Formula: Poiseuille's Equation Volumetric Flow Rate    Length    Viscosity    Radius    Pressure

Formula: Poiseuille's Equation
Pipe with Fluid and a Volumetric Flow Rate

Volumetric Flow Rate

Volumetric Flow Rate (Volume velocity) is the volume of a fluid (e.g. water) that passes through a cross-sectional area of a pipe per second. The volume flow is due to a pressure difference \( \Delta \mathit{\Pi} = \mathit{\Pi}_1 - \mathit{\Pi}_2 \) between the ends of the pipe.


Length of a pipe through which a fluid moves.

Dynamic viscosity

Viscosity \( \eta \) (pronounced: Eta) is a property of a fluid (liquid or gas) and describes how difficult it is to move a body through this fluid.

Liquid Viscosity \( \eta \)
Olive oil\( 108 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{m}\cdot \mathrm{s} } \)
Honey\( 10\,000 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{m}\cdot \mathrm{s} } \)
Glycerin\( 1500 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{m}\cdot \mathrm{s} } \)
Water\( 1.008 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{m}\cdot \mathrm{s} } \)
Tar\( 100\,000 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{m}\cdot \mathrm{s} } \)
Viscosity of some liquids.


Radius of the pipe through which a fluid moves. If you double the radius, then the flow rate becomes 16 times larger!

Pressure at one end

Pressure at one end of the pipe. \(\Pi\) is pronounced as "Pi".

Pressure at the other end

Pressure at the other end of the pipe.

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