Experimental and numerical study on the heat transfer to supercritical water in an inclined smooth tube

Abstract

Heat transfer to supercritical water in a smooth tube with an inclined angle of 25° was investigated experimentally and numerically. Experimental results show that the increase of mass flux improves the heat transfer. As the pressure increases, influence of physical property variation to the heat transfer becomes gentle. Thereby, the increase of pressure reduces the heat transfer under an enhanced condition. Dimensionless buoyancy parameters Grq*/Grqth and Gr‾/Re2.7 are compared on the basis of experimental results. The evaluated result shows that Grq*/Grqth is applicable to the inclined tube flow. Base on the supercritical data, a new heat transfer correlation is proposed. Numerical analysis was completed with the shear stress transport k-ω model. Corresponding results show that the influence of variable mass flux and pressure on supercritical heat transfer is realized by changing radial distributing characteristics of turbulence and physical property. The increase of mass flux improves the radial turbulence and heat-absorbing capacity of the boundary fluid, so the supercritical heat transfer is enhanced. At a low mass flux condition where heat transfer reduction occurs, the increase of pressure improves the heat transfer. At a high mass flux condition where heat transfer enhancement occurs, the increase of pressure reduces the heat transfer. Influence of natural convection caused by the buoyancy leads to the occurrence of heat transfer disparity between top and bottom sides of the inclined tube. The increase of mass flux weakens the influence of natural convection and improves local heat transfer at the top side. At the low mass flux condition, the increase of pressure conducts the same effect with the increase of mass flux. At the high mass flux condition, the increase of pressure reduces the local heat transfer at the top side.