![]() ![]() In the SI system the dynamic viscosity units are N s/m 2, Pa s or kg/(m s) - where (1) can be rearranged to express Dynamic viscosity as ![]() Μ = dynamic viscosity of fluid (N s/m 2 )Įquation (1) is known as the Newtons Law of Friction. The shearing stress between the layers of a non turbulent fluid moving in straight parallel lines can be defined for a Newtonian fluid as Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to an other plane - at an unit velocity - when maintaining an unit distance apart in the fluid. There are two related measures of fluid viscosityĪbsolute viscosity - coefficient of absolute viscosity - is a measure of internal resistance. viscosity is the measure of a fluid's resistance to flow.The shear resistance in a fluid is caused by inter-molecular friction exerted when layers of fluid attempt to slide by one another. The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. Motor Oil Viscosity Excerpt from " The Practical Handbook of Machinery Lubrication".Viscosity is an important fluid property when analyzing liquid behavior and fluid motion near solid boundaries. Oils that are suitable for use at higher temperatures have viscosities within the ranges also shown in the table below.ĬOLD CRANKING SIMULATOR CENTIPOISES (cP) AT TEMPERATURE ☌ These grades of oil must meet maximum viscosities at specified temperatures and also must meet maximum requirements for the borderline pumping temperatures as shown in the table below. Oils that are suitable for use in colder temperatures are designated by the letter “W” when indicating the SAE viscosity grade. The number reflects the time required for a fixed amount of fluid to flow through a certain sized orifice on the testing device. The other unit is the Centistoke (cSt) which is used to report the kinematic viscosity of motor oil at high temperatures. This number indicates the ease with which the oil can be moved. It is used to report the absolute viscosity of an motor oil at colder temperatures. ![]() Because the viscosities are tested in two different temperature ranges, the results are reported in two different units. With the introduction of viscosity measurement at cold temperatures, using a rotating viscometer called a cold cranking simulator temperatures are reported as low as -30☌. The most common temperatures in the high temperature range are 40☌ and 100☌. Therefore, the SAE has developed two separate viscosity measurements, one at cold temperatures and one at high temperatures. It has more recently been recognized that oil viscosity at colder temperatures, as well as at high operating temperatures, is very important in the long life performance of an engine. Oils are assigned numbers based on the viscosities displayed at certain temperatures. For this reason the Society of Automotive Engineers (SAE), in co-operation with engine manufacturers, developed a classification system for motor oils based on viscosity measurements. Even at this early stage, viscosity was recognized as one of the most important characteristics of an oil. The earliest attempts to classify motor oils were made when automobiles first appeared.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |