Abstract:

Global warming is becoming increasingly serious, new environmentally friendly refrigerant research is imminent. The refrigeration industry also needs to replace existing refrigerants and further enhance the heat transfer efficiency of heat exchangers. Experimental research on the flow boiling heat transfer of R513A in different structures of tubes was conducted to explore the mechanism of different enhanced structures, mass flow rates [300—500kg/(m²·s)], and evaporating temperatures (5—10℃) on the heat transfer coefficient and pressure drop. The results showed that the heat transfer coefficient of R513A in microfin tubes was 23%—120% higher than that in smooth tube, while the pressure drop was higher than that in smooth tube. Larger helix angles exacerbated the generation of secondary flow in the tube; a larger number of teeth can increase the effective heat transfer area of boiling heat transfer, enhancing heat transfer. The boiling heat transfer coefficient and pressure drop of R513A increased with increasing mass flow rate; as the evaporating temperature rose, the heat transfer coefficient increased while the pressure drop decreased. By comparing the unit pressure drop heat transfer coefficient, it can be concluded that the 4# microfin tube had the best heat transfer performance. The differences in thread parameters mainly affected the comprehensive performance of microfin tubes in the low and medium vapor quality, with less impact in the high vapor quality. Under the present experimental conditions, the Kaew-on correlation and Chisholm correlation had the highest accuracy in predicting the heat transfer coefficient and pressure drop inside the smooth tube for R513A, with a mean relative error of -4.74% and 7%, respectively; and the Yu correlation and Miller-Steinhagen correlation were better in predicting the heat transfer coefficient and pressure drop inside the microfin tube, with a mean relative error of 14.16% and 3.66%, respectively.

Key words: enhanced structure, flow boiling, R513A, coefficient of heat transfer, pressure drop, correlation

摘要：

全球变暖日趋严重，新型环保型制冷剂研究迫在眉睫，制冷行业需要对现有的制冷剂工质进行替换并进一步强化换热器的传热效率。本文在不同肋结构的水平管内进行R513A的流动沸腾实验研究，探究了不同肋结构、质量流速[300~500kg/(m²·s)]、蒸发温度（5~10℃）对传热系数及压降变化的机理。结果表明，R513A在内螺纹管的管内沸腾传热系数相比光管有23%~120%的提高，但其在内螺纹管内的压降均高于光管；对比肋结构对换热的影响，发现较大的螺旋角可以加剧管内二次流的产生，较大的齿条数可以增加沸腾传热的有效传热面积，使得换热增强；R513A沸腾传热系数和压降随着质量流速的增大而增大；随着蒸发温度升高，沸腾传热系数增大，而压降减小；通过比较单位压降传热系数可知4^#螺纹管综合换热性能最优，肋结构参数对内螺纹管综合性能的影响集中在低、中干度区域，在高干度区域影响较小。在本实验工况下，Kaew-on关联式和Chisholm关联式分别对R513A在光管内传热系数和压降的预测精度最高，平均相对误差分别为-4.74%和7%；Yu关联式和Miller-Steinhagen关联式分别对内螺纹管内传热系数和压降的预测效果更好，平均相对误差分别为14.16%和3.66%。

关键词: 肋结构, 流动沸腾, R513A, 传热系数, 压降, 关联式