跨临界二氧化碳两级循环优化的循环分离法

Cycle Separation Method for Two-stage Transcritical Carbon Dioxide Cycle Optimization

为了达到最佳COP,跨临界二氧化碳两级压缩循环的高压和中间压力需同时进行优化,而优化过程比较复杂。本文提出一种简便的循环分离法,将两级压缩循环分离为两个复叠的单级压缩循环:高压循环为跨临界循环,以中间压力为其蒸发压力;低压循环为亚临界循环,以中间压力为其冷凝压力。先通过高压循环优化高压,再优化两级循环的中间压力。对一种典型的两级循环进行了优化计算,建立了相应的最优高压和最优中间压力的经验关联式,与直接优化的结果相比,预测循环最佳COP的最大值和平均误差分别为-0.85%和-0.15%。对于其他不同类型的跨临界二氧化碳两级压缩循环的优化,使用循环分离法只需再重复中间压力的优化过程。

High pressure and intermediate pressure of two-stage transcritical carbon dioxide cycles were usuallyoptimized simultaneously for achieving maximum cycle efficiency, and the optimization process is morecomplicated. This paper proposed a simple and convenient cycle separation method. A two-stage transcriticalcycle was separated into two cascaded single-stage cycles. The high pressure cycle is transcritical and takesintermediate pressure as its evaporating pressure. The low pressure cycle is subcritical and takes intermediatepressure as its condensing pressure. Consequently, the high pressure can be optimized with the high pressure cycleonly. Afterwards the intermediate pressure can be optimized. With the proposed method, a typicaldouble-compression cycle was optimized. Correlations of optimal high pressure and intermediate pressure weredeveloped. Compared with the result of direct optimization, maximum and average COP losses are ?0.85% and?0.15%, respectively. Moreover, only the intermediate pressure optimization would be repeated for theoptimization of the different two-stage cycles.