Viscosity of a Fluid

Viscosity is the measurement of a fluids internal resistance to flow. It is usually represented in centipoise (cps) or poise (100 Centipose = 1 poise). The higher the viscosity of a liquid, the thicker it is and the greater the resistance to flow; temperature will also affect the viscosity of most materials.

There are several categories of fluid viscosities which include:

Newtonian: At a fixed temperature their viscosity does not change through agitation or pumping. Water and oils are classed as newtonian.

Thixotropic: At a fixed temperature these reduce their viscosity with agitation or pressure increase. Ketchup and mayonnaise are good examples as they appear thick but pump quite easily.

Paste: Some paste viscosity materials will seek their own level or flow slowly. The shorter the time it takes the easier they are to pump. Some do not seek their own level or flow at all and require pressure to move them. To reduce the viscosity of paste materials usually heat is applied. Special consideration needs to be given during the design to ensure they remain at the correct temperature in all stages of the process.

Common Material Viscosities at Room Temperature (Approximate):