Experimental investigation on hydrodynamic characteristics of 1,1,1,2-tetrafluoroethane (R134a) in a horizontal tube at supercritical pressures

Abstract

In this study, we experimentally assessed the hydrodynamic characteristics of supercritical-pressure R134a in a horizontal circular tube at pressure, inlet temperature, and heat flux ranges of p = 4.2 – 5.4 MPa, Tin = 20 – 50 °C, and q = 60 – 300 kW/m2, respectively. The hydrodynamic curves of R134a were plotted under various working conditions to assess the underlying mechanisms. The hydrodynamic characteristic curve of supercritical-pressure R134a does not possesses a negative-slope region but has a transition region compared with that under subcritical pressure. The transition region becomes more evident with increasing heat flux, while it weakens with increasing pressure and inlet temperature. Moreover, the onset of the transition region shifts in the direction of high mass flow rate with increasing heat flux. The transition region, generated by the relative changes in viscosity and density, is indicated by a dimensionless heat quantity Qratio, whose boundary is 1.8–2.2.