Experimental Study On Condensation Heat Transfer And Pressure Drop Of R1234ze(E)/R152a In Horizontal Tubes

The global greenhouse effect and the destruction of the ozone layer are becoming more and more serious.The emission of refrigerants is one of the main reasons for the destruction of environment.At present,R22,the widely used refrigerant,has not yet found a long-term alternative refrigerant.Moreover,the Montreal Protocol stipulated that China must complete the phase out of HCFCs by2030.Therefore,it is urgent to look for environmental protection and excellent performance refrigerants to replace R22.Through literature search and preliminary research of our group,it was found that the mixture of R1234ze(E)and R152 a in the mass ratio of 40:60(named NCUR01)is an environmentally friendly and good performance near azeotropic refrigerant,which is technically feasible to replace R22.In the refrigeration systems,the condenser is an important component,and the operation of the condenser has a great impact on the system performance,cost and user experience.For the new refrigerant,its thermal properties and transport characteristics are different from those of the traditional refrigerant,so the condensation heat transfer characteristics of the new refrigerant are necessary to carry out a systematic study.In this project,a horizontal flow condensation heat transfer test bench was designed and built,the experiments on the flow condensation heat transfer and pressure drop characteristics of NCUR01 in horizontal tubes(smooth tubes and micro-fin tubes)were conducted,the flow patterns of NCUR01 in horizontal tubes with the help of classical flow pattern diagrams were judged,the effects of mass flux,saturation temperature,heat flux,mean vapor quality and other factors on the condensation heat transfer coefficients and friction pressure drops were analyzed,and the law of condensation heat transfer of NCUR01 in the horizontal tube was summarized.It was shown that the flow pattern of NCUR01 is mainly annular flow and semi-annular flow when condensing in a smooth tube,and the flow pattern is mainly stratified flow and wavy flow when condensing in a micro-fin tube under this experimental condition.The condensation heat transfer coefficients of NCUR01 increase with mass flux and heat flux,while decrease with saturation temperature;the smaller the tube diameter,the higher the surface tension and shear force,the thinner the liquid film,the lower the thermal resistance,so the higher the condensation heat transfer coefficients.The condensation heat transfer coefficient as well as the frictional pressure drop gradient of NCUR01 increase with the mean vapor quality both in the horizontal smooth tube and micro-fin tube;the frictional pressure drop gradient of NCUR01 increase with mass flux and decrease with saturation temperature,while the correlation between the heat flux and the frictional pressure drop is not significant.In this paper,six classical condensation heat transfer correlations in the literature were selected to predict the condensation heat transfer coefficients in this experiment.Among them,Shah correlation has the best prediction effect on the condensation heat transfer coefficients in smooth tube,Kedzierski and Goncalves correlation has the least prediction error on the condensation heat transfer coefficients in micro-fin tube.In order to improve the prediction accuracy,based on the theory of the existing prediction correlations,the prediction correlations specifically applicable to the NCUR01 condensation heat transfer in the smooth tube and micro-fin tube were proposed respectively,and the mean absolute errors of the new correlations for smooth and micro-fin tube are 15.15% and 23.89%,respectively,and the proportion of data points falling within ω±30% are 82% and 77.5%,respectively.