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 fluidCaused by significant pressure gradients within process equipmentPressure gradients typically generated by high velocity flow aroundValves – throttling (partially closed valves)Vanes – moving portions of pump impellersProtrusions – pitot tubes, vortex shedders, etc.
4 Pressure Gradient Formation Arrows indicate flow directionFluid is compressed above vane creating a high pressure regionFluid is rarified below vane creating a low pressure regionBehind this low pressure region is another high pressure region
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 formedVapor bubble is in theprocess of implodingtowards the nearby hardsurfaceShockwaves generated by microjetting can be up to 145,000,000 psiThis pressure vastly exceeds the compressive strength of any metal alloy
10 The Alternative to Rigid - Elastic Cavitation energy can be dissipated two waysInto a rigid metallic substratePlastic deformationUltimate compressive failureInto an elastic substrateHook’s LawWe 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 testAt the time, the best product lasted 12 hoursSecond formulation Belzona submitted lasted 20 hoursCoast 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 PlantProblemMild cavitation was decreasing generating efficiencyScored shafts are most commonly repaired with Belzona 1111 (Super Metal) which here is applied via a split former technique.SolutionRunner 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 monthsScored shafts are most commonly repaired with Belzona 1111 (Super Metal) which here is applied via a split former technique.SolutionImpeller 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!