Fluids in motion

Introduction to Fluids

• Definition of Fluids: Liquids or gases that flow.

• Importance of Fluids:

  • Commonly encountered in various industries and everyday life.

  • Examples include fluids in pipes, chemical plants, engines, and space shuttles.

Key Concepts in Fluid Mechanics

• Mass Flow Rate:

  • Definition: The mass of a fluid passing a point per unit time (e.g., kilograms per second).

  • Conservation: Mass flow rate must remain constant in a closed system; fluid is not gained or lost.

• Volume Flow Rate:

  • Another important concept related to how fluids flow through pipes.

Behavior of Incompressible Fluids

• Properties of Water:

  • Water is recognized as virtually incompressible; particles cannot be squashed closer together.

  • Effect of Pipe Diameter:

    • Decrease in pipe diameter results in increased velocity of the fluid to maintain mass flow rate.

• Example with a Nozzle:

  • Observations: Water exiting a nozzle flows at higher speeds due to narrow diameter.

  • Bernoulli's Principle: Explains how flow rate is affected by pipe cross-sectional area.

Bernoulli's Principle

• Basic Explanation:

  • In a pipe, where fluid travels on the same streamline, a relationship exists:

    • High pressure = Slow flow

    • Low pressure = Fast flow

• Applications:

  • Real-life implications (e.g., car traffic flow analogy).

  • Memory Aid: "Big area, high pressure, slow; small area, low pressure, fast."

• Head:

  • Definition: Additional pressure caused by the height (elevation) difference in a fluid column.

  • Higher elevation correlates with lower pressure in a fluid system.

Pressure Demonstration and Applications

• Can Demonstration:

  • Water flows out of holes at different heights in a can:

    • Top holes: Slow water flow due to low pressure.

    • Bottom holes: Fast water flow due to high pressure.

  • Illustrates the importance of height in determining fluid pressure.

• Dams:

  • Structural considerations: Concrete in dams must be thicker at the bottom to withstand higher water pressure.

Aerofoil and Lift

• Definition of Aerofoil:

  • Example: The wing of an airplane.

• Functionality in Fluid Dynamics:

  • Wing shape designed to create differing air travel speeds:

    • Air over the wing travels faster (lower pressure).

    • Air under the wing travels slower (higher pressure).

  • Result: Pressure difference creates lift, allowing the airplane to fly.