# Variable viscosity

1. Jul 4, 2011

### hoomanya

Hi,
I think I'm mixing things up..... For a flow with low compressibility, I know density varies but does viscosity also vary? Does that depend on whether the flow is laminar or turbulent.
Thanks,
H

2. Jul 7, 2011

### ameeno97

For liquids, both the dynamic and kinematic viscosities are practically independent of pressure, and any small variation with pressure is usually disregarded, except at extremely high pressures.

For gases, this is also the case for dynamic viscosity (at low to moderate pressures), but not for kinematic viscosity since the density of a gas is proportional to its pressure

Viscosity is due to the internal frictional force that develops between different
layers of fluids as they are forced to move relative to each other.

Viscosity is caused by the cohesive forces between the molecules in liquids and by
the molecular collisions in gases, and it varies greatly with temperature.

The viscosity of liquids decreases with temperature, whereas the viscosity of
gases increases with temperature