Optimal design of two-stage ejector for subzero refrigeration system on fishing vessel

Abstract

It is essential to improve the energy efficiency of the subzero refrigeration system on fishing vessels for harvested fishery products frozen because of its large amounts of fossil consumption. In this paper, a subzero refrigeration system based on a two-stage ejector is proposed and the optimal design method of the two-stage ejector considering Area ratio (Ars) as the designed parameter in each stage is developed to achieve maximum entrainment performance. A Computational Fluid Dynamics model is built to investigate the performance of the proposed two-stage ejector under subzero refrigeration working conditions. In each stage, Ar is used as the design parameter to get the maximum entrainment ratio under the feasible range of intermediate pressure. Moreover, the water-cooled condenser is employed to reduce the pressure difference between the condenser and evaporator so that a higher entrainment ratio can be achieved. Simulation results indicate that the proposed two-stage ejector can achieve evaporating temperature as low as −25 °C with an entrainment ratio as high as 0.0961, 36.12% improvement compared with the one without optimal design. Furthermore, the entrainment performance and Coefficient of Performance of subzero refrigeration system with the proposed two-stage ejector and water-cooled condenser are increased by 30.57% and 28.77%, respectively, compared with the one with air-cooled condenser. It can conclude that it is energy efficient to utilize the waste heat from fishing vessels to drive a subzero refrigeration system with the optimal designed two-stage ejector and a water-cooled condenser.