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Viscosity is a measure of a fluid's rate-dependent resistance to a change in shape or to movement of its neighboring portions relative to one another. [1] For liquids, it corresponds to the informal concept of thickness; for example, syrup has a higher viscosity than water. [2]
kinematic viscosity: meter squared per second (m 2 /s) neutrino: xi: electromotive force: volt (V) pi: 3.14159... (irrational number) unitless rho: mass density usually simply called density kilogram per cubic meter (kg/m 3) volume charge density: coulomb per cubic meter (C/m 3) resistivity: ohm meter (Ω⋅m)
where it is assumed that all body forces are describable as gradients (for example it is true for gravity), and density has been divided so that viscosity becomes kinematic viscosity. The second vector calculus identity above states that the divergence of the curl of a vector field is zero.
ν is the kinematic viscosity of the fluid, ν = μ / ρ (m 2 /s); ρ is the density of the fluid (kg/m 3 ). For such systems, laminar flow occurs when the Reynolds number is below a critical value of approximately 2,040, though the transition range is typically between 1,800 and 2,100.
Its effect on the mean flow is like that of a stress term, such as from pressure or viscosity. To obtain equations containing only the mean velocity and pressure, we need to close the RANS equations by modelling the Reynolds stress term R i j {\displaystyle R_{ij}} as a function of the mean flow, removing any reference to the fluctuating part ...
A built-in density measurement based on the oscillating U-tube principle allows the determination of kinematic viscosity from the measured dynamic viscosity employing the relation =, where: ν is the kinematic viscosity (mm 2 /s), η is the dynamic viscosity (mPa·s), ρ is the density (g/cm 3).
Increasing temperature results in a decrease in viscosity because a larger temperature means particles have greater thermal energy and are more easily able to overcome the attractive forces binding them together. An everyday example of this viscosity decrease is cooking oil moving more fluidly in a hot frying pan than in a cold one.
The dilute gas viscosity contribution to the total viscosity of a fluid will only be important when predicting the viscosity of vapors at low pressures or the viscosity of dense fluids at high temperatures. The viscosity model for dilute gas, that is shown above, is widely used throughout the industry and applied science communities.