多管程微通道冷凝器热力性能计算方法

多管程平行流微通道冷凝器的管程设计方案对换热器管内热力性能影响较大。但目前一直尚未有对其管内换热系数和压降进行理论预测的较为简单可行方法。本文针对各管程工质流量可变,平均干度可变的多管程平行流冷凝器管内热力参数提出一种分程计算方法：在假设管壁温度不变及同管程内流量均匀分配的前提下,采用了Koyama与Wang冷凝换热模型,以及Zhang和Koyama提出的摩擦压降模型,建立了壁温与热流量之间的关系式,通过迭代求得管内平均换热系数和压降的理论值。以一个商用R134a、流程分配为12-8-8-6微通道冷凝器作为示例,用理论和实验方法分别得到了其管内冷凝平均换热系数和压降。结果表明,二者的偏差均落在30%以内。其中Koyama和Zhang 提出的模型预测偏差较小,分别为-4.96%~11.31%,0.42%~25.14%。

In-tube heat transfer performance calculation of condensing zone in micro-channel condenser

The tube pass design method of the multi-pass parallel micro-channel condenser has great effect on the in-tube thermodynamic performance. However, there are no simple and effective methods which can predict the in-tube heat transfer coefficient and pressure drop. This paper proposed a stepwise calculation method for the thermodynamic parameters of the multi tube pass parallel micro-channel condenser under varying mass flux and average vapor quality of each pass. Based on the assumption that the tube wall temperature is constant and the distribution of refrigerant in each tube-pass is uniform, the heat transfer models of Shigeru Koyama, Wang and the pressure drop models of Zhang M, Shigeru Koyama were chosen to establish the correlation between tube wall temperature and heat flux, calculating the in-tube heat transfer coefficient and pressure drop via iteration. This paper investigated a micro-channel condenser whose number of tube pass is 12-8-8-6 using R134a.The in-tube heat transfer coefficient and pressure drop were got through theoretical calculation and experiment, respectively. The results demonstrated that both heat transfer coefficient and pressure drop fell within 30%.The predicted data deviation of Shigeru Koyama model and Zhang M model were smaller, ranging from -4.96%~11.31% and 0.42%~25.14%, respectively.