The viscosity of water decreases smoothly from the freezing point while the density remains essentially constant except for the small maximum in density near 4☌. The basic unit is the centipoise (cP), the cP is equivalent to 0.01 Poise. In the industry of petroleum, centiPoise (cP) or milliPascal-second (mPas) is offen used as the unit of dynamic viscosity. In cgs units the unit is called the centistoke. There are two commonly used units of measurement for the dynamic viscosity of fluids. The kinematic viscosity is the dynamic viscosity divided by the density of the fluid. The unit centiPoise = 0.001 Pa s and is is sometimes written mPa s. These viscosities are at 20☌ except for the blood and blood plasma which are at body temperature, 37☌, and for steam which is at 100☌. The Poise is used in the table because of its more common usage. More commonly used is the dyne sec/cm 2 which is called Poise. Temperature will affect the viscosity of most materials. The centipoise value indicates how easily or difficultly the liquid will flow higher centipoise values correspond to more viscous (thicker) liquids that flow more slowly. This unit is used in honor of French physicist, Jean Lonard Marie Poiseuille (1797-1869), who worked with Gotthilf Hagen on the widely known Hagen-Poiseuille law which applies to laminar flow. It is defined as one hundredth of a poise (P). The most commonly used unit for dynamic viscosity is the CGS unit centipoise (cP), which is equivalent to 0.01 Poise (P). The higher the viscosity of a liquid, the thicker it is and the greater the resistance to flow. Centipoise (cP) is a unit of dynamic viscosity commonly used to measure the thickness or resistance to flow of a liquid. While less common than kinematic viscosity, absolute viscosity and the Brookfield viscometer are used in formulating engine oils. In layman’s terms, viscosity defines a fluid’s resistance to flow. This method is commonly referred to as the Brookfield method and is described in ASTM D2983. Viscosity has the SI units Pascal seconds (Pa s) which is called the Poiseuille. Absolute viscosity is reported in centipoise (cP), equivalent to mPa·s in SI units. Note: poise (P) is a unit of dynamic viscosity (g cm-1 s-1) which in the above table is divided by density (lb ft-3). Viscosity of Liquids and Gases Viscosity of Liquids and Gases Liquids
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