CO_(2)混合工质热力学模型及冷却换热特性的研究

Thermodynamic performance and cooling heat transfer characteristics of CO_(2) mixture

为了深入研究CO_(2)混合工质系统性能和换热特性,首先通过空气源热泵热水系统热力学模型对多种CO_(2)混合工质进行了筛选计算,结果表明:随着混合制冷剂质量分数增大时,只有R41混合工质的系统最优COP呈上升趋势,最大提高了12.81%,而压力最大降低了23.35%,证明其适合与CO_(2)混合。另外,CO_(2)/R41空气源热泵系统中蒸发器的损失最大。之后对不同入口压力、雷诺数和混合物组分下,CO_(2)/R41圆管内冷却换热过程进行了数值研究,分析了各参数对换热系数的影响机理。随着R41组分的含量增大,换热系数极值点向高温段移动,并且换热系数最大值也会随之减小。当CO_(2)/R41的混合质量比为0.5/0.5时,与纯CO_(2)工质相比,平均换热系数降低了8.78%。

To investigate system performance and heat transfer characteristics of CO_(2) mixture,an appropriate CO_(2) mixture was selected by thermodynamic model assessment firstly.The results show that with the increase of the mixture mass fraction,the maximum COP of the CO_(2)/R41 system is increased by 12.81%compared with CO_(2) system,and the pressure is reduced by 23.35%,which shows that R41 is suitable for mixing with CO_(2).In addition,the exergy loss of evaporator in CO_(2)/R41 air source heat pump system is the largest.Then,the cooling heat transfer process of CO_(2)/R41 in the circular tube under different inlet pressures,Reynolds numbers and mixture compositions was numerically studied.The mechanism of the influence of various parameters on the heat transfer coefficient is also analyzed.With the increase of R41,the extreme point of heat transfer coefficient moves to high temperature section,and the maximum value of heat transfer coefficient decreases.As the mixing mass ratio of CO_(2)/R41 is 0.5/0.5,the average heat transfer coefficient decreases 8.78%compared with CO_(2).