12/23/2023 0 Comments Water viscosity mm2 s![]() ![]() Many substances, such as the gums employed in pharmacy, have variable viscosity, and most of them are less resistant to flow at higher flow rates. The approximate viscosity in square millimetres per second at room temperature of ether is 0.2 of water, 1 of kerosene, 2.5 of liquid paraffin, 20 to 70 and of honey, 10,000.Ībsolute viscosity can be measured directly if accurate dimensions of the measuring instruments are known, but it is more common practice to calibrate the instrument with a liquid of known viscosity and to determine the viscosity of the unknown fluid by comparison with that of the known. The sizes of the units are such that viscosities in the ordinary ranges are conveniently expressed in square millimetres per second. kinematic viscosity = (absolute viscosity)/(density). To obtain the kinematic viscosity from the absolute viscosity, the latter is divided by the density of the liquid at the same temperature, i.e. While on the absolute scale viscosity is measured in pascal second or millipascal second, for convenience, the kinematic scale, in which the units are square centimetres per second (cm 2 .s –1) and square millimetres per second (mm 2 .s –1), commonly is used. The specifying of temperature is important because viscosity changes with temperature in general, viscosity decreases as temperature is raised. The unit1 is the pascal second (Pa.s), viscosities commonly encountered represent fractions of the pascal second, so that the millipascal second (mPa.s) proves to be the more convenient unit. In other words it is the shear stress divided by the rate of shear strain. ![]() It is defined in terms of the force required to move one plane surface continuously past another under specified steady-state conditions when the space between is filled by the liquid in question. Viscosity is a property of liquids that is closely related to the resistance to flow. ![]()
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