setrflow.blogg.se - Viscosity definition fluid mechanics

In simpler words, kinematic viscosity is the measure of any fluid’s internal resistance to the flow across the cross-section area per unit of time. It is determined by measuring the time required for a fixed volume of fluid to flow across a known distance under the influence of gravity through a capillary action within a calibrated viscometer in a fixed temperature range.

Kinematic viscosity – It is the measure of a fluid’s internal resistance to flow under gravity.

It rotates a probe in the liquid sample, and the viscosity is determined by measuring the force used to turn the probe. The dynamic viscosity of a fluid is measured using a rotational viscometer. Where τ = shear stress, μ = viscosity, and du/dy = velocity gradient. Its formula is similar to that of viscosity. The SI unit of dynamic viscosity ( μ ) is the Pascal-second. In simple words, it is a fluid’s viscosity that is referred to as dynamic viscosity. In other words, it is defined as the force needed by a fluid to overcome its internal molecular friction so that it can flow.

Dynamic viscosity – A way to measure a fluid’s resistance to its flow under the influence of any external force or stress.

Viscosity is divided into two types: dynamic viscosity and kinematic viscosity.

Here, du is the velocity difference, and dy is the distance between the layers.Īccording to Newton’s law of viscosity, shear stress is proportional to velocity gradient. Where τ= shear stress, μ= viscosity, and du/dy= velocity gradient. The equation of newton’s law of viscosity is τ = μ du/dy Newton’s law of viscosity says that the shear stress is directly proportional to the velocity gradient.

The velocity gradient is defined as the velocity difference between the layers of fluid that are adjacent to each other. Shear stress refers to the amount of force acting per unit area on a particular fluid parallel to the surface of the fluid. Newton’s law of viscosity tells us about the relationship between the shear stress and velocity gradient of fluids. For liquids, viscosity decreases with an increase in temperature, and for gases, viscosity increases with an increase in temperature. The viscosity of any substance depends on the temperature and the state of the matter. The SI unit of viscosity is pascal-second or poiseuille. Viscosity is defined as the ability of a fluid or solid to resist the change in its shape and structure concerning stress or force from the ad jacent layer in other words, it is the opposite of fluidity.