Lecture Notes on Fluid Dynamics

Introduction

  • Lecture number four begins with announcements due to UQ being closed for Cyclone Alfred.

  • Online recording made for convenience; aim to assist all students despite disruptions.

Weekly Schedule Changes

  • Week three and four lectures to be available online.

  • Tutorials on Monday, March 18:

    • 8:00 - 8:15: Recap of previous lectures

    • 8:15 - 9:15: Week three tutorial

    • 9:30 - 9:45: Recap of today's lecture

    • 9:45 - 10:45: Week four tutorial

  • Emphasis on attending tutorials to enhance understanding of fluid dynamics and practical exercises.

Overview of Fluid Dynamics

  • Week four topic: Fluid dynamics, including how liquids behave and flow.

  • Definition of fluid mechanics: the science that studies all behavior of fluids.

  • Key to understanding fluid mechanics:

    • Fluid Statics: Study of fluids at rest.

    • Kinematics: Study of fluids in motion without external forces.

    • Fluid Dynamics: Study of fluids in motion with external forces.

Hydrostatic Pressure

  • Hydrostatic pressure is a force exerted by a fluid at rest due to gravity.

  • Demonstrated using a bottle with holes to show that pressure increases with depth.

  • Pascal's Law: Any change in pressure applied to an enclosed fluid is transmitted throughout the fluid, providing efficiency in hydraulic systems.

Static Pressure and Measurement

  • Determining static pressure involves understanding height, density, and gravitational acceleration.

  • Manometer: The device used to measure pressure differences by showing height differences in liquid columns.

Flow Rate and Mass Flux

  • Flow Rate: Mass per time.

  • Mass Flux: Mass flow rate per unit area.

  • Definitions include:

    • Volume Flow Rate: Volume per time.

    • Volume Flux: Volume flow rate per area.

Types of Flow

  • Laminar Flow: Smooth and organized, e.g., fluid flows in straight paths.

  • Turbulent Flow: Chaotic and irregular, with high velocities and disturbances.

  • Importance of Flow Type: Laminar flow is preferred in food industry to minimize damage to products like milk or water.

Shear and Viscosity

  • Shear: Deformation of materials caused by parallel forces.

  • Shear Rate: Change of shear over time.

  • Shear Stress: Force per area.

  • Viscosity defined as the ratio of shear stress to shear rate.

Non-Newtonian Fluids

  • Non-Newtonian fluids exhibit properties where viscosity changes with stress:

    • Bingham Plastics: Behave as solids until a yield stress is reached (e.g., toothpaste).

    • Pseudoplastic: Viscosity decreases with increasing shear rate (e.g., ketchup).

    • Dilatant: Viscosity increases with shear (e.g., cornstarch in water).

    • Thixotropic: Viscosity decreases over time under constant shear.

    • Rheopectic: Viscosity increases over time when subjected to shear.

Reynolds Number

  • Definition: Ratio between inertial force and viscous force, crucial for determining flow type:

    • Laminar: < 2300

    • Turbulent: > 4000

    • Transitional: 2300 - 4000

  • Importance in calculations of flow patterns in various systems.

Bernoulli's Equation and Energy Balance

  • Presents conservation of energy in flowing fluids: potential energy, kinetic energy, and pressure head.

  • Fundamental for solving flow problems by equating energies at different points.

  • Provides a basis for understanding the dynamics at work in fluid systems.

Momentum and Energy Loss in Fluids

  • Analysis of forces involved in liquid flow includes friction and shear stress impacts.

  • Understanding volume flow rates, factors affecting pump efficiency and performance in continuous fluid systems.

  • Emphasis on losses in fluid systems is crucial for effective designs, especially in food processing.

Practical Applications

  • Importance of careful selection of pumps and maintenance of hydraulic systems to avoid issues such as cavitation.

  • Overview of different types of pumps and their efficiency in conveying fluids across systems.

Conclusion

  • Recap of major points and preparation for upcoming tutorial sessions.

  • Importance of understanding these concepts for practical applications and potential exam questions.

  • Encouragement for students to engage in practical exercises and tutorials for enhanced learning experience.