The other quantity called kinematic viscosity (represented by the Greek letter ν "nu") is the ratio of the viscosity of a fluid to its density. The quantity defined above is sometimes called dynamic viscosity, absolute viscosity, or simple viscosity to distinguish it from the other quantity, but is usually just called viscosity. There are actually two quantities that are called viscosity. Ten poise equal one pascal second making the centipoise and millipascal second identical. The most common unit of viscosity is the dyne second per square centimeter, which is given the name poise after the French physiologist Jean Poiseuille (1799–1869). The pascal second is more rare than it should be in scientific and technical writing today. Despite its self-proclaimed title as an international system, the International System of Units has had little international impact on viscosity. The SI unit of viscosity is the pascal second, which has no special name. Or if you prefer calculus symbols (and who doesn't)… F The similarity to Newton's second law of motion ( F = ma) should be apparent. The more usual form of this relationship, called Newton's equation, states that the resulting shear of a fluid is directly proportional to the force applied and inversely proportional to its viscosity. (dynamic) viscosityįormally, viscosity (represented by the symbol η "eta") is the ratio of the shearing stress ( F/ A) to the velocity gradient ( ∆ v x/∆ y or dv x/ dy) in a fluid. Fluids resist the relative motion of immersed objects through them as well as to the motion of layers with differing velocities within them. In addition to technical articles and white papers, our application scientists are available to discuss your particular application needs and help you find solutions to your most pressing testing issues.Informally, viscosity is the quantity that describes a fluid's resistance to flow. For articles and white papers pertaining to General Viscosity, Our scientists contribute to industry knowledge by authoring papers in various technical publications. Intrinsic viscosity reflects the capability of a polymer in solution to enhance the viscosity of the solution. Intrinsic Viscosity (): The ratio of a solution’s specific viscosity to the concentration of the solute, extrapolated to zero concentration. Measured in stokes (St) or centistokes (cSt). Also known as the coefficient of kinematic viscosity. Kinematic Viscosity: The absolute viscosity of a fluid divided by the density of the fluid. Also known as coefficient of viscosity.Īpparent Viscosity: The value obtained by applying the instrumental equations used in obtaining the viscosity of a Newtonian fluid to viscometer measurements of a non-Newtonian fluidĭilute Solution Viscosity: The viscosity of a dilute solution of a polymer, measured under prescribed conditions, is an indication of the molecular weight of the polymer and can be used to calculate the degree of polymerization. These manual glass viscometers require the use of a Constant Temperature Bath in order to stabilize the sample temperature for measurement.Ībsolute Viscosity: The tangential force per unit area of two parallel planes at unit distance apart when the space between them is filled with a fluid and one plane moves with unit velocity in its own plane relative to the other. Most laboratory instruments use glass capillaries or "tubes". There are several standardized capillaries in use. The more viscous an oil, then the longer it takes to flow via a capillary under the influence of gravity alone. Generally, measurements made using capillary viscometers rely on the relation between time and viscosity. The most common method for measuring kinematic viscosity is the use of a gravimetric capillary (Figure 1) that is usually temperature controlled at 40 ☌ and 100 ☌ for multigrade oils, and 40 ☌ for single grade oils. Video courtesy of Ekeeda - Measuring Kinematic Viscosity
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