Viscosity

The fluid’s viscosity depicts the level of resistance of the fluid in terms of its fluid motion or movement. In layman’s terms, the thickness of a liquid matter that directly affects its capacity of movement or its resistance level is known as viscosity. For instance, we can take the example of honey and water; in terms of thickness, honey is relatively thicker in consistency than water. Hence, the viscosity of honey is greater than water. The concept of viscosity is used in determining the factors that are to be overcome to use the fluid mediums for transportation or the purpose of lubrication.

What is Viscosity?

The literal meaning of the term viscosity defines fluid state when it is in a thicker consistency, such as honey and molasses. In the case of liquids and fluids, the term viscosity relates to the thickness of the fluid. The symbols- µ and ƞ, denote viscosity. The unit of viscosity is Poiseuille which is denoted as PI. Also, the dimensional formula for viscosity is [ML^-1T^-1]. The viscosity concept states that the inner layers of a fluid matter experience a certain resistive force. For instance, if we take the example of a fluid matter flowing through a pipe: We can easily observe that the liquid body flows from one end of the pipe to another. But, the concept of viscosity states that the fluid matter flows much easier near the axis than at the pipe walls. This sort of experiment proves the fact that in order for the liquid matter to flow from one end of the tube to another, some friction between the two ends is required. Now, this explains that the fluid flowing from one pipe to another experiences a certain resistive force. The fluid that faces absolutely no resistance can be termed the ideal in-viscous fluid. The viscosity of a fluid is measured in terms of the shearing stress to the velocity gradient in a fluid. For example, if a spherical object is sinking in a fluid matter, the viscosity of the fluid can be calculated by the following equation: Ƞ = 2ga²(∆ρ) /9v Where ∆ρ denotes the difference between the densities of the spherical object and the fluid matter g denotes the acceleration of the sinking spherical object due to gravity a denotes the radius of the spherical object and v denotes the velocity of the spherical object.

Dynamic viscosity

Dynamic viscosity, also known as absolute viscosity, is the measurement of the internal resistance of a fluid substance. In other terms, dynamic viscosity can be defined as the amount of force required by a fluid substance to overcome its own internal resistance to flow. The dynamic viscosity is directly proportional to the shear stress. The symbol denotes dynamic viscosity- µ The SI unit of dynamic viscosity is N-s/m² (Newton-second per square meter). The following equation can calculate dynamic viscosity: η=T/γ Where, η denotes dynamic viscosity T denotes shearing stress in a fluid And, y denotes the shear strain rate

Kinematic viscosity

The kinematic viscosity can be defined as the absolute viscosity or dynamic viscosity of a liquid divided by its density at the same given temperature. There is absolutely no involvement of force in kinematic viscosity. Kinematic viscosity can be calculated through the following equation: ν = μ/ρ v denotes the kinematic viscosity µ denotes the absolute or dynamic viscosity and  ρ = density of the fluid The SI unit of kinematic viscosity is m²/s Kinematic viscosity is calculated in terms of the Stokes (St) unit. Where, 1 St = 10-4m²/s = 1 cm²/s The concept of fluid mechanics proposed by Sir Isaac Newton uses the example of fluid matters which are consistent in terms of their viscosity. Hence, these fluid matters are termed Newtonian fluids. Water, oil, gases, gasoline, and alcohol are examples of Newtonian fluids. The kinematic viscosity of fluid matters is calculated in terms of both Newtonian and Non-Newtonian fluids. The examples of Non-Newtonian fluids used in the calculation of kinematic viscosity are as follows: Rheopectic fluids: These types of fluids have the tendency to become more viscous when they are agitated. Such as printer ink. Thixotropic fluids: These types of fluids have the tendency to become less dense when they are agitated, for example, yogurt and tomato ketchup. Shear-thickening fluids: The viscosity of these fluid substances increases with an increase in shear stress. For instance, when turmeric is mixed in milk, the consistency of the milk starts to get gradually thicker. Shear-thinning fluids: The viscosity of these fluid substances decreases with the constant decrease in shear stress. For instance, paint tends to get thinner as we stir it.

Conclusion

Viscosity can be defined as the internal resistance faced by a liquid or fluid substance, measured in terms of the shear stress of the fluid. When the viscosity of a fluid is absolutely zero, the liquid matter is considered the ideal non-viscous fluid.