Condensation flow patterns and model assessment for R1234ze(E) in horizontal mini/macro-channels

Knowledge regarding the condensation flow patterns of environment friendly refrigerant R1234ze(E) in mini/macro-channels was important for alternative industrial applications. In this paper, the condensation heat transfer and pressure drop characteristic of R1234ze(E) in horizontal circular channels with diameter ranged from 0.493 to 4.57 mm were numerically investigated and compared with that of R134a. The detailed liquid film distribution, local film thickness and velocity field were presented for better understanding the condensation process. Both the heat transfer coefficients and pressure gradients increased with the mass flux, vapor quality and the decrease of the tube diameter. The heat transfer coefficients of R1234ze(E) were smaller than that of R134a, but the pressure gradients of R1234ze(E) were larger than that of R134a. The difference in heat transfer and pressure drop performance was found to be smaller in macro-channels. The effects of surface tension and gravity on liquid film distribution are significantly influenced by the tube diameter. The liquid film distribution was very close for R1234ze(E) and R134a for their similar physical properties. The average film thickness of R1234ze(E) was thinner than that of R134a. The axial velocity of the vapor phase decreased with the vapor quality, while the variation of the liquid phase velocity was associated with the circumferential position for the gravity effect. The simulated heat transfer coefficients and pressure gradients were compared with predicted values from the available well-known correlations. A new pressure drop correlation was proposed for practical application.