• Energy Research

Abstract This paper presents a two-stage ejector-based multi-evaporator refrigeration system using R134a as the refrigerant and the effects of variable operating conditions such as back pressure and evaporating temperature and cooling loads on each stage are investigated by using CFD simulations. The simulation results indicate that: (1) three operational modes: critical mode, subcritical mode and back flow mode are available for each stage when two stages combine with each other, but the range of pressure lifting ratio generating subcritical and back flow modes is not the same with each other; (2) the entrainment ratio of the first-stage is mainly influenced by the variation of the evaporating temperature of refrigerating and freezing chambers, while the entrainment ratio of the second-stage of is more influenced by the change of the evaporating temperature of the air-conditioning chamber; (3) the effect of the mass flow rate of the first-stage primary flow on the entrainment ratio of the first-stage is more significant, while the effect of the mass flow rate of the second-stage primary flow on the entrainment ratio of the second-stage is more evident.

Abstract A three-evaporator and dual-ejector refrigeration system was presented in this paper. By combining two single ejectors as a whole, the authors attempted to discuss the effects of key geometric dimensions of each stage on both stage performances with two-dimensional CFD simulation method. First, the CFD models were validated by experimental data. Then, the primary nozzle diameters of both stages were determined by the cooling load demands of the refrigerating and air-conditioning chambers. Next, the detailed effects of key geometric parameters such as the length of constant-pressure mixing section, the length of constant-area mixing section and area ratio of each stage on two-stage performances were identified with simulations. Finally, the optimum values of the key geometric parameters were obtained, and the results showed that the area ratio had the most significant influences on the entrainment ratio of both stages as compared to other parameters.

Abstract In this paper, a novel ejector-based multi-evaporator refrigeration system using R134a is proposed to meet different working modes of refrigerated trucks running in tropical regions. The Computational Fluid Dynamics (CFD) simulation is implemented to research the performance of ejectors utilized in both air conditioning - refrigerating mode and air conditioning - freezing mode. Consequently, crucial ejector geometrical parameters such as area ratio (AR), nozzle exit position (NXP), lengths of primary nozzle and diffuser are optimized for each mode. Moreover, a novel approach by taking the deviation of the entrainment ratio or secondary mass flow rate over the deviation of the geometrical parameter into account to evaluate the ejector performance sensitivity to each geometrical parameter is first time presented to the best of the authors’ knowledge. The results show that: 1) Area ratio, NXP, lengths of primary nozzle and diffuser of the ejector in the air conditioning - freezing mode are almost twice as those in the air conditioning - refrigerating mode; 2) The performance of both ejectors is primarily influenced by area ratio and NXP; 3) The proposed sensitivity indicator can better evaluate the sensitivity of the ejector performance to geometrical parameters.