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Why Measuring Viscosity is Important For Many Industries

Measuring viscosity reveals the degree of a liquid or gaseous substance’s resistance to flow, usually in terms of its unwillingness to flow under conditions where it is deformed by shear or extensional stress. A viscosimeter is the instrument used to measure the relative fluidity or viscosity of the material.

Nearly all fluids (with the notable exception of the liquid form of the helium isotopes helium-3 and helium-4) have some degree of resistance to flow, with the measurement being used to determine the degree of viscosity on a spectrum ranging from no stress resistance (called an ideal liquid) to total resistance.

The study of this property of substances is known as rheology, with researchers engaged in measuring viscosity in order to determine this often important property of a given liquid of gas. This property is measured with a viscosimeter to provide this data, which is important to quality control applications in the production of a wide variety of products, including inks, paints, motor oils, foods, pharmaceuticals and cosmetics, to name just a few.

Viscosity is most commonly expressed as a figure called the coefficient of viscosity; however, there are several different types of coefficient which may be used. The specific viscosity coefficient used to denote the results obtained from measuring viscosity is largely dependent on the type of stress applied to the fluid as well as the particular qualities of the liquid in question.

Different coefficients used to express the results from a viscosimeter include absolute (or dynamic) viscosity, kinematic viscosity (which is absolute viscosity divided by density), volume (or bulk) viscosity, shear viscosity and extensional viscosity. Each of these coefficients are more or less suitable for specific fluids, with absolute and shear viscosity being the best known and most widely used when measuring viscosity.

There are many different types of rheometers and other instruments used to measure the viscosity of substances which can be grouped into five broad categories based on the style of measurement used. The rotational method measures this characteristic by immersing rotors in a sample and measuring the running torque. A vibro viscosimeter is used with a transducer with adjustable amplitude immersed in the sample; the current used to drive this transducer is then measured. The capillary method measures the difference in pressure in either end of a capillary which the sample is allowed to flow through. The falling ball method of measuring viscosity involves taking a measurement of the amount of time required for an object (generally a sphere or cylinder) to fall through the sample material. The cup method determines the viscosity of a sample by measuring how long it takes for a sample to flow out of a hole in a container.

Since the temperature of a liquid and its viscosity are correlated, a viscosimeter or viscometer must be used in carefully temperature controlled conditions to produce accurate results. Even a small change in temperature can have enough of an effect to negatively impact the outcome of a quality control test or production process. Measuring viscosity is an exacting task, but one which is essential to a wide range of scientific inquiry as well as the manufacture of a variety of goods for the business to business and consumer markets.

Source by Andrew K Long

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