Summary of "Fluid Mechanics | Module 1 | Thermodynamic Properties of Fluids (Lecture 8)"
Summary of "Fluid Mechanics | Module 1 | Thermodynamic Properties of Fluids (Lecture 8)"
This lecture, taught by Pal Sharma from Get Academy Plus, focuses on the Thermodynamic Properties of Fluids, specifically covering Compressibility, Vapor Pressure, and Cavitation. The content includes definitions, explanations, mathematical formulations, and practical implications related to these properties.
Main Ideas and Concepts
1. Compressibility of Fluids
- Definition: Compressibility is the ability of a fluid to decrease in volume under applied pressure.
- Volumetric Strain: Change in volume relative to original volume when pressure is applied.
- Mathematical Expression:
- Compressibility (β) is defined as the fractional change in volume per unit increase in pressure.
- Formula:
β = - (1/V) (dV/dP) - Alternatively expressed in terms of density (ρ):
β = (1/ρ) (dρ/dP)
- Compressible vs Incompressible Fluids:
- Compressible fluids have density that varies with pressure.
- Incompressible fluids have constant density regardless of pressure changes.
- Bulk Modulus (R):
- The reciprocal of Compressibility.
- Expressed as:
R = 1/β
- Isothermal Compressibility:
- Compressibility measured under constant temperature.
- For ideal gases, it can be related to pressure and temperature via the ideal gas law.
- Adiabatic (Isentropic) Compressibility:
- Compressibility under no heat transfer conditions.
- Expressed with the adiabatic index (γ), which relates pressure and density changes.
- Practical Example: Calculating bulk modulus and Compressibility from changes in pressure and volume.
2. Vapor Pressure and Evaporation
- Vapor Pressure: Pressure exerted by vapor in equilibrium with its liquid at a given temperature. It arises because molecules evaporate from the liquid surface and exert pressure.
- Evaporation: Process where molecules escape from the liquid surface into vapor phase at any temperature. Occurs due to molecules gaining enough energy to overcome intermolecular forces.
- Saturation Vapor Pressure: The Vapor Pressure at which the rate of evaporation equals the rate of condensation. At this point, vapor and liquid are in dynamic equilibrium.
- Boiling Point: Temperature at which Vapor Pressure equals the external atmospheric pressure. Boiling involves vaporization throughout the liquid, not just at the surface.
- Difference Between Evaporation, Vaporization, and Boiling:
- Evaporation: Surface phenomenon, can occur at any temperature.
- Vaporization: General term for phase change from liquid to vapor.
- Boiling: Vaporization occurring throughout the liquid when Vapor Pressure equals atmospheric pressure.
3. Cavitation
- Definition: Formation of vapor bubbles in a liquid when local pressure falls below the Vapor Pressure.
- Cause: Occurs in pumps, turbines, and propellers where fluid velocity is high, causing pressure drops.
- Effects:
- Vapor bubbles collapse violently when they move to higher pressure zones.
- This collapse causes intense localized pressure and erosion of metal surfaces (impeller plates, pump components).
- Net Positive Suction Head (NPSH): A measure to prevent Cavitation by maintaining pressure above Vapor Pressure. Ensures that pressure in the pump does not drop below Vapor Pressure.
- Practical Importance: Cavitation leads to damage and failure in hydraulic machinery. Understanding and controlling Cavitation is critical in fluid machinery design.
Methodologies / Formulas Presented
- Compressibility (β):
β = - (1/V) (dV/dP)In terms of density:β = (1/ρ) (dρ/dP) - Bulk Modulus (R):
R = 1/β - Isothermal Compressibility for Ideal Gas:
Using ideal gas law \( PV = RT \),
β = 1/P - Adiabatic Compressibility:
β = 1/(γ P)Where γ = ratio of specific heats (Cp/Cv). - Vapor Pressure Measurement:
Category
Educational
