Liquid purification or separation – Processes – Utilizing electrical or wave energy directly applied to...
Patent
1989-08-02
1991-04-09
Jones, W. Gary
Liquid purification or separation
Processes
Utilizing electrical or wave energy directly applied to...
210542, 209 1, 209155, 73505, B01D 4300
Patent
active
050062662
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the use of ultrasonic wave energy for the manipulation of particulate material in a liquid medium.
The particulate material is influenced by the acoustic forces in an ultrasonic standing wave which attracts the individual particles to the nodes or the antinodes (for the purposes of the present invention it is immaterial which and to simplify the following description only the nodes will be referred to and it is to be understood that the mechanisms are identical for such particles as are attracted by the antinodes)
In our European patent application 147032 (84.307496.4) there is described how two axially opposed ultrasonic transducers can establish a standing wave to control the movement of particles in a coaxial column of liquid interposed between the transducers, and how, by displacing the standing wave, it is possible to move particles under the influence of the standing wave along the column in the axial direction of the standing wave.
The working length of the standing wave occupies only a part of the axial spacing between the transducers because although the transducers may be matched to give corresponding power outputs, attenuation of the ultrasonic energy as it travels along the column causes an increasing imbalance between the two outputs at different points along the column as the distance from the midpoint between the two transducers increases Attenuation is experienced as an acoustic energy gradient in the direction of propagation of the standing wave and these gradients generate unwanted acoustic streaming in the liquid along the column in a direction parallel to that in which the particles are being displaced Because the rate of attenuation increases with the frequency of the transducer output, this effect is more pronounced at higher ultrasonic frequencies and the effective working length of the standing wave can be reduced to only a very small part of the distance between the transducers The use of high frequency ultrasonic sources, e.g. 100 kHz upwards, also means that air must be totally excluded from the system because ultrasound is rapidly attenuated in air at such frequencies making it effectively a non-conductor There must be no air gaps, therefore, between the transducers and the column, nor can bubbles be allowed to exist in the liquid.
Obviously, problems arise if these conditions cannot conveniently be fulfilled. As an example, if it is required to employ a high frequency ultrasonic system for separation and/or analysis of particulate material in a column of liquid, so as to subject the column to a standing wave along the whole length, a method of operation may be required that allows this to be done even when the liquid column terminates at a liquid-gas interface.
According to one aspect of the present invention, there is provided apparatus for controlling the movement of particulate material in a liquid column comprising ultrasonic generating means for producing at least two standing waves that have axes extending transversely across the column at different orientations to the longitudinal axis of the column, the standing waves intersecting within the column, and means being provided for relative movement along the column between the intersections of the nodes of the standing waves and the particle-containing liquid in the column.
The invention also provides a method of controlling the movement of particulate material in a liquid column wherein at least two ultrasonic standing waves are established with axes extending transversely across the column at different orientations to the longitudinal axis of the column and intersecting within the column to retain particulate material at the intersections of the standing waves, and by relative movement along the column between the column and said intersections, the material retained at said intersections is displaced in the liquid medium.
Because of the different orientations of the standing waves produced by the ultrasonic generating means in an arrangement according to the invention, the standing waves interac
REFERENCES:
patent: 4759775 (1988-07-01), Peterson et al.
patent: 4877516 (1989-10-01), Schram
IBM Technical Disclosure Bulletin, vol. 25, No. 1, Jun. 1982 (New York, US), H. W. Curtis et al., pp. 192-193, see the whole document.
WO, A, 85/01892 (UNILEVER), 9 May 1985 see abstract, p. 3, line 23, p. 4, line 26, claims 1, 2, 10.
WO, A, 87/07178 (UNILEVER), 3 Dec. 1987 see abstract, p. 12, line 2, p. 16, line 12, Figures 3-8.
Jones W. Gary
National Research Development Corporation
Savage Matthew O.
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