We are trying to fluidize sand of diameter 300 to 600 microns using a fluidized bed of diameter 65mm. The bed is fluidizing at 0.7 meters per second. According to the literature, the bed must fluidize at 0.1 to 0.15 m/sec. The distributor plate is having 19 holes of 1.5 mm dia in triangle pitch. If we increase the no of holes, will minimum fluidization velocity decease?
I mean how did you decide the minimum fluidization condition, by observation? The normal way to experimentally decide the minimum fluidization velocity is by measuring the pressure drop over the bed. You also need to check if there is any leakage.
There is no leakage in the setup.. I have measured the pressure drop over the bed vs superficial velocity also and umf is coming around 0.8 m/sec
As the pitch hole increased, Umf decreased, which means Umf increases with the increasing number of holes. For a lower Umf with perforated distributors of large hp is the greater gas flow rates through the hole when the pitch is larger, giving a higher interstitial gas velocity. The increased gas velocity creates a circulation of particles in the vicinity of the holes, thus inducing the condition of fluidization, and hence a lower value of Umf.
Yes.
Increasing the number and size of distributor plate holes will decrease the fluidization velocity. The gas velocity will decrease but the superficial gas velocity won’t change.
Note:
Large holes and many hole numbers will decrease the pressure hence less power consumption but the bubbling fluidized bed will not be stable.
But less hole number leads to more power consuption due to high gas velocity thus the stability of the BFB.
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