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Fluidized Bed Dryer Velocity Calculator engineering
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Fluidized Bed Dryer Velocity Calculator

Calculate minimum fluidization velocity (Umf), particle terminal free-fall velocity (Ut), operating velocity ratio, and total drying blower SCFM.

Solid Particle Properties

Drying Air Conditions & Bed Geometry

Typical bubbling fluid bed range: 1.8 to 3.5× Umf.

Hydrodynamic Velocities

Min Fluidization (Umf)
-- m/s
-- ft/min
Operating Velocity (U)
-- m/s
-- ft/min
Terminal Velocity (Ut)
-- m/s
Elutriation Limit
Total Air Volume Flow: -- m³/hr (-- ACFM)
Geldart Powder Group: --
Archimedes Number (Ar): --
Operating air velocity must be maintained strictly between Umf (to prevent dead defluidized spots) and Ut (to avoid blowing powder into dust collectors).

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Frequently Asked Questions

What is the physical meaning of minimum fluidization velocity (Umf)?

Umf is the superficial gas velocity at which the upward frictional drag force exerted by the flowing gas on the particles exactly balances the buoyant gravitational weight of the bed. At this threshold velocity, the packed bed loosens, expands slightly, and begins to behave hydrodynamically like a boiling liquid.

What does the Geldart powder classification mean for dryer design?

Geldart Group B powders (100–1000 microns, such as sugar, crystalline chemicals, and silica sand) fluidize easily with immediate bubbles upon reaching Umf. Group C fine powders (<30 microns) are cohesive and form gas channels rather than fluidizing smoothly, requiring mechanical agitation or vibration.

Why must operating velocity be kept safely below terminal velocity (Ut)?

If superficial gas velocity exceeds the particle terminal free-falling velocity (Ut), particles will be pneumatically conveyed out of the dryer (elutriation), overloading cyclones and baghouse filters and causing excessive product loss.