Thermodynamic analysis of optimal condensing temperature of cascade-condenser

jerryxie2004

Thermodynamic analysis of optimal condensing
temperature of cascade-condenser in CO2/NH3
cascade refrigeration systems
+ w2 |; U. P$ x5 O4 l$ `Tzong-Shing Lee*,1
, Cheng-Hao Liu, Tung-Wei Chen
( a' K5 h  g5 R9 v( wDepartment of Air-Conditioning and Refrigeration Engineering, National Taipei University of Technology,
( L4 L+ W" E& k- ]6 I+ ]No. 1, Sec. 3, Chung-Hsiao East Road, Taipei 106, Taiwan
Received 10 November 2005; received in revised form 6 March 2006; accepted 6 March 2006
) N! ]' [! f# w7 f: `/ g9 p3 O3 ~Available online 5 June 2006
- W% [1 ]# i3 ~1 RAbstract
This study thermodynamically analyzed a cascade refrigeration system that uses carbon dioxide and ammonia as refriger-
! J1 i: r- I$ b7 x4 P8 L# I) gants, to determine the optimal condensing temperature of the cascade-condenser given various design parameters, to maximize
# G9 T. c- t  ^  ithe COP and minimize the exergy destruction of the system. The design parameters include: the evaporating temperature, the
' ]' v/ T  o: _, O3 p+ g! x( U! u" bcondensing temperature and the temperature difference in the cascade-condenser. The results agreed closely with the reported
" Z  j" X* s, t. n: L" [- i  ^experimental data. The optimal condensing temperature of the cascade-condenser increases with TC, TE and DT. The maximum
1 n0 g, [+ _3 A1 g- S% eCOP increases with TE, but decreases as TC or DT increases. Two useful correlations that yield the optimal condensing temper-
3 D) c5 R/ B9 ~4 `  T9 oature of the cascade-condenser and the corresponding maximum COP are presented.
) F) U9 S: z& F( h  o8 C* v' ]
2006 Elsevier Ltd and IIR. All rights reserved.
Keywords: Refrigeration system; Compression system; Cascade system; Ammonia; Carbon dioxide; Optimization; Temperature; Condensa-
tion; COP