Analysis of Heat Transfer Oscillation and Buoyancy Effects of Supercritical R1234ze(E) Cooled in Horizontal Helically Coiled Tubes

Abstract

The helically coiled tubes (HCTs) have been attracting huge attention for enhancing the heat transfer of supercritical fluids and improving energy efficiency. Moreover, the new refrigerant R1234ze(E) has excellent environmental properties and system performance, but few researches have been concentrated on the supercritical R1234ze(E) heat transfer. In this work, the shear stress transport (SST) turbulence model is adopted for the numerical simulation of the cooling heat transfer performance of s-R1234ze(E) in horizontal HCT. The influences of heat flux, mass flux, coil pitch, and tube radius on the heat transfer coefficient, gravitational buoyancy effect, and centrifugal buoyancy effect are, respectively, investigated. Furthermore, the results reveal heat transfer oscillation occurs when Rig*|cosβ|max>0.17, and the oscillation mechanism is analyzed. Different from that in the vertical HCT, the angle between the radial component of gravitational buoyancy and centrifugal force varies continuously in the horizontal helical tube, resulting in the fluid with lower temperature may locate in the inner-left region or the inner-right region. Subsequently, the heat transfer piecewise correlation for supercritical R1234ze(E) in horizontal HCT is developed. The average absolute deviation of the predicted results is 5.88%.