Numerical study on condensation annular flow of R1234ze(E) inside an inclined tube

Abstract

The condensation characteristic of R1234ze(E) inside an inclined circular tube (D = 4.57 mm) were numerically investigated. The mass flux covered from 300 to 800 kg·m−2 s−1 and the inclination angle varied from −90° to 90°. The inclination effects on film distribution, local film thickness, local heat transfer coefficient and velocity profile were detailed presented. Inclining the tube has a negligible effect on heat transfer coefficients at high mass fluxes and vapor qualities, but may cause an increase or decrease in heat performance when decreasing the mass flux and vapor quality. At the same inclination angle, slightly higher heat transfer coefficients were observed for the down-flow configuration. Increasing the inclination angle would thicken the film thickness of thin film region while reducing the film thickness of stratification region, which affected local heat transfer performance. Compared with heat transfer coefficients, the pressure gradients were more sensitive to the inclination angle. The local pressure gradients generally increased with the inclination angle for down-flow configuration. While the reverse was true for up-flow configuration. The simulated heat transfer coefficients and pressure gradients were compared with predictions of well-known correlations. The pressure drop models developed for horizontal tubes were not able to precisely predict the data of inclined tubes.