Study On Evaporation Of Micro-fin Tubes With Different Diameters

As the heat exchangers become more and more miniaturized,it is necessary to consider more about the diameter of tubes during the design of the heat exchanger.Therefore,it is meaningful to study on the influence of the pipe diameter on the heat transfer performance of the tubes.In this paper,an experimental investigation of evaporation heat transfer was conducted inside three micro-fin tubes with different outer diameters-which are 5mm,7mm and 9.52mm-and two micro-fin tubes with the same outer diameter and different inner diameters.The experiment was performed using R410A as working fluid.The mass flow rate was controlled in the range of 100-550 kg/(m2 · s).The inlet and outlet qualities were controlled at 0.1 and 0.9,respectively.The evaporation temperature was set to 10?.The experimental results show that the evaporation heat transfer coefficient(HTC)of the micro-fin tube with a smaller diameter is larger than that of the micro-fin tube with a larger diameter at the same mass flow rate.The micro-fin tube with an inner diameter of 6.8 mm has a lower HTC at G<200 kg/(m2 · s)and a higher HTC at G>200kg/(m2 · s)?compared with the other 7-mm-outer-diameter micro-fin tube with an inner diameter of 6.4 mm.The micro-fin tube with 7 mm outer diameter has the largest fin height to inner diameter ratio,so its pressure drop is the largest among the three types of tubes.Considering the heat transfer coefficient and pressure drop together,the comprehensive performance of the micro-fin tube with an outer diameter of 5 mm is the best among all tubes.The existing correlations are compared with the experimental data in this paper.It shows that Wu et al correlation,Yu et al correlation,and Thome et al correlation have good prediction results for the HTC of 5mm micro-fin tube.Yun et al correlation shows better prediction results for the HTC of 7mm and 9.52mm micro-fin tubes.Yu et al correlation was revised to improve the accuracy of the prediction in the paper.For the existing correlations of pressure drop,the Beattie-Whalley correlation and Friedel et al correlation show the good results with the average deviation within±30%.