CYLINDER-TO-BED HEAT TRANSFER IN AERATED VIBRATED BEDS OF SMALL PARTICLES

Abstract

ABSTRACT Cylinder-to-bed heat transfer in aerated vibrated beds was studied experimentally. Beds of various model particles were vibrated in the vertical direction with a frequency varying from 0–25 Hz and half-amplitude from 0–4 mm. Alumina and molecular sieve particles of sizes ranging from 27 μm to 1400 μm were used as the model particles. A single-orifice bottom plate was used to supply the air flow at rates varying from 0 to the minimum fluidizing velocity. For small-panicle beds which display resonant behaviour, the cylinder-to bed heat transfer coefficient remains close to the packed bed value as the frequency is increased. Close to the resonant frequency, it increases rapidly to reach a maximum at the resonant frequency. Thereafter, h decreases only gradually with further increase of frequency. The cylinder-to-bed heat transfer coefficients at resonance are much higher than those in packed beds (up to 19 times). The high heat transfer rates are due to particle mobility which reaches a maximum at the resonant point. Surface coverage is greatly affected by both the resonant frequency and aeration rates. It affects the heat transfer rate but is not rate limiting even at low bed bulk densities and surface particle coverage.