Performance evaluation of an ejector based transcritical R-744 refrigeration system with evaporative gascooler

Abstract

In recent times, instead of looking for an alternative to synthetic refrigerants, there has been a fast-growing interest in technology based on environmentally safe natural refrigerants. Among the various natural refrigerants, eco-friendly R-744 technology was revived due to its attractive thermal properties and wider application areas. It is perceived that the R-744 system outperforms synthetic refrigerants at low ambient temperatures. However, due to the transcritical mode of operation at high ambient temperatures, the system performance deteriorates promptly due to the unavoidable significant throttling loss. In the present study, evaporative cooling has been introduced and adopted to reduce the outlet temperature of the gascooler to enhance the system’s overall performance by reducing the system operational pressure. To design the evaporative cooler, honeycomb structured cellulose material is used as cooling pads of three different thicknesses, 5, 10, and 15 cm. It is observed that the maximum drop in air temperature and the corresponding efficiency of the evaporative cooling system was found to be 6.02⁰C and 72.75 % respectively, at 15 cm pad thickness, 2.5 m/s air velocity, 60 % relative humidity and 46⁰C ambient temperature. Moreover, the maximum overall improvement in the R-744 system cooling performance observed in terms of COP was 32.44 %.