中文摘要：

超临界水流化床反应器可以有效气化湿生物质并且高效产氢。超临界水流化床反应器工作的表观流速比较低，颗粒与流体之间的自然对流换热是主要的传热方式。本文通过Boussiesq模型和真实物性流体模型模拟研究了层流条件下单颗粒与超临界水在拟临界点附近的自然对流换热。由于物性变化的影响，颗粒表面附近呈现高速度梯度、高表面涡量和高温度梯度的现象。临界水导热系数和比热的变化对拟临界区的自然对流传热起主导作用，Grashof数和平均Nusselt数在对数坐标下为线性关系。

英文摘要：

Free convection heat transfer from particle in supercritical water （SCW） is a major basic heat transfer mechanism in supercritical water fluidized bed （SCEFB）. Numerical study on the steady free convection heat transfer from a single sphere particle SCW has been conducted. Both the Boussinesq approximation method and real property model （considering variable specific heat, density, viscosity, and conductivity of SCW） are incorporated to simulate the flow and temperature field. Comparing with Boussinesq approximation, high vorticity, high temperature gradients, high local Nusselt number, and high heat transfer rate were observed in the vicinity of the sphere surface. The increasing trend of Nusslet number mainly depends on variation of specific heat and conductivity. The relationship between Grashof number and Nusselt number for variable property flow is nearly linear in logarithmic coordinates.