Acoustic streaming, ultrasonic waves

Methods which have been developed for the monitoring of radiation forces can be very sensitive (up to 1 mW). They are better suited in free-field and noncavitating conditions, but involve errors due to acoustic streaming. The uncertainty for such methods ranges from 2.2% at 1 MHz to 12% at 30 MHz, and accuracy depends on the shape of the ultrasonic wave. Radiation force measurement provides a good method for the calibration of transducers in specifically devised chambers, but its use in chemical reactors of defined geometry could prove to be difficult. 

QCM technique was applied to the solubilization study in CO2. Basics of QCM were reviewed, and applications of QCM to experiments in static and dynamic systems were conducted. Roughness effect should be considered when measuring absolute mass change. Solubilization of Cu(acac>2 in CO2 was measured, and the diflfiisivity was estimated. Ultrasonic waves enhance solubilization mainly due to acoustic streaming. Co ion solubility in a cyanex-C02 solution was obtained by the QCM technique in a dynamic system... 

Ultrasonic wave clearly enhances the solubilization process (Figure 7, 8). Figure 8 also indicates that diffusion-controlled dissolution maintained even under ultrasonic pulses. The diffusivity under ultrasonic pulses was measured to increase about 3-4 times at the given geometry and power used in this experiment. There are two known effects of ultrasonic waves on solubilization i) acoustic streaming, and ii) cavitation/implosion[24,25]. 

QCM technique can supply in-situ kinetics of the reaction inside the cell. Solubilization of Cu(acac)2 L/SC CO2 was diffusion-controlled. Difftisivities of Cu(acac)2 in L/SC CO2 were also obtained. Ultrasonic waves enhance dissolution of Cu(acac)2 in CO2 mainly due to acoustic streaming. Cavitation/implosion in L/SC CO2 does not occur as often as in water. 

Ultrasonic pumps are pumps that use acoustic streaming to create a fluid motion inside microchannels. Acoustic streaming is the time-averaged flow induced hy an ultrasonic wave (periodic pressure oscillation). Attenuation of the acoustic energy (via reflection and other distortion) generates a body force within the fluid and converts acoustic energy into kinetic energy of the fluid [1]. 

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