Report on Cavitation
Name: Ahmed AlSAYED Mostafa Alnakeep.
SEC: 1.
1. Introduction:
Cavitation is a condition that can affect any fluid flow system. Despite it being an
ever-present threat, it is not well understood. In the simplest possible terms,
cavitation involves the formation of water vapor bubbles that damage metal
components when they collapse back to the liquid phase.
And it can be defined also as a common yet serious problem in hydraulic machinery,
especially in pumps, turbines, and propellers. It can lead to significant damage,
reduced efficiency, and costly repairs if not properly addressed.
2. Meaning of Cavitation:
Cavitation refers to the formation and collapse of vapor bubbles in a liquid. It
typically occurs when the local pressure in the liquid falls below its vapor pressure,
causing small vapor-filled cavities (bubbles) to form. When these bubbles move into
higher pressure regions, they collapse violently, generating shock waves that can
damage nearby surfaces.
3. How does cavitation damage system components?
One aspect of cavitation that is not widely understood is why these apparently
harmless bubbles are so destructive when they implode. The answer is in the
release of latent heat energy of condensation when the water vapor returns to its
liquid phase. The collapse of the bubble and the energy released creates a small
pressure jet that can strike a nearby solid surface, potentially damaging it. Because
of the large number of bubbles formed in a cavitating system, these bubbles of water
vapor can cause extensive damage to system components over time. Because
cavitation takes place on the entry to a pump, the first system component that the
bubbles encounter is the pump impeller.
4. What causes cavitation in pumps?
• a. Low Pressure Zones.
When the pressure in a liquid drop below its vapor pressure (especially at the
suction side of a pump or near the blades of a turbine), vapor bubbles form.
• b. High Flow Velocity
High velocity of fluid flow can reduce the local pressure due to the Bernoulli
effect, increasing the likelihood of cavitation.
• c. Improper Pump Selection or Operation
Operating a pump outside its recommended range (too high or too low flow
rate) can lead to cavitation.
• d. High Temperature
Higher temperatures reduce the vapor pressure of the liquid, making it easier for
cavitation to occur.
• e. Blocked or Narrowed Suction Line
Restrictions or obstructions in the suction line can cause pressure drop and
cavitation.
5. Effects of Cavitation:
1-Surface pitting and erosion. 2- Vibration and noise. 3-Decreased efficiency.
4-Mechanical failure. 5-Increased maintenance cost.
6.How can I predict if a pump is going to cavitate?
First, by looking at the net positive suction head
required (NPSHr) curve of the pump. This is a
calculation of how much absolute pressure is
needed at the inlet to keep the system from
cavitating.
Second, calculate the NPSH available (NPSHa). This
value represents the absolute pressure available at
the pump inlet. If the NPSHa is 3 feet more than the
NPSHr, the pump will not be cavitated. Be aware,
NPSHr is measured under ideal conditions for
repeatability and accurate benchmarking. Pumps
connected to a short radius elbow on the inlet are
hardly ideal. When this type of poor inlet pipe is in
place, up to 50% may need to be added to the
declared value of NPSHr to be on the safe side.
7. How to Prevent or Face Cavitation:
• a. Maintain Proper Pressure
Ensure the suction pressure stays above the vapor pressure of the liquid.
• b. Design Modifications
Use impellers designed to minimize pressure drop. Streamline suction lines to
avoid turbulence and frictional losses.
• c. Lower the Pump Height
Place the pump as close as possible to the fluid source to reduce suction lift.
• d. Control Fluid Temperature
Keep the temperature of the fluid low to avoid reducing the vapor pressure.
• e. Use Cavitation-Resistant Materials
For critical components, use materials that can withstand cavitation damage, like
stainless steel or hardened alloys.
• f. Regular Maintenance
Inspect and clean suction lines, filters, and valves to ensure smooth fluid flow.
8.References:
• What Is Cavitation? | Pumps & Systems.
• Cavitation.
• 4. Hydraulic Institute. (2020). Pump Standards.
• www.sciencedirect.com - Scientific research articles related to cavitation
• www.metso.com - Cavitation in Pump Systems
