![]() This is because the molecules in the fluid move at a slower speed as temperature decreases, so they spend more time in contact with each other as they collide. ![]() Case in point: Viscosity tends to increase at lower temperatures. Image credit: Wikipedia And When Viscosity Varies Over TimeĮnvironmental factors can also affect the viscosity of fluids. Non-Newtonian fluids can be described as shear thickening or shear thinning. Our e3 series systems use peristaltic pumps to move fluids gently during application, without causing shear. This is one of the benefits of Designetics automated fluid application systems. Adhesives are typically non-Newtonian fluids, so it’s important to keep the shear rate to a minimum during fluid application. This change in viscosity with shear rate is sometimes referred to as shear thickening (increase in viscosity with increase in shear rate) or shear thinning (decrease in viscosity with decrease in shear rate). Non-Newtonian fluids have viscosities that do fluctuate as the shear rate changes. For example, water and honey are Newtonian fluids – their viscosity doesn’t change with shear rate. Newtonian fluids have a constant viscosity for a given temperature and shear stress, regardless of the shear rate (rate at which shear is applied). A Poise (P) is defined as one dyne second per square centimeter (dyne-s/cm2), and 1 cP = 0.01 P.įluids with low viscosity are often described as “thin,” while fluids with high viscosity are often described as “thick.” Image credit: When Viscosity Isn’t Constantįluids can be generally classified as Newtonian or non-Newtonian. However, another common unit for viscosity – and one typically used by Designetics and our customers – is the centipoise (cP). ![]() The SI unit for viscosity is the Newton-second per square meter (N-s/m2), which can also be expressed as a Pascal-second (Pa-s). The formal definition of viscosity is the ratio of shearing stress (force divided by area, F/A), to the velocity gradient (dv/dz) in a fluid. This movement between layers of fluid is referred to as shear, and a fluid’s viscosity is related to the amount of force required to produce shear. High viscosity fluids, such as molasses, are typically described as “thick,” while low viscosity liquids, such as water, are often described as “thin.” A fluid’s resistance to flow is caused by internal friction between the molecules in the fluid, which becomes apparent as the layers of fluid move relative to one another. ![]() Viscosity is often defined as a measure of how easily a fluid flows. ![]()
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