Effect of Pressure on Viscosity:įor liquid, viscosity is practically independent of pressure except at extremely high pressure. In Gases: In the case of gases temperature increases kinematic viscosity increases. In liquid: In the case of liquids temperature increases kinematic viscosity decreases. In Gases: In the case of gases temperature increases dynamic viscosity increases.Įffect of temperature on kinematic viscosity In liquid: In the case of liquids temperature increases dynamic viscosity decreases. The reason for the above phenomena is that in liquids viscosity is primarily due to molecular cohesion which decreases with an increase in volume due to temperature increment, while In gases, viscosity is due to molecular momentum transfer that increases with an increase in the number of collisions between gas molecules.Įffect of temperature on dynamic viscosity The viscosity of liquids decreases with an increase in temperature, whereas the viscosity of gases increases with an increase in temperature. Kinematic viscosity is a more fundamental property. It is utilized when inertia and viscous force are dominant

This represents the ratio between dynamic viscosities to density.ĭynamic force is utilized only when viscous force is dominant This represents the ratio between shear stress to shear strain. The symbol of the kinematic viscosity is ν

It represents the inertia, as well as the viscous force of fluid. Whereas dynamic viscosity, represents the viscous force of the liquid. To be precise, it describes how fast a liquid is moving when a certain amount of external force is applied. It is defined as the diffusivity of motion. It gives more information about the force required to make a liquid flow at a specific rate. Note: kinematic viscosity of air is about 15 times greater than the corresponding value of water.ĭifference Between Dynamic Viscosity And Kinematic Viscosity in Fluid Mechanics: Dynamic Viscosity Value of kinematic viscosity for air is 15 × 10-6 m²/sec Value of kinematic viscosity for water is 1 × 10-6 m²/sec At 20☌ and at standard atmospheric pressure,.Kinematic viscosity unit in CGS system.SI unit of kinematic viscosity is m²/sec.Kinematic viscosity (ν) is = dynamic viscosity/mass density = μ/ρ.Kinematic viscosity is denoted by the symbol “ν”.Note: Water is nearly 55 times viscous than air. SI unit of dynamic viscosity is Pa-sec, or N-sec/m² or kg/m-secġ poise = Dyne-sec/cm².Dynamic viscosity is denoted by the symbol “µ”.Water, air, and gasoline are Newtonian under normal conditions. Μ = absolute viscosity, “or” coefficient of viscosity “or” dynamic viscosity

Τ = shear stress opposing the movement of fluid The fluid for which the rate of deformation is linearly proportional to shear stress. The fluid that obeys newton’s law of viscosity is known as a Newtonian fluid. The rate of change of angular deformation is equal to the velocity gradient across the flow.īased on the relationship between the applied shear stresses and the rate of flow or deformation, fluids can be classified as Newtonian and non-Newtonian fluids. Rate of change od shear strain (dθ/dt) = Velocity gradient (du/dy) In time dt, the top layer will move with respect to the bottom layer by a distance ds= du.dt Similarly, as a reaction to this, the lower layer tries to retard the upper one. The upper layer which is moving faster tries to draw the lower slowly moving layer along with it. Suppose one layer of fluid is moving with respect to the other layer by a velocity du and the vertical gap between the two layers be dy. It is a measure of the resistance of the fluid to deformation It is duo lo cohesion and molecular momentum exchange between fluid layers and as flow occurs, these effects appear as shoring stressors between the moving layers This is mainly due to cohesion and molecular motion exchange between fluid layers, and as flow occurs, these effects manifest as shear stresses between the moving layers. Viscosity in fluid mechanics is a property of the fluids by virtue of which they offer resistance to shear or angular deformation.

Viscosity formula fluid mechanics