中间温度对复叠式制冷系统影响的(火用)分析

Exergy Analysis of Influence of Intermediate Temperature on Cascade Refrigeration System

为提高R404A/R23复叠制冷系统的热力性能及降低系统能耗,通过建立热力学模型,应用热力分析和(火用)分析法,分析中间温度与蒸发温度对复叠式制冷系统总能耗、热力性能、(火用)损及(火用)效率的影响。结果表明,在无过热、过冷工况下,随着中间温度T3(低温级冷凝温度)升高,系统总功耗和(火用)损先减小后增大,热力性能COP和(火用)效率先增大后减小。因此,确定工况下存在一个最优中间温度T3使得系统能耗、(火用)损最小,系统热力性能COP和(火用)效率最大。通过分析系统各部件(火用)损随中间温度的变化,得出系统(火用)损主要集中在蒸发冷凝器、高温级压缩机、高温级节流阀和冷凝器。随着中间温度T3变化,此四部件(火用)损占总(火用)损的57.5%~85.7%。在最优中间温度T3下,此四部件(火用)损占系统总(火用)损的66.9%。分析蒸发温度对系统的影响,得出蒸发温度变化会改变最优中间温度,且随着蒸发温度升高,最优中间温度也会升高,系统热力性能及(火用)效率也显著提高。

In order to improve the thermal performance and reduce the energy consumption of R404A/R23 superposed refrigeration system,the effects of intermediate temperature and evaporation temperature on total energy consumption,thermal performance,exergic loss and exergic efficiency of superposed refrigeration system are analyzed by establishing thermodynamic model and using thermal analysis and exergic analysis. The results show that under the condition of no superheating and subcooling,with the increase of intermediate temperature T3(low-temperature cycle condensation temperature),the total power consumption and exergic loss of the system first decrease and then increase,and the thermal performance COP and exergic efficiency increase first and then decrease and thus determine conditions exist an optimal intermediate temperature T3make the system energy consumption,minimum exergic loss,thermal performance COP and exergic efficiency of system is the largest. By analyzing the change of the exergy loss of each component of the system with the intermediate temperature,it is concluded that the exergy loss of the system is mainly concentrated in the evaporative condenser,high temperature level compressor,high temperature level throttle and condenser. With the change of the intermediate temperature T3,the exergy loss of these four components accounts for 57.5% to 85.7% of the total exergy loss. In the optimal intermediate temperature T3,the four parts exergic damage accounted for 66.9% of the system total exergic loss. The influence of evaporation temperature on the system is analyzed. It is concluded that the change of evaporation temperature will change the optimal intermediate temperature,and with the increase of evaporation temperature,the optimal intermediate temperature will also increase,and the thermal performance and exergic efficiency of the system will also increase significantly.