Non-Newtonian Fluids

Definition

Non-Newtonian fluids are fluids whose viscosity changes under stress or strain, meaning they do not follow Newton's law of viscosity, which states that the viscosity of a fluid remains constant regardless of the applied stress. This behavior makes them unique and interesting, as their flow characteristics can be altered by external forces such as pressure, shear rate, or time, leading to a variety of applications in different fields.

5 Must Know Facts For Your Next Test

1. Non-Newtonian fluids can be categorized into different types based on their flow behavior, such as shear-thinning, shear-thickening, and Bingham plastics.
2. Common examples of non-Newtonian fluids include ketchup, cornstarch mixed with water (oobleck), and paint.
3. The viscosity of non-Newtonian fluids can depend on factors such as temperature, concentration, and the duration of applied stress.
4. Understanding non-Newtonian fluids is crucial in industries like food processing, cosmetics, and pharmaceuticals, where precise control over flow properties is essential.
5. These fluids often exhibit time-dependent behavior; for example, some may show thixotropic properties where they become less viscous over time under constant shear.

Review Questions

• How does the behavior of non-Newtonian fluids differ from that of Newtonian fluids when subjected to stress?
  • Non-Newtonian fluids behave differently than Newtonian fluids because their viscosity changes under stress. In contrast to Newtonian fluids, which maintain a constant viscosity regardless of the applied shear rate, non-Newtonian fluids can either thin out (shear-thinning) or thicken (shear-thickening) when force is applied. This unique behavior means that the flow characteristics of non-Newtonian fluids can be manipulated by changing the amount or duration of stress applied.
• Discuss the practical implications of non-Newtonian fluid behavior in industrial applications.
  • Non-Newtonian fluid behavior has significant implications in various industries. For instance, in food processing, understanding how sauces like ketchup flow under pressure can optimize production and packaging. In cosmetics and pharmaceuticals, the formulation of creams and gels often relies on non-Newtonian properties to ensure proper application and stability. Additionally, in civil engineering, knowing how certain slurries behave under different loads can influence construction practices and material selection.
• Evaluate the role of temperature and time in influencing the viscosity of non-Newtonian fluids and how this understanding can lead to better industrial practices.
  • Temperature and time play critical roles in determining the viscosity of non-Newtonian fluids. As temperature increases, many non-Newtonian fluids experience a decrease in viscosity, which can enhance their processing and application. Furthermore, time-dependent behaviors like thixotropy or rheopexy indicate that a fluid's viscosity might change during mixing or application. By evaluating these factors, industries can tailor processes for better product consistency and performance, improving manufacturing efficiency and product quality.

Related terms

Viscosity: The measure of a fluid's resistance to flow, which in Newtonian fluids remains constant regardless of the applied shear rate.

Shear Thinning: A type of non-Newtonian behavior where a fluid's viscosity decreases with increasing shear rate, making it easier to flow under stress.

Bingham Plastic: A type of non-Newtonian fluid that behaves like a solid until a certain yield stress is applied, after which it flows like a viscous fluid.