Research On Two-stage Ejector For Refrigerated Truck

With the improvement of living life,people pursue food with high quality and colorful variety.The cold chain logistics industry which is closely related to food demand has entered a period of rapid development.However,as the carrier of food,there are many problems for refrigerated truck.For example,its refrigeration system has a low fuel utilization and large amount energy consumption which exacerbated the energy shortage problem.With a simple structure,low cost and few energy consumption,ejector refrigeration system has the unique advantages comparing with other refrigeration method.However,ejector refrigeration system can rarely be applied to subzero refrigeration due to its limited boost ability.In order to achieve energy saving and emission reduction of refrigerated vehicle using ejector refrigeration system,a large boost capability two-stage ejector is proposed in this paper.Under the design condition,a design method of two-stage ejector has been presented in this paper.Firstly,the ejector model with detailed experimental data and large amount of cited was selected as the baseline ejector.The baseline ejector was corrected using experimental data and numerical simulation data.Secondly,the first stage and the second stage ejector were designed by changing the nozzle throat and NXP of the baseline ejector.Lastly,the first stage and the second stage ejector were integrated to the two-stage ejector through the serial mode.Also,the three-dimensional model of the two-stage ejector was established.The two-stage ejector,using R134a as the working fluid,was operated at 63-74 ? generator temperature and-24 ? to 0 ? evaporator temperature.For the one hand,the velocity field,pressure field and temperature field in the two-stage ejector were studied,also the positions of shock waves in the two-stage ejector were captured.For the other hand,the effects of working conditions on the performance of the two-stage ejector has been detected.Simulation results showed that(1)when secondary flow pressure is constant,the critical back pressure increases with the increase of primary flow pressure,while the maximum entrainment ratio decreases with the increase of primary flow pressure;(2)when primary flow pressure is constant,both maximum entrainment ratio and critical back pressure increases with the increase of secondary flow pressure;and(3)when secondary flow pressure and outflow pressure are constant,the two-stage ejector has an optimum entrainment ratio value with the increase of primary flow pressure,and that the optimum entrainment ratios of 0.0736,0.0761 and 0.0813 can be achieved when saturated temperature is at-22 ?,-20 ?,-18 ?,respectively.Based on above research,the total cooling capacity of the refrigerated truck under different refrigeration temperatures were analyzed in this paper.The total cooling capacity of the refrigerated truck were 7.69kw,9.21kw,11.94kw,13.53kw when the refrigerated compartment temperature is at 0?,-5?,-14?,18?,respectively.Due to the huge output volume of refrigerated truck,the waste heat can be generally more than 20kw which is sufficient to drive the ejector refrigeration system.The solar heat source can be supplement when the waste heat is not enough.In summary,the research shows that it is feasible that the proposed two-stage ejector is used for subzero refrigeration applications which can benefit for cold chain logistics systems.Also other methods are needed to improve the cooling efficiency.