Experimental investigation of evaporators with smooth and inner grooved tubes using CO2 as a refrigerant.

Use of CO2 (R744) in refrigeration systems as a natural refrigerant has greatly attracting refrigeration industry. Furthermore, this environmentally friendly refrigerant is being abundant in the atmosphere demonstrates nonflammable, non-explosive and nontoxic behavior. Having a zero ODP (Ozone depletion potential) and GWP (Global warming potential) of one makes CO2 as a great candidate for a future refrigerant. In this study, CO2 is chosen as a refrigerant in a refrigeration system and an air cooled evaporator is considered to determine heat transfer characteristics in the tube side. Two identical evaporators with smooth-grooved copper tubes are used for experiments. The evaporators were in 720 mm x 812 mm dimensions and had 0.12 mm wavy aluminum fins and copper tubes. The tests were conducted in a wind tunnel that was located in a conditioning room. The air-side constant inlet conditions of temperature and humidity are maintained by the conditioning room which consists of an air handling unit; a refrigeration section, an electric heater with 18 kW power, a humidifier and three centrifugal fans to ensure adequate air recirculation in the system. It is noted that nearly 9% increase in inner grooved tube evaporator capacity is observed when compared to non-grooved tube evaporator capacity (11.2 kW).