R134a在微肋管内的冷凝换热特性

Heat Transfer Characteristics during Condensation of R134a inside Micro-fin Tubes

本文在35、40和45℃三种冷凝温度下,对R134a在微肋管内的冷凝换热进行了实验研究。选用质量流量、冷凝温度、微肋管结构参数为变量,以总传热系数、水侧传热系数、制冷剂侧表面传热系数及压降为评价指标。结果表明:总传热系数、制冷剂侧表面传热系数、压降均随着质量流量的增加、冷凝温度的降低和管径的减小而增大,而水侧传热系数随质量流量的增加而稍有降低,冷凝温度对其值影响并不大。热阻分析时发现:随着质量流量的增加,水侧热阻占总热阻比值逐渐增加,而制冷剂侧热阻所占比值逐渐减小,但制冷剂侧热阻总小于水侧热阻;对换热器进行综合性能进行评价时,以表面传热系数与压降的比值(单位压降表面传热系数)为指标,发现该比值均随质量流量的增加呈先减小后增大的趋势,并随着冷凝温度的降低、管径的减小而增大。

Experimental study of R134a during condensation heat transfer inside the micro-fin tube for the condensation temperatures of35℃,40℃and45℃was made.The mass flux,condensation temperature,structural parameters of micro-fin tube were chosen as influencing factors and the total heat transfer coefficient,water-testing heat transfer coefficient,refrigerant surface heat transfer coefficient and pressure drop were selected as evaluation indexes.Experimental results show that:the total heat transfer coefficient,refrigerant surface heat transfer coefficient and pressure drop increase with increasing mass flux,and decreasing condensation temperature and tube diameter,but the water-testing heat transfer coefficient slightly decreases with increasing mass flux and the condensation temperature has a small influence on it.The thermal resistance analysis shows that the water-testing thermal resistance increases and refrigerant thermal resistance decreases with increasing mass flux,and the refrigerant thermal resistance is always less than the water-testing thermal resistance.To evaluate the comprehensive performance of micro-fin tubes,the ratio of refrigerant surface heat transfer coefficient and pressure drop(the surface heat transfer coefficient of unit pressure drop)was proposed,results show the ratio decreases first and then increases with the increase of the mass flux,and increases with decreasing condensation temperature and tube diameter in the micro-fin tubes.