Classifying – separating – and assorting solids – Miscellaneous
Patent
1985-06-20
1988-05-10
Reeves, Robert B.
Classifying, separating, and assorting solids
Miscellaneous
209155, 209158, 210243, 210748, B03B 500
Patent
active
047433612
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the manipulation of particulate matter in a fluid medium by the use of ultrasonic wave energy, and in particular for the separation of particles, including the segregation of dissimilar particles from a mixture of particles in a fluid, whether for example for concentrating particular types of particle or for finely separating or "chromatographing" particulate matter.
The use of standing waves generated by low (sonic) frequency sources in a fluid medium has been proposed for separating particulate matter by precipitation, for example in U.S. Pat. Nos. 2,300,761 and 3,826,740 and WO No. 84/01527. In U.S. Pat. Nos. 4,276,913 and 4,280,823 there is described the use of a transducer emitting an ultrasonic frequency signal of relatively low frequency (150 kHz) to produce a standing wave in a gaseous medium as an aid to the manipulation of particles for gas column chromatography.
In U.S. Pat. No. 4,280,823 the transducer is positioned at one end of a hollow gas-filled tube and is reflected back from the opposite end. Along the same axis the interference between the incident aand reflected waveforms produce a standing wave that is said to function as the plates of a conventional chromatographic column, as is known for molecular separation, by retaining different size molecular particles at the nodes of the wave pattern for different times. In an instrument described in this disclosure, the standing wave pattern is generated in a vertical gas column into which a sample of body fluid components, such as blood cells or bacteria, are injected to be transported by the combined effects of gravity and the carrier gas flow through the column and past a detector for detecting the passage of constituents of the sample which have undergone some degree of separation by the standing wave pattern. The standing wave is produced by tuning the generator driving the transducer to a resonant frequency of the column length so that interference between the emission from the transducer and the reflection from the opposite end of the column produces a stationary pattern of nodes and antinodes.
Such an arrangement is subject to many practical limitations, such as the difficulty of injecting a particulate sample into a gas stream, the difficulty of controlling the separation rate in the carrier gas flow while maintaining the particles suspended therein, and the practical impossibility of achieving a measurable separation between sample components that act very similarly to external forces, such as gravity, upon them.
U.S. Pat. No. 4,280,823 suggests that the wave frequency can be changed to control the resolution of the column, (i.e. altering the distance between nodes or "plates") and if the wavelength is small in relation to the column length there would be a number of discrete resonant frequencies. It is also suggested that a non-resonant mode can be employed, although with a loss of efficiency, but unless there is resonance the transducer emission will then be unable to produce a standing wave pattern. Control of the separation of the constituents of a samaple is thus limited in practice to varying the introduce undesirable secondary effects. Any control of selectivity by change of frequency must be limited to a relatively small number of discrete steps if the standing wave pattern is to be maintained.
In U.S. patent application No. 29,112 of 1982 by Barmatz et al (NASA NPO 15559-1) there is described an apparatus for the separation of particles of different types as they pass along the length of a horizontal chamber. An acoustic transducer at one end of the chamber operates at a resonant frequency of the chamber to generate a standing wave with a wavelength that is half the height of the chamber. This results in a so-called force potential well in the mid-height region of the chamber, in which the particles will tend to concentrate. The particles are also subjected to an external force, in particular gravity, acting transversely to the flow and there is some separation within the well depending upon t
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Hajec Donald T.
Internationale Octrooi Maatschappij "Octropa" BV
Reeves Robert B.
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