This document discusses vapour pressure and cavitation. It defines vapour pressure as the pressure exerted by a vapor in equilibrium with its liquid state. Vapour pressure increases with increasing temperature as more vapor is generated. Cavitation is defined as the formation of vapor bubbles in a liquid when the pressure drops below vapor pressure. There are two types of cavitation: inertial cavitation, where bubbles rapidly collapse producing shock waves; and incipient cavitation, where bubbles begin to form but not yet destructively. Cavitation can cause damage through pitting and erosion on exposed surfaces.

1. Vapour Pressure and Cavitation
G.H Patel College of Engineering and Technology, V. V. Nagar.
Presented By:
150110119124 ( Mitul )
150110119125 ( Deep )
150110119126 ( Sharvil )
150110119127 ( Vishvak )
(2-19)Mechanical Engineering
Academic Year: 2016-17 ( Even sem. )
Class: Second Year Mechanical Engineering
2141906 – FLUID MECHANICS

2. Vapour Pressure
• Vapour Pressure – the pressure exerted by a vapor in equilibrium with its
liquid state.
• Liquid molecules at the surface escape into the gas phase.
• These gas particles create pressure above the liquid in a closed container.

3. H2O(g)
molecules
(water vapor)
H2O(l)
molecules

4. • Vapour Pressure increases with increasing temperature.
• As temperature increases, the amount of vapor generated by a liquid in a
closed container increases.
• This occurs because as the liquid gains kinetic energy, the molecules can
overcome the intermolecular forces of attraction that are prevalent in the
liquid phase.

5. Vapour Pressure Curves
Graph shows how boiling points change with
change in vapor pressure.

6. • Cavitation is defined as the phenomenon of formation of vapor bubbles of a
flowing liquid in a region where the pressure of the liquid falls below its
vapour pressure.
• Cavitation is usually divided into two classes of behavior: inertial (or transient)
cavitation and Incipient cavitation. Inertial cavitation is the process where a
void or bubble in a liquid rapidly collapses, producing a shock wave.
• Incipient cavitation is the point at where cavitation begins, but has not
reached a destructive state
What is Cavitation?

7. Cavitation Phenomena
P1
V1
V2
P2
Pvapour
Vvc
CavitationFlashpoint Pvc
Pressure
Velocity
Local Fluid Pressure Drops Below Fluid
Vapour Pressure
Formation of
Vapour Bubbles
Downstream Pressure
Recovery Above Vapor
Pressure
Bubbles
Collapse

8. Bubble implosion

9. P2
Valve Cavitation Damage
• Pitting and erosion of
exposed surfaces
– Accelerates valve wear
– Increases maintenance and
process down-time
• Larger Scale Cavitation:
potential catastrophic failure
of valve body & pressure
vessel walls

10. • Localized Erosion
• Sounds like rocks
• Will attack any
material
• Worse with high
pressure
Cavitation

11. Thank You