RESEARCH ARTICLES CURRENT SCIENCE, VOL. 92, NO. 4, 25 FEBRUARY 2007 472 *For correspondence. (e-mail: kaynakli@uludag.edu.tr) Thermodynamic analysis of absorption refrigeration system based on entropy generation Omer Kaynakli* and Recep Yamankaradeniz Department of Mechanical Engineering, Faculty of Engineering and Architecture, Uludag University, TR-16059, Bursa, Turkey In this study, the first and second law thermodynamic analysis of a single-stage absorption refrigeration cycle with water/lithium bromide as working fluid pair is per- formed. Thermodynamic properties of each point in the cycle are calculated using related equations of state. Heat transfer rate of each component in the cycle and some performance parameters are calculated from the first law analysis. From the second law analysis, the entropy generation of each component j ( ) S and the total entropy generation of all the system components t ( ) S are obtained. Variation of the performance and entropy generation of the system are examined at various op- erating conditions. The results show that high coeffi- cient of performance (COP) value is obtained at high generator and evaporator temperatures, and also at low condenser and absorber temperatures. With in- creasing generator temperature, total entropy generation of the system decreases. Whereas maximum entropy generation occurs in the generator at various operat- ing conditions, entropy generation in the refrigerant heat exchanger, expansion valve and solution pump is negligibly small. Keywords: Absorption refrigeration, coefficient of per- formance, entropy generation, thermodynamic analysis. IN recent years, theoretical and experimental researches on the absorption refrigeration system (ARS) have increased, because these systems harness inexpensive energy sources (like waste heat from gas and steam turbines, solar, geo- thermal, biomass) in comparison to vapour compression systems 1 . Besides, ARSs cause no ecological dangers, such as depletion of ozone layer and global warming, and hence they are environment-friendly. In order to protect the ozone layer, CFC-free conventional compression systems are currently being developed 2 , mainly with HFCs. Nevertheless, these new refrigerants produce some greenhouse effect and might be banned in the next decades 3 . As already known, ARSs using water–lithium bromide working fluid pair are used extensively in air-conditioning and other high-tempe- rature applications. However, with water as the refrigerant, they are not suitable for use in any applications where the evaporator is below 0°C. A suitable working fluid is one of the most important factors affecting the performance of the ARSs. Hence many researchers have focused on investigating new working fluid pairs to improve the performance of the ARSs 4–8 . Water-based vapour-absorption refrigeration system with four binary mixtures has been used in the study by Sara- vanan and Maiya 4 . Sun 5 has provided thermodynamic properties of ammonia-based binary mixtures (NH 3 –H 2 O, NH 3 –LiO 2 , NH 3 –NaSCN) and the performances of the cycles were compared using the first law of thermo- dynamics. The basis of thermodynamics is stated in the first and second laws. The first law of thermodynamic analysis is still the most commonly used method in the analysis of thermal systems. The first law is concerned only with the conservation of energy, and it gives no information on how, where, and how much the system performance is degraded. The second law of thermodynamic analysis is a powerful tool in the design, optimization, and performance evaluation of energy systems 9 . The continuous increase in the cost and demand for energy has led to more research and development to utilize avail- able energy resources efficiently by minimizing waste en- ergy. The principles of the second law of thermodynamics are effective to identify the components for high entropy generation and for minimizing the total entropy genera- tion for improved performance of thermal systems. In order to increase the efficiency of a system, the entropy genera- tion should be minimized. Information about ‘which component of the absorption refrigeration system should be developed’ can be given by the second law analysis 10–13 . The second law analysis calculates the system per- formance based on entropy generation, which always in- creases owing to thermodynamic irreversibility. Some researchers 13,14 have used the principle of entropy genera- tion minimization to analyse different systems to improve the performance, while others 10,15 have used the exergy analysis based on the second law. Wall 16 has presented a number of exergy-based concepts and methods, e.g. effi- ciency concepts, exergy flow diagrams, exergy utility diagrams, life cycle exergy analysis and exergy economy optimization. Ishida and Ji 17 have used the graphical ex- ergy methodology based on energy-utilization diagrams for the analysis of absorption heat transformer. Cornelissen