A chart for predicting the possible advantage of adopting a suction/liquid heat exchanger in refrigerating system R. Mastrullo, A.W. Mauro, S. Tino * , G.P. Vanoli D.E.T.E.C., Federico II University, Naples, Italy – Department of Engineering, University of Sannio, Benevento, Italy Received 28 August 2006; accepted 1 March 2007 Available online 12 March 2007 Abstract This paper presents the effects produced by a suction/liquid heat exchanger installed in a refrigerating cycle, evidencing that, its use can improve or decrease the system performance depending on the operating conditions. Attention is focused on developing an easy operating method in order to predict the behaviour of the system introducing the heat exchanger, changing the operating conditions and/or the refrigerant fluids. To this aim, 19 different ozone friendly fluids (R-22, R-32, R-152a, R-125, R-134a, R-236a, R-227a, RC- 318, R-410A, R-413A, R-407C, R-417, R-502, R-507A, R-717, R-290, R-600, R-600a and R-1270) have been considered, varying evap- orating and condensation temperatures, respectively in the range 40 °C/10 °C and 25 °C/50 °C. The advisability of the installation of the heat exchanger can be evaluated as a function of thermodynamic properties. Furthermore, a simple chart allowing to verify the effec- tiveness of installation of heat exchanger has been developed for each refrigerating fluids and for the specified operating conditions. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Refrigerating cycle; Heat exchanger; Coefficient of performance 1. Introduction A suction/liquid heat exchanger (SLHX) is commonly installed in refrigerant system [1–6] to warrant a suitable function of the system protecting the components. In fact using of SLHX ensures the single-phase liquid at the inlet of the expansion device and the single-phase vapour at the compressor suction. The SLHX realizes subcooling of liquid refrigerant at the expense of superheating of the vapour entering the compressor. The cooling of the con- densate fluid occurring on the high pressure side reduces the risk of flashing gas at the inlet of the expansion device. Furthermore, the SLHX reduces the possibility that liquid refrigerant exits from the evaporator, damaging the com- pressor. A scheme of a basic system of a vapour compres- sion cycle with a suction/liquid heat exchanger is reported in Fig. 1; the realized cycle, without pressure drops and with isentropic compression is outlined on the pressure- enthalpy and temperature-entropy diagrams, in Fig. 2. In both diagrams the two cycle with (1 0 -2 0 -3 0 -4 0 ) and without (1-2-3-4) the SLHX are represented. Referring to pressure-enthalpy diagram, the enthalpy of the refrigerant at the condenser out-let (point 3) decreases before entering the expansion device (point 3 0 ), so that a reducing of the part of the evaporator capacity, lost due to liquid flashing, is obtained. On the other hand, the increase of the vapour temperature at the inlet of the compressor cor- responds to a greater compression work; in fact at increasing vapour superheat the slope of isentropic line decreases in the pressure-enthalpy diagram. Then, the coefficient of perfor- mance of the system, that is the ratio between the refrigerat- ing effect and the compression work, could be higher or lower when a SLHX is introduced in a basic refrigerating system, depending on the thermodynamic properties of working fluid and on operating conditions. Due to the necessity of a global reducing of energy con- sumptions also the refrigerating system requires higher effi- ciencies. Therefore, it is relevant the evaluation of the system performances [7–10] using SLHX even if this 1359-4311/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2007.03.001 * Corresponding author. Tel.: +39 0824 305576; fax: +39 0824 325246. E-mail address: simonetta.tino@unisannio.it (S. Tino). www.elsevier.com/locate/apthermeng Applied Thermal Engineering 27 (2007) 2443–2448