Refrigerant charge reduction in small commercial refrigeration systems

This paper presents analysis of location of refrigerant inventory and numerical results of charge reduction in a typical bottle cooler. The original unit was first characterized by determining its capacity, the coefficient of performance (COP), pull-down characteristics, and total charge using non-intrusive instrumentation. Then the unit was instrumented by insertion of valves to separate main components and allow measurement of the charge in each of them, as well as pressure transducers, a mass flow meter, and thermocouples. Charge optimization and charge distribution experiments were conducted. The condenser is found to be the component that retains the most charge. The system was modeled using Engineering Equation Solver (EES) for calculation of performance and charge. Models were fully validated by experimental results at steady state. Different void fraction correlations were analyzed and utilized to predict charge distributions in heat exchangers. Discussion of the results and recommendation for charge reduction is provided. With the aim of reducing charge without penalizing system performance significantly, the tubes of the round-tube finless condenser were flattened. Charge optimization and charge distribution experiments were again conducted for the system with a flattened-tube condenser. Experimental results show good match with the model prediction