Viscosity is the measure of the internal friction/resistance to the flow of a Liquid. Lower viscosity fluids flow easily in pipes where high viscosity fluids have a have a higher pressure drop.

Viscosity of fluids is typically temperature dependent and is not affected as dramatically by pressure as gas viscosity. In fact, typically as a liquid temperature increases, the velocity decreases. When a gas temperature increases, the viscosity increases!

There are two different types of viscosity, absolute viscosity and kinematic viscosity.Higher the viscosity the more resistance to flow. Lower the viscosity the less resistance to flow. Temperature also plays a part, lower the temperature, higher the resistance. Higher the temperature, lower the resistance. A Viscometer meter can be used to measure viscosity.

Viscosity of a Mixture

To calculate the effective viscosity of gasses, use the following equation:

\mu = \frac{\sum ({\mu_i y_i sqrt{M_i}})}{\sum ({y_i sqrt{M_i}})}

Where:

\mu_i Dynamic Viscosity of a gas component, i
\mu Dynamic Viscosity of the Gas Mixture
y_i Mole Fraction or Percent of Gas Component, i
M_i Molecular Weight of Gas Component, i
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