Acoustic Mixing

FIGURE 3.45 Experimental results of a mixer constructed with one pair of side channels. The pressure perturbations created from the side channels induce lobe-like distortions of the interface and facilitate rapid mixing [481]. Reprinted with permission from the Institute of Physics Publishing. 

FIGURE 3.46 Schematic drawing of the cross section of a mixer. A glass plate was etched with channels. It was anodically bonded with a Si wafer consisting of the oscillating diaphragm to which a PZT disk was adhered [327]. Reprinted with permission from Wiley- 

In another report, an ultrasonic mixer was constructed on a PDMS-quartz chip using a ZnO film. The ZnO film (8 pm) was deposited on the quartz plate with a patterned Au electrode (300 nm) for excitation. Operation frequency was 450 MHz. No heating or bubble formation were observed with a power level of 15 dBm (or 30 mW at 1.2 VJ [489]. 

It should be noted that at some resonance frequencies (or its harmonics), a standing wave will be established in the chamber when the two chamber walls are vertical and parallel to each other. This results in stagnant zones at the nodes of the standing wave, in which no mixing occurs [84]. 

FIGURE 3.47 The ultrasonic mixing process, (a) Videocamera scene at standby state. Ethanol and water were in laminar flow. Limited diffusion occurred at the interface of the ethanol and water flows, (b) Ultrasonic vibration ON. The laminar flow changed and turbulence occurred, (c) After 2 s of ultrasonic vibration, ethanol was mixed well with water, (d) Ultrasonic vibration OFF. The laminar flow resumed [327]. Reprinted with permission from Wiley-VCH Verlag. 

---

Figure 1.30 Dye penetration results for acoustic mixing by (a) one hole, one bubble, (b) four holes, four bubbles, and (c) five holes five bubbles. Also shown is the flow-field geometry given by the velocity vectors at the inflow and outflow portions of the wall oscillation cycle [23] (by courtesy of RSQ.

M 12] [P 11] To analyze the effect of the number of holes and their positions on the acoustic mixing, three artificial mixing micro chambers were proposed, the first with one bubble pocket in the center (a), the second with four bubble pockets at the corners and the third with five air pockets with four at the comers and one in the center [23]. It was found that acoustic mixing depends largely on the number of holes and their positions (see Figure 1.30). 

Other micromixers based on various principles have also been constructed. These principles include vortex [492], eddy diffusion [493-501,654,955], rotary stirring [502], turbulence [495,503], EK instability [504—506], chaotic advection [248,507-513], magnetic stirring [514], bubble-induced acoustic mixing [515], and piezoelectric actuation [516,517]. 

It was also found that the hybridization kinetics were found to be faster in a moving sample, as compared to a stationary sample [939]. In another report, active acoustic mixing was used to achieve a five-fold faster DNA hybridization rate. Hybridization was detected electrochemically (by AC voltammetry) based on the ferrocene redox chemistry [62],... 

Ende DJA, Anderson SR, Salan JS (2014) Development and scale-up of cocrystals using resonant acoustic mixing. Org Process Res Dev 18 331-341... 

Siitharan K et al (2006) Acoustic mixing at low Reynold s numbers. Appl Phys Lett 88 054102... 

The proof of concept for acoustic mixing was reported by Moroney et al. [122] with a flexible-plate-wave (FPW) device. An analysis of the focused acoustic wave model in a... 

Reproduced from Catarino, S.O. et al., 2014. Piezoelectric actuators for acoustic mixing in microfluidic devices—numerical prediction and experimental validation of heat and mass transport. Sens. Actuators B 205, 206-214. Available at http //www.sciencedirect.com/ science/article/pii/S0925400514009988 (accessed 02.09.14.) with permission from -Elsevier. 

The phenomenon of acoustic cavitation results in an enormous concentration of energy. If one considers the energy density in an acoustic field that produces cavitation and that in the coUapsed cavitation bubble, there is an amplification factor of over eleven orders of magnitude. The enormous local temperatures and pressures so created result in phenomena such as sonochemistry and sonoluminescence and provide a unique means for fundamental studies of chemistry and physics under extreme conditions. A diverse set of apphcations of ultrasound to enhancing chemical reactivity has been explored, with important apphcations in mixed-phase synthesis, materials chemistry, and biomedical uses. 

Lead zirconate [12060-01 -4] PbZrO, mol wt 346.41, has two colorless crystal stmctures a cubic perovskite form above 230°C (Curie point) and a pseudotetragonal or orthorhombic form below 230°C. It is insoluble in water and aqueous alkaUes, but soluble in strong mineral acids. Lead zirconate is usually prepared by heating together the oxides of lead and zirconium in the proper proportion. It readily forms soHd solutions with other compounds with the ABO stmcture, such as barium zirconate or lead titanate. Mixed lead titanate-zirconates have particularly high piezoelectric properties. They are used in high power acoustic-radiating transducers, hydrophones, and specialty instmments (146). 

Air handling unit A self-contained unit for the introduction or removal of air from a space. It consists of one or more of the following plant items heating or cooling coils, filters, fans, damper provision for mixing and recirculation, humidification controls, and acoustic treatment. 

Cavitations generate several effects. On one hand, both stable and transient cavitations generate turbulence and liquid circulation - acoustic streaming - in the proximity of the microbubble. This phenomenon enhances mass and heat transfer and improves (micro)mixing as well. In membrane systems, increase of fiux through the membrane and reduction of fouling has been observed [56]. 

The adjacent building is on the site of the main telephone central for downtown Victoria. Slab cores showed very poorly mixed concrete from 1917 construction. It will be taken down to two floors and a 8-storey atrium will take its place. Acoustics are a concern. The Telus Building will be opened up to this atrium changing dramatically the present closed in feeling. 

Mass Transport. Cavitation improves mixing but, on a macroscopic scale, it is probably less effective than a high speed stirrer. On a microscopic scale, however, mass transport is improved at solid surfaces in motion as a result of sound energy absorption. This effect is called acoustic streaming and contributes to increasing reaction rates. 

Apart from inversions, there is another way to determine whether or not there is mixing in the Sun. Any spherically symmetric, localized sharp feature or discontinuity in the Sun s internal structure leaves a definite signature on the solar p-mode frequencies. Gough (1990) showed that changes of this type contribute a characteristic oscillatory component to the frequencies z/ / of those modes which penetrate below the localized perturbation. The amplitude of the oscillations increases with increasing severity of the discontinuity, and the wavelength of the oscillation is essentially the acoustic depth of the sharp-feature. Solar modes... 

Fig. 3. The amplitude of the CZ-base signal plotted as a function of the acoustic depth for solar data and several solar models. Note that only models which incorporate mixing have amplitudes similar to that of the Sun.

---