Question: Pressure Drop Across A Bed Of Stone

AI Thread Summary
To determine the required pressure for air to pass through a bed of stone in a cooling tower, the permeability of the stones (15-20mm size) is crucial, as indicated by the equation U = C (deltaP/L), where U is superficial air velocity, C is permeability, delta P is pressure drop, and L is bed length. There is confusion regarding whether to use superficial velocity or just velocity in calculations, as many sources refer to velocity without clarification. The Ergun equation, commonly used for calculating pressure drop, is also related to superficial velocity. The discussion highlights the need for clarity on which model—David Mills' or the Ergun equation—is more appropriate for this specific application. A resource for calculating rock bed permeability is also provided.
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Dears,

I am going to find out the required pressure for the air to pass through a bed of stone in a cooling tower.

I have read the book: Handbook of pneumatic conveying engineering (by David Mills) and it said that it can be determined by permeability of the stones (15-20mm size). The equation is:
U = C (deltaP/L)
Here it said that:
U is superficial air velocity
C is the permeability
delta P is pressure drop
L is bed length

However, when i try to find out more information on permeability in the internet (actually can't find much information), I find someone just simply mention velocity rather then superficial velocity...Thus, I am frustrated on which velocity should I used in the calculation and experiment determination...

Also, I also find that most ppl calculate the pressure drop by Ergun equation (and is related to superficial velocity this time).

Which model is more suitable for my case indeed??

Thank you very much!...
 
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