Impact of the refrigerant charge and environmental temperature on draft beverage cooler performance

This study experimentally investigated how refrigerant charge and ambient temperature affect the performance of draft beverage coolers in pull-down operation. The cooler operates in vapor compression cooling cycle, and it is hermetically sealed. It has reciprocating compressor, coil type evaporator immersed in a water bath, a built-in air-cooled condenser and a capillary tube as an expansion device. The refrigeration system is filled with propane as refrigerant. Monitoring of evaporation and condensing pressure, mass flow rate of refrigerant through the compressor and capillary tube, temperatures of refrigerant across the refrigeration system and water in the cooling bath was performed during the experiments. Special attention was paid to measuring the amount of ice formed and the energy consumption of the compressor and the complete beverage cooler. The configuration with a charge of 170 g and 190 g of refrigerant was tested at two different ambient temperatures (24 degrees C and 32 degrees C) in series of experiments which lasted 10800 s each. In the nominal configuration with a charge of 170 g at an ambient temperature of 24 degrees C, superheating of the refrigerant in the evaporator occurs throughout the process, but with a thin layer of ice on the last coil of the evaporator. Increasing the refrigerant charge from 170 g to 190 g at the ambient temperature of 24 degrees C increases the mass of the ice bank (1.2 kg - 8.5%) and results in slightly better energy efficiency, but results in wet vapor entering the suction line at the end of the process. Increase of the ambient temperature reduces the mass of the ice layers and the energy efficiency for both cases of refrigerant charge, but the difference is larger for the case of 190 g refrigerant charge.