研究了强制对流条件下水平内螺纹管内R404A气液两相流冷凝换热特性，主要讨论油浓度对小管径水平内螺纹管内R404A冷凝换热的影响。实验油浓度变化范围为0到5%。设置入口平均饱和冷凝温度为40°C，质流密度变化范围为200-400 kg/m2·s，热流密度变化范围为 5-45 kW/m2。实验研究表明：油的出现恶化了换热，在油浓度为1%以下时恶化作用可以忽略，但随着油浓度的增加换热恶化作用越来越明显；对于纯R404A和油浓度为1%的R404A-油混合物，冷凝换热系数随着制冷剂蒸汽干度的降低而逐渐减小；对于油浓度为3%和5%的R404A-油混合物， 随着制冷剂蒸汽干度的下降， 冷凝换热系数先增加然后逐渐减小，在干度为0.7-0.75之间呈现出一个冷凝换热系数的峰值。同一质量流密度下，换热系数惩罚因子会随着干度的增加而减小，即干度越大，恶化作用越大；当质流密度从200 kg/m2·s增加到400 kg/m2·s时，同一油浓度下油对换热系数的恶化作用相对变小。

Current research on the condensation heat transfer characteristics of R404A-oil mixture is only for 7mm、9.52mm and other big diameter smooth tubes or microfin tubes, not for 5mm small diameter microfin tubes. The effect of oil on condensation heat transfer has not been studied in detail. Two-phase heat transfer coefficient characteristics of R404A condensing under forced flow conditions inside microfin horizontal tubes are experimentally investigated, mainly discussing the effect of oil concentration on the condensation heat transfer of R404A in the small diameter horizontal microfin tube. Experimental parameters include a lubricating polyol ester oil concentration varied from 0 to 5%. The test runs were done at average inlet saturated condensing temperatures of 40°C. The mass fluxes were between 200 and 400 kg/m2·s, and the heat fluxes were varying from 5 to 45kW/m2. The test results indicate that the presence of oil deteriorates the heat transfer. The deterioration effect is negligible at nominal oil concentration of 1%, and becomes obvious with the increase of nominal oil concentration. For pure R404A and R404A-oil mixture with oil concentration of 1%, condensation heat transfer coefficient decreases with the decrease of the vapor quality. For R404A-oil mixture with oil concentration of 3% and 5%, the condensation heat transfer coefficient increases at first and then decreases with the decrease of the refrigerant vapor quality, and the peak value of the condensation heat transfer coefficient occurs between 0.7-0.75. For the same mass flux, EF decreases with the increase of the vapor quality, that is, the greater the vapor quality, the greater the deterioration is. When the mass flux increased from 200 kg/m2·s to 400 kg/m2·s, the deterioration effect of same oil concentration on heat transfer coefficient becomes smaller.

TK124

上海市科委建设项目(13DZ2260900)