The effects of gas velocity and mean particle size on the transport disengaging height (TDH) and solids entrainment rates below and above TDH regions have been determined in a fluidized bed (0.28 m-ID x 2.6 m-high) with or without a centrally located draft tube (0.1 m-ID x 0.3 m-high). The entrainment rates of sand ($d_p$ = 210, 270, 390, 460, 610 μm) and PVC (d = 130 μm) particles along the axial position of the bed have been measured by an isokinetic sampling probe.
The solids entrainment rate in the freeboard region decreases exponentially with the freeboard height for both fluidized bed with or without draft tube. The entrainment rate at the bed surface can be determined by extrapolation of the entrainment rate profile in the freeboard to the bed surface. The solids entrainment rate at the bed surface rapidly increases with an increase in excess gas velocity (U -Umf). The obtained entrainment rate data at the bed surface are consistent with the values obtained from wen and chen's correlation equation(982) based of draft tube diameter gas velocity in the draft tube in a fluidized bed.
The exponential decay constant can be determined by the slope of the entrainment rate in the freeboard. The decay constant decreases with an increase in gas velocity, and increases with increasing particle size. The obtained exponential decay constant has been correlated with the ratio of particle size to gas velocity.
$a=304(dp/U)^{0.5}$
Transpot disenging height (TDH) increases with an increase in gas velocity, and decreases with increasing particle size. The obtained TDH values in both the fluidized bed with or without a draft tube
$TDH=(1/a)\times{in}(E_0/0.005)$
