Effect of tube shape on the condensation patterns of R1234ze(E) in horizontal mini-channels

Abstract

In this paper, the condensation characteristic of R1234ze(E) in horizontal circular, square and triangle channels were numerically investigated. The detailed liquid-vapor interfaces, local film thickness and stream traces were presented for better understanding the condensation process in circular and non-circular tubes. Under the same hydraulic diameter, the void fraction in square and triangle tubes was lower than that in circular tubes at the same vapor quality. The square tube exhibited higher heat transfer coefficients than that of the circular tube, while the triangle tube showed similar heat transfer performance with the circular tube. The tube shape had no significant effects on the pressure gradients. The gravity played a dominant role in local film distribution in the circular tube, but was almost negligible in the square tube. Both the surface tension and gravity played an important role in film distribution in the triangle tube. The number and structure of vortexes in the square and triangle tube were very different from that in the circular tube. The tube shape has a significant effect on the liquid phase velocity at different circumference positions. Under the same external perimeter, either the heat transfer coefficients or the pressure gradients of the square or triangle tube were larger than that of the circular tube. The numerical data of heat transfer coefficients and pressure gradients were also compared with the predicted values from the available well-known correlations. The results of this paper are important for the industrial applications of alternative refrigerants.