Theoretical investigations on combined power and ejector cooling system powered by low-grade energy source

Abstract

A combined power and cooling system is proposed for cogeneration, which integrates the ejector cooling cycle with the Rankine cycle. Low-temperature heat source such as industrial waste heat or solar energy can be used to drive the Rankine cycle. This system will provide electricity and cooling effect simultaneously without consuming primary energy. The partially expanded vapor (from low-grade energy) will be bleed off and enter into ejector's primary nozzle, which achieves cooling effect. Simulations have been carried out to analyze the effects of various working conditions on the overall system performance, on ejector entrainment ratio and turbine power output. Five different refrigerants HFE7100, HFE7000, methanol, ethanol and water have been selected, and the above three parameters were compared, respectively. The simulation results indicated that turbine expansion ratio, heat source temperature, condenser temperature and evaporator temperature play significant roles on the turbine power output, ejector entrainment ratio and the overall thermal efficiency of the system. At a heat source temperature of 1208C, evaporator temperature of 108C and condenser temperature of 358C, methanol showed the highest thermal efficiency (0.195), followed by ethanol and water (0.173). It is recommended that the evaporator temperature and the appropriate working fluid should be selected according to the different working cooling requirements, and the turbine power output can then be determined accordingly.