Abstract
Mixed convection heat transfer between supercritical water and particles is a major basic problem in supercritical water fluidized bed reactor, but little work focused on this new area in the past. In this paper, a numerical model fully accounting for thermophysical property variation has been established to investigate heat transfer between supercritical water and a single spherical particle under gravity. Flow field, temperature field and Nusselt number are analyzed based on the simulation results. Results show that buoyancy force has a remarkable effect on flow and heat transfer process. When the direction of gravity and flow are opposite, the gravity enhances the heat transfer before the separation point and inhibits the heat transfer after the separation point. When gravity is incorporated in calculation, a higher temperature gradient and a thinner boundary layer in the vicinity of the particle surface are observed before separation point, and the situations are just the reverse after separation point. Variation of specific heat and conductivity plays a main role in determination of heat transfer coefficient.
Highlights
Supercritical water fluidized bed reactor (SCWFBR) is a new promising reactor for gasifying wet biomass to product hydrogen [1]
This paper studied the mixed convection around a sphere particle in SCW of pseudocritical zone with moderate range of Reynolds number (5 ≤ Re ≤ 200), which represents supercritical water fluidized bed works at relatively low superficial velocity
The buoyancy force is determined by the density difference which results from the nonuniform temperature field
Summary
Supercritical water fluidized bed reactor (SCWFBR) is a new promising reactor for gasifying wet biomass to product hydrogen [1]. Chen and Mucoglu (1977) numerically investigated the laminar mixed convection around a sphere with constant surface temperature They found that both the local friction factor and the local Nusselt number increase with increasing buoyancy force for aiding flow and decrease with increasing buoyancy force for opposing flow [13]. Antar and El-Shaarawi (2002) numerically studied the problem of mixed convection around a liquid sphere in an air stream for aiding and opposing flows [15] They found that increasing Reynolds number or decreasing the interior-to-exterior viscosity ratio delays the flow separation. This paper studied the mixed convection around a sphere particle in SCW of pseudocritical zone with moderate range of Reynolds number (5 ≤ Re ≤ 200), which represents supercritical water fluidized bed works at relatively low superficial velocity. Effect of thermophysical property on the flow and heat transfer is studied
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