At minimum fluidization the total weight of the
packed bed is supported by the upward force created by
the gas moving upward through the porous structure. As
the superficial velocity is increased above minimum fluidization
velocity, the pressure drop remains practically
the same (Kunii & Levenspiel (1991)). In some cases
the pressure drop does not remain constant in the fully
fluidized regime but actually increases. The explanation
for the slight increase of pressure drop with an increase
of superficial velocity may be attributed to wall effects
which occurred due to the physical dimensions of the
experimental tower used. More specifically, some slugging
can occur and due to the formation of slugs additional
potential energy is required to move the slug vertically.
The result is an approximate linear increase in
pressure drop across the fluidized bed (Chen, Gibilaro
& Foscolo (1997)). In the present study the pressure
drop in the fluidized regime will be assumed constant.
This constant pressure drop will be assumed as the upper
bound, y∞{q}, in our powered-addition correlation
given in equation (1). At minimum fluidization velocity
the pressure-drop is given by
∆p = (1 − ϵ)(ρp − ρf )Lg, (2)
with ρp the particle’s density, ρf the fluid density and L
the bed height.
In previous studies it has been found that the shifting
parameter s was relatively independent of the particle
sizes that were investigated (Rautenbach, Melaaen
& Halvorsen (2010)). The three particle size distributions
that were used were 100-200 µm, 400-600 µm and
750-1000 µm. It was found that a shifting parameter
value greater than about 12 but smaller than about 20
produced an acceptable correlation in the transition region
between the fixed to fluidized regime.
At minimum fluidization the total weight of thepacked bed is supported by the upward force created bythe gas moving upward through the porous structure. Asthe superficial velocity is increased above minimum fluidizationvelocity, the pressure drop remains practicallythe same (Kunii & Levenspiel (1991)). In some casesthe pressure drop does not remain constant in the fullyfluidized regime but actually increases. The explanationfor the slight increase of pressure drop with an increaseof superficial velocity may be attributed to wall effectswhich occurred due to the physical dimensions of theexperimental tower used. More specifically, some sluggingcan occur and due to the formation of slugs additionalpotential energy is required to move the slug vertically.The result is an approximate linear increase inpressure drop across the fluidized bed (Chen, Gibilaro& Foscolo (1997)). In the present study the pressuredrop in the fluidized regime will be assumed constant.This constant pressure drop will be assumed as the upperbound, y∞{q}, in our powered-addition correlationgiven in equation (1). At minimum fluidization velocitythe pressure-drop is given by∆p = (1 − ϵ)(ρp − ρf )Lg, (2)with ρp the particle’s density, ρf the fluid density and Lthe bed height.In previous studies it has been found that the shiftingparameter s was relatively independent of the particlesizes that were investigated (Rautenbach, Melaaen& Halvorsen (2010)). The three particle size distributions
that were used were 100-200 µm, 400-600 µm and
750-1000 µm. It was found that a shifting parameter
value greater than about 12 but smaller than about 20
produced an acceptable correlation in the transition region
between the fixed to fluidized regime.
การแปล กรุณารอสักครู่..
