Fluid viscosity changes with temperature. Pressure has a small impact on gas viscosity and the pressure impact on the viscosity of a liquid is very small. When studying multiphase liquids (a mixture of gas, liquid and solids) there are other factors that come into play.
Besides, what is the effect of pressure on liquids?
Pressure Effects. Changes in presure have very little effect on the volume of a liquid. Liquids are relatively incompressible because any increase in pressure can only slightly reduce the distance between the closely packed molecules. If the pressure above a liquid is increased sufficiently, the liquid forms a solid.
How does viscosity of liquids vary with temperature?
The former effect causes a decrease in the shear stress while the latter causes it to increase. The result is that liquids show a reduction in viscosity with increasing temperature. With high temperatures, viscosity increases in gases and decreases in liquids, the drag force will do the same.
What does the viscosity depend on?
Even for a Newtonian fluid, the viscosity usually depends on its composition and temperature. For gases and other compressible fluids, it depends on temperature and varies very slowly with pressure. The viscosity of some fluids may depend on other factors.