viscosity - This is the ratio of the dynamic viscosity and...

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Viscosity A plate of area "A" moving under the action of a force "F" with a resulting velocity "V" over a fixed plate separated by a film of fluid "h" thick. The shear stress on the fluid is "F / A". For a Newtonian fluid the shear stress is directly proportional to the velocity gradient (or shear rate) in the fluid- "dV /dy". P / A = µ . dV /dy The proportionality constant " µ " is the viscosity and has units of ( N/m 2 ) .( m ). ( m / s ) = N . s / m 2 . Dynamic Viscosity The coherent SI unit of dynamic viscosity is the pascal second (Pa s). This equates to a Newton second per square metre (N.s / m 2 ). In the cgs unit the poise is the corresponding unit which has dimensions of dyne seconds per cm 2 . The centipoise (cP = 10 -2 poise) is the most common unit used in tables and handbooks. 1 Pas = 1000. cP. The viscosity of water at room temperature is approximately 1 cP Kinematic Viscosity
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Unformatted text preview: This is the ratio of the dynamic viscosity and the fluid density ρ ( kg / m 3 ). The SI unit of kinematic viscosity is the m 2 / s. The equivalent cgs unit is the stoke (St) which has the unit of cm 2 / s. The unit commonly used is the centistoke(cSt). 1 m 2 / s = 10 6 cSt Absolute Kinematic Viscosity (m 2 / s ) = µ ( Pa s ) / ρ (kg / m 3 ) Kinematic viscosity (centiStokes) = µ (centiPoise) / ρ ( grams /cubic cm ) Saybolt Universal Viscosity A method of determining a lubrication fluids viscosity is to measure the rate of flow of the fluid through a test device. The rate is measured in seconds the greater the number of seconds the more viscous the fluid. This viscosity is seconds τ = Saybolt universal Viscosity - seconds. The dynamic viscosity relates to the Saybolt universal viscosity ( τ ) by the following formula Viscosity µ (Poise) = (0.00022 . τ — 0.18 / τ )...
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