The separation of micron-sized bacterial spores (Bacillus cereus) from a steady flow of water through the use of ultrasonic standing waves is demonstrated. An ultrasonic resonator with cross-section of 0.0254 m x 0.0254 m has been designed with a flow inlet and outlet for a water stream that ensures laminar flow conditions into and out of the resonator section of the flow tube. A 0.01905-m diameter PZT-4, nominal 2-MHz transducer is used to generate ultrasonic standing waves in the resonator. The acoustic resonator is 0.0356 m from transducer face to the opposite reflector wall with the acoustic field in a direction orthogonal to the water flow direction. At fixed frequency excitation, spores are concentrated at the stable locations of the acoustic radiation force and trapped in the resonator region. The effect of the transducer voltage and frequency on the efficiency of spore capture in the resonator has been investigated. Successful separation of B. cereus spores from water with typical volume flow rates of 40-250 ml/min has been achieved with 15% efficiency in a single pass at 40 ml/min.
A novel emulsion splitting separation technology has been developed using acoustic radiation forces to recover the dispersed oil phase from an oil water emulsion. Current separation technologies suffer from high energy costs, use of consumables, fouling, and limited efficiency in separation of micron-sized particles. Multi-dimensional ultrasonic standing waves are used to trap a dispersed phase in a fluid. The action of the acoustic forces results in clustering and coalescence of droplets. Upon reaching a critical size, they are continuously separated through enhanced buoyancy. A second mode of operation uses acoustic radiation forces to increase the average droplet size and reduce the sub-20 micron droplet concentration. Earlier work was presented at ICA 2013(Dionne [1]). New results are shown for prototypes with a 1x2, 3x4 and 6x6 inch flow chamber driven by 2 & 3 MHz PZT transducers operating at flowrates of 1L/h, 30L/h, and 227-1136 L/h, tested with produced water samples from four US locations. Measured separation efficiencies of over 90% have been documented as well as particle size shifts of >100 micron. The particle size shift is particularly appealing as it acts as a complimentary technology to existing oil & gas separation technology. [1] J. Dionne, B. McCarthy, B. Ross-Johnsrud, L. Masi, and B. Lipkens, “Large volume flow rate acoustophoretic phase separator for oil water emulsion splitting,” J. Acoust. Soc. Am., Vol. 133, No. 5, Pt. 2, May 2013, pp. 3237. [Work supported by NSF SBIR IIP- 1330287.]
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