Fluidized bed freeboard measurements of heat transfer

Abstract

Local surface‐to‐suspension heat transfer coefficients in the freeboard of a fluidized bed reactor were measured by a newly designed miniature probe. Four types of plate orientations were used to test directional effects of surface on heat transfer rate. Variations of heat transfer coefficients with radial position are more significant at lower freeboard. For plate parallel both to the axial and radial directions of the column, the heat transfer coefficient (h) is higher at the center than at wall. For plate with exposed surface parallel to the axial and perpendicular to the radial directions, the plate gives nearly the same value of h at the center and the wall. At low heights of freeboard, center‐facing surface exhibits higher heat transfer rate than wall‐facing one. The phenomena of higher solids concentration and center to wall movement of particles account for this observation. Variations of heat transfer coefficients with elevation in the freeboard are as much as an order of magnitude, decreasing to gas convection with increasing elevation. These variations are relatively insensitive to the types of plate orientation investigated.

Surface‐to‐suspension heat transfer model in lean gas–solid freeboard flow

“…Particle size distributions for selected solids samples in the freeboard were analyzed by a laser-scattering type particle size analyzer (Leeds & Northrup Microtrac Model 7991-01, USA). The details for bed construction, testing, and operation were discussed in Tsai (1991), and Farag and Tsai (1992).…”