Effect of an Internal Heat Exchanger on the Performances of a Double Evaporator Ejector Refrigeration Cycle

A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger(IHX).The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure.Moreover,the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor.To assess accurately the influence of the IHX on the DEERC performance,a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors.The model also accounts for the friction effect in the ejector mixing section.The equations of this model are solved using an Engineering Equation Solver(EES)for different fluids.These are:R134a as baseline fluid and other environment friendly refrigerants used for comparison,namely,R1234yf,R1234ze,R600,R600a,R290,R717 and R1270.The simulation results show that the DEERC with an IHX can achieve COP(the coefficient of performance)improvements from 5.2 until 10%.

CO_2跨临界循环热力学对比分析

对带回热器和带膨胀机的CO2 跨临界循环过程应用热力学进行了对比分析。结果表明 ,带回热器的CO2 跨临界循环过程虽然也能够在一定程度上提高系统效率 ,但只要膨胀机的效率达到一定值 。

三种单级CO_2跨临界循环性能

基于CO2跨临界循环系统原理,对三种单级循环进行了性能分析。结果表明:SCV循环、SCV+IHX循环和SCE循环都存在最优高压压力;随压缩机排气温度变化,SCV循环系统COP最小,SCE循环COP最大;随着蒸发温度的增加,三个单级循环COP均增加,SCE循环性能最优,SCV循环性能最差;随着气体冷却器出口温度的增加,三个单级循环COP均下降,SCE循环性能最优,节流阀SCV循环性能最差。与蒸发温度相比,气体冷却器出口温度对最优高压压力的影响较大。