The refrigerant charge used in the hermetic cycle of refrigerating appliances is an important parameter for the thermodynamic conditions in which the cycle functions. The ambient temperature determines the condenser temperature and the heat load of the evaporator, which, in turn, determine the optimum amount of charge. A void fraction correlation for the description of two-phase flow conditions is presented and compared with measurements. This void fraction model is then used in a steady-state numerical analysis of an appliance; here it concerns a static version of an upright freezer. Apart from the ambient temperature, the capacity of the capillary tube and the control strategy also prove to be important parameters for the determination of the optimum refrigerant charge. Recommendations for components are given for the case where the appliance has to fi~nction well over a broad ambient temperature range with a fixed refrigerant charge; three modes of operation are considered, i.e., continuous running, continuous control, and on/off control.

Units: SI