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Cavitation Demystified

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Presentation on theme: "Cavitation Demystified"— Presentation transcript:

1 Cavitation Demystified
This is a nice short and hopefully informative presentation on cavitation. I put this together because so many customers I visit mistake

2 Phase Diagram of Water STP (Standard temperature and pressure)
I’m quite sure everyone in the room is familiar with the three phases of water; solid, liquid, and gas. For this example we’ll be starting at STP (standard temperature and pressure). Water is most commonly boiled by heating it at constant pressure [click]. What is less intuitive is that water can also be boiled by dropping the pressure at a constant temperature [click]. Indeed, any change or changes in temperature or pressure that move across the normal boiling curve result in a transition from liquid to gas [click].

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 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

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 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

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 Problem Solution
Hydro Runner at a small Canadian Power Plant Problem Mild cavitation was decreasing generating efficiency Scored shafts are most commonly repaired with Belzona 1111 (Super Metal) which here is applied via a split former technique. 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 Problem Solution ITT 3480 Impeller
Severe cavitation was necessitating a full rebuild every 3 months Scored shafts are most commonly repaired with Belzona 1111 (Super Metal) which here is applied via a split former technique. 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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