Rheology and Dynamic Viscosity – Fluid Dynamics

Rheology and Dynamic Viscosity

The study of the flow or deformation of substances is known as rheology.
Viscosity is the specific characteristic that describes a fluid’s ability to flow easily. Some materials can display both fluid (viscous) and solid (elastic) characteristics, and they are called viscoelastic materials. These materials need a more comprehensive analysis than just viscosity to fully understand their behavior.
Viscosity, in general, measures a fluid’s internal friction. A standard viscometer (or rheometer) evaluates shear stress by bringing the spindle’s analysis area into contact with a sample and creating shear stress through rotation or oscillation of the spindle. The gadget measures both the spindle speed and the fluid’s drag against the spindle torque necessary to generate a certain degree of shear stress.
The viscometer measures this resistance and generates findings expressed in milliPascal seconds (mPa-s) or centipoise (cP) units. Comparable analysis settings across analyses and equipment are critical 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 developing, researching, and managing liquid and semiliquid products.
When friction is applied, one fluid plane moves about another plane; this force is called shear. Dense materials require more excellent shear than less dense ones. The illustration that follows shows how to define viscosity. The force required to maintain dv when two fluid planes separated by dx are traveling 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 relative to 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 called shear stress.
When attempting to understand material behavior, viscoelastic materials present a little bit more of a challenge. Traditional viscosity measurements may provide data on the characteristics of viscous fluids, but they cannot 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 behavior, for example, and elastic properties prevail, it can be determined by the phase shift angle. This is helpful for materials that experience periods of low strain followed by times of high strain.
For example, consider a lotion stored in a bottle and then applied through a nozzle.
Many industries use rheology testing to analyze significant aspects that can impact a product’s performance, quality, and efficiency 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 a customer’s sensory experience. Rheology also predicts how a substance behaves 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, how 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. They are used in the automobile sector for hydraulic or engine lubricants. Semiliquid inks are tested in the printing business. The paint and coating industries test coatings and finishes 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, various 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