Calculations

Conversion of pressure units

bar mbar psi Pa hPa kPa MPa N/m² N/cm² Torr mmHg bar mbar psi Pa hPa kPa MPa N/m² N/cm² Torr mmHg

Conversion of volume units

ml l US gal. US liq.qt. µl m³ dm³ cm³ mm³ ml l US gal. US liq.qt. µl m³ dm³ cm³ mm³

Conversion of volume flow units

ml/min l/h GPM GPH ml/min l/h GPM GPH

Pressure drop in a tube

When a medium is delivered through a tube, a pressure drop occurs. This pressure drop depends on the volume flow and the viscosity of the medium as well as the length and the inner diameter of the tube.

The volume flow Q of a liquid with dynamic viscosity η in a tube with length L and inner diameter D causes a pressure drop Δp

The pressure drop in laminar case is calculated as follows:

Calculation

volume flow Q
dynamic viscosity η
specific gravity ρ
tubing length L mm cm m inch feet
inner diameter D
pressure loss Δp bar mbar psi Pa hPa kPa MPa N/m² N/cm² Torr mmHg
velocity v m/s
Reynolds number Re

Conversion

kinematic viscosity ν mm²/s
specific gravity ρ g/ml
dynamic viscosity η mPas

Viscosity

Dynamic viscosity η: 1 mPas = 1 cP (P = Poise)
Kinematic viscosity ν: 1 mm²/s = 1 cSt (St = Stokes)

Examples of viscosities

Liquid η [mPas] water, liquid, 0 °C 1,79 water, 20 °C 1 water, 50 °C 0,55 water, 80 °C 0,36 water, liquid, 100 °C 0,28

Liquid η [mPas] Acetone 0,36 Benzene 0,65 Ethanol 1,2 Methanol 0,58 Toluene 0,59