带膨胀机的二氧化碳跨临界循环变工况特性

Characteristic of CO_2 Trans-critical Cycle with Expander at Variable Working Condition

分析了带膨胀机的二氧化碳跨临界循环变工况特性,发现它与传统的蒸汽压缩式制冷循环不同的特点:循环存在一个最佳排气压力使COP最大,且最佳排气压力对冷却器出口温度的变化比较敏感;随蒸发温度的下降,单位质量制冷量先增大后减小;COP随着吸气温度的增加呈现振荡变化,且振荡变化的总体趋势是降低,带膨胀机吸气过热为无效过热的系统安装回热器有助于COP的提高。然而带膨胀机的二氧化碳跨临界循环与传统的蒸汽压缩式制冷循环也有类似之处,它也存在一个最大功率工况。

The characteristic of carbon dioxide trans-critical cycle with expander was analyzed at variable working condition. Following differences from conventional vapor compression refrigeration cycle was found： there is an optimal discharge pressure at which COP reaches maximum; the optimum pressure is sensitive to the outlet temperature of cooler, as the evaporating temperature decrease, special refrigerating output firstly increases and finally decreases ; COP takes oscillation as suction temperature increase and the amplitude reduces with the increment. It is useful to enhance COP for cycles with expander whose suction overheat is inefficiency by adding regenerator. It is similar with conventional vapor compression refrigeration cycle that a maximum power can be found.