Tuned cylindrical radial mode ultrasonic horns offer advantages over ultrasonic probes in the design of flow-through devices for bacterial inactivation. This study presents a comparison of the effectiveness of a radial horn and probe in the inactivation of E. coli K12. The radial horn is designed using finite element analysis and the predicted modal parameters are validated using experimental modal analysis. A validated finite element model of the probe is also presented. Visual studies of the cavitation fields produced by the radial horn and probe are carried out using luminol and also backlighting to demonstrate the advantages of radial horns in producing a more focused cavitation field with widely dispersed streamers. Microbiological studies show that, for the same power density, better inactivation of E. coli K12 is achieved using the radial horn and, also, the radial horn offers greater achievable power density resulting in further improvements in bacterial inactivation. The radial horn is shown to be more effective than the probe device and offers opportunities to design in-line flow-through devices for processing applications.

Measurements of the reverberation time of a small (29 m3) room have been made using the Schroeder impulse response method while the air in the room was agitated by a 0.65-m-diam, 14-bladed, 2.6-kW fan and compared with similar measurements made with the fan off. The decay times were found to be shorter when the fan was on and this decay time difference is ascribed to an effective extra attenuation α1, due to scattering of the sound field by the fan-generated turbulence. Only order-of-magnitude estimates of α, are possible; α1 ∼ 10−3 m−1 and is frequency-independent from 600 Hz to 5 kHz. The results agree to an order of magnitude with recent turbulence scattering theories. Some of the implications of these measurements for present theories and future experiments are discussed.

Abstract. Applications of power ultrasonics in engineering are growing and now encompass a wide variety of industrial processes and medical procedures. In the field of power ultrasonics, ultrasonic vibrations are used to effect a physical change in a medium. However, the mechanism by which a process can benefit from power ultrasonics is not common for all applications and can include one or more of such diverse mechanisms as acoustic cavitation, heating, microfracture, surface agitation and chemical reactions. This paper presents two applications of power ultrasonics involving some of these different characteristics by concentrating on two case studies involving material failure (ultrasonic cutting) and acoustic cavitation (bacterial inactivation).

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