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Cavitation

Cavitation is the formation and implosion of vapor bubbles in a fluid caused by significant pressure gradients within equipment. Pressure gradients are typically generated by high velocity flow around valves, vanes, and protrusions. Vapor bubbles tend to implode asymmetrically towards hard surfaces due to pressure gradients, generating microjets that can have pressures over 145 million psi. Cavitation energy can be dissipated into rigid materials, causing plastic deformation and failure, or into elastic materials through Hook's Law. Belzona 2141 elastomer coating has been shown to better withstand cavitation, allowing coated equipment like impellers and rudders to last significantly longer before repairs are needed.

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Wael Shammout
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125 views14 pages

Cavitation

Cavitation is the formation and implosion of vapor bubbles in a fluid caused by significant pressure gradients within equipment. Pressure gradients are typically generated by high velocity flow around valves, vanes, and protrusions. Vapor bubbles tend to implode asymmetrically towards hard surfaces due to pressure gradients, generating microjets that can have pressures over 145 million psi. Cavitation energy can be dissipated into rigid materials, causing plastic deformation and failure, or into elastic materials through Hook's Law. Belzona 2141 elastomer coating has been shown to better withstand cavitation, allowing coated equipment like impellers and rudders to last significantly longer before repairs are needed.

Uploaded by

Wael Shammout
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPS, PDF, TXT or read online on Scribd
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Cavitation

Demystified

Phase Diagram of Water

STP (Standard
temperature
and pressure)

Cavitation A Simple Process


Cavitation is the formation and subsequent
implosion of vapor bubbles in a fluid
Caused by significant pressure gradients within
process equipment
Pressure gradients typically generated by high
velocity flow around
Valves throttling (partially closed valves)
Vanes moving portions of pump impellers
Protrusions pitot tubes, vortex shedders, etc.

Pressure Gradient Formation

Arrows indicate flow


direction
Fluid is compressed
above vane creating a
high pressure region
Fluid is rarified below
vane creating a low
pressure region
Behind this low pressure
region is another high
pressure region

Impeller Cavitation Regions

Typical Impeller Cavitation Pattern

Cavitation Demonstration

Microjetting
Vapor bubbles do not implode symmetrically
Because of pressure gradients, they tend to
implode towards hard objects

Microjetting High Speed Photograph


Microjet has formed
Vapor bubble is in the
process of imploding
towards the nearby hard
surface
Shockwaves generated by microjetting can be up to
145,000,000 psi
This pressure vastly exceeds the compressive
strength of any metal alloy

The Alternative to Rigid - Elastic


Cavitation energy can be dissipated two ways
Into a rigid metallic substrate
Plastic deformation
Ultimate compressive failure

Into an elastic substrate


Hooks Law

We modified our Durable & Abrasion


Resistant Elastomer to better withstand
cavitation

Belzona 2141 (ACR-Fluid)


Project sprung from a US Coast Guard
request
Products had to survive 16+ hours in a high
speed test
At the time, the best product lasted 12 hours
Second formulation Belzona submitted lasted 20
hours
Coast Guard currently in the process of coating
all rudders with Belzona 2141 (ACR-Fluid) to
resist the severe cavitation of their service

Equipment
Hydro Runner
at a small
Canadian Power
Plant

Problem
Mild cavitation
was decreasing
generating
efficiency

Solution
Runner was coated with Belzona 2141 (ACR-Fluid Elastomer) to
restore and maintain efficiency. After 2 years it is still in perfect
condition.

Equipment
ITT 3480
Impeller

Problem
Severe cavitation
was necessitating
a full rebuild
every 3 months

Solution
Impeller received two coats of Belzona 1321 (Ceramic S-Metal) and
a final coat of Belzona 2141 (ACR-Fluid Elastomer). Impeller now
lasts 28 months between rebuilds!

Questions?

Thank You Very Much

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