Radial Liquid Dispersion in Liquid-Solid and Three-Phase Fluidized Beds

Abstract

The radial dispersion coefficient for liquid mixing, E_rl, was measured by using a tracer dispersion technique in liquid-solid and gas-liquid-solid fluidized beds. Four kinds of glass beads (mean diameter=1.1-4.8 mm, density=2500 kg/m³) and one kind of non-porous alumina beads (mean diameter=2.0 mm, density=3550 kg/m³) were fluidized by a concurrent upflow of air and water in columns of 0.074 and 0.15m i. d.
The value of E_rl in both fluidized beds had a maximum at an intermediate bed voidage and increased with increasing column diameter. The relationship between the modified Peclet number, Pe_{rl, m}, and the modified Reynolds number, Re_m, for both fluidized beds was expressed well by the following equation.
Pe_{rl, m}=5.0 (Re_m/Re_{m, mf}) ^-2.4+7.2×10^-4 {Re_m (μ_l/μ₀)} ^1.3
where Pe_{rl, rm}=d_e (U_g+U_l) / (ε_l E_rl), Re_m=d_eU_lρ_l/ (ε_l μ_l) and d_e= (ε_g+ε_l) ×D_c/ {1+1.5 (D_c/d_p) (1-ε_g-ε_l)}. The values of U_g and ε_g in these parameters should be set to zero in the case of liquid-solid fluidization. Re_{m, mf}=Re_m at incipient liquid-solid fluidization. U_g, U_l=superficial velocity of gas and liquid, D_c=column diameter, d_p=particle diameter, ε_g, ε_l, ε_s=holdup of gas, liquid and solid, μ_l=liquid viscosity and μ₀=water viscosity at 20°C.
A similarity was observed between radial heat transfer and radial liquid mixing, and the same correlation as given above was applied to the radial dispersion coefficient of liquid for heat transfer.