Experimental investigation of an ejector-compression cascade system activated with low-grade waste heat.

A novel two-stage cascade refrigeration system, combining a sub-critical CO2 mechanical vapor compression loop (lower stage) and a gas-gas ejector loop using R245fa (upper stage), was developed. The system, designed to deliver a cooling capacity of 15 kW at an evaporating temperature of -20°C was thermally driven by low grade industrial waste heat. In the present work an experimental investigation was performed in order to study the thermal performance of the cascade system. The tests covered the following ranges of the governing parameters: the upper stage condensation temperature varied from 25 to 35°C, the lower stage evaporation temperature ranged from -15 to -25°C, the ejector primary mass flow rate was set to 0.33 kg/s, and the temperature of the heat source was kept constant at 80°C. The effects of the ejector primary mass flow rate as well as the condensation and evaporation temperatures on the system coefficient of performance were examined.