Experiments on Boiling Heat Transfer of Low-pressure Refrigerants Inside a Horizontal Smooth Tube

Abstract

In this study, the boiling heat transfer characteristics inside a horizontal smooth tube of low-GWP refrigerants R1224yd (Z), R1233zd (E), R1336mzz (E) and R1336mzz(Z) are expected to be used as alternative refrigerants to R245fa used in high-temperature heat pump and binary power generators systems using organic Rankine cycle were experimentally clarified. The smooth tube used has an outer diameter of 9.52 mm and an inner diameter of 8.40 mm, and a heat flux range of 2–15 kWm^-2, a mass velocity range of 50–300 kgm^-2s^-1, and a saturation temperature of 40 °C was conducted in this experiment. The boiling heat transfer coefficient was measured, and the applicability of the correlation proposed in the previous research was verified. It was found that the heat transfer coefficients were generally lower in the high mass velocity range than the previous correlations. Therefore, the new correlation for boiling heat transfer coefficient was proposed based on the experimental values of R245fa, R1224yd (Z), R1233zd (E), R1336mzz (E) and R1336mzz (Z) in the experiment. The new present correlation showed high prediction accuracy not only for our experimental values but also for the experimental values of low-pressure refrigerants such as R114 and R123 reported by other researchers.