Non-uniform wall temperature distribution of nucleate boiling heat transfer in helically coiled tubes

Highlights: • Two-fluid model is used to simulate nucleate boiling heat transfer in helical tube. • The model is suitable to simulate the non-uniform wall temperature distribution. • Vapor-liquid phase distribution and secondary flow are obtained at cross sections. • The effect of operating conditions and shape on wall temperature is simulated. • The causes and influencing factors of non-uniform wall temperature are obtained. - Abstract: Numerical simulation is carried out for nucleate boiling heat transfer of a helically coiled tube. The boiling heat transfer characteristics and the non-uniform wall temperature distribution are in basically consistent with existing experimental data. The influences of operating conditions and shapes on wall temperature are discussed in detail. The results show that the liquid gathers at the outside and the bottom of the cross section during nucleate boiling heat transfer, resulting in a lower wall temperature in these locations. However, the movement of the vapor phase to the top and the inside walls results in higher local wall temperatures. The maximum temperature difference throughout the cross section is approximately 10 K. Furthermore, the distribution of vapor volume fraction becomes uniform as the secondary flow enhances. Due to the vapor–liquid phase distribution, the wall temperature of the cross section shows a sharp rise before decreasing. Under different experimental conditions, the position of the maximum wall temperature changes from 90° to 180° and the maximum deviation is more than 60°.