Newtonian Fluids

Definition

Newtonian fluids are a class of fluids that exhibit a linear relationship between the shear stress and the rate of shear strain, known as the viscosity of the fluid. This means that the viscosity of a Newtonian fluid remains constant regardless of the applied shear stress or the rate of shear strain.

5 Must Know Facts For Your Next Test

1. Newtonian fluids have a constant viscosity that is independent of the rate of shear strain or the applied shear stress.
2. Examples of Newtonian fluids include water, air, and most common liquids and gases at standard conditions.
3. The viscosity of Newtonian fluids is a measure of their resistance to flow and is a fundamental property that determines their behavior in various applications.
4. Laminar flow is a characteristic of Newtonian fluids, where the fluid layers slide smoothly past each other without turbulence or mixing.
5. Poiseuille's Law is a key equation that describes the volumetric flow rate of a Newtonian fluid through a cylindrical pipe, taking into account the pressure drop, pipe radius, fluid viscosity, and pipe length.

Review Questions

• Explain the relationship between shear stress and shear strain rate in Newtonian fluids, and how this differs from non-Newtonian fluids.
  • In Newtonian fluids, the relationship between shear stress and shear strain rate is linear, meaning the viscosity of the fluid remains constant regardless of the applied shear stress or the rate of shear strain. This is in contrast to non-Newtonian fluids, where the viscosity can change with the applied shear stress or shear strain rate, leading to more complex flow behavior.
• Describe how the viscosity of a Newtonian fluid affects its behavior in the context of Poiseuille's Law.
  • According to Poiseuille's Law, the volumetric flow rate of a Newtonian fluid through a cylindrical pipe is inversely proportional to the fluid's viscosity. This means that as the viscosity of the Newtonian fluid increases, the flow rate decreases for a given pressure drop, pipe radius, and pipe length. The viscosity of the Newtonian fluid is a key parameter that determines the resistance to flow and, consequently, the flow characteristics described by Poiseuille's Law.
• Analyze how the laminar flow behavior of Newtonian fluids is related to their viscosity and the principles of fluid mechanics.
  • The linear relationship between shear stress and shear strain rate in Newtonian fluids, as defined by their constant viscosity, is a key factor in the development of laminar flow. Laminar flow is characterized by the smooth, parallel movement of fluid layers, without turbulence or mixing. This flow regime is favored in Newtonian fluids due to the balance between the viscous forces, which resist changes in fluid motion, and the inertial forces, which drive the fluid flow. The viscosity of the Newtonian fluid, as a measure of its internal friction, plays a crucial role in maintaining the laminar flow pattern and determining the overall fluid mechanics in various applications.

Related terms

Viscosity:

The measure of a fluid's resistance to flow, which determines its internal friction and the force required to make it flow.

Laminar Flow:

The smooth, parallel flow of a fluid where adjacent layers slide smoothly past one another without turbulence or mixing.

Poiseuille's Law: The equation that describes the volumetric flow rate of a Newtonian fluid through a cylindrical pipe, taking into account the pressure drop, pipe radius, fluid viscosity, and pipe length.