ISBN 978-1-84626-023-0 Proceedings of 2010 International Conference on Chemical Engineering and Applications (CCEA 2010) Singapore, 26-28 February, 2010 Efect Of Working Fluid On The Performance of Thermosyphon Heat Exchangers In Series Used In An Air Conditioning System Iman Abrishamchi 1 , S. Mostafa Nowee 1+ , Reza Rezazadeh 2 and S. Hossein Noie 1 1 Department of Chemical Engineering, Faculty of Engineering Ferdowsi University of Mashhad, P.O. Box 91775-1111, I.R. Iran 2 Department of Chemical Engineering, Shahrood Azad University, Shahrood, I.R. Iran Abstract. The effect of working fluid on Heat Pipe Heat Exchangers (HPHX) in series used for the purpose of energy conservation in an air conditioning system has been investigated at pilot scale in this paper. The significance of this study is comparison between Methanol and Acetone as working fluids of two HPHXs in series which make them more efficient in contrast to a single HPHX. The results show that use of Acetone in both of HPHXs has the most energy saving in comparison with other cases. However, it is observed that also by filling one HPHX with methanol and one with acetone, acceptable amount of energy is recovered. Keywords: Air conditioning, Heat pipe heat exchanger, Working Fluid, Thermosyphon, Energy saving 1. Introduction Because human population is increasing, energy demand and consequently its price have risen. Therefore, energy saving is one of the main subjects in industry. Air conditioning is amongst the most energy consuming systems which need more attention regarding reduction of energy consumption. Heat pipe heat exchangers (HPHX) are proposed as a solution to this problem. Using HPHX will reduce primary energy consumption, thus reducing air pollutions. HPHXs have many advantages such as high heat recovery effectiveness, high compactness, no moving parts, light weight, relative economy, no external power requirements, pressure tightness, complete separation of hot and cold fluids, and high reliability[1]. An important role of the HPHX is to recover heat from warm outdoor air and reheat the dew-point air stream and as a result save energy of reheating. Evaporator of the HPHX acts as a pre-cooler for the warm outdoor air before it reaches the refrigerant system, resulting in enhanced capability of the cooling coil. The condenser of the HPHX is reheating the outlet air stream from the cooling coil and reducing that the relative humidity below 70%. The heat pipe heat exchanger which used in this study is essentially a gravity-assisted wickless heat pipe, which is very efficient for the transport of heat with a small temperature difference via the phase change of the working fluid. It consists of a number of individual thermosyphons. Its tubes filled with a certain amount of working fluid. The operating characteristics of vertical heat pipe heat exchanger have been investigated extensively in recent years [2-8]. One of the applications of heat pipes that recently has been paid attention is in air conditioning systems, as dehumidifier to reduce the air of input air[9]. Application of heat pipe and thermosyphon technology in air conditioning systems have been studied by numerous researchers. Abd El Baky et.al, in 2007 used HPHX for recovering energy in air conditioning systems. They expressed that when the temperature of inlet fresh air is about 40C ,heat transfer in condenser and evaporator of HPHX increases about 48% also the results show that HP has the best performance when the inlet temperature is near the temperature of the HP’s working fluid[10].