Pool boiling performance of enhanced tubes on low GWP refrigerants

Low GWP refrigerants have drawn increasing attention as an alternative to HFC refrigerants that are regulated as a leading cause of global warming. The present study was focused on R-1234ze(E) and R-1233zd(E) refrigerants among other alternative refrigerant candidates and experimented on three types of tubes, i.e., a plain tube and two type of enhanced tubes, in terms of pool boiling heat transfer performance. The investigation was conducted under the experimental condition at saturated temperatures 4.4 °C and 26.7 °C and heat flux of 10-50 kW/m2. The heat transfer coefficients of R-1234ze(E) and R-1233zd(E) for the plain tube showed approximately 10.8-19.0%, 54.1-62.8% lower than those of R-134a respectively. Also, the results were compared against the previous empirical correlations, which proved satisfactory predictability for all conditions. For the enhanced 1 tube, the heat transfer coefficients of R-1234ze(E) and R-1233zd(E) showed 9.8-14.0%, 60.0-75.0% lower than those of R-134a, while the heat transfer coefficients of R-1234ze(E) and R-1233zd(E) for enhanced 2 tube showed 13.3-17.9%, 39.5-43.7% lower than those of R-134a respectively.