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Low temperature viscosity
Definition:
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 in the fluid- "dV /dh" .
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
This is the ratio of the dynamic viscosity and the fluid density μ (
kg /cubic m ) 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 / m3
)
Kinematic viscosity (centiStokes) = μ(centiPoise) / ρ( grammes /cubic
cm ) |
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