Theoretical And Experimental Investigation On The Impact Of Irreversibility On Ejector Performance

With the vogue of low-grade energy utilization, ejector refrigeration, as one of the heat-driven refrigeration systems featured by up-raised energy efficiency, low high-grade energy consumption and green-house gas emission, system compactness and simplicity, low initial investment, reliable operation and low maintenance cost, is envisioned with wide application in future. Besides, ejector refrigeration could achieve a low temperature beneath0℃with the temperature of driving heat source down to60℃, which renders the system with access to lower grade heat source.Ejector, as the key component of the ejector refrigeration system, its performance is directly of relevance to the system efficiency. As of now, most models for predicting the ejector performance are on the basis of ideal gas assumption, which is believed to yield considerable discrepancy compared to those experimentally acquired. This type of error is even more severe for cases with higher pressure and closer to the two-phase region, regarding which real gas model is used, and the existence of two phases is also considered in the present study for the prediction of ejector performance. The proposed model will be used to study the impact of the internal irreversibility, including those from primary flow through the converging-diverging nozzle, secondary flow expansion in suction chamber and those in mixing chamber and diffuser as well, on the ejector performance. Based on the1-D model, the effect of these irreversibilities on entrainment ratio, ejector outlet pressure, ejector efficiency, etc., will be deeply investigated theoretically, which facilitates the design of ejector with improved performance.Efficiency coefficients are constantly used for depicting the aforementioned irreversibilities. Regularly, these coefficients are set as design variables simultaneously for optimization. However, although mathematically the optimal solution sets can be obtained, the physical mechanism cannot be illustrated thereafter. A more realistic optimization process with better physical interpretation is proposed in the current work. For the validation of the process mentioned above, an ejector using R134a as refrigerant is designed and fabricated, test setup is built for performance data acquisition under different working conditions. The ejector characteristic is for the first time being investigated with zero secondary mass flow rate.The determination method for efficiency coefficients is proposed and applied in the present work, which yielded better results with real gas model and two-phase existence consideration than those from ideal gas model and is therefore proved with more reasonability.