The force required to rotate the body is then measured. A body is rotated in a liquid by a motor. Rotational viscometers: Rotational viscometers employ the idea that the force required to rotate an object immersed in a fluid can indicate the viscosity of the fluid. The capillary of the kinematic viscometer produces a fixed resistance to flow. Kinematic viscosity is traditionally measured by the time it takes for an oil sample to pass through a capillary orifice under the force of gravity (Figure 1). How is the viscosity of a lubricant measured? Dynamic viscosity, designated μ, is measured, in SI units, in pascal-seconds (Pa s), or N s m-2, or kg m−1 s−1.ĭefinition of viscosity Viscosity is the thermophysical property of fluids caused by their molecular cohesion forces and results in the opposition they oppose to flowing, thus requiring the application of an effort or pressure. The viscosity of a fluid is the resistance that the different sheets slide against each other. What is viscosity and in what units is it expressed? That is, it is equivalent to a force of 1 dyne per 1 cm², generated by a speed difference of 1 cm per second, in a space of 1 cm. The poise (French: /pwaz/ symbol: P) is the dynamic viscosity unit of the Cegesimal System of Units: 1 poise (P) ≡ 1 g (s cm)−1 ≡ 1 dyne s cm−2 ≡ 0.1 Pa s. s) This is the SI unit of viscosity, equivalent to one newton-second per square meter (N The most common units used to express kinematic viscosity are: stokes (St) or centistokes (cSt, where 1 cSt = 0.01 St), or in SI units such as square millimeters per second (mm2/s, where 1 mm2/s = 1 cSt). Viscosity determined in this way is called dynamic or absolute. How to go from cSt to CPS?Ī simple way to convert from kinematic to dynamic viscosity is to multiply the value in centistokes by the specific gravity of the liquid, obtaining the corresponding value in centipoise. Its symbol is St and in engineering the centistokes (cSt) is generally used. However, the commonly used unit is the Stokes (or Stoke), and 1 St = 10-4 m²/s. Kinematic viscosity is obtained by dividing the absolute viscosity of a fluid by its mass density. The kinematic viscosity units are: m2/sec (Sist. It is calculated using the relationship: φ= µ /ρ. What is the unit of measurement for viscosity?
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