Heat exchanger optimization of a domestic refrigerator with separate cooling circuits

Abstract

In this study, the effects of evaporator type and geometry, capillary tube diameter and capillary length on the cooling system performance and energy consumption in the bypass two-circuit cycle have been examined experimentally. In the experiments, wire on tube and finned tube evaporators were used in the fresh food compartment of a 500 L top mount freezer refrigerator. 0.66 mm and 0.8 mm capillary tube diameters and 3000 mm and 3500 mm capillary tube lengths were selected as other design parameters. Experiments were performed according to IEC 62552 household refrigerating appliances standard at 25 °C ambient temperature when the average temperature of the fresh food compartment is set to 5 °C and the warmest temperature of the freezer compartment is −18 °C. The Design of Experiments (DOE) technique which is a six sigma method has been used to determine simultaneously the individual and combined effects of parameters on the refrigerator performance. General linear model method, which is a useful framework for comparing how several variables affect different continuous variables, was chosen to identify the effectiveness of the parameters. According to the experimental results, it was found that the most effective parameter of the system is the evaporator type. Finned tube evaporator with 12 tube passes were found the best option for the bypass two-circuit refrigeration cycle among the 8 different options. The optimum cooling performance and the lowest energy consumption were provided with 0.66 mm capillary tube diameter and 3500 mm capillary tube length in the experiments.