Experimental investigation of R1234ze(E) flow boiling inside a 2.4 mm ID horizontal microfin tube

Abstract

There are two possible viable options to cope with the new environmental regulations: more efficient heat exchangers and environmental-friendly refrigerants. This paper explores the use of a new low-GWP refrigerant, R1234ze(E), during flow boiling inside a horizontal mini microfin tube, which has an inner diameter at the fin tip of 2.4 mm and 40 fins with a height of 0.12 mm along the inner circumference. During the experimental tests, the mass velocity was varied between 375 and 940 kg m−2 s−1, heat flux from 10 to 50 kW m−2, and vapor quality from 0.10 to 0.99. The saturation temperature at the inlet of the test section was kept constant and equal to 30 °C. The experimental tests show that the flow boiling mechanism is governed by nucleate boiling and two phase forced convection: at low vapor quality and high heat flux, nucleate boiling prevails over convective boiling, whereas at high vapor quality and low heat flux convective boiling overcomes nucleate boiling. The experimental values of heat transfer coefficient, frictional pressure drop, and vapor quality at the onset of dryout were also compared against the values estimated by empirical correlations available from the open literature. The thermal and hydraulic performances of the microfin tube are also compared against the ones estimated for an equivalent smooth tube.