Summary

The aim of this work is to numerically and experimentally investigate the performance of skin condensers applied to household refrigerators. To this end a two-dimensional CFD (Computational fluid Dynamics) code was firstly developed to support the development of the mathematical model. The developed model takes into account both the heat transfer to the ambient and to the refrigerated compartments by considering the heat transfer through the tube wall, aluminum tape, outer steel shell and insulation layer. The model predicts the heat transfer rates based on the internal and external temperatures, condenser geometry, refrigerant mass flow rate, pressure and temperature at the condenser inlet. In a second step, the condenser model was added to a simulation model of refrigerating systems. In this way it becomes possible to evaluate the effect of the condenser characteristics on the, cooling capacity, energy consumption and coefficient of performance. Steady-state tests ? compressor running continuously under the action of electric heaters placed inside the refrigerated compartments ? were carried out in different operating conditions with the product positioned within a climate-controlled chamber. The tests were carried out at different values of ambient temperatures, fresh-food compartment temperatures, freezer compartment temperatures and compressor speeds. Thermo graphic images of the temperature fields of the refrigerator outer steel shell were also recorded during the experiments. The model predictions were compared with the experimental database with the deviations falling inside a ?5% error band. It was shown that, independently of the operating conditions, the condenser rejects 60% of the heat to the ambient and the remaining 40% to the refrigerated compartments. It was also found that radiation is responsible by over 80% of the heat rejected to the ambient. It was also shown that the condenser parameters with the largest effect on the energy consumption are the thermal conductivity and thickness of the outer shell and thermal insulation layer. Furthermore, it was shown that there are some performance gains when the condenser tubes are not placed in the freezer walls.

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