Experimental Study Of Pool Boiling Heat Transfer Of Low GWP Refrigerant HFO1234ze Outside Tubes

The replacement of refrigerants has become a common problem in the world today,HFO1234ze,as a new refrigerant,is concerned by scholars at home and abroad because of the lower GWP value.At present,the research on HFO1234ze at home and abroad are relatively few studies on boiling heat transfer outside the tube.In this experiment,HFO1234ze was used as a refrigerant,The boiling experiments ofHFO1234zein the smooth tube and three enhanced tubes（E43a,E44a,E45a）were carried out at the evaporation temperature of 6±0.05℃and 10±0.05℃.The experimental data are analyzed and to get the boiling characteristics of HFO1234ze outside the tube.The main results are as follows:（1）The Wilson heat resistance separation method is used to get the multiple heat transfer of the tube inside the tube compared with the smooth tube under the same condition.The enhancement ratio of E43a（46fpi）is 3.152,the enhancement ratio of E44a（50fpi）is 2.717,and the enhancement rate of E45（56fpi）is 2.773.（2）With the increase of the evaporation temperature,the heat transfer coefficient outside the tube increases.The evaporation temperature in the smooth tube has little effect on the heat transfer coefficient,the evaporation temperature has a great influence on the heat transfer coefficient outside the tube when the heat flux is less than 40kWm.^-2;the evaporation temperature has little effect on the heat transfer coefficient outside the tube When the heat flux is greater than 40kWm.^-2.（3）In smooth tube,the heat transfer coefficient outside the tube increases with the increase of heat flux;the heat transfer coefficient outside the tube increases first and then decreases with the increase of heat flux.The heat transfer coefficient outside the tube is the largest when the heat flux is 40-60kWm.^-2.（4）Under the same heat flux,the experimental data basically showed the boiling heat transfer coefficient E45a（56fpi）>E44a（50fpi）>E43a（46fpi）>smooth tube.When the working temperature is 6℃and the heat flux is 50kWm.^-2,the heat transfer coefficient outside the smooth tube is 8.3kW/m².K^-1,the heat transfer coefficient of E43a is 15.9kW/m².K^-1,the heat transfer coefficient of E44a is 19.5kW/m².K^-1,and the heat transfer coefficient of E45a is 19.6kW/m².K^-1,there is a positive correlation between the enhanced heat transfer coefficient outside the tube and the feet per inch（fpi）,and increases with the increase of the feet per inch.（5）The heat resistance outside the tube is obviously larger than the heat resistance in the tube When the evaporation temperature is 6±0.05℃and 10±0.05℃,so it is of great significance to improve the heat transfer outside the tube.It is of great significance to increase the total heat transfer coefficient by strengthening the boiling heat transfer outside the tube and reducing the heat resistance outside the tube.（6）On the basis of experimental analysis and summarization,a correlation equation for the enhancement of boiling heat transfer by pure refrigerant is put forward,and the maximum deviation of experimental value and predicted value is no more than+20%,which can provide reference for the study of boiling heat transfer in the future.