LYCOS RETRIEVER 
Viscosity
built 276 days ago
Viscosity is first and foremost a function of material. The viscosity of water at 20°C is 1.002 centipoise. Most ordinary liquids have viscosities on the order of 1 to 1000 centipoise. Pastes, gels, emulsions, and other complex liquids are harder to summarize. Some fats like butter or margarine are so viscous that they seem more like soft solids than like flowing liquids. From everyday experience, it should be common knowledge that viscosity varies with temperature.
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Viscosity is the property of fluids responsible for their resistance to flow. A high viscosity is characteristic of a liquid that flows slowly, and a relatively low viscosity characterizes liquids that flow freely. The measurement of viscosity is made by a number of methods, including passing the liquid through a narrow tube or dropping a ball through the liquid. The measurements are usually made by measuring the time required for a flow process to be completed and comparing this with the time required for a standard liquid (often water). In the falling-ball method the liquid is placed in a tube and a ball is dropped into it. The viscosity is determined from the length of time required for the ball to sink through a calibrated distance on the tube.
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Viscosity has two distinct effects on the PTF rotor. First, the profile causes boundary layer thickness to increase as viscosity increases for a fixed volume. This means that rotor-blade shape and length will be important in determining the K-factor as the flow around the blade tip region changes with respect to viscosity. This boundary layer thickness causes the turbine flowmeter to be non-linear. Formation of a shroud around the turbine rotor, with the shroud outer diameter slightly smaller than the inside diameter of the flow tube, increases the viscosity and creates a drag (resistance to rotation). This drag offsets the non-linear effect of the boundary layer.
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Viscosity has the SI units Pascal seconds (Pa s) which is called the Poiseuille. More commonly used is the dyne sec/cm2 which is called Poise. One Pa s is 10 Poise. The Poise is used in the table because of its more common usage. Data from Gustafson. These viscosities are at 20°C except for the blood and blood plasma which are at body temperature, 37°C, and for steam which is at 100°C.
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Cambridge Viscosity has developed an innovative new viscometer with the smallest sample size requirement for any automated viscosity measurement system on the market: only 75 μl (microliters). The VISCOlab 5000 micro-sample viscometer is ideal for drug discovery/delivery and research applications where sample volume is very limited and very expensive.
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Viscosity relates directly to pump performance and therefore, to the system connected to the pump. Prior to designing a pump, it is important to determine the viscosity of the fluid at the expected operating conditions. An increase in liquid viscosity generally increases the required net inlet pressure and the required pump input power. Furthermore, an increase in the viscosity generally corresponds to a decrease in the maximum allowable pump speed.
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