What is Viscometer? Types, Purpose, Advantages & applications

Viscometer measures the viscosity of a fluid. Viscosity measurement can be important for all liquid to semi-solid materials that we know from daily ‎life. A viscometer is used primarily to measure fluid viscosity and other flow-related characteristics.  ‎

The viscosity of a fluid is measured by the friction force that occurs between the “layers” that make it ‎up. Viscosity is simply the internal resistance of fluids to flow. A centipoise (cP) is a unit of dynamic ‎viscosity. ‎

Let us understand the few lines regarding the basics of viscosity before discussing Viscometers.‎

Definition of Viscosity

Viscosity is a type of mass property defined as the resistance of a liquid to flow. When intermolecular ‎attractive forces are strong within a liquid, there is a higher viscosity. Mathematically, viscosity can be ‎defined as the ratio between the shear stress and the velocity gradient of the fluid.‎

Purpose of Viscosity Measurement

Monitoring the physical characteristics of fluids is critical in industrial sectors that manufacture liquid ‎products or use them in their production processes. Precise measurements of the viscosity of a liquid ‎can guarantee the control of processes in the industry. Viscosity measurement is an indicator of the ‎quality of the final product.‎

Monitoring of this property is essential, as it affects the performance of the fluid, for example, during ‎its pumping from one place to another.‎

Importance of Viscosity Measurement in Lubricants

For example, let us take LUBRICANTS. They have extensive applications – the quality control ‎of ‎these is rigorous. Hence, viscosity requirements are strictly followed. ‎

If the viscosity of a lubricant is too high, a fluidity problem will occur in the product. This ‎causes ‎increased friction, thereby heat gets generated, accelerating the oxidation process, and lessening the ‎useful ‎life of the lubricant. Thereby increase in energy consumption. Finally, high viscosity lubricant ‎increases wear ‎of the equipment, with the consequent increase in repairs and shortening of the useful ‎life of the ‎components.‎

On the other hand, if the viscosity of a lubricant is too low, the fluid will not adequately cover and ‎protect the ‎parts, with consequent component wear. Thereby increase in repairs or component ‎replacements. Increased ‎friction, and heat, help faster oxidation, and high formation of sludge, which ‎finally leads to greater ‎energy consumption.‎

Types of Viscometers

In the industrial sector, viscosity is very crucial. It is measured and controlled using viscometers. This ‎parameter can be measured using several different models, each of which is appropriate for the ‎specific conditions of the manufacturing process. ‎

To find the model of laboratory equipment that best suits a given application, some factors must be ‎considered first. First, the viscosity range of a sample must be reviewed (low, medium, or high). ‎

The following are the most widely used.‎

  • Rotational Viscometer
  • Capillary tube Viscometer
  • Falling ball Viscometer

Rotational Viscometers

Rotational Viscometers

This type of viscometer is the most suitable for evaluating Non-Newtonian fluids. ‎

The rotational viscometer comprises a spindle, rotated by a motor while immersed in the sample fluid, whose viscosity is to be determined. The spindle is rotated at a constant speed. It measures viscosity by analyzing the torque requirement to rotate a spindle. ‎The torque demand is ‎proportional to the viscous drag on the spindle, therefore, the sample viscosity.  ‎

Many liquids are exposed to thermal loads and therefore change their viscosity, for example, motor ‎oils. This is exactly where the rotational viscometer comes into play. It is equipped with a probe to ‎measure the temperature of the sample to be able to control it at all times. The immersion ‎temperature sensor determines the temperature of the sample in a range between 0 to 100 °C during ‎the measurement. ‎

Viscometer accuracy depends not only on the design of the equipment but also on the accuracy of the ‎temperature control. An accurate result is often obtained by averaging several repeated viscosity ‎measurements.  ‎

To obtain the measurement history, the viscometer can be connected to a PC through the RS-232 ‎interface.  ‎

Capillary Viscometer

Capillary Viscometer

The primary apparatus used in a capillary viscometer test is a glass tube, used to measure non-Newtonian liquids. It is typically “U” shaped, ‎giving ‎it its commonly associated name, the U-tube. A temperature-controlled bath usually 40 or 100° C is ‎required for this procedure. ‎

Its simple design consists of a U-shaped glass tube with two bulbs (one on top, one at the ‎bottom).  ‎The fluid passes from the upper bulb to the lower bulb through a capillary. Now, the ‎viscosity is measured ‎by measuring the time taken by the fluid to pass through the tube either by ‎suction or by gravity force.‎

This measured time is then multiplied by a constant value associated with the particular tube to ‎calculate ‎the absolute (suction) or kinematic (force of gravity) viscosity. ‎

U-tube viscometer comes in several variations. The most well-known three types are ‎Ostwald, ‎Cannon-Fenske, and Ubbelhode.‎

Falling ball Viscometer

Falling ball Viscometer

A falling ball viscometer uses Hoppler’s principle to measure the viscosity of fluids. By measuring ‎the ‎time required for the fall of the ball by gravity through the fill tube with the sample.‎

A falling ball viscometer is designed to measure the viscosity of Newtonian liquids and gases. That is, mainly low-viscosity ‎substances.‎

The device consists of two glass tubes, one is a thick-wall glass tube inserted into another glass ‎tube. ‎Water is circulated in this space, a temperature probe is inserted in it. The whole arrangement ‎is ‎slightly tilted at an angle (50°, 60°, 70°, or 80°) on a stand. The tube is rotated at 180° around an ‎axis ‎perpendicular to both tubes.‎

The inner tube is filled with a liquid whose viscosity is to be determined. The spherical ball made of ‎glass ‎or solid supplied by the manufacturer is dropped through it. The speed of fall depends on the ‎greater or lesser ‎coefficient of viscosity of the sample to be measured. ‎

The average time of three tests can be used to measure viscosity. ‎

Advantages of Viscometer‎

  • Viscometers are very helpful for quality control of the final product.
  • In the production process, Viscometer is a part and parcel of quality control.
  • The viscosity of solutions, suspensions, emulsions, and melts can be determined during formulation, transport, storage, and handling.  
  • By using viscometers in process control, industrial operations can be carried out efficiently. One can expect product quality, and with the least amount of variation possible.
  • A viscometer in process control is to identify and correct variations in liquid specifications.

Applications of Viscometer

  • In the industrial sector, the viscometer has a broad range of applications and is an important instrument for the verification of quality products.
  • In glass manufacturing, viscosity control is carried out throughout the manufacturing process, since this parameter has a significant effect on other physical properties, such as melting, softening, and crystallization.
  • The calculation of viscosity oil refining is important because it is a key element in determining the amount of liquid that can be transported in a pipeline during a specific period. Fluid properties can be dramatically affected by small changes in viscosity.
  • Printing inks – water-based lacquers, inks, printing inks.
  • Paper industry – Pigment dispersion, Paper additives, emulsions.
  • Food industry – honey, milk, jelly sugar solution, beer, fruit juice.
  • Chemical industry – Solvents, resin solutions, adhesives solutions, polymer solutions.
  • The use of the viscometer to verify the quality of the final product of cosmetics, biotechnological products, paints, and adhesives.
  • Detergents – washing liquids, liquid washing agents, and surfactant solutions.

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