Thermal modeling of a shell and tube type evaporator with R404A

In this study, the two-phase heat-transfer coefficient of R404A inside horizontal tubes is analyzed through the evaporator's overall heat-transfer coefficient, obtained using the effectiveness-Number of Transfer Units thermal design approach. This method constitutes an approximation that can be used in the evaporator's thermal design with an attempt to break some of the initial assumptions established in the heat exchanger thermal design method development. For the analysis, an experimental refrigeration system that is commercially available is built up with a shell and tube evaporator. All the experiments are performed at different evaporator pressures (270, 570 kPa), evaporator temperatures (-20, 0 degrees C) and cooling water temperatures (20, 40 degrees C). For these parameters, overall heat-transfer coefficient of the heat exchanger is found in the range of 0.05-0.35 kW degrees C (1). Copyright (C) 2010 John Wiley & Sons, Ltd.