A mass transfer probe for measurements of cavitation activity in ultrasonic fields

A new type of probe was developed to evaluate the distribution of kinetic, thermal, and acoustic energy in an ultrasonically induced cavitation field. The probe is based on an electrochemical mass transfer technique for direct measurement of the flux of reactants to a surface. Cavitation was generated in a focused ultrasonic field at 1.58 MHz over a large range of focal intensities. Electrochemical measurements of the reduction of ferricyanide to ferrocyanide in a NaOH solution show that the focal area dimensions (as characterized by the cavitation activity) increased almost an order of magnitude in the presence of intense cavitation. The cavitation activity is attributed to fluid motion generated by cavitation-induced jets and microstreaming. A mathematical model is proposed to predict the mass transfer rate at the surface under cavitation conditions and to relate the mass transfer coefficient to the acoustic focal intensity. The concept of the mass transfer probe resulted from the author’s previous work in the study of the electrochemistry of metals in the presence of ultrasound [S. Perusich, Ph.D. thesis, University of Illinois at Urbana, Urbana, IL (1985)].