the resistance offered by a fluid (liquid or gas) to flow The viscosity is a characteristic property and is a measure of the combined effects of adhesion and cohesion
Viscosity is the quality that some liquids have of being thick and sticky. the viscosity of the paint. Resistance of a fluid to a change in shape, or movement of neighbouring portions relative to one another. Viscosity denotes opposition to flow. It may also be thought of as internal friction between the molecules. Viscosity is a major factor in determining the forces that must be overcome when fluids are used in lubrication or transported in pipelines. It also determines the liquid flow in spraying, injection molding, and surface coating. The viscosity of liquids decreases rapidly with an increase in temperature, while that of gases increases with an increase in temperature. The SI unit for viscosity is the newton-second per square metre (N-s/m^2)
The resistance to flow of a fluid (strictly speaking the resistance to shearing) It is defined as the ratio of shear stress (Tangential Force/Area) to shear rate (velocity/gap) The viscosity of a polymer decreases as the shear rate increases This property is referred to as pseudoplastic behavior or shear thinning The viscosity of a polymer at (near) zero shear for a polymer like PE might be 5,000 to 10,000 Pa s while during flow in an extrusion channel it could be much lower (i e 500 Pa s or less) Melt flow index corresponds to just one point on a viscosity curve (actually inverse) High viscosity implies low melt index and high molecular weight Viscosity is measured in units of Pa s or poise 1 Pa s = 10 poise The viscosity of water is 10-3 Pa s (1 centipoise) and for a typical polymer melt at least one million times larger (i e over 1000 Pa s)
Measurement of a fluid's resistance to flow The common metric unit of absolute viscosity is the poise In addition to kinematic viscosity, there are other methods for determining viscosity, including Saybolt Universal Viscosity (SUV), Saybolt Furol viscosity, Engier viscosity, and Redwood viscosity Since viscosity varies in inversely with temperature, its value is meaningless until the temperature at which it is determined is reported
Resistance of a fluid to flow Internal friction caused by molecular cohesion in fluids The internal properties of a fluid that offers resistance to flow Viscosity of drilling muds may be reported in different ways: (1) Marsh funnel seconds The time it takes for 1000 cm3 of drilling mud to flow through the funnel The longer the time in seconds, the more viscous is the mud (2) Yield point and plastic viscosity in centipoises Using the combination of plastic viscosity and yield point, the plastic viscosity indicates the flow characteristics of the mud when it is moving rapidly, and the yield point indicates the flow characteristics when it is moving very slowly or at rest In both cases, higher values indicate a more viscous mud
The property of a fluid as ability to flow; amount of shearing stress dependent on velocity of flow and resistance to flow (High viscosity = thick liquid)
One of the physical properties of a liquid, namely its ability to flow It is expressed inversely, i e the less viscosous the fluid the greater its mobility The viscosity of oil in a reservoir affects the rate and amount of recovery While viscosity is related to specific gravity, it is also affected by the amount of gas in solution in the oil Greater recoveries can be obtained where the solution gas is not allowed to escape prior to the time the oil is removed from the reservoir
Resistance of a liquid to flow Thick liquids have high viscosity, thin liquids have low viscosity
A property of fluids, either liquid or gaseous, that can briefly be described as causing resistance to flow Viscosity is the measure of the combined effects of cohesion and adhesion It is one of the most important physical properties of an oil, varnish or lacquer Viscosity is usually measured with the GardnerHoldt Bubble Viscometer