Dynamic characteristics of R1234ze(E) boiling two-phase flow patterns and heat transfer in a horizontal tube

As a new type of halogenated olefins (HFOs) environmentally friendly refrigeration, R1234ze(E) is considered to be a new generation of refrigerant that can replace R134a. In this paper, a three-dimensional unsteady-state analysis of the flow boiling process of R1234ze(E) in a 6 mm horizontal tube was conducted using FLUENT software on a Workbench platform. The simulation was carried out under the mass flux from 67 kg m-2 s-1 to 258 kg m-2 s-1, saturation pressure from 0.215 MPa to 0.415 MPa, and heat flux from 10.6 kW m-2 to 43.3 kW m-2. To better understand the boiling process, the detailed two-phase flow patterns, phase distribution and velocity field were analyzed. The results indicate that the flow transitions from plug flow to slug flow and then to annular flow as vapor quality increases. With the increase of mass flux, the initial vapor quality of flow pattern conversion gradually decreases, while the saturation pressure has the opposite effect. The axial velocity distribution along the Y-axis is asymmetrical, with a thicker liquid film at the bottom than at the top. As the vapor quality increases, the distribution of the liquid film around the tube becomes more uniform. The liquid film becomes thinner as a consequence of an increase in mass flux, a decrease in saturation pressure and a decrease in heat flux. The heat transfer coefficient of R1234ze(E) increases as the mass flux increases and decreases as the saturation pressure increases. The calculated and experimental heat transfer coefficient data show excellent agreement, with a mean absolute relative deviation (MARD) of 8.2 %, all data within +/- 30 % deviation.