Numerical investigation on the secondary flow of supercritical water in a four-head internally ribbed tube

Abstract

In this paper, the secondary flow characteristics of supercritical water in a vertical, four-head internally ribbed tube are examined with the computational fluid dynamics (CFD) technique using CFX 14.0. The performance of the forced convection heat transfer in the circumferential and radial directions is determined and the corresponding heat transfer mechanism is analyzed. The simulation begins with sensitivity analyses of the turbulence model, near-wall treatment, and mesh dependency. The SSG Reynolds stress model with an enhanced wall treatment gives the best predictions with the experimental data. Based on the results of further simulations, the local forced convection heat transfer in the circumferential and radial directions of the tube are not uniform. The local heat transfer near the rib top surface is much better than that near the substrate surface. Variation in the bulk enthalpy has little effect on the basic structure of the secondary flow. The individual vortex that forms near the rib top surface creates a region of relative low pressure and augments the heat transfer near this region. The heat transfer heterogeneity is more pronounced in the great specific heat region due to the drastically changed physical properties. Because the substrate is the weak point of heat transfer, the internal structure of the tube in this region must be optimized.