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Cavitation Demystified

Cavitation Demystified. STP (Standard temperature and pressure). Phase Diagram of Water. 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

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Cavitation Demystified

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  1. Cavitation Demystified

  2. STP (Standard temperature and pressure) Phase Diagram of Water

  3. 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.

  4. 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 Pressure Gradient Formation

  5. Impeller Cavitation Regions

  6. Typical Impeller Cavitation Pattern

  7. Cavitation Demonstration

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

  9. 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 Microjetting – High Speed Photograph

  10. 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 • Hook’s Law • We modified our Durable & Abrasion Resistant Elastomer to better withstand cavitation

  11. 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

  12. 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.

  13. 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!

  14. Questions? Thank You Very Much

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