equaions (3), (4), (5). f c v (5) RESULTS AND DISCUSSION T o (Tower oule emp.) c :00 13: 14:00 14: 15:00 15: 16:00 16: 17:00 17: operaion daa model daa we bulb emperaure 18:00 18: 19:00 19: 20: T wb (We bulb emp.) c Operaion ime (hr.)

6 Fig. (5): Cooling ower oule emperaure variaion during shif ime. T ci (Core inle emp.) c :00 13: 14:00 14: 15:00 15: 16:00 Operaion ime (hr.) Fig. (6): Core inle emperaure variaion during shif operaion ime. Figures (5), (6) illusrae he variaion of oule emperaure from he presen cooling ower (T o ) and he variaion of core inle emperaure (T ci ) during he shif operaion represening summer condiion. The we bulb emperaure is measured during he considered operaion ime (one reading per hour).the reacor power is regisered on he monior abou 18.8MW during his shif. All daa is aken in seady sae operaion condiion. I is shown from resuls ha he average oule emperaure of waer from he cooling ower is sable around (28.2ºc) a he considered shif ime. The oule emperaure from model is found very close o operaional daa. T ci (Core inle emp.) c Jan. Feb. 40 c 37 c 35 c 33 c T TIA =31 c Mars. April May Monh Fig. (7): Core inle emperaure wih various ower waer inle emperaures. 16: June 17:00 July 17: 18:00 Aug. operaion daa model daa 18: Sep. 19:00 19: Oc. 20:00 core inle emp. (model) alarm emperaure power reducion emp. Nov. Dec.

7 Fig. (7), illusraes core inle emperaure a various ower inle emperaure and reacor power 22MW, so he resuls show how he reacor wih his cooling ower can perform good and ke he emperaure inle o core is far away from power reducion and alarm T o (Tower oule emp.) c design poin T wb =24 c T wb =20 c T wb =16 c T wb =12 c T wb =8 c T i (Tower inle emp.) c emperaure. Fig. (8): Presen ower waer oule emperaure vs. inle emperaure. i (air vapor enhalpy) J/kg / (i -i ) Sauraion enhalpy Air-vapor enhalpy 3.45x x x x x x x x10-5 1/ (i -i ) kg/j x x T (Tower packing emp.) K Fig. (9): Enhalpy diagram of cooling ower.

8 T ( K) (Packing emp.) Me p (Merkel no.) Fig. (10): Merkel number of cooling ower vs. ower packing emperaure. Fig. (8) illusraes ower oule emperaure wih ower inle emperaure a various we bulb emperaure, he design poin is very close o nufacuring daa which defines ha waer inle cooling ower a 37ºc and exi from ower a ºc. Fig. (10) shows he predicion of Merkel number of reacor cooling ower and equal 1.253, so his value is greaer han 0.9 which saed by Cooling Tower Insiue. CONCLUSION This sudy deals wih invesigaion of hea ransfer phenomena in direc conac we couner flow cooling ower in Egypian Tesing and Research Reacor (ETRR-2), he resuls show ha a we bulb emperaure around 24ºc he waer emperaure exi from ower a 29ºc wih reacor power 18.8MW, and core inle emperaure is 36ºc, while operaing he reacor a 22MW and assumed he inle emperaure equal design emperaure 37ºc he core inle emperaure does no exceed 40ºc is sill away from seings, so he design value of inle emperaure o ower resuls in.3ºc oule emperaure, he Merkel number prediced is which considered saisfied value. REFERENCES (1) J. R. Singham," Hemisphere Handbook of Hea Exchanger Design", Hemisphere, New York (1983). (2) J. E. Braun, S. A. Klein and J. W. Michell; ASHREA Transacion; 95, 2, (1989). (3) Giaquina, R. Arhur, Croley and E. Thos; ASCE; 106, 1, 89 (1980). (4) Sidi-Ali-Kamel; inernaional conference on nuclear engineering proceedings ICONE; 3 (2002).

9 (5) ASHREA handbook, HVAC sysems and equipmen, American Sociey of Heaing, Refrigeraing and Air condiioning Engineers, Inc. (1996). (6) J. C. Kloppers and D. G. Kroger; Inernaional journal of hea and ss ransfer; 48, 765 (2005). (7) S. A. Klein and F. L. Alvarado; EES nual; Middleon, Wisconsin, USA (1999).