Experimental Investigation On Heat Transfer Enhancement And New Correlation Of Supercritical R1234ze(E) In Horizontal Helically Coiled Tube

Abstract

HFOs refrigerant R1234ze(E) has been widely applied in supercritical heat pump system and supercritical Organic Rankine Cycle (ORC) in recent years due to zero ODP and extremely low GWP. In this paper, experimental research on the cooling heat transfer performances of supercritical HFO-1234ze(E) in horizontal helically coiled tube (HCT) is performed. The impacts of mass flux (G) and pressure (P) on the heat transfer coefficient (h), the relative proportion of gravitational buoyancy effect and centrifugal buoyancy effect ( g c Ri / Ri ), the heat transfer enhancement of HCT and the distribution of secondary flow velocity (Vs) are detailed analyzed. The increasing P suppresses the impact of G on h, while the increasing G strengthens the influence of P on h. g c Ri / Ri decreases with the enhancement of G, yet increases with the rising P. The higher the mass flux is, the more obvious the influence of centrifugal force on the cross-sectional distribution of Vs will be, and the more significant the heat transfer enhancement of HCT will become. When G is 240 and 400 kg/m 2 s respectively, h of s-R1234ze(E) in helical tube is 12.73% and 18.69% higher than that in straight tube. The variation of P hardly changes the centrifugal effect on the distribution of Vs, thus having little impact on the heat transfer enhancement of HCT. When P is 4.5 and 5 MPa respectively, h of helical tube is 15.38% and 15.12% higher than that of straight tube. In the region of Tb>Tpc, the correlation of straight tube has large prediction deviations for the performances of s-R1234ze(E) in helical tube owing to the absence of Ric term.