R Nagarajan

Cavitation erosion is predominant in pipelines for liquid transportation, causing damage to pipe wall, impeller and their accessories. The present study is focused on development of cavitation -wear resistant nano-ceramic particle-reinforced polymer matrix material; and on study of its feasibility to be used as lining material in hydraulic transportation. The polymer/nano composite is fabricated using power ultrasound in all three process steps: synthesis of nano-dimensional particles of white fused alumina (WFA) from micron size particles, optimized blending and finally reinforcement into poly methyl methacrylate (PMMA) matrix. The effect of ultrasonic parameters on nanocomposite/ virgin polymers (like polyethylene and polypropylene) is studied by measuring mass loss of the materials and suspension turbidity during exposure time. At low frequency (20-60 kHz), cavitation intensity is predominant; this effect is utilized for fabricating sub-micron particles, and for performing accelerated cavitation erosion tests. At high frequency, acoustic streaming is predominant; this effect is utilized for blending and reinforcing of the nano ceramic particles into polymer matrix. The size and quantity of the particles generated by cavitation erosion was analyzed by Laser Particle Size Analyzer (20 nm-1400 micron range). The nano-composite coupons were analyzed before and after the ultrasonic erosion test using SEM. It is concluded that lowfrequency sonication is a viable option for cavitaton erosion testing of ceramic/polymer composites.

Ultrasonic cleaning, employing frequencies in the range between 40 kHz to 200 kHz, is widely used in many industries requiring precision cleanliness in the micrometer to submicron particle size range-e.g., semiconductor wafer fabrication, hard disk drive manufacturing, integrated circuit assembly, etc. One overriding concern with the use of ultrasonic cleaning for delicate components and assemblies has been the specter of cavitation erosion-surface material loss and other functional degradation due to impact of shock waves generated by collapsing bubbles and bubble-clusters in an oscillating acoustic field. The simultaneous processes of surface cleaning and of surface erosion in the presence of a highfrequency ultrasonic field (>/= 58 kHz) are described here mathematically, and the equations are coupled in such a way as to allow conceptual optimization of parametric settings to maximize the cleaning efficiency, even while minimizing the level of erosion damage. This theoretical analysis is presented for various ultrasonic field conditions (frequency, intensity, etc.), fluid medium properties (viscosity, density) and various surface conditions (hardness, smoothness, etc.). The contribution of "acoustic streaming" to surface cleaning is incorporated in the model, and is shown to have minimal influence on the optimum cluster collapse pressure, but to have a significant effect on the net cleaning efficiency for the surface.

Ultrasonic cleaning, employing frequencies in the range of 40-200 kHz, is widely used in many industries requiring precision cleanliness in the micrometer to submicron particle size range-e.g., semiconductor wafer fabrication, hard disk drive manufacturing, and integrated circuit assembly. One overriding concern with the use of ultrasonic cleaning for delicate components and assemblies has been the specter of cavitation erosion-surface material loss and other functional degradation due to the impact of shock waves generated by collapsing bubbles and bubble clusters in an oscillating acoustic field. The simultaneous processes of surface cleaning and surface erosion in the presence of a high-frequency ultrasonic field (≥ 58 kHz) are described here mathematically, and the equations are coupled to allow conceptual optimization of parametric settings to maximize cleaning efficiency while minimizing the level of erosion damage. This theoretical analysis is presented for various ultrasonic field conditions (frequency, intensity, etc.), fluid medium properties (viscosity, density), and surface conditions (hardness, smoothness, etc.). The contribution of acoustic streaming to surface cleaning is incorporated in the model, and is shown to have minimal influence on the optimum cluster collapse pressure, but to have a significant effect on the net cleaning efficiency for the surface.

Cavitation erosion is predominant in pipelines for liquid transportation, causing damage to pipe wall, impeller and their accessories. The present study is focused on development of cavitation -wear resistant nano-ceramic particle-reinforced polymer matrix material; and on study of its feasibility to be used as lining material in hydraulic transportation. The polymer/nano composite is fabricated using power ultrasound in all three process steps: synthesis of nano-dimensional particles of white fused alumina (WFA) from micron size particles, optimized blending and finally reinforcement into poly methyl methacrylate (PMMA) matrix. The effect of ultrasonic parameters on nano-composite/ virgin polymers (like polyethylene and polypropylene) is studied by measuring mass loss of the materials and suspension turbidity during exposure time. At low frequency (20-60 kHz), cavitation intensity is predominant; this effect is utilized for fabricating sub-micron particles, and for performing accelerated cavitation erosion tests. At high frequency, acoustic streaming is predominant; this effect is utilized for blending and reinforcing of the nano ceramic particles into polymer matrix. The size and quantity of the particles generated by cavitation erosion was analyzed by Laser Particle Size Analyzer (20 nm-1400 micron range). The nano-composite coupons were analyzed before and after the ultrasonic erosion test using SEM. It is concluded that low-frequency sonication is a viable option for cavitaton erosion testing of ceramic/polymer composites.

This paper investigates the accelerated mixing of hot and cold liquid layers in storage tanks of different physical dimensions by the application of high-frequency, high-intensity pulsed ultrasound. In pulsed operation, the ultrasonic field is switched on for a few seconds and then switched off. This cycle is repeated several times. Pulsed mixing of hot and cold water due to ultrasonics was measured in this study. Acoustic streaming and cavitation phenomena associated with the ultrasonic field can induce enhanced mixing in the storage containers leading to de-stratification of liquid. The experimental results indicate that dual frequency operation, which combines one high-frequency mode with one low-frequency mode, is optimal in enhancing mixing compared to other frequencies. Mixing efficiency increases with cavitation intensity and the introduction of acoustic streaming augments it further. The experimental result indicates that as the height of the cylinder increases, the mixing time also increases. The ultrasonic mixing times obtained for different frequencies indicate that as the frequency increases, the time required to reach the steady state temperature also increases, due to decrease in cavitation intensity. © 2008 The Institution of Chemical Engineers.