I am looking for a derivation of the constant "4005" that is used in hvac vav's for air flow vs. velocity pressure in a round pipe. Q(cfm) = 4005 * aspect ratio * sqrt [velocity pressure (in h20)]
So V = [(2 x 115820)*dP/(0.075 x 0.1922)][sup]1/2[/sup]
i.e V = 4008.6 x dP[sup]1/2[/sup] (there may be some conversion problems for the costant to be high by 3.6)
Q = A x V (it is not aspect ratio here but the product of two sides)
Regards,
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