ID: 934 HEAT TRANSFER ANALYSIS OF THE COMPACT HEAT EXCHANGER WITH DIFFERENT MICROCHANNEL GEOMETRY GLAZAR V. (*) , FRANKOVIC B. (*) (*) Faculty of Engineering, University of Rijeka, Vukovarska 58, Rijeka, HR-51000, Croatia vladimir.glazar@riteh.hr, bernardf@riteh.hr ABSTRACT In this paper an analysis of heat transfer and fluid flow of compact heat exchanger has been done. 3D numerical simulation results of a heat exchanger with microchannel coil were compared with experimental results carried out in this research. Microchannel coil composed of flat tubes with rectangular microchannels of different geometries has been installed in an open circuit wind tunnel. Air and distilled water were used as working fluids in heat exchanger with single phase heat transfer. Same geometry and parameter setup have been analyzed with commercial fluid flow and a heat transfer solver Fluent. Air/water model has been used. Good agreement between experimentally measured and calculated results has been accomplished. The influence of different microchannel geometry on heat transfer effectiveness and pressure drop have been studied numerically. Comparison of results has been made accompanied by the commentaries and final conclusions. 1. INTRODUCTION Compact heat exchangers are widely used in many ways in residential, commercial and industrial HVAC systems. According to Kuppan (2000), compact heat exchangers are those that have high heat transfer surface area to volume ratio (>700 m 2 /m 3 ). Serious development and their rapid growth of usage have began with demands of (mostly) automotive industries for heat exchangers that use reduced space, weight, support, energy requirement and cost for desired thermal performance. Fin-and-tube heat exchangers are representatives of compact heat exchangers with high compactness ratio. Further size reduction of heat exchanger passages has lead to heat exchangers with flat tubes, commercially known as microchannel coil. In this paper numerical and experimental analysis of such heat exchanger has been performed. In last decades CFD has become an important heat exchanger research technique. Current work in this field is usually based on air flow models with assumptions of constant temperature of heat transfer surface. Wolf et al. (2004) carried out a thermodynamic analysis of the airside heat transfer performance of a wavy fin-and- tube heat exchanger for three-dimensional steady-state fluid flow and heat transfer. They found a good agreement between numerical results and experimental measurements and existing correlations. Carija and Frankovic (2008) analysed fluid flow on the air side of multi-row fin-and-tube heat exchanger. They made comparison of thermo dynamical properties between fin-and-tube heat exchanger with flat and louvered fins. The CFD procedure was validated by comparing the numerical simulation results with the published experimental results. Comparison of results showed minimal average Nusselt number deviation and good correspondence of resulting pressure drops. When dealing with micro scale, heat transfer can be suitably described by standard theory and correlations, but scaling effects precisely described by Morini (2006) and Rosa et al. (2009), which are often negligible in macro scale channels, should not be neglected. Air/water side model proposed by Borrajo-Pelaez et al. (2010) allows implementation of some scaling effects (entrance effects, conjugate heat transfer and viscous heating). Therefore, to achieve higher accuracy of the heat transfer and better predictions on the exchanger performance, especially when dealing with micro scale, air/water model should be used. Although numerical approach gives inexpensive prediction method, compared to expensive testing of numerous prototypes, experimental research should not be neglected. Junqui et al. (2007) studied experimentally a total of 11 cross-flow heat exchangers having wavy fin and flat tube. They analysed air side thermal performance and proposed general correlations for Colburn and Fanning factors. Agarwal et al. (2010) experimentally tested several non-circular flat tube geometry shapes. They examined flat tubes with square, barrel, triangular, rectangular channels, channels with W and channels with N shaped inserts during condensation of refrigerant. In this paper results accomplished by numerical and experimental analyses of heat exchanger with flat tubes have been compared in order to obtain physical ICR 2011, August 21 - 26 - Prague, Czech Republic