The sonoluminescence intensity and its spectral distribution, and the sonochemical yields from saturated aqueous solutions of carbon tetrachloride, were measured simultaneously. The variation of these quantities with static pressure was also determined for static pressures ranging from 1 to 20 atm. The sonoluminescence intensity was found to increase linearly with increasing percentage saturation of CC14 in water. The intensity of sonoluminescence was found to depend on the static pressure, while its spectral distribution remained virtually independent of the static pressure. The increased luminescence in the presence of CC1, is shown to be due to chemiluminescence and not due to blackbody radiation. The products of the sonochemical decomposition that were detected were HCl and HOC1. The sonoluminescence intensity was found to be linearly related to the yield of the sonochemical decomposition products over the entire pressure range.
The first-order properties of acoustic waves (i.e., the to and fro particle displacement and velocity) can produce a number of second-order phenomena: cavitation, acoustic streaming, surface instability and radiation pressure. The dependence of cavitation induced phenomena (erosion, luminescense, chemical reactions) on the physical and acoustical parameters of a system are discussed. Some of the past work carried out in this field is analyzed and reinterpreted. In the light of this, it appears that the extent of the solubility of a gas has a pronounced effect on cavitation related phenomena in addition to the effect of other variables such as the ambient liquid temperature, the hydrostatic pressure, the specific heat ratio, the thermal conductivity of dissolved gas and the intensity and frequency of acoustic field. A summary of the application of sonic and ultrasonic energy to industrial processing operations is also provided. This discussion includes how the other second-order effects (e.g., interfacial instability) are related to the enhancement of these operations. The wide variety of processes in which the applications of acoustic energy has a beneficial effect suggests the versatility and broad commercial potential of sonochemical engineering.
The sonoluminescence intensity of nitrogen-saturated water was studied at static pressures ranging fram 1 to 14.6 atm. The total sonoluminescence intensity was found to increase with static pressure up to a maximum at about 6 atm. Further increases in static pressure resulted in a decrease in the sonoluminescence intensity with eventual extinction occurring at 14.6 atm. The effect of static pressure on the spectral distribution of sonoluminescence is reported for the first time. The spectral distribution was found to remain virtually unchanged over the pressure range studied, although the total intensity changed by over 600% over the same pressure range. The increased sonoluminescence is attributed to an increase in the number of cavitation events at higher static pressure rather than an increase in the intensity of the events.
Acoustic irradiation can result in increased inter-phase mass and heat transfer rates. The second-order acoustic effects of cavitation, interfacial instability, radiation pressure and acoustic streaming are responsible for the enhancement in these rate processes. The application of sonic and ultrasonic energy in industrial processing is reviewed. A number of units using acoustic energy to enhance rates of conventional unit processes, for example, drying, solid-liquid extraction, etc, are described. In addition, new applications in waste water treatment and oil-water emulsion fuels are described. The development of newer, more efficient generators should lead to a greater use of acoustic energy for large-scale industrial processing.
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