On the Nonuniformity in Fluidized Bed

Abstract

Mean (μc) and variance (σ) of local particle concentration in fluidized bed were measured by capacitance probe method using integrator and vacuum tube thermocouple. Particle concentration in bubble and dense phases (cb and cd), rise velocity of bubble (ub), bubble thickness (y) and its frequency (f) were also measured from the signal current recorded on oscillograms. The effects of fluidizing conditions on μc and σ were studied. In the bulk of bed, μc remains at a value fixed by the fluidizing conditions. It decreases with air velocity. σ, on the other hand, increases with probe level up to considerably higher portion of bed and there arrives at a constant value which increases with bed height and air velocity. The following equation was introduced to represent μc by the fluidizing characteristics. μc=yf/ubcb+(1-yf/ub)cd μc calculated by this equation coincides well with the measured μc. A regression equation of σ upon fluidizing characteristics, σ=0.72{yf/ub(1-yf/ub)}⁰.⁴⁶(cd-cb)².⁸⁹ was obtained, and the statistical analyses on this equation revealed that σ changes chiefly with (cd-cb), and accordingly, σ represents the nonuniformity in fluidized bed mainly in the form of particle concentration difference between bubble and dense phases.