(word processor parameters LM=1, RM=70, TM=2, BM=2) Taken from KeelyNet BBS (214) 324-3501

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(word processor parameters LM=1, RM=70, TM=2, BM=2) Taken from KeelyNet BBS (214) 324-3501 Sponsored by Vangard Sciences PO BOX 1031 Mesquite, TX 75150 Acoustophoresis - A New Separation Concept ultrasound separates chemical species Langley Research Center, Hampton, Virginia courteously contributed by Mr. Jack Veach A concept under development may expand the technology of chemical separation to includ ultrasonic-radiation pressure. When an ultrasonic wave passes through a medium, it carries energy and momentum; the loss of energy by the wave is accompanied by a transfer of momentum to the substance that carries the energy. For example, since molecular chains have different nonlinear properties and absorb ultrasonic energy through such mechanisms as resonance relaxation, the forces on these chains depend on the frequency of the sound. Therefore, by selecting a specific frequency, one can "tune in" to a selected chemical property - acoustic absorption - and separate chemical species (with different absorption coefficients) that may be impossible to separate by other means. For the separation of particles, the choice of acoustic wavelength will change the acoustic scattering process and thus the force imparted to the suspended particles. As the frequency is varied from low to high, the larger particles (those with higher scattering cross section) will scatter the sound first, followed by the smaller particles. Thus, the larger suspended particles will be swept from the liquid FIRST by the transferred momentum. As shown in the figure, the feed source supplies the liquid medium containing the desired species in mixture with other species. The liquid is fed into the separation container. An ultrasonic transducer connected to an ultrasonic driver sends an ultrasonic wave into the liquid, exerting on the desired species an acoustic-radiation force that DEPENDS ON THE ABSORPTION of the acoustic wave and on nonlinear interactions. Thus, the propagation results in a separation based on the absorption (or scattering) of the acoustic wave. The separated species are removed sequentially by a pump and placed in different compartments (a,b,c,d). If the absorption in the different species is nearly equal, then acoustic streaming may mix the liquid, preventing separation. To minimize that effect by counteracting the streaming, a second transducer is driven by an antistreaming device. In effect, the second acoustic wave can be tuned to a frequency different from that of the first, and to a different amplitude, thereby producing a high-resolution "shearing" of the liquid into its separate species. The acoustophoresis concept can utilize not only bulk compressional waves but also surface waves or boundary waves between a solid (or liquid) container wall and the subject liquid. The free surface of the subject liquid acts as a waveguide that contains the input acoustic energy. This work was done by Joseph S. Heyman of Langley Research Center. This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Langley Research Center. Refer to LAR-13388. Taken from NASA Tech Briefs, January 1990


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