Microfin tube, Flow boiling, R1233zd(E), R245fa, heat transfer, pressure drop
This paper presents R1233d(E) and R245fa flow boiling heat transfer and pressure drop measurements inside a mini microfin tube having internal diameter at the fin tip equal to 4.2 mm, 40 fins 0.15 mm high, and a helix angle of 18°. The tube was brazed inside a copper plate and electrically heated from the bottom. Sixteen T-type thermocouples were located in the copper plate to monitor the wall temperature. The experimental measurements were carried out at a constant mean saturation temperature of 30 °C, by varying the refrigerant mass velocity between 100 kg m-2 s-1 and 300 kg m-2 s-1, the vapour quality, and the heat flux from 15 to 90 kW m-2. The experimental results are here presented in terms of two-phase heat transfer coefficient, onset dryout vapour quality, and frictional pressure drop. Moreover, R1233zd(E) has been proposed as low GWP alternative to R245fa. In this paper, the two fluids performance is compare under the same working conditions and commented. Finally, the experimental measurements were used to assess a few selected models for boiling heat transfer coefficient and frictional pressure drop estimations available in the open literature for microfin tubes.