Non-newtonian fluid

Definition

A non-newtonian fluid is a type of fluid whose viscosity changes under stress or strain, meaning its flow behavior cannot be described by a single constant viscosity. This characteristic makes them distinct from Newtonian fluids, where the viscosity remains constant regardless of the applied force. Non-newtonian fluids can exhibit a range of behaviors such as shear-thinning, shear-thickening, or even displaying time-dependent viscosity, which makes their behavior interesting and complex in various applications.

5 Must Know Facts For Your Next Test

1. Non-newtonian fluids can be classified into various categories based on their flow behavior, such as pseudoplastic (shear-thinning), dilatant (shear-thickening), and Bingham plastics.
2. Common examples of non-newtonian fluids include ketchup, paint, and cornstarch mixed with water (often referred to as oobleck).
3. The change in viscosity in non-newtonian fluids can be reversible or irreversible depending on the type of fluid and the nature of the applied stress.
4. Non-newtonian fluids are important in many industries, including food processing, cosmetics, and pharmaceuticals, where precise control over flow behavior is crucial.
5. Understanding non-newtonian fluids is essential for chemical engineers as they often encounter these materials in processes like mixing, pumping, and transport.

Review Questions

• How does the viscosity behavior of non-newtonian fluids differ from that of Newtonian fluids?
  • The primary difference between non-newtonian and Newtonian fluids lies in how their viscosity responds to applied stress or strain. While Newtonian fluids maintain a constant viscosity regardless of the force applied, non-newtonian fluids have a variable viscosity that changes with the level of stress. This means that non-newtonian fluids can become either more or less viscous when subjected to different shear rates, leading to a range of unique behaviors not observed in Newtonian fluids.
• Discuss the implications of shear-thinning and shear-thickening behaviors in industrial applications involving non-newtonian fluids.
  • Shear-thinning and shear-thickening behaviors have significant implications for industrial processes that utilize non-newtonian fluids. Shear-thinning fluids, like many paints or inks, become less viscous under high shear conditions, making them easier to apply and spread. In contrast, shear-thickening fluids may resist flow under certain conditions but provide additional stability when at rest, which can be beneficial in products like protective gear. Understanding these behaviors helps engineers design more effective mixing, pumping, and application methods tailored to specific materials and processes.
• Evaluate how the unique properties of non-newtonian fluids can impact process design and efficiency in chemical engineering applications.
  • The unique properties of non-newtonian fluids significantly impact process design and efficiency in chemical engineering applications by influencing factors like mixing rates, pump selection, and energy consumption. Engineers must consider the variable viscosity characteristics when designing equipment and processes to ensure optimal performance. For instance, improper handling of a shear-thinning fluid could lead to insufficient mixing or uneven product quality. Conversely, understanding how to manipulate these properties can enhance product formulation and processing efficiency, making it crucial for engineers to integrate this knowledge into their designs.

Related terms

Viscosity: A measure of a fluid's resistance to flow, defined as the ratio of shear stress to shear rate.

Shear-thinning: A behavior of certain non-newtonian fluids where viscosity decreases with an increase in shear rate, making them easier to flow under stress.

Bingham plastic: A type of non-newtonian fluid that behaves as a rigid body at low stress levels but flows as a viscous fluid when a certain yield stress is exceeded.