HIGH TEMPERATURE INCIPIENT FLUIDIZATION IN MONO AND POLYDISPERSE SYSTEMS

Abstract

Tests have been made on the behaviour of fluidized beds at high temperature (15-950^°C). Bed materials used were silica sand of different sizes.

Bed voidage at minimum fluidization conditions was found to be dependent on temperature rise and on increase in Reynolds number. Plots of bed voidage function, bed voidage and Ar versus Re_mf show a change in the behaviour at Reynolds numbers between approximately 0.75-2. This is explained in terms of a variation in the fluid flow pattern inside the bed: at very low Re_mf creeping flow exists, but at higher values of Reynolds number, separation of boundary layer takes place and a wake appears at the rear of the particle, creating a low pressure zone. This contributes to attractive forces between particles at the minimum fluidization conditions, decreasing the value of ϵ_mf. If Re_mf increases, the separation point moves towards the rear of the particle and the wake shrinks; attractive forces decrease, and ϵ_mf increases.

Data on u_mf , both for monodisperse systems and binary mixtures, are compared with predictions from different equations.

KEYWORDS:

• Fluidization
• Hydrodynamics

Additional information

Notes on contributors

A. LUCAS

To whom inquiries should be addressed.