Coefficient of viscosity unit and dimension Where η = symbol of viscosity coefficient of liquid.Īccording to the above mathematical formula, viscosity is defined as the force per unit area originating between the two layers moving with the unit velocity gradient. The returning force originates due to internal friction between moving layers with the velocity gradient = (dv/dx) and area = A is expressed by the equation, The coefficient η is the measured viscosity of liquids and gases and is defined by the Newton law of viscous flow in science. In liquid, it increases with an increase in pressure.In gas, the viscosity originates due to the exchange of momentum between two moving layers and no effect of pressure unless it is very low.This is due to the different origins of the term viscosity in the liquid and gas phases. Viscosity in the liquid increases with the rise of temperature but in gases, it increases with the increase of temperature. The fraction between two layers moving with different velocities originates from the intermolecular attraction in liquid. The capillary tube is used in viscosity measurement to maintain a streamlined flow of liquid since the diameter of the tube is very small.
When Re 1500, turbulent flow persists in the liquid.Reynolds numberĪ dimensionless quantity, named, Reynolds number (Re) uses to define different types of liquid flow having the value, (dρu/η), where, η = viscosity coefficient, ρ = density, d = diameter of the tube and u = velocity of the liquid. The velocity of the liquid at a point varies with time irregularly. When the rate of discharge of moving liquid is high, the condition of streamline flow is not maintained and turbulent flow is started. Newton’s law of viscous flow is only applicable to the laminar flow of the liquids.
The streamlines do not cross each other at any point in the flow. The velocity of the fluid (liquid and gas) is always the same in magnitude and direction at any particular point. In Laminar or streamline flow, the velocity of the discharge of a liquid is low and all the layers of liquid move parallel to each other. The main types of fluid flow may include, The resistance that one part of a fluid flowing with one velocity offers to another part of a fluid flowing with different velocities is known as viscosity. Therefore, there is a velocity gradient, (dv/dx) of the flowing liquid.Įach layer of the liquid surface flowing with a higher velocity experience a retarding effect due to the internal friction of the two layers. The velocity of the successive layers from the wall of the pipe increases and remains maximum for the central layer. A thin layer immediately in contact with the wall of the pipe remains almost stationary. When the fluid flows within the pipe, all the parts of the fluid do not move with equal velocity. Recently it was used in the determination of the molecular weight of polymers. It is also used to deal with various problems solve in fluid mechanics, especially in the paint, ink, colloids, rubber, textiles, etc. The measurement of viscosity data of fluids is important in the study of biology, chemistry, and physiology. It is defined as kinematic viscosity = viscosity coefficient (η)/ density (ρ) and expressed or calculate in the Stoke unit in the honor of the scientist Stoke.
Kinematic viscosity in physics sometimes is used in engineering studies to compare the following property of the different liquids. The reciprocal of viscosity is called fluidity which measures the flowing tendency of the liquid for learning chemistry and physics. The former liquids are called high viscous liquids while the latter liquids are called low viscous liquids. The flow of some liquids is slower than the others due to this property.įor example, glycerol, ester, and oil flow slowly while water, ether, and alcohol flow rapidly on the solid surface due to viscosity. Viscosity of liquids in chemistry is the resistance to flow exhibited by fluids (liquids or gases) like glycerol, ester, oils, water, alcohol, and ether.
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