property of any liquid, which is reflected in its ability to prevent free displacement or shift of its own particles, describes the concept of viscosity.Physico-chemical properties of the meaning of this is that the moving liquid, there are certain forces of internal friction between molecules, which, in turn, owe their existence to the presence of the forces of molecular attraction.
fact that liquids amount of distance between the molecules is very low, and because they are less mobile than, say, gas molecules.Penetration into the other layer is only possible in forming therein a space sufficient for the liquid to penetrate the molecule.The formation of such a cell consumes energy, which thus decreases with increasing temperature and decreasing the pressure and vice versa.
Today, we should recognize that strict scientific theory of this phenomenon has not yet been established.
main indicators of the viscosity of the liquid, are the dynamic factor, oboznachaemy - μ, and besides him, the kinematic designated - ν.
For measuring the dynamic coefficient of the metric used GHS unit poise (P), which is: • x 1 dyne / cm2 = 1 g / cm • x s).The system gravitational metric system, this ratio is measured in kgf • s / m2;and the most common SI - in Pa • s to.You can set the mathematical relationship of these variables with each other.It is as follows: P 1 is about 0.0101 kgf • s / m2, which in turn was 0.1 Pa • s p.In addition, 1 kg x • s / m2 P = 98.1, which is equal to 9.81 x Pa • s.
According to the formula: ν = μ / ρ is possible to calculate the kinematic viscosity of the liquid, and the unit of measure Stokes (St, in the GHS), which is equal to 1 cm2 / s.In other systems - gravitational metric system and the SI to measure this factor is used unit equal to 1 m2 / s, which is 10000 Art.
physical laws is that with increasing temperature, the viscosity of the liquid is reduced.This relationship for the dynamic coefficient is determined by the equation μ = μ0 • e x a (t-t0), which identifies: μ and μ0 - corresponding coefficient for the given temperature t, and t0, and - an exponent whose value is determined by the characteristics of the fluid,and which is volatile, for example, for oils, its values ranging from 0.025 to 0.035.
There is also dependent on this index and temperature.This is particularly important when dealing with oils or other lubricants are used in various mechanical devices, units, engines.The formula of this dependence has the form: νt = ν x 50 x • (50 / t0) n.It marked: νt - the value of the kinematic coefficient of some consider the value of the temperature, ν x 50 - the value of the coefficient of the value of the temperature 50 ° C, t - the temperature at which we need to determine the value of the coefficient, n - characteristic properties of the liquid varies depending on thetemperature, and the value of ν x 50.
True enough, you can calculate the value of n, if we use the formula n = lg ν x 50+ 2.7.In order not to make calculating in each case, the values of n, characterizing the initial viscosity at 50 ° C, is reduced in a special table.This greatly speeds up the process of calculation.
Furthermore, there is a summary table of viscosity of liquids, which reflects all at once and the respective data of both dynamic and kinematic coefficients for specific types of fluids.
correct determination of the values that characterize the viscosity of the fluid is of great practical value, it depends on him the efficiency and durability of many mechanisms that we use both at work and at home.