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