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Velocity Pressure 4005

Velocity Pressure 4005

Velocity Pressure 4005

(OP)
I know Pv = (V/4005)^2  in English Unit.

Who can tell me how to get the 4005? I need the process of transform.

RE: Velocity Pressure 4005

Pv is in inches of water

V is in feet per minute.

Density of air = .075 lb/ft^3 is built in.  More general formula is

V = 1097 * Sqrt(Pv/d)

where d is density.

Throw enough 12's and 60's at it and you're there.

RE: Velocity Pressure 4005

(OP)
Thank! But where's 1097 from?  

RE: Velocity Pressure 4005

The 1097 is the average velocity at the traverse plane. In order to use this constant one has to meet certain qualifacations, otherwise the final results could be bogus!
Example:  For a duct with a 28-by-20-in. airway, the Log-Tchebycheff method calls for a five-by-five grid
of unequally spaced measurements, while the Equal Area method requires a five-by-four grid with the distance between measurements no more than 6 in. To read more goto
    http://www.hpac.com/member/archive/pdf/2001/0301/K....
pdf

RE: Velocity Pressure 4005

The velocity pressure expressed in Ft of the fluid flowing =
V^2/2g   (Equation 1)

Where V = Ft/sec
g = 32.1722 Ft/Sec^2

But Ft of Air = ((in. wg) x 62.3215 ) / (12 x .075) (Equation 2)

Where 62.3215 lb/ft^3 is density of water

12 = inches/ft

.075 = lb/ft^3 density of air

and in. wg. = inches of water gauge
 
Equate Equation 1 to Equation 2 & solve for In. wg.
and get 4005 = 60 x((2 x 32.1722 x 62.3215) / (12 x .075))^0.5

RE: Velocity Pressure 4005

To lilliput1, excellent presentation. I think, however, the final V = 4005 ΔP0.5 is in feet per minute, not fps. Please advise.

RE: Velocity Pressure 4005

(OP)
Really helpful! Thank you all!  

RE: Velocity Pressure 4005

The 60 in the term converts FPM to FPS.
Velocity pressure in Inches wg = (FPM velocity/4005)^2

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