GB2308182A

GB2308182A - Treating a flowing medium with ultrasonic waves

Info

Publication number: GB2308182A
Application number: GB9622170A
Authority: GB
Inventors: Andreas Mues; Michael Ubrich
Original assignee: AlliedSignal Elac Nautik GmbH
Current assignee: Wartsila Elac Nautik GmbH
Priority date: 1995-11-07
Filing date: 1996-10-24
Publication date: 1997-06-18
Anticipated expiration: 2016-10-24
Also published as: DE19541417A1; DE19541417C2; GB2308182B; GB9622170D0

Description

0 AlliedSignal ELAC Nautik GmbH D-24118 Kiel Apparatus for Treating

Flowing Fluids with Ultrasonic Waves 2308182 it is known to treat flowing fluids such as drinking water with ultrasonic waves, in order to possibly together with other measures - inactivate micro-organism. German patent 591 948 descriffies a method for sterilizing liquids by ultrasonic waves. Search results in connection Vaith,.The influence of ultrasonic waves onto micro-organism" were published by L.Gruen and J.Stelter io in the.Zeltschrift fuer Flygiene", vol. 141, 1995. More recent developments for the application of this technique is shown in German patent application 43 23 212, which discloses an apparatus for generating standing ultrasonic waves in a medium, wherein sound reflectors provided with flowthrough openings are located in the flow path of the medium.

The frequencies used for inactivating micro-organism are mostly in the range between 6kHz and 5MHz. Accordingly, wave lengths between 30cm and 0,3mm are in use. For the most frequently used frequencies In the order of 40kHz the wave length of the sound waves in water is 3,75cm. These wave lengths are in the order of the dimensions of the irradiation equipment; i.e. the flow cross section, the dimensions of the transducer etc. are in the order of a few wave lengths. The sound field therefore is subject to strong interferences and is by no means homogeneous. The sound 20 field I's essentially determined by the superpositioning of the radiation characteristic of the ultrasonic wave transducer und the spatial response of the reaction space. In general, inactive zones are present in closed reaction spaces, because the shape of the sound field results from the superpositionof the radiation characteristic xvith the natural modes of the irradiated space. Normally, a uniform treatment of the medium is not guaranteed, because there is no uniform 25 distribution of sound waves.

In many cases it proved advantageous to use standing waves for amplifq'ng cavitation effects. In standing waves, cavitation bubbles which are smaller than the resonance bubble size, are driven into the pressure maximum areas or are maintained there, respectively. The bubbles oscillate stably over long periods of time, so that a tight bubble curtain is formed in the area of the pressure maxima.

in the edge areas of the treatment zone, in particular if an air filled spase is adjacent, and in the sound pressure nodes within the treatmant space, a sound pressure minimum is present, so that flow portions flowing there are not, or are at least are not sufficiently, irradiated. If the medium flows parallel to the sound radiation surface of the transducers some partial flows may pass through the treatment zone without being treated, in particular if reflectors are arranged opposite the transducers in a parallel fashion.

The invention as characterized in claim 1 removes this problem by forcing the flow within the trearment zone to flow along a helical path, so that all flow portions at least along a portion of the flow path within the reaction zone are exposed to an intensive sound field. If the flow channel has io a large cross section it is recommended to form a plurality of helical streams flowing parallel to each other.

As a flow guiding means for generating a rotation of the flow about an axis in flow direction skewed lamina, flow guiding sheet metal arrays, or guide blades are particularly useful. The 1. ndividual blades may be plane or curved in flow direction. The arrangemant of the transducers and the geometric shape of the reaction space are preferably choosen such that the core of the stream or of a partial stream, respectively lies within a zone having a homogeneous distribtion of the sound pressure. The acceleration of the medium before entering the guiding device as required for the operation of the flow guiding means may be generated in a simple manner by a restriction of the flow cross section either upstream of the guiding means or combined with said guiding device.

Also, the individual flow openings in the guiding means may have a cross section which is tapered in flow direction. Further advantageous embodiments can be seen from the dependent claims.

The invention will now be described with reference to embodiments schematically shown in the drawings. Therein:

Fig. 1 shows the sound field of a chamber through which the medium flows in a direction perpendicular with respect to the plane of the drawing, when four helical partial streams are formed; Fig.2 shows a sound field within a tube through which four partial streams flow in a direction perpendicular with respect to the plane of the drawing., Fig." shows a closed reaction chamber having at ist outlet a p id with parallel flow 1 J 1 _-T 1 1 openings for smoothening the flow after treatment, which grid simultaneously acts as a sound reflector, Flig.4 is a flow guiding device consisting of four quadrants for generating four essentially parallel partial streams.

In Fig. 1 a channel K can be seen, which e.g. is open at ist top side and through which the medium flows in a direction perpendicular with respect to the plane of the drawing. Ultrasonic transduceres.

not shown, irradiate the channel from one side. Because of the geometric characteristics of the channel and the properties of the flowing medium, e.g.water, different sound pressures are s generated across the cross section of the channel. The diffemt zones A, B, and C are shown at the right side of Fig. 1 by different hatching.

In a zone A adjacent to the water surface pressure maxima can be formed which are offset with respect to each other. This zone is dominated by the radiation pattern of the transducer. No determined field of standing waves is accomplished.

Zone B below, however, shows fields of standing waves which extent parallel to the wall of the channel or vessel K. In this zone the spatial response dominates the sound field. The transit between zones A and B is gradual. Under particular structural circumstances zone A may be missing.

Within the area of the pressure maxima in zones A and B an intensive treatment of the medium is achieved. In the case of drinking water or water for industrial use, micro-organism are inactivated or desintegrated by cavitation as a result of the large pressure differences. In other liquids chemical or physical reactions may be enhanced by the sound field.

Finally, there is a boundary zone C close to the channel walls where standing waves exist which are parallel to the wall of the vessel. This in particular happens, when the wall of the vessel is thin in relation to the sound wave length and a gaseous medium is behind the wall of the vessel, as this is regularly the case in reaction vessels made of steel, or at the water surface. The sound pressure minima in this zone may result in portions of the medium being not sufficiently irradiated with sound waves.

In the case of a faminar stream the stream portion flowing through a nonirradiated zone would remain almost untreated. This can be avoided, if according to the invention the flow is forced to rotate about an axis which extends along the flow direction. By flow guiding mean which are to be described later, the stream is guided into a helical path or, as shown in Fig. 1, is divided into four helical flow paths filling the four quadrants of the channel cross section. The length of the radiating surface of the transducer in flow direction and the steepness of the flow helix are adjusted such that the length of the transducer extends at least over one pitch of the helix. Now, all stream portions at least for part of the time flow through areas with sound pressure maxima of the standing waves and are exposed there to an intensive treatment by the sound field. The effect is still increased when, as shown by arrows P in Fig. 1, adjacent partial streams are rotated in opposite directions.

In Fig.2 the medium flows through a tube R with an axially extending transducer W provided in the centre of said tube and radiating sound waves omnidirectionally. Also in this case the total flow is divided by means of appropriate flow guiding means into four partial streams each of which rotates helically about an axis extending parallel to the flow direction. Therewith an effective irradiation of all flow portions is achieved. The direction of rotation of adjacent partial streams or helices again is opposite. Said division could be made in less or more than four partial streams. In particular, in the case of a non-circular cross section of the channel or tube said division may be omitted. Important is the helical rotation of the stream or of the partial streams, respectively.

A perspective view onto a closed reaction chamber is schematically shown in Fig.3, wherein the left side wall seen in flow direction SR and the cover are removed from the reaction chamber RK. At the inlet of the chamber there is provided the flow guiding device LV, which in this case is divided into eight columns SP and four lines ZL. This results in 32 individual arrays of the guiding means. which guide the respective partial streams such that adjacent partial streams have an opposite rotational direction of the flow helix. The flow acceleration in the area of the guiding means, caused by the guiding means or by a reduced total cross section upstream of the guiding means, together with the guiding blades or metal sheets which are inclined with respect to the flow direction, provide the desired rotation of the partial streams about their flow axis. At the bottom of the chamber RK three ultrasonic transducers UW are arranged in two rows side by side and radiate upwards. The cover (not shown) of the chamber simultaneously acts as a sound reflector. At the outlet of the chamber a sieve or punched grid LG is provided for smoothening the flow. This punched grid simultaneously serves as a sound reflector through which the medium flows. The same is true for said guiding means LY If the guiding device is supplied with water from a basin without a predetermined flow direction, vortecis and tubulences can be kept apart from the guiding means LV by a sieve or grid located upstream. The transducers UW are energized with current via accordingly isolated supply wires AL.

There are numerous well-known possibilities for the structural design of the flow guiding device or of the individual guiding arrays, respectively. For the supply of water turbines e.g. guiding rims or guiding wheels are known which provide the flow with a twist. For increasing the flow rate within the guiding means and therewith for generating the required acceleration of the stream, the openings between the metal sheets or blades may have a cross section taperimg in flow direction. In many cases the reduction of the actual cross section caused by the guiding blades and their supporting means may be suffient. For channels or chambers of rectangular cross section, arrays consisting of several parallel guiding blades or bars may be used and arranged like a Jalousie in the flow path. If required, the inclination of the guiding blades can be adapted to the actual flow velocity of the medium, if that changes during operation, e.g. at the outlet of a storage basin or another storage vessel or at the controlled supply inlet to collector vessels. The individual guiding blades may be plane or curved. For plane guiding blades the angle of incidence shoud be larger than 0.

s Fig.4 shows as one of numerous possibilities an array of a flow guiding device, which array is divided into four groups of guiding blades and which - as indicated by dotted lines - may be part of a larger guiding device, e.g. the apparatus of Fig.3. The guiding blades LB of the individual groups a to d have different orientations of the blade inclination, as this is schematically shown in the section views of Figures 4a to 4d. These figures show a front view onto a group of guiding blades in the direction of arrows 14a, 14b, 14c, and 14d, respectively. With these four groups of guiding blades a rotation of the total stream in the direction of arrow P about the flow direction is achieved, which flow direction is perpendicular with respect to the plane of the drawing. The groups of guiding blades LB are supportet by a frame RA, which is inserted into the channel or into the Inlet of the reaction chamber or is combined with further arrays of this type as shown in Fig.1

Claims

1. An apparatus for treating a flowing medium with ultrasonic waves in fields of standing waves, characterized by at least one flow guiding device (LV) located outside the field of said standing sound waves, which device forces the stream (SR) inside the field of standing sound waves into a rotational movement about an axis directed parallel to the flow direction such that no portion of the flowing medium exlusively flows in the zone of a sound pressure minimum.

2. The apparatus of claim 1, characterized in that the flow guiding device (LV) consists of a plurality of guiding blades (B) which are inclined with respect to the flow direction (SR).

3. The apparatus of claim 2, characterized in that the angle of incidence of said guiding blades (LB) is larger than 30'.

4. The apparatus of clai, 1, 2,or 3, characterized by such a structue and arrangement of the flow guiding device (LV) that the core of the helical stream is located within a pressure maximum.

The device of one of the claims 1 to 4, characterized by such a structure and arrangement of the flow guiding device (LV) that a plurality of parallel helical streams is generated which flow side by side and/or one above the other.

6. The device of claim 5, characterized in that the direction of flow rotation in adjacent helical streams is opposite.

7. The apparatus of one of the claims 1 to 6, characterized in that means for increasing the flow rate within the flow guiding device (LV) are located upstream of said flow guiding device.

8. The apparatus of one of the claims 1 to 6, characterized in that means for increasing the flow rate within the flow guiding device (LV) are integrated into said flow guiding device.

9. The apparatus of one of the claims 1 to 8, characterized in that it is an acoustically closed reaction chamber (RK) and comprises at least one sound reflector (LG) through which the stream flows, and a flow guiding device (LV) which acts as a sound reflector.

10. The apparatus of claim 9, characterized in that one or several ultrasonic transducers (M) is/are located at the bottom or in the cover of the chamber (RK), and the opposite wall serves as a sound reflector.

11. Tle apparatus of one of the preceeding claims, characterized in that ultrasonic transducers are provided at more than one side wall of a channel or vessel through which the medium flows, and preferably are provided at two opposing side walls.

12. Apparatus according to Claim 1 and substantially as hereinbefore described with reference to any Figure of the accompanying Drawings.