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Cohesive forces between particles can have a significant effect on the
bulk flow in fluidized beds. These forces can come from a number of
sources including liquid bridging, van der Waals forces and electrostatic
forces. Mild cohesive forces can lead to changes in the minimum
fluidization velocity, the minimum bubbling velocity and the bed
expansion. High levels of cohesion can lead to total defluidization and
the formation of plugs and channels.
In this work, we are using a modified form of the Multiphase Flow with
Interphase eXcahanges (MFIX) computer code that includes a
discrete-particle treatment of the solid phase. We have incorporated
cohesive forces using a square-well potential model. Our goal is to gauge
the effectiveness of the square-well model by assessing its ability to
predict specific phenomena in cohesive fluidized beds such as inversions,
transitions in particle type with regard to the Geldart classification
system and general trends in the minimum fluidization velocity and minimum
bubbling velocity.
In the above snapshots, the particles
were given sufficient cohesive forces that the bed was unable to fluidize
but instead formed static channels that evolved over the span of
approximately two seconds.
Download an AVI animation [3.14 Mb] :
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This animation, shows the results of a fluidized bed
simulation with decreasing inlet velocity. The level of cohesion
in this simulation is sufficient that the particles initially
raise a single plug. |
Student: Michael Weber (Ph.D. candidate)
Faculty: Christine Hrenya
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