Experiments on Condensation Heat Transfer and Frictional Pressure Drop of Zeotropic Mixtures R245fa/R1234ze(E) Inside Horizontal Micro-Fin Tubes

Abstract

This study addresses the urgent need to reduce greenhouse gases by investigating high-temperature heat pump systems and binary organic Rankine cycle generators that utilize low-temperature industrial waste heat. Traditionally, R245fa has been used in these systems due to its low working pressure and high critical temperature. However, its high Global Warming Potential necessitates a transition to alternative refrigerants. This research focuses on the heat transfer and pressure drop characteristics of the R245fa/R1234ze(E) refrigerant mixture, a promising alternative with a lower GWP. Experiments were conducted using horizontal micro-fin tubes with copper test tubes of 9.52 mm outer diameter, varying fin heights and numbers, under mass velocities of 100 and 200 kgm\(^{-2}\)s\(^{-1}\) and mass fractions of 90/10, 80/20, and 65/35 (R245fa/R1234ze(E)) at an average saturation temperature of 60°C. The results showed that the R245fa/R1234ze(E) mixture had lower condensation heat transfer coefficients and frictional pressure drops compared to pure R245fa. The minimum heat transfer coefficient occurred at a 65/35 mass % mass mixture, which is close to the point where the largest temperature glide appeared. Additionally, the frictional pressure drop decreased with increasing mass fractions of R1234ze(E). These findings suggest that the R245fa/R1234ze(E) mixture, despite its lower heat transfer performance compared to pure R245fa, presents a viable lower-GWP alternative for high-temperature heat pump and binary generation systems. This contributes to the development of more efficient and environmentally friendly refrigerant systems, supporting global efforts to reduce greenhouse gas emissions. Further research is needed to optimize the performance of these mixtures in practical applications.