Abstract
Heat exchangers are major components in refrigeration systems where they are used as evaporators or condensers. Better understanding their thermal and hydrodynamic behaviour is therefore important, in order to improve their design and maximize their performance. In this paper, a new model simultaneously accounting for the thermal and hydrodynamic behaviour of fin and tube heat exchangers working under conditions of no condensation of air moisture (dry case), is presented. The equations describing these aspects are strongly coupled, and their decoupling is reached by using an original method of resolution. A FORTRAN program based on this procedure was developed and allowed to study a large range of complex refrigerant circuit configurations. Each circuit may have several inlets, outlets and bifurcations and feed one or several other tubes inlets. The coil was subdivided into several elementary control volumes and was analysed in order to obtain detailed information in X, Y and Z directions. The model was validated using data from a CO2 secondary refrigeration loop test bench built in CanmetENERGY Laboratories. These data were predicted satisfactorily over the operating range corresponding to refrigeration applications. The model was then applied to study an evaporator typically employed in supermarkets. Circuiting, even though common practice in refrigeration coils must be well designed if it is to impact positively on operation and performance. Therefore, two circuit configurations for CO2 were selected for analysis in this investigation. In terms of capacity and heat transfer, it was shown that the two circuits were well balanced. Low CO2 pressure drop resulted in reduced temperature glide. This is a remarkable advantage for CO2 when used as a refrigerant. (C) 2010 Elsevier Masson SAS. All rights reserved.