(word processor parameters LM=1, RM=70, TM=2, BM=2) Taken from KeelyNet BBS (214) 324-3501
(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
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
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
E-Mail Fredric L. Rice / The Skeptic Tank