基于传热和压降耦合的混合工质冷凝器结构优化

Structural Optimization of Condensers with Refrigerant Blends Based on Heat Transfer and Pressure Drop Coupling

基于传热和压降的耦合作用,针对R744/R290(20/80)和R125/R290(25/75)混合工质逆流换热冷凝器建立基于熵产最小化的管长优化数学模型,并结合Cavallini凝换热性能评价指标PEI(performance evaluation index)和温度惩罚因子TTP(total temperature penalization),得到了混合工质PEI与传热系数α之间的函数关系,具体分析了管径、冷凝温度和被动压降对管长优化结果的影响。研究表明,制冷剂饱和温度降为制冷剂与壁面之间传热驱动温差的0.6倍,高压工质R744/R290(20/80)(临界温度低的工质)的PEI值更小,冷凝换热性能更优,同时小管径的冷凝器最优管长更小,且最优管长随随着冷凝温度的增大而增大,随着被动压降的增加而减小。

A tube length optimization model based on minimum entropy production was proposed for R744/R290(20/80) and R125/R290(25/75) counter-flow condensers considering coupling of heat transfer and pressure drop. The concept of performance potential evaluation index(PEI) and Total Temperature Penalization(TTP) for mixed refrigerant condensation proposed by Cavallini was used, and the relationshipbetween PEI and heat transfer coefficient was obtained. The effects of condensing temperature, tube diameterand passive pressure drop on optimal tube length were analyzed. The results indicate that the saturation temperature drop value of refrigerants is 0.6 times of that of heat transfer temperature difference between refrigerant and wall. The higher pressure refrigerant (lower critical temperature) R744/R290 (20/80) has lower PEI value and better performance than others, and smaller tube diameter condenser has shorter optimal tubelength. The optimal tube length increases with the increase of condensing temperature, while it decreases with the increase of pressure drop.