Viscosity describes the ability of gases or liquids to create resistance between moving relative to each other layers of fluid (not solid) bodies.That is, this value corresponds to the power of internal friction (the English term: viscosity), derived from the movement of gas or liquid.Different bodies, it will be different, as it depends on their nature.For example, water has a low viscosity compared with honey viscosity is much higher.The internal friction or the flow of solid (granular) substances rheological characteristics.
viscosity word comes from the Latin Viscum, which means the mistletoe.This is due to the bird-lime, which is made from mistletoe berries and used for catching birds.Adhesive smeared with tree branches and birds sitting on them, became easy prey for humans.
What is the viscosity?Units of the specifications will be given, as is customary in the SI system, as well as other non-SI units.
Isaac Newton in 1687 established the basic law of the flow of liquid and gaseous bodies: F = ƞ • {(v2 - v1) / (z2 - z1)} • S. In this case, F - is the force (tangential), which causes a shiftlayers of the movable body.The ratio (v2 - v1) / (z2 - z1) shows the rate of change of velocity of flow of fluid or gas in the transition from one layer to another mobile.Otherwise known as the velocity gradient or shear flow.The quantity S - is the area (in cross section) of flow of the movable body.Ƞ proportionality factor is the dynamic viscosity coefficient of the body.Size, its inverse j = 1 / ƞ, a fluidity.Force exerted per unit area (in cross section) of the flow can be calculated according to the formula: μ = F / S. It is absolute or dynamic viscosity.Units of its SI expressed as Pascal second.
Viscosity is the most important physical and chemical characteristics of many substances.Meaning it into account in the design and operation of pipelines and apparatus in which there is a movement (for example, if they are used for pumping) liquid or gaseous medium.It may be oil, gas or products thereof, molten slags or glass and the like.Viscosity in many cases, is a qualitative characteristic of semi-finished products and various industries, as it depends on the structure of matter and shows the physico-chemical state of the material and the changes in technology.Often, to estimate the amount of deformation resistance or expiration does not use dynamic, and kinematic viscosity units in the SI system is expressed in square meters per second.Kinematic viscosity (denoted ν) is the ratio of the dynamic viscosity (μ) for medium density (ρ): v = μ / ρ.
Kinematic viscosity - a physico-chemical characteristics of the material, showing its ability under the force of gravity to resist flow.
The SI unit of kinematic viscosity is recorded as m2 / s.
The system GHS viscosity is measured in Stokes (St) or centistokes (cSt).
between these units there is the following relationship: 1 St = 10-4 m2 / s, then 1 cSt = 10-2 = St 10-6 m2 / s = 1 mm2 / s.Often, the kinematic viscosity are other non-SI units of measurement - it Engler degrees, the translation of which can be carried out at Stoke by the empirical formula: v = 0,073oE - 0,063 / oE or table.
To convert the system of units of dynamic viscosity may be used in non-SI equality: 1 Pa • s = 10 poise.Short name written: P.
Typically, units are regulated by fluid viscosity standard documentation of the finished (commercial) product or process procedures for intermediate with the allowable range of changes of quality characteristics, as well as the accuracy of its measurement.
To determine the viscosity in the laboratory or production environment use viscometers of various designs.They can be rotary, Ball, capillary, ultrasound.The principle of measuring the viscosity of a glass capillary viscometer is based on determining the time of the expiration of a liquid through a calibrated capillary tube a certain diameter and length, thus should be considered a permanent viscometer.Since the viscosity of the material depends on the temperature (with an increase in her she will decrease, due to the molecular-kinetic theory as a result of acceleration of the chaotic motion and interaction of molecules), so the test sample must be maintained for some time at a certain temperature to average last throughout the volume of the sample.There are several standardized methods of testing viscosity, but the most common - is an interstate standard GOST 33-2000, which is determined on the basis of the kinematic viscosity, the units in this case mm2 / s (cSt), and the dynamic viscosity of the converted, as the product of the kinematic viscosity by the density.
