Performance and exergy destruction analyses of optimal subcooling for vapor-compression refrigeration systems Min-Hsiung Yang a,⇑ , Rong-Hua Yeh b,1 a Department of Naval Architecture and Ocean Engineering, National Kaohsiung Marine University, Taiwan, ROC b Department of Marine Engineering, National Kaohsiung Marine University, Taiwan, ROC article info Article history: Received 13 February 2014 Received in revised form 26 March 2015 Accepted 27 March 2015 Keywords: Optimum Subcooling Vapor-compression refrigeration system COP Exergy destruction abstract Performance enhancement and exergy destruction analyses were conducted numerically for vapor-com- pression refrigeration systems using R22, R134a, R410A, and R717. The first law of thermodynamics com- bined with finite-temperature-difference heat transfer theory and the second law of thermodynamics were applied to calculate the COP, heat-exchanger area, irreversibility, and friction loss that occurs in heat exchangers used in this system at various condensation and evaporation temperatures. The effects of cooling water in a subcooler, refrigerant pressure drop among heat exchangers, and superheating in an evaporator were also considered. Two dimensionless parameters, which represented initial cost saving and the total exergy destruction of the system, were introduced and evaluated to obtain the optimal degree of subcooling. Compared with evaporation temperature, condensation temperature plays a con- siderably more crucial role in determining the optimal degree of subcooling for achieving maximal initial cost saving. In addition, the optimal degrees of subcooling obtained according to the second law of thermodynamics were consistently higher than those obtained according to the first law of thermodynamics. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction A substantial amount of heat is released into the environment by the thermodynamic cycle of refrigeration systems because of the widespread application of air conditioning and refrigeration for industrial and domestic use. Saving energy and increasing effi- ciency has become increasingly critical in refrigeration systems because of the vast amount of energy consumed. The properties of refrigerants strongly affect the performance and apparatus cost of refrigeration systems. Furthermore, manufacturing environmen- tally friendly refrigerants to achieve zero ozone depletion potential (ODP) and low global warming potential (GWP) is essential for applications of refrigeration systems. Recently, several academics have focused on environmental protection and analyzed the per- formance of alternative refrigerants. According to the Montreal protocol, the phasing-out deadline for R22 is in 2020. Dalkilic and Wongwises [1] investigated the performance of vapor-com- pression refrigeration systems at various degrees of subcooling and superheating by using blends of R134a, R152a, R32, R290, R1270, and R600a according to the first law of thermodynamics. At the condensation temperature of 50 °C and evaporation tem- peratures ranging between 30 °C and 10 °C, the result indicated that the blends of R290/R600a and R290/R1270 were the most suitable alternatives to current refrigerants. To obtain the optimal relative size of condensers, Wu [2] investigated the performance characteristics of a Carnot refrigerator. The relationship between the coefficient of performance and the cooling load of the refrigera- tor was obtained numerically without considering the heat trans- fer mechanisms of heat exchangers. The heat transfer coefficient, pressure-drop characteristics, and performance comparisons for 404A, R410A, and R290 were investigated numerically by Spatz and Yana Motta [3]. Based on their result, R410A was proposed to be an efficient and environmentally acceptable option for replacing R22 in medium-temperature applications. To compare the performance of refrigeration systems, experi- mental analyses of vapor compression systems were conducted on R22 and its candidate substitutes, which were R407C, R507, and R417A [4,5]. The analysis of R22 and R407C flowing through an expansion valve was conducted experimentally by Zhang et al. [6], and the performance of the refrigeration system was eval- uated. In their study, the effects of inlet and outlet pressures on http://dx.doi.org/10.1016/j.ijheatmasstransfer.2015.03.085 0017-9310/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: No. 142, Haizhuan Rd., Nanzi Dist., Kaohsiung City 81157, Taiwan, ROC. Tel.: +886 7 3617141x3404; fax: +886 7 3656481. E-mail address: mhyang@webmail.nkmu.edu.tw (M.-H. Yang). 1 Postal address: No. 482, Zhongzhou 3rd Rd., Qijin Dist., Kaohsiung City 80543, Taiwan, ROC. International Journal of Heat and Mass Transfer 87 (2015) 1–10 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt