不凝气体对跨临界 CO2制冷系统性能影响的分析

摘要

本文选择不凝气体氮气作为添加剂加入到 CO2跨临界制冷循环系统中,通过理论分析和计算仿真研究氮气对系统制冷性能的影响。首先分析 CO2工质和氮气的基本物性参数,N2的加入会改变 CO2工质物性参数,本文通过计算得出添加剂使CO2工质的饱和压力和液体比热提高,粘度系数﹑表面张力﹑液∕汽密度比和导热系数降低。同时分析 N2在蒸发器内可作为汽化核心,实现非均匀核化过程,从而降低成核温度,提高换热系数。同时 N2的加入会降低压缩机排气温度,减小压缩机功率,从而提高系统制冷性能,并随浓度的增加而增加。本文为跨临界 CO2制冷循环系统高效应用研究提供理论依据。%In this paper, non_condensable gas (N2 ) was added to CO2 transcritical refrigeration cycle as additive.And the the effect on refrigerant performance is studied by theoretical analysis and computer simulation.The major thermophysical parameters of CO2 and N2 are analysed.The addition of N2 results in the change of the thermophysical parameters of CO2 .The calculated results have shown that addi_tives can increase saturation pressure and liquid specific heat of CO2 , but reduce viscosity coefficient, surface tension, the liquid∕vapor density ratio and coefficient of thermal conductivity of CO2 .N2 can increase gas nucleus in evaporator, and leads to heterogeneous nuclea_ting process in liquid.So the nucleation temperature decreases and heat transfer coefficientis increases.Moreover, the discharge tempera_ture and specific power of compressor are reduced and refrigeration efficiency improves.The more the N2 is added in the system, the more the refrigeration system performance coefficient increases.The paper provides theoretical basis for the research on highly efficient applica_tion of CO2 refrigeration system.