Rheology and Dynamic Viscosity – Fluid Dynamics

Rheology and Dynamic Viscosity

Rheology is the study of the flow or deformation of matter. A fluid’s ability to flow freely is specifically described by its viscosity. Often, materials may exhibit both viscous (fluid) and elastic (solid) behaviour—these are known as viscoelastic materials, which require more than a standard viscosity analysis for complete quantification of material behaviour.

Viscosity, in general, measures the internal friction of a fluid. By bringing the analysis area of a spindle into contact with a sample and creating shear stress through rotation or oscillation of the spindle, this is evaluated using a standard viscometer (or rheometer). The gadget measures both the spindle speed and the drag of the fluid against the spindle torque necessary to generate a certain degree of shear stress.

The viscometer measures this resistance and generates findings that are expressed in milliPascal seconds (mPa-s) or centipoise (cP) units. It is critical to have comparable analysis settings across analyses and equipment because the size and form of the spindle, rotational speed, sample container, and fluid temperature (25°C by default) all significantly affect a viscosity measurement. This testing is essential for the development, research, and process management of liquid and semi-liquid products.

One fluid plane moves in relation to another plane when friction is applied; this force is referred to as shear. Greater shear is needed for viscous materials than for less viscous ones. The illustration that follows shows how to define viscosity. The force needed to maintain dv when two fluid planes separated by dx are travelling in the same direction but at different speeds depends on the gradient in velocity.

It has a constant called viscosity,. The difference in the speeds of various fluid layers concerning one another is known as the velocity gradient and is denoted by the ratio dv/dx. The force per area, or F/A for short, is also referred to as shear stress. 

When attempting to get a complete understanding of material behaviour, viscoelastic materials present a little bit more of a challenge. Traditional viscosity measurements may provide data on the characteristics of viscous fluids, but they are unable to provide data on the elastic characteristics of such material. Oscillatory testing is preferred in this situation. An oscillating test will sinusoidally partially rotate back and forth. With some lag and a phase shift, the sample will take some time to react to the rotation. When viscous qualities predominate in a sample’s behaviour, for example, and when elastic properties prevail, it can be determined by the angle of the phase shift. This is helpful for materials that experience periods of low strain followed by times of high strain. For example, consider lotion that is stored in a bottle and then applied by pumping it through a nozzle.

Rheology testing is used by many industries as a quick and accurate method of analysing significant aspects that can have an impact on a product’s performance, quality, and/or efficiency, both during manufacturing and for quality control testing of finished consumer items. For instance, the food business uses viscosity measurements to identify or address issues with the look, feel, or consistency of food products, all of which affect the sensory experience of a customer. Rheology is also used to predict how a substance will behave during production, such as when a viscous liquid must be pumped through pipes or other machinery.

Rheology is used by the pharmaceutical business to forecast how medicines will act when used by consumers, such as how medicine will flow, pour, or spread. For instance, the way a cough syrup or other suspension will pour out of a bottle or how thoroughly an ointment will cover the skin.

Measurements of viscosity are frequently used in other sectors. Measurements are used in the automobile sector for hydraulic or engine lubricants. Semi-liquid inks are put through tests in the printing business. Coatings and finishes are tested by the paint and coating industries to enhance their application characteristics. To improve the effectiveness of coverage, the cosmetics industry tests the flowability and spreadability of liquid makeup and creams.

In conclusion, any product or business that uses liquid in the production process or the finished product can benefit from understanding and controlling viscosity.

Advantages

• Analysis of viscoelastic materials through rheology and free-flowing liquids by dynamic viscosity
• An extensive range of testing procedures and analysis settings to satisfy the needs of various materials and data reporting standards
• Onsite, a variety of spindle types are available to guarantee the optimal fit for a material.

Considerations

• Choosing The Right Exam To Use With The Test Material
• The Brookfield DV-II+ Pro Viscometer functions in the 20°C to 80°C temperature range.
• The Anton Paar Modular Compact Rheometer functions between -20°C and 180°C.
• The sample size must match the anticipated viscosity.

Video 01: Understanding Viscosity