Numerical study on heat transfer of supercritical water in different sub-channels

In this paper, heat transfer characteristics of supercritical water in vertical tubes with a square cross section, circular cross section and regular triangle cross section, respectively, were studied using ANSYS CFX 14.5 at working conditions of mass flow rate 800 kg/(m2s), pressure from 23, 25 MPa and heat flux from 300-1000 kW/m2. The results showed that when the heat flux increased, the heat transfer coefficient decreased, the wall temperature decreased when the heat flux increased. Because of the circumferential heterogeneities of square channels and regular triangle channels, point-to-point simulation from the vertex angle to the midpoint of the edge is necessary. For square channels and regular triangle channels, the midpoint of the edge had the highest heat transfer coefficient and the vertex angle had the lowest heat transfer coefficient, it was necessary to compare the heat transfer coefficients at the vertex angle of the triangular channels and the square channels with the circular channels. For the three channels, there was no difference between the circular channels and other two channels in the low enthalpy region and the high enthalpy region, but it was obvious that the heat transfer coefficients of circular channels was higher than others in the vicinity of the pseudo-critical point. The reason for this was the separation between the boundary layer and the wall.