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### Harris Formula Pressure and Fluid Flow Equation and Calculator

Harris Formula for Pressure Change at Standard Conditions Equation and Calculator

Equation 1
ΔP = L Q2 / ( 2390 P d5.31 )

where:

ΔP = pressure drop, psig
L = pipe length, ft
Q = volume flow rate at standard conditions, SCFM
P = average pressure, psia
d = pipe inside diameter, in

Harris Formula in terms of mass flow rate

Equation 2
ΔP = L M2 / ( 13.95 P d5.31 )

where:

ΔP = pressure drop, psig
L = pipe length, ft
M = volume flow rate at standard conditions, lb/min
P = average pressure, psia
d = pipe inside diameter, in

In terms of flow rate Q and upstream and downstream pressures P1 and P2, the following formula is used.

Equation 3
Q = 34.5 [ ( P21 - P22 ) d5.31 ) / L ] 1/2

where:

Q = volume flow rate at standard conditions, SCFM
P1
= upstream pressure, psia
P2
= downstream pressure, psia
L
= pipe length, ft
d
= pipe inside diameter, in

Where:

f = friction factor, (dimensionless)
ε = absolute pipe roughness, (in, mm) depends on the condition of the pipe. It ranges from 0.001 to 0.01.
d = inside diameter of pipe, (in, mm)
Re = Reyonds number, (dimensionless)

The Churchill equation for the friction factor yields comparable results with that obtained using the Colebrook-White equation.

Related:

Reference:

• Piping Calculations Manual,
E. Shashi Menon
SYSTEK Technologies, Inc