Variations of Superheat and Subcooling

Variations of Superheat and Subcooling Points : variations of superheat and subcooling The degree of subcooling is defined as the difference between refrigerant temperature and refrigerant saturation temperature corresponding to the pressure at the condenser exit. The subcooling at the condenser exit, which strongly affects cooling capacity and refrigerant flow rate, can be increased by three methods: (1) an enhancement of condenser capacity, (2) an addition of refrigerant charge, and (3) a rise of restriction on expansion devices. Degree of superheat is defined as the difference between refrigerant temperature at the evaporator exit and evaporating temperature. The superheat has been used as a controlling parameter to adjust refrigerant flow rate through a variable expansion device and to ensure that only superheated vapor enters the compressor. Fig. 4.3 shows the subcooling of the capillary tube system as a function of refrigerant charge at four water temperature entering the condenser. As the refrigerant charge increased, the condensing pressure increased due to an accumulation of refrigerant in the high-pressure side, and the subcooling became high. These trends were also observed by Stoecker et al. and Farzard and O’NeaI. The subcooling was reduced when the water temperature entering the condenser increased at all charge conditions except for -20% of full charge. When the water temperature entering the condenser increased, the mean temperature difference between the water and the refrigerant decreased and less heat was rejected in the condenser. For +20% of full charge, the subcooling decreased from 10.4°C to 7.7°C as the water temperature entering the condenser varied from 30°C to 42°C.