Use Of Ejectors To Increase The Performance Of CO₂ Refrigeration Systems

Ejector is increasingly utilized for expansion work recovery of low grade heat to produce additional cooling effect. In this report, a mall capacity R744 Single-phase ejector cycle is studied. This cycle applies pump and ejector to replace the compressor in conventional refrigeration systems.Firstly, experimental investigations of the optimum operating conditions were performed. Different operating conditions, including the inlet temperature and pressure of the ejector(high-s ide temperature and pressure) were examined respectively. Based on the experimental results over a wide range of temperatures and pressures, the influences of high-s ide temperature and pressure on the mass entrainment ratio, overall COP, actual COP and ejector efficiency were obtained. The best performance was attained with the temperature of around 75 ℃ and pressure of around 85* 10-1MPa under certain ejector geometry and fixed evaporator of 51*10-1MPa and condensing pressure of 58*10-1MPa.Then around optimum operating conditions, experimental tests on the influences of pressure differences between the condenser and evaporator as well as operating ranges on the cycle performance were also conducted. Through comparison among several pressure differences, the influences on mass entrainment ratio, ejector efficiency, overall COP and actual COP under four different operating conditions were performed. The optimum pressure difference was obtained and also validated with another group of tests. Then under the best pressure difference, three points at different operating ranges were examined to show the change of cycle performances and find out the suitable operating range.Besides, a modified ejector analys is model was raised to calculate mass entrainment ratio. The relative fitting error is within 8%, thus this model has rather high efficiency.