Hard mineral scale fouling results in significant economic losses both industrially and domestically. Recently, attempts have been made to use ultrasound to mitigate scale formation and its removal based on the phenomena of cavitation. Cavitation erosion is the removal of material from a solid surface by pressure shock waves associated with the formation and collapse of bubbles. This paper reviews the literature on cavitation erosion of brittle crystalline materials in an attempt to better understand the relationship between the material properties of CaCO 3 scale deposits and its potential removal by cavitation. The study finds that from a materials perspective cavitation erosion is intimately associated with both a material's bulk properties and importantly to its microstructure. The situation is further complicated because the macro and micro-properties of CaCO 3 scale are dependent on many factors relating to its depositional environment. The type of scale formed will affect how it is removed by cavitation.
This paper presents a novel non-contact method for simultaneous analysis of pressure and velocity conditions in cavitating flows. The method (implemented in our software ADMflow) is based on high-speed camera flow visualization and was evaluated in an experiment with ultrasonically induced acoustic cavitation of different intensities. Attached cavitation with clearly visible cavitation structures occurred on the tip of an ultrasonic probe immersed in distilled water. Using the high-speed imaging data, pressure fluctuations were calculated by a computer-aided algorithm based on the Brennen's theory of cavitation cloud kinematics and a modified version of the Rayleigh-Plesset equation. Reference measurements of pressure pulsations were conducted by a hydrophone installed at the bottom of the liquid container. The analysis of cavitation structure dynamics was complemented by calculation of velocity fields from the imaging data, the algorithm for which is based on the advection-diffusion equation. Calculated pressure fluctuations were analyzed in the spatial, temporal and spectral domain. Presented results indicate a strong correlation between the fields of velocity and pressure fluctuations during the growth and collapse of cavitation structures. A comparison of time series and power spectra demonstrates that our cavitation analysis method is in a reasonably good agreement with results of the reference measurement methods and can therefore be used for non-contact analysis of pressure and velocity conditions in cavitating flows.
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