Numerical simulation research on two-phase flow boiling heat transfer in helically coiled tube

In this paper, the partial geometric models of helically coiled tube type heat exchanger with different tube diameters (d = 12, 19, 25 mm), tube pitches (P = 50, 100, 150 mm) and helical radius (R = 100, 150, 200 mm), were established. Numerical simulation and performance comparison were carried out using water and water vapor as the working fluid. The gas–liquid phase distribution in the helically coiled tube, the gas volume fraction at different cross-sections, and the changes of heat transfer coefficient and pressure drop along the length of the helically coiled tube were analyzed. The results showed that the gas phase was concentrated in the inner side (near the side of the central axis) and the upper side of the helically coiled tube under boiling condition, and the liquid phase was concentrated in the bottom of the helically coiled tube and is stratified with the gas phase. As the helical radius and tube diameters increased, the heat transfer coefficient and unit pressure drop decreased gradually. Based on the simulated data, the boiling heat transfer correlation was fitted by the method of multiple nonlinear regression, and the mean absolute error was 4.5% compared with the modified Chen's correlation. Therefore, the numerical results were correct and trustable.