Viscosity Calculator Formula
Understand the math behind the viscosity calculator. Each variable explained with a worked example.
Formulas Used
Kinematic Viscosity
kinematic = dynamic_visc / densityKinematic Viscosity (cSt)
centistokes = dynamic_visc / density * 1e6Variables
| Variable | Description | Default |
|---|---|---|
dynamic_visc | Dynamic Viscosity (mu)(Pa-s) | 0.001 |
density | Fluid Density (rho)(kg/m^3) | 1000 |
How It Works
Viscosity Conversion
Dynamic viscosity measures the shear resistance of a fluid. Kinematic viscosity is the ratio of dynamic viscosity to density.
Formula
nu = mu / rho
where mu is dynamic viscosity (Pa-s), rho is density (kg/m^3), and nu is kinematic viscosity (m^2/s). Kinematic viscosity is what appears in the Reynolds number formula.
Worked Example
Water at 20 deg C: mu = 0.001 Pa-s, rho = 998 kg/m^3.
- 01nu = 0.001 / 1000 = 1.0 x 10^-6 m^2/s
- 02In centistokes: 1.0 x 10^-6 x 10^6 = 1.0 cSt
Frequently Asked Questions
What are common units for viscosity?
Dynamic: Pa-s (SI), cP (centipoise, 1 cP = 0.001 Pa-s). Kinematic: m^2/s (SI), cSt (centistokes, 1 cSt = 10^-6 m^2/s). Water at 20 deg C is about 1 cP or 1 cSt.
How does temperature affect viscosity?
For liquids, viscosity decreases with increasing temperature (molecules move faster, less cohesion). For gases, viscosity increases with temperature (more molecular collisions).
What is meant by a Newtonian fluid?
A Newtonian fluid has constant viscosity regardless of shear rate. Water, air, and most common fluids are Newtonian. Non-Newtonian fluids (paint, ketchup, blood) change viscosity with shear rate.
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