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Capillary Number and Pressure Formulas and Calculators

Civil Engineering Design and Engineering
Fluids Engineering and Design

Capillary Number and Pressure Formulas and Calculators

The capillary number (Nc) is a dimensionless quantity representing the relative effect of viscous drag forces versus surface tension forces acting across an interface between a liquid and a gas, or between two immiscible liquids.

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Eq. 1
Nc = µ_w V / σ_ow

Where:

µ_w = Viscosity of Displacing Fluid (cP)
V = Characteristic Velocity (ft/D)
σ_ow = Surface or Interfacial Tension of Oil and Water Phases (dyn/cm)
Nc = Capillary Number (dimensionless)

cP = centipose

Capillary pressure formula

Eq. 2
P_c = 2 σ cos(θ) / r

Where:

σ = Fluid interfacial Tension (dyn/cm)
θ = Angle of Wettability (degree)
r = Radius of Capillary (cm)
P_c = Capillary Pressure (dyn/cm)

Source:

Wikipedia

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