Definition of Dynamic Viscosity
Dynamic viscosity (denoted as η) quantifies the internal friction within a fluid as layers of the fluid move past one another. In simple terms, it is the resistance of the fluid to deformation due to shear stress. The higher the dynamic viscosity, the more force is required to move the fluid at a given rate.
The unit of dynamic viscosity in the International System (SI) is the pascal-second (Pa·s), although in practical applications, it is often measured in centipoise (cP), where 1 cP = 0.001 Pa·s.
Formula for Dynamic Viscosity
Dynamic viscosity is mathematically defined by the following formula:
Types of Fluids and Dynamic Viscosity
Fluids can be classified as Newtonian and Non-Newtonian based on how their viscosity behaves under different shear rates:
- Newtonian Fluids: These fluids exhibit a constant viscosity regardless of the shear rate. Water, air, and many simple liquids are examples.
- Non-Newtonian Fluids: These fluids have a viscosity that changes with the shear rate. They include substances like ketchup, blood, and paints, which exhibit varying flow properties depending on the forces applied.
Factors Affecting Dynamic Viscosity
Several factors influence the dynamic viscosity of a fluid:
- Temperature: Viscosity generally decreases with an increase in temperature for liquids and increases for gases.
- Pressure: For most liquids, viscosity increases with pressure, although the effect is usually less pronounced than temperature.
- Composition of the Fluid: The molecular structure and presence of suspended particles can significantly affect the viscosity.
Example of Dynamic Viscosity in Various Fluids
Dynamic Viscosity in Separation Technologies
Dynamic viscosity is a fundamental property that influences the behavior of fluids across various industrial applications. Understanding the dynamic viscosity of the fluid being processed allows for better control of flow characteristics. It helps in fine-tuning operational parameters to improve separation efficiency. Additionally, accurate viscosity data can lead to reduced energy consumption by enabling more effective use of machinery, particularly in processes like filtration, centrifugation, and other separation technologies. Higher viscosity fluids may require modifications to equipment like pumps or centrifuges to ensure efficient processing.
For example, in centrifugation, the viscosity of the fluid determines the separation efficiency. In high-viscosity fluids, particles move more slowly, which can impact the separation speed.
Reference
- Yaw’s Transport Properties of Chemicals and Hydrocarbons, 2003.
- McCabe, W.L., Smith, J.C., & Harriott, P. (2005). “Unit Operations of Chemical Engineering” (7th Ed.). McGraw-Hill Education.
Dynamic Viscosity in Separation Technologies
Dynamic viscosity is a fundamental property that influences the behavior of fluids across various industrial applications. Understanding the dynamic viscosity of the fluid being processed allows for better control of flow characteristics. It helps in fine-tuning operational parameters to improve separation efficiency. Additionally, accurate viscosity data can lead to reduced energy consumption by enabling more effective use of machinery, particularly in processes like filtration, centrifugation, and other separation technologies. Higher viscosity fluids may require modifications to equipment like pumps or centrifuges to ensure efficient processing.
For example, in centrifugation, the viscosity of the fluid determines the separation efficiency. In high-viscosity fluids, particles move more slowly, which can impact the separation speed.
Reference
- Yaw’s Transport Properties of Chemicals and Hydrocarbons, 2003.
- McCabe, W.L., Smith, J.C., & Harriott, P. (2005). “Unit Operations of Chemical Engineering” (7th Ed.). McGraw-Hill Education.
