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
measurement of a fluids resistance to flow The common metric unit of absolute viscosity is the poise, which is defined as the force in dynes required to move a surface one square centimeter in area past a parallel surface at a speed of one centimeter per second, with the surfaces separated by a fluid film one centimeter thick For convenience, the centipoise (cp) - one one-hundredth of a poise - is the unit customarily used Laboratory measurements of viscosity normally use the force of gravity to produce flow through a capillary tube (viscometer) at a controlled temperature The measurement is called kinematic viscosity The unit of kinematic viscosity is the stoke, expressed in square centimeters per second The more customary unit is the centistoke (cSt) - one one-hundredth of a stoke Kinematic viscosity can be related to absolute viscosity by the equation
(Otomotiv) The thickness or pourability of a liquid. Oil comes in a variety of thickness', or weights. It also comes in single viscosity (single-weight oil) and in a blend of viscosities (multi-weight oil), which enable it to flow easily in cold weather and reduce thinning in hot weather. The higher the weight, the greater the viscosity of the oil. You can find the weight of the oil on the outside of the oil container
A quality analogous to that of a viscous fluid, supposed to be caused by internal friction, especially in the case of gases
The quality or state of being viscous; the physical property of a liquid or semiliquid that enables it to develop and maintain a certain amount of shearing stress dependent upon the velocity of flow and then to offer continued resistance to flow
is an internal property of a fluid that offers resistance to flow For example, pushing a spoon with a small force moves it easily through a bowl of water, but the same force moves a cornstarch very slowly Simply put, it is how thick the liquid is
The resistance of a fluid to flow measured in centipoise (cps) The viscosity of water is 1 0 cps Guidelines for categories of epoxies: 1200 cps: super low viscosity; 2002000 cps: low viscosity; 200010,000 cps: medium viscosity; above 10,000 cps is classified as a non-sag gel High viscosity = high resistance to flow, low viscosity = low resistance to flow
A liquid's resistance to flow resulting from the combined effects of adhesion and cohesion
Property of a liquid that measures resistance to speed of deformation; more formally, the ratio of shear stress to the rate of change of shear strain
In printmaking, an intaglio method whereby multiple colors of ink may be printed simultaneously from the same plate, utilizing inks of varying viscosity, plates with multiple levels of etching and hard and soft brayers for applying the inks to the plate
empirical, unitless number indicating the effect of temperature change on the kinematic viscosity of an oil Liquids change viscosity with temperature, becoming less viscous when heated; the higher the VI of an oil, the lower its tendency to change viscosity with temperature The VI of an oil - with known viscosity at 40°C and at 100°C - is determined by comparing the oil with two standard oils having and arbitrary VI of 0 and 100, respectively, and both having the same viscosity at 100°C as the test oil The following formula is used , in accordance with test method ASTM D 2270
An empirical number indicating the effect of change in temperature on the viscosity of an oil A high viscosity index (VI) signifies a relatively small change of viscosity with temperature Ref ASTM D 2270-64
A measurement of viscosity with a change of temperatures A low VI (example 60) will thin out a lot at high temperatures whereas, a VI of 95 or higher will thin out less Some high grade oils already have naturally occurring high VI's Other VI's can be controlled through refinery processes or VI Improvers can be added
A commonly used measure of a fluid's change of viscosity with temperature The higher the viscosity index, the smaller the relative change in viscosity with temperature
The degree to which a fluid resists flow under an applied force, measured by the tangential friction force per unit area divided by the velocity gradient under conditions of streamline flow
The turbulent transfer of momentum by eddies giving rise to an internal fluid friction, in a manner analogous to the action of molecular viscosity in laminar flow, but taking place on a much larger scale
An approximation to turbulent flow whereby the net effect of molecular diffusion enhanced by strain flows between eddies is parametrized by an eddy viscosity acting on large scale motion Eddy viscosity may be taken as constant or dependent on the length scale of motion The former case is equivalent to assuming that the Reynolds stresses are proportional to the gradients of the large scale flow velocity