This thesis describes an investigation into the effect of fluid and flow parameters on
cavitation dynamics and cavitation erosion. A rotating disc test apparatus was developed
fo: dow-type cavitation studies. A vibratory test device was also developed to study the
role of cathodic and anodic potentials applied to cavitating bodies. Some major results
are given below.
Erosion "peaksat about 50°C in water, but under certain conditions material degradation
caused by increased corrosion rate cancels out thermodynamic effects at higher
temperatures. An erosion peak is also observed as a function of static pressure. Damage
increases with velocity until cavitation is fully developed, at which stage the influence of
velocity becomes negligible. The changes in erosion zone geometry and mass loss caused
by temperature, velocity and pressure variations may be correlated with the effect these
parameters have on the cavitation pressure profile. Efforts are described to develop a
system for measuring this profile in the rotating disc device.
Water quality including dissolved ions, as well as solid and gas impurities, influences both
cavitation inception and the amount of cavitation damage caused. The synergism
between cavitation erosion and corrosion causes high damage rates in corrosive,
cavitating liquids. Solid impurities at medium concentrations may enhance or retard
cavitation damage substantially, depending on the physical properties of the solid. Below
the saturation level, increasing concentration of dissolved air in water results in a slight
decrease in damage, but damage can be almost completely eliminated by the release of
air bubbles into the cavitation region.
Another important result is that the gas developed by the application of external
potentials to a cavitating body provides protection against cavitation erosion through a
gas cushioning mechanism. Cathodic protection of cavitating bodies will thus serve to
decrease damage rates even in the case of corrosion-resistant materials like stainless / GR 2016
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21329 |
| Date | January 2016 |
| Creators | Auret, Johannes Gerhardus |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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