![]() ![]() Liquid viscosity decreases quickly as temperature increases. Viscosity changes with temperature in different ways depending on whether the fluid is a liquid or gas. The units of dynamic viscosity are Ns/m 2 (Ns m -2), or mPa.s, or the SI unit Poiseuille (where 1 centi-Poiseuille = 1 mPa.s for water at 20 oC).įluids that produce a viscosity constant are known as Newtonian fluids.įluids that don’t produce a constant are called Non-Newtonian fluids.Ī different type of viscosity measure that is useful for some applications is kinematic viscosity which is calculated by dividing the dynamic viscosity by density and is measured in m 2/s (m 2s -1). The calculated constant for the fluid is known as the absolute or dynamic viscosity.ĭynamic viscosity = (Force x Time) / Area In many fluids, there is proportionality between the shearing stress that creates flow and the rate of deformation (or shear strain).Īnother way to look at this is that when you divide the shear stress by rate of deformation, you get a constant value for a certain fluid held at a specific temperature. It is also important when assessing and controlling liquid flow in industrial processes such as injection moulding and spraying. Viscosity is commonly used to assess lubrication in mechanical systems and to determine the opposition forces that arise when transporting fluids in pipelines. A simple comparison between the flow of water (low viscosity) and honey (high viscosity) can help to illustrate the principle. ![]()
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