Viscosity

Viscosity, resistance of fluid (liquid or gas) to shape change, or movement of adjacent parts to each other. Viscosity is opposite to flow. The reciprocal of viscosity is called fluidity and is a measure of liquidity. For example, molasses have a greater viscosity than water. Since a part of the forcibly moving fluid carries part to some extent, the viscosity can be thought of as internal friction between molecules, and this friction hinders the occurrence of the speed difference within the fluid. Viscosity is a major factor in determining the force that must be overcome when fluids are used for lubrication and transport within pipelines. Control the flow of liquid with processes such as spraying, injection molding, surface coating and so on.

For many fluids, the tangential or shear stress causing the flow is proportional to the shear strain rate or deformation rate. In other words, the shear stress divided by the shear strain rate is constant for a given fluid at a fixed temperature. This constant is called dynamic or absolute viscosity and is often simply called viscosity. The fluid thus expressed is called Newtonian fluid in commemoration of Sir Isaac Newton which first developed a mathematical description of viscosity.

The magnitude of kinematic viscosity is force × time ÷ area. Therefore, the unit of viscosity is Newtons per square meter, usually expressed in seconds per second in SI.

As the temperature rises, the viscosity of the liquid drops rapidly and as the temperature rises the viscosity of the gas rises. Therefore, heating will make the liquid easier to flow and gas will flow more slowly. For example, the water viscosities at 27 ° C (81 ° F) and 77 ° C (171 ° F) are 0.85 × 10 -3 and 0.36 × 10 -3 Pascal seconds, respectively, but the viscosity in air is 85 × 10- 5 and 08 × 10 -5 Pascal seconds

Depending on the application, kinematic viscosity is more convenient than absolute or dynamic viscosity. Kinematic viscosity is the absolute viscosity of a fluid divided by its mass density. The magnitude of the kinematic viscosity is the area divided by the time, the appropriate unit is square meters per second. A unit of kinematic viscosity in the centimeter - gram - second (CGS) system known as Stokes in the UK and Stokes in the United States. It is from British physicist Sir George Gabriel Stokes. Give your name. The stroke is defined as 1 square centimeter per second

Actually there are two quantities called viscosity. The amount defined above may be referred to as dynamic, absolute or simple viscosity to distinguish it from other quantities, but in many cases it is called viscosity. Another quantity called kinematic viscosity (represented by the Greek letter ν "nu") is the ratio of the viscosity of the fluid to its density. Kinematic viscosity is a measure of the resistance flow of a fluid under the influence of gravity. It is usually measured using a device called a capillary viscometer - basically a calibrated can with a thin tube at the bottom. When two equal volumes of fluid are placed in the same capillary viscometer and flow under the influence of gravity, it takes time for the more viscous fluid to flow through the tube than the non-viscous fluid. Capillary viscometer is explained in detail later in this section.

The fluid flowing through the stationary surface undergoes a force countering the flow. This tendency to resist flow is known as the viscosity of the fluid. Fluids such as air have low viscosity, thicker fluids like water are more viscous, fluids such as honey and oil are more viscous. Viscosity represents the internal flow resistance of a fluid and can be regarded as a measure of fluid friction. The higher the viscosity of the liquid, the slower the flow rate. Viscosity can be measured by calculating the time required for a given amount of liquid to flow through the capillary under gravity. The more viscous liquid, the more time it takes. The viscosity can also be determined by measuring the rate at which the steel ball falls into the liquid. As the viscosity increases, the sphere descends more slowly. Viscosity is related to the relative mobility of individual molecules of a liquid relative to each other.