NUMERICAL STUDY ON LAMINAR FREE CONVECTION HEAT TRANSFER BETWEEN SPHERE PARTICLE AND HIGH PRESSURE WATER IN PSEUDO-CRITICAL ZONE

Supercritical water fluidized bed reactor is a promising new reaction vessel which can effectively gasify, wet biomass and efficiently produce hydrogen. Free convection heat transfer from particle in supercritical water is a major basic heat transfer mechanism in a fixed bed or fluidized bed with low superficial velocity. In this paper, numerical study on the steady free convection heat transfer around a single sphere particle in high pressure water of pseudo-critical zone was carried out. Both the Boussinesq approximation method and real properties model (considering variable specific heat, density, viscosity, and conductivity of supercritical water) were incorporated to simulate the flow and temperature field. With respect to Boussinesq approximation, real properties model shows higher vorticity and temperature gradients in the vicinity of the sphere surface, which shows variation of thermo-physical property has remarkable effect on the free convection heat transfer process. High local Nusselt number and high heat transfer rate were observed with real properties model.