RESUMO
Bubble dynamics in water close to the tip of an ultrasonic horn (â¼23 kHz, 3 mm diameter) have been studied using electrochemistry, luminescence, acoustics, light scattering, and high-speed imaging. It is found that, under the conditions employed, a large bubble cluster (â¼1.5 mm radius) exists at the tip of the horn. This cluster collapses periodically every three to four cycles of the fundamental frequency of the horn. Following the collapse of the cluster, a short-lived cloud of small bubbles (each tens of microns in diameter) was observed in the solution. Large amplitude pressure emissions are also recorded, which correlate temporally with the cluster collapse. Bursts of surface erosion (measured in real time using an electrochemical technique) and multibubble sonoluminescence emission both also occur at a subharmonic of the fundamental frequency of the horn and are temporally correlated with the bubble cluster collapse and the associated pressure wave emission.
Assuntos
Ultrassom/instrumentação , Técnicas Eletroquímicas , Desenho de Equipamento , Gases , Luz , Medições Luminescentes , Movimento (Física) , Tamanho da Partícula , Fotografação , Pressão , Espalhamento de Radiação , Processamento de Sinais Assistido por Computador , Sonicação , Propriedades de Superfície , Fatores de Tempo , ÁguaRESUMO
This paper reports on noninertial cavitation that occurs beyond the zone close to the horn tip to which the inertial cavitation is confined. The noninertial cavitation is characterized by collating the data from a range of measurements of bubbles trapped on a solid surface in this noninertial zone. Specifically, the electrochemical measurement of mass transfer to an electrode is compared with high-speed video of the bubble oscillation. This gas bubble is shown to be a "noninertial" event by electrochemical surface erosion measurements and "ring-down" experiments showing the activity and motion of the bubble as the sound excitation was terminated. These measurements enable characterization of the complex environment produced below an operating ultrasonic horn outside of the region where inertial collapse can be detected. The extent to which solid boundaries in the liquid cause the frequencies and shapes of oscillatory modes on the bubble wall to differ from their free field values is discussed.
Assuntos
Transdutores de Pressão , Ultrassom/instrumentação , Técnicas Eletroquímicas , Desenho de Equipamento , Gases , Modelos Teóricos , Movimento (Física) , Oscilometria , Pressão , Sonicação , Tensão Superficial , Fatores de Tempo , Gravação em Vídeo , ViscosidadeRESUMO
An electrochemical technique that can detect inertial cavitation within an ultrasonic reactor is reported. The technique relies on the erosion and repassivation of an oxide covered electrode (specifically aluminum). The sensitivity of the technique (<46 fg per erosion event) is significantly greater than normal weight loss measurements. A novel opto-isolation system is discussed which enables the electrochemical measurements to be undertaken within an earthed metallic container. Events detected in this manner are reported and compared to the noise in the absence of appropriate isolation. This system is combined with a multichannel analyzer to map the erosion/corrosion activity within an operating ultrasonic bath.