Viscosity: What is it?
The resistance of a substance to motion when a force is applied is measured by its viscosity.
The internal friction degree in a fluid is measured by its viscosity. When a fluid layer is made to move with another layer, this friction becomes visible. The force needed to produce this shearing movement increases as friction increases. Every time the fluid is distributed or physically moved, such as when spraying, spreading, pouring, mixing, etc., shearing happens. Therefore, it takes more force to move highly viscous fluids than it does to move less viscous materials.
The following equation is used for calculating viscosity:
viscosity = shear stress / shear rate
Usually, the result is given in cP - centipoise, equal to 1 mPa s. - millipascal second.
Shear stress - the amount of force per unit area necessary to move one fluid layer relative to another.
Shear rate - a unit used to describe how quickly intermediate layers move relative to one another.
Fluids: Newtonian vs Non-Newtonian
Isaac Newton, the person who came up with this formula, believed that a fluid's viscosity would remain constant independent of changes in the shear rate at a specific temperature and shear stress.
He wasn't entirely wrong. Some liquids, like water and honey, do exhibit this behaviour. These fluids are known as Newtonian fluids. However, the viscosities of most fluids vary according to the shear rate. They are referred to as non-Newtonian fluids.
Non-Newtonian fluids come in five varieties: thixotropic, rheopectic, pseudoplastic, dilatant, and plastic. Each fluid kind needs to be measured with a different set of factors in mind.
Why Measure Viscosity?
Manufacturers can forecast how a material will behave in the real world by collecting data on the viscosity of the material. For instance, if toothpaste does not have the proper viscosity, it may be either too tough or too easy to pump out of the tube.
A material's viscosity influences the design of the production and transportation operations.
Who Performs Tests for Viscosity?
Examples of applications for viscosity measurements include:
Food
Measurements of viscosity are utilized in the food business to increase productivity and cost-effectiveness. It impacts how quickly a product moves through a pipe, how long it takes to set or dry, and how quickly the fluid is dispensed into packaging. The viscosity of the substance must be considered while designing the production process. Thus pipes must be slanted to maximize flow, and dispensers must exert just the proper amount of force to encourage flow without overfilling the container.
The texture of food is also characterized by its viscosity. To guarantee that each batch is consistent and will proceed through the production process effectively, the product's viscosity must be evaluated and monitored during production.
Viscosity measurement's significance in food production and processing
Food of a high calibre is becoming more and more significant to consumers. Analysts in this industry face a problem in producing goods that live up to the high standards of the end consumers. As a result, pertinent measures must be swift, precise, and reasonably priced. This especially holds for physical measurement factors like viscosity.
In any industrial field using liquid media, understanding viscosity is crucial.
For instance, viscosity is important in almost every stage of food preparation. For instance, it is necessary to pump a lot of liquid media through pipes safely. This industry's viscosities range from aqueous to pasty.
Different kinds of sugar, such as glucose syrup, are often used in industrial food processing to sweeten foods and beverages. Syrup comes in various forms due to the enzymatic breakdown of starch and is a vital product for the starch industry. Syrups are employed frequently in manufacturing food as binders because they are sticky, such as in chocolate cereal mixtures or sauces. The adhesive qualities of the starch included in the food significantly impact the viscosity and flow characteristics. Depending on the location and the temperature, starch has different properties. For instance, rising temperatures have a hardening effect. However, it liquefies when it is heated in water. When it cools down once again, it solidifies once more. Viscosity is a characteristic of these circumstances. Even in soups, thickeners are used to get the correct consistency. The temperature-dependent viscosity is crucial in establishing the flow characteristics of sauces, dips, mayonnaise, and liquid additives for quality control.
Adhesives
Consider how the glue must flow—or not flow—on a part after the adhesive is applied when choosing the appropriate viscosity for an adhesive. High-viscosity adhesives are the best choice if you want the adhesive to stay put after dispensing rather than spreading out since low-viscosity adhesives flow more easily.
Other Industries
Petroleum: Although viscosity is a fundamental quality, it can also fluctuate based on the environment. Viscosity can be affected by changes in temperature, particularly extreme heat, moisture, and air exposure. As a result, the oil or lubricant you use may not exactly match the viscosity level required for the substance to function properly in your real-world circumstances. Viscosity measurements forecast the performance of lubricating oil and identify pipeline design components.
Concrete: A mix's ability to self-level and pump depends on its viscosity.
Cosmetics: Viscosity testing is essential for maintaining high production standards for cosmetics and personal care products. One of the many test procedures used in quality control involves analyzing the viscosity at different shear rates to replicate the sample's processability during production and application behaviour to assure customer satisfaction. In addition, the viscosity should be considered when deciding how to make cosmetic products feel and flow.
Viscosity measurement
A viscometer is an instrument most frequently used to gauge and monitor viscosity. Thanks to rotating viscometer technology, viscometers of today are exceedingly useful and user-friendly. These viscometers have an accuracy range of 1 percent to 0.2 percent and measure a wide viscosity range from 200 to 106 million. The viscosity of a product is measured by submerging a chosen spindle inside a product sample. Violent stirring produces a vortex while the spindle rotates at a specified speed. The torque that is required to rotate the spindle at a specific speed is calculated based on the amount of drag produced by the spindle moving in the liquid. The device detects rotation, and the recorded torque value is computationally transformed into a viscosity reading in milliPascal-seconds (MPS) or centipoise (cP) units (mPa.s).
The reference substance used to determine water's benchmark viscosity value of 1cP is water. The viscosity of every other substance is then evaluated in relation to water. Up to 10,000 data points can be recorded and stored by the rotational viscometer. With the help of the offered software, users may quickly view flow curves, plot up to four data sets simultaneously, and show data graphically. The user has countless reporting options and can download these findings to a spreadsheet. To get the best quality, it is crucial to monitor batches to ensure they retain the same viscosity level throughout manufacturing.
Flow resistance is determined by spindle design.
With increasing spindle speed and spindle size, the flow resistance rises. Depending on the available sample size, the torque range employed, the required temperature, and the consistency of the material, different samples and materials require different types of spindles. Users can swap out different spindles based on their demands because today's viscometers are flexible and configurable. A cone spindle or parallel plate is employed for more viscous and thicker samples. A concentric cylinder spindle is suitable for pourable liquids that are thinner and less viscous. A T-bar can be used with a gel-like substance. This is a reasonably cheap process, and many suppliers of viscosity equipment offer practical packages that let customers save money by buying the device, spindles, and cleaning supplies all at once.
During testing, take spindle speed and time into account.
Another element to consider when doing a viscosity test is the spindle's rotational speed and duration, as both impact the samples. Before a value is recorded, the spindle should have completed at least five rotations, and the number of rotations should be limited by a certain amount of time. If the sample is too high or too low for the chosen spindle, an over and under range warning will often go off in rotating viscometers. The amount of time that fluid is sheared will influence the viscosity of some fluids more than others. Today's viscometers have 2,600-speed options, letting the user set the speed up to 250 rpm. No matter the sample, the user has total flexibility thanks to this. Speed, viscosity, spindle, shear rate, percentage of torque, and shear stress are all readouts on the LCD. The viscometer will compute and display kinematic viscosity when the density of the sample is entered. The device can also detect the shear stress (the torque required to rotate the spindle), determine the shear rate (the speed at which the spindle rotates), and plot the results on a graph. The slope of that line represents the viscosity at a given temperature. Users of viscometers equipped with networking capability can download data to a computer for use in spreadsheets. For the greatest quality of a product to be generated, it is crucial to monitor the viscosity of a sample and generate an in-depth report.
The significance of temperature regulation
Temperature becomes a key role in measuring viscosity because the sample will test differently depending on its temperature. For instance, honey that has been heated or cooled in the refrigerator may have a viscosity value that is very different from honey that has been tested at room temperature. Because temperature significantly impacts the results, the test conditions used to evaluate viscosity should be strictly regulated. The temperature of the food sample must be kept within +-0.05°C limits to obtain precise readings of viscosity. To assist the user in maintaining precise sample temperatures, several viscometers incorporate built-in RTD temperature probes that display the temperature on the instrument.
Testing for viscosity to ensure quality
Viscometers have a significant impact on the food business, as is clear. Viscosity is assessed either in the middle of processing or at the end to determine whether the finished product meets accepted criteria for quality. Samples are routinely selected from the manufacturing floor and taken to the quality control lab for testing to guarantee that the quality is maintained throughout the process.
Final Words
Numerous businesses utilize viscosity testing to guarantee that quality is maintained, in addition to the food industry. The same rotating viscometers are used by the food industry, the chemical business, the biofuels industry, the paint industry, the petroleum industry, and the pharmaceutical sector. Rotating viscometers satisfy various purposes due to their versatility, accuracy, usability, and ability to deliver reproducible findings.
