Experimental And Simulation Study On Flow Boiling Characteristics Of R245fa Horizontal Micro Fin Tube

Organic Rankine Cycle(ORC) is a promising technology for conversion of low-grade heat into electricity. As a new generation of high-temperature refrigerant,R245 fa has been widely used in ORC system due to its good environmental performance and thermal physical properties. Shell and tube heat exchanger is a key component of organic Rankine cycle. have been widely used in organic Rankine cycle power system driven by low-grade waste heat. Shell and tube heat exchanger is a key component of organic Rankine cycle. The boiling heat transfer and flow resistance in evaporator will directly affect the irreversible loss and thermal efficiency of ORC system. An experimental apparatus was developed to investigate the frictional pressure drop and heat transfer performance of R245 fa under different conditions.The results can provide a theoretical basis for design of the evaporator. Therefore, it is of significant importance in both theoretical research and practical applications..In this paper, experimental measurement and numerical simulation were used to study the flow boiling characteristics of R245 fa in a horizontal micro-fin tube. The main work and conclusions are as follows:1) Experimental platform has been designed for studying basic flow boiling characteristics of R245 fa in micro-fin tube. The experimental platform mainly includes four parts, such as refrigerant circuit, cooling water loop, electric heating system, data acquisition system. On this basis, the experimental parameters measurement and processing method are introduced in this paper.2) The characteristics of R245 fa flow boiling heat transfer were studied within7 mm horizontal micro-fin tube. The effect of vapor quality, mass flux, heat flux and saturation temperature on the boiling heat transfer coefficient has been analyzed. The heat transfer correlation has been selected to predict the experimental data. The results show that boiling heat transfer coefficient significant increases with the mass flow rate. While it decreases with the increment of saturation temperature and heat flux. As the increase of vapor quality, boiling heat transfer coefficient increases firstly and then decreases. Kandlikar correlation has the best prediction accuracy for boiling heat transfer coefficient of R245 fa among the four widely used correlations. The correlation covers 91.6% of experimental heat transfer coefficients within thedeviation range of-25%~25%. Compared with experimental data, the correlation has a mean deviation of 4.7% and an absolute mean deviation of 11.2%.3) The pressure drop of R245 fa within 7mm horizontal micro-fin tube were tested. The effect of vapor quality, mass flux, heat flux and saturation temperature on pressure drop was analyzed And the suitable pressure drop correlation was selected.Studies show that pressure drop increases with the mass flux and heat flux. However,it decreases with the increase of saturation temperature. Muller-steinhagen-heck correlation shows the best prediction accuracy for frictional pressure drop among the four widely used correlations. It covers 84.1% of frictional pressure drop within the deviation range of-25%~25%. Compared with experimental data, the correlation has a mean deviation of 9.36% and an absolute mean deviation of 10.1%.4) The boiling heat transfer and flow resistance of R245 fa in micro-fin tube and smooth tube were simulated by Fluent. Compared with smooth tube,the boiling heat transfer coefficient and the friction pressure drop of the mico-fin tube increased by23.4% and 19.8%,while the comprehensive heat transfer performance increased by about 17%, respectively.