[Atomic-S (OP)]

What is the formula for the flow rate (e.g., litres/sec) of a liquid in a pipe of a given length and diameter, having a given pressure difference between the ends?

[eric l]

Poiseulle's formula

D = [(π.r⁴.d)/8.η].[(p₁-p₂)/l]

with

• π = pi (or 3.1416)
• D = flow rate in kg/sec
• r = radius of the pipe in m
• d = density in kg/m³
• η = dynamic viscosity in Ns/m²
• (p₁- p₂) = pressure difference in N/m²
• l = length in m

You'll find this formula in any advance handbook on physics or engineering.  I copied it from "polytechnisch zakboekje", a Dutch pocketbook with all kinds of physical and chemical constants, formulae and other things useful for engineers.
I'm affraid it will require some converting to more traditional units.
 

[Atomic-S (OP)]

Thanx; I knew it depended steeply upon the diameter, but was not sure just how steeply.