An Optimized Design of the Refrigerating Systems Using a Small Channel Heat Exchanger

A global model simulating the behavior in steady-state of a refrigerating system using a small channel condenser, is presented in this paper. Its objective is to optimize the design of this system in term of improving its efficiency and minimizing the refrigerant charge, in order to reduce the greenhouse effect. We were interested mainly on the small channel condenser model in which heat exchange and pressure drop were calculated with laws adapted, when it is necessary, to the small channel configuration. The refrigerant charge contained in the condenser was determined from correlations giving the local void fraction. The numerical results were compared with the experimental ones obtained with a device conceived for this objective. This comparison has shown a good agreement. Then, the model was used as a design tool for an optimal refrigerating system with a minimum TEWI. The optimization mainly concerned the small channel condenser geometry. The results have shown an absence of limit to the channel diameter reduction, in term of TEWI: an increase in the total tube number makes it possible to limit the system pressure drop. Moreover, the global model permits to determine the optimum tube distribution for a configuration of a condenser with two passes: this optimum is about 80% in the first pass and 20% in the second one.