1*/ What difference between dynamic and kinematic viscosity for liquids?
2*/ What's the physical meaning of these two viscosity ?
3*/ which of the two, gives more conclusion or interpretation on molecular interaction ?
Viscosity is defined as a fluid’s resistance to flow, or the fluid’s resistance to deform when subjected to a force.
Dynamic viscosity is usually reported in Centipoise (cP) and Brookfield rotary method is useful for it measurement.
Kinematic viscosity is traditionally measured by noting the time taken for a fluid sample to travel through an orifice in a capillary under the force of gravity. The time taken is noted and converted into Kinematic Viscosity, reported in Centistoke units (cSt).
Dynamic Viscosity (cP) = Kinematic Viscosity (cSt) x Fluid Density (kg/m3)
The viscous forces in liquids are equivalent to friction forces in solids. The dynamic viscosity is involved in the relation between stress and strain tensors. The kinematic viscosity is equal to the ratio of the dynamic viscosity by the density. The kinematic viscosity is involved in the classical Navier Stokes equation governing the fluid motion. If you are particularly interested in the interaction between molecules that can be interpreted in terms of mechanical stress, the dynamic viscosity is more appropriate. Nevertheless, the kinematic viscosity is recommended when you are interested in fluid motion and velocity field. It can inform us about the propagation of the movement by friction.
You can also think about "kinematic viscosity" as a "diffusivity of momentum" in a fluid, analogous to the role of "thermal diffusivity" in heat transfer. (Dynamic) viscosity is then the equivalent thermal conductivity and (mass) density is the equivalent to heat capacity per unit volume. I find it easier to think of dynamic viscosity as the more basic property and kinematic viscosity as a "derived" property, but it depends on where you're coming from scientifically and what type of problems you're trying to solve.
Kinematic viscosity is a flow property also referred as " momentum diffusivity " . It basically describes the ease with which or ability of a medium to respond to transfer of a property (momentum). It can also be thought as resistance to flow of property, since at high viscosity, large of momentum will absorbed by the medium(body) itself then transferring it to other side for example solid-liquid interface.
1. Dynamic viscosity is the quantitative expression of fluid’s resistance to flow, while Kinematic viscosity is the ratio of the fluid’s viscous force to the inertial force.
2. Dynamic viscosity is symbolized by either ‘µ’ or ‘n’, while Kinematic viscosity is mathematically symbolized by ‘v’.
3. In a cgs unit system, dynamic viscosity is in a unit called ‘poise’, which is taken from the name of Jean Louis Marie Poiseuille, while Kinematic viscosity is expressed in ‘stokes’ (St) or centistokes (ctsk or cSt), which are named after George Gabriel Stokes.
4. Dynamic viscosity is sometimes referred to as absolute viscosity, or just viscosity, while Kinematic viscosity is sometimes called the diffusivity of momentum.
Read more: Difference Between Kinematic and Dynamic Viscosity | Difference Between | Kinematic vs Dynamic Viscosity http://www.differencebetween.net/science/difference-between-kinematic-and-dynamic-viscosity/#ixzz3przyIwVs
Dynamic viscosity, also called absolute viscosity.It measures the resistance of a fluid to flow .
Kinematic viscosity, measures the resistance of the liquid to flow in the presence of gravity. This measure is obtained by taking the liquid’s dynamic viscosity and dividing it by the liquid’s density.
kinematic viscosity is a ratio of the viscose force to the inertial force
Dynamic viscosity is a measure of the internal resistance of a fluid. it is important in explaining the flow characteristics of fluid, particularly, non-Newtonian Fluid. While dynamic viscosity is a measure of how difficult i a fluid flows, the kinematic viscosity is the dynamic viscosity of a fluid divided by its density.
mathematical relationship
Kinematic x Density = Dynamic (cP)
Dynamic (cP)/Density = Kinematic
Dynamic viscosity tells the force required to make fluid flow at certain rate.Whereas kinematic viscosity tells the how fast the fluid is moving when a certain force is applied.
It is analogous to force (dynamic) and acceleration (kinematic) definition . Consider the mass block of 5 kg .So for moving it with 2 m/s^2 acceleration 10 N force (dynamic) is required.
And we can perform it in different manner like after applying the 10 N force on the 5 kg block it moves with 2 m/s^2 acceleration .It is more easy and practical to find out acceleration by applying the force instead of finding the force to maintain certain strain rate.
Dear Mohamed
Viscosity is due to the following two factors:
1st Molecular gravity force in liquids.
2nd The forces of molecular momentum exchange in gases.
1*
Unlike the dynamic viscosity, the kinematic viscosity is related to pressure. With increasing pressure, the kinematic viscosity of the gases decreases, but the kinematic viscosity of the liquids increases.
And due to the significant reduction in the density of gases with temperature, the changes in the kinematic viscosity of gases with a temperature are higher than changes in the kinematic viscosity of gases with a dynamic viscosity.
2*
Viscosity is the resistance of a liquid against shear stresses. The viscosity of a fluid is the strength of its various layers against slipping on each other during movement.
The higher the viscosity of the liquid, the more shear stress needed to create the same deformation. For example, the viscosity of honey is much higher than the viscosity of milk.
With increasing temperature, the viscosity of liquid fluids is reduced, but in gases, the opposite is true.
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