The present application claims priority from Australian Provisional Patent Application No 2014901937 filed on 23 May 2014, the content of which is incorporated herein by reference.

Technical Field

Embodiments relate to an improved ultrasound device. Such a device is envisioned for treating a pumpable or flowable medium. In particular, certain embodiments relate to an improved ultrasound device for cleaning objects, or a substance such as food, or for enabling product transformation, for instance emulsification. Other embodiments relate to an improved ultrasound device for the pre-treatment of air-dried fruit. Background

Ultrasonic cleaning involves the use of sound waves to remove a variety of contaminants from solids immersed in a liquid. Ultrasonic cleaning is used in such diverse applications as optics, semiconductors, electronics, medical and pharmaceutical products, food preparation, aerospace and a variety of consumer products.

Cavitation implosion plays an essential role in ultrasonic cleaning mechanisms and occurs when high energy ultrasonic waves (20kHz to 500kHz at about 0.3-1 W/cm ² ) travel in a liquid medium. The ultrasonic waves interact with the liquid medium to generate a highly dynamic agitated solution producing micro-vapor bubbles. The bubbles grow to maximum sizes inversely proportional to the applied ultrasonic frequency and then implode, releasing energy.

Transient cavities (also referred to as vacuum bubbles or vapour voids) ranging from 50 to 150 m in diameter at 25kHz are produced during the half cycles of the sound waves. During the rarefaction phase of the sound wave, the liquid molecules are extended outward against and beyond the liquid natural physical attraction forces, generating vacuum nuclei which continue to grow. A violent collapse or implosion occurs during the compression phase. When the implosion occurs near a hard surface, the bubble transforms into a jet of about a tenth of the bubble size which then travels at very high speed toward the hard surface. With the combination of pressure, speed and temperature, the jet frees contaminants from their bonds with the substrate. Because of the inherently small size of the jet and the relatively large energy, ultrasonic cleaning has the ability to reach into small crevices and remove entrapped contaminants effectively.

A variety of mechanisms are available to effect ultrasonic cleaning. A plate arrangement is available whereby electroacoustic transducers operating between 20 kHz to 3000 kHz are located at selected positions on the wall and/or bottom surfaces of a treatment vessel. The transducers can be fixed directly into the treatment vessel, or watertight immersible units can be placed directly into the liquid or sludge mixture. Such an arrangement is typically used for surface cleaning in open tanks or gutters. Current ultrasonic tank set ups including such transducers produce a mixture of high intensity and low intensity zones across the treatment vessel's length. This results in build-up of deposits in the low intensity zone during continuous operations.

A further type of arrangement consists of a radial or focus rod transducer system operating at between 15 kHz and 100 kHz, whereby the radial transducer emits sounds across the surface of the rod and the focus transducer emits most of its ultrasonic energy from the rod's tip towards the area underneath. These arrangements are energy inefficient since most sound energy remains in close proximity of the rod with low and high intensity zones along the length of the transducer. This configuration also provides build up problems in liquid solid mixtures and causes blockages along the treatment vessel or flow cell. Ultrasonic waves not only play an essential role in ultrasonic cleaning mechanisms but also in the emulsification, crystallization, de-emulsification or separation of pumpable products and also extraction, such as the extraction of vegetable materials. The application of ultrasound disrupts the cell wall structure and accelerates diffusion through membranes and hence facilitates the release of cell contents. The use of ultrasound or sonication to break cell membranes has the advantage of reducing considerably the extraction time and increasing the extract yield.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

Summary

The subject of this application is an ultrasound device for treating a pumpable or flowable medium, the device comprising: ;

a treatment vessel comprising a hollow longitudinal member having an entrance aperture and an exit aperture for transporting a pumpable or flowable medium therethrough;

at least three transducer attachment cavities provided for in a sidewall of the hollow longitudinal member; and

an acoustic transducer mounted in each of the cavities, wherein the transducers are operable to be driven at a frequency and an amplitude to impart energy into the pumpable or flowable medium and to produce cavitation within the pumpable or flowable medium in the treatment vessel; and wherein the transducer attachment cavities in the sidewall of the hollow longitudinal member and hence the respective transducers are distributed in a helical path around an axial length of the hollow longitudinal member.

The distribution of the transducer attachment cavities in a helical path around an axial length of the hollow longitudinal member may be defined by the angular separation between neighboring cavities and the longitudinal separation between neighboring cavities. The angular separation between neighboring cavities may be between 1 degree and 179 degrees, most likely between 10 degrees to 70 degrees, with respect to the axial length of the hollow longitudinal member. The longitudinal separation between neighboring transducer attachment cavities may be between 3mm and 300mm.

Each transducer attachment cavity allows for the attachment of a single transducer. Each cavity may be defined by a sidewall and a base, the latter of which may be void. The cavity is preferably formed such that the base is angled with respect to the longitudinal sidewall of the pipe. The angle of elevation of the base may be formed to be between 3 degrees and 87 degrees, more preferably formed between 5 degrees and 30 degrees. A further position includes changing the angle of the cavity according to the horizontal cross section of the pipe. The angle of elevation of the base may be formed to be between 0 degrees and 45 degrees, most likely formed between 0 degrees and 15 degrees.

The produced sound pressure waves and subsequent streaming created in the device, may be established by determining the angle of elevation of each cavity and hence transducer with respect to the longitudinal sidewall of the pipe and the angular shift across the horizontal plane, the angular separation between neighboring cavities and hence transducers, and the longitudinal separation between neighboring cavities and hence transducers.

The pumpable or flowable medium may be a sludge, a slurry, a liquid, a solution, a substance (such as a gas), particulate or object (such as a food product) contained or introduced into a liquid or solution, or the like. The ultrasound device may further comprise an inlet to enable the flowable medium to be transported through the treatment vessel.

Treatment of the pumpable or flowable medium may comprise product transformation, sanitization for example sanitization of particulate materials, liquid-liquid emulsification or de-emulsification, extraction of plant/vegetable materials, cleaning of solid/semi-solid particulate or larger objects suspended or immersed therein, extraction of biomaterials, crystallization, degassing, antifouling, particle/cell disintegration, microbial inactivation, enhanced heat and mass transfer, dispersion, deflocculation and the enhancement of chemical reactions including enzymes. It should be appreciated that the phrase treatment includes the step of pre-treatment of an object. The invention has particular application to the pre-treatment of foods, for instance the pre-treatment of tropical fruits prior to air drying. Improved treatment of the pumpable or flowable medium may be achieved by providing more than three cavities and hence transducers in the wall of the hollow member. The number of transducer cavities and hence transducers may be fewer than 50 in a single hollow longitudinal member. The hollow longitudinal member may have straight parallel sides and have one of a circular, polygonal or irregular cross section. The hollow longitudinal member may be formed from stainless steel or other non- corrosive and reflective materials such as ceramics, copper, platinum or titanium alloys. The surface area of the hollow longitudinal member shall allow adequate sound reflection.

The length of the hollow longitudinal member will depend upon its application. For instance, in one example it may have a length of between 0.3 m and 3 m. The entrance aperture may comprise an inlet pipe for supplying a fluid into the treatment vessel and the exit aperture may comprise an outlet pipe for removing the fluid.

At least one or each of the entrance and exit apertures of the hollow longitudinal member may be configured with a connection means to enable releasable connection of an exit aperture of a first hollow longitudinal member with an entrance aperture of a second hollow longitudinal member. In this way, and depending on its application, several hollow longitudinal members may be fitted together to attain the required ultrasonic power, multi frequency and total specific energy as desired by the application. The first and second hollow longitudinal members may be driven at the same or different frequencies to enhance a desired processing effect.

Each transducer may comprise of an ultrasonic generator and driver for producing ultrasonic pressure waves at a selected frequency and an amplitude to impart energy into and to produce cavitation within the pumpable or flowable medium in the treatment vessel.

The ultrasonic generator drives each of the transducers to emit ultrasonic waves at a single predetermined frequency. Optionally a group of ultrasonic generators may be combined into a multiple transducer unit to emit ultrasonic waves over two or more frequencies or a range of frequencies to maximize sound pressure uniformity. The system may use sinusoidal or square wave forms.

The total power output from the sum of the transducers in a single treatment vessel is preferably below 10 kW. Advantageously, high specific energy input is possible by the combination of multiple transducers operating at a low power, and by varying the power at single or multiple frequencies. An advantage of at least one embodiment of the invention is that the sound pressure distributed from the configuration of the plurality of transducers is optimized over a relatively short section of the tubular member (in the order of 0.3 m to 3 m). It has been found in tests that the helical configuration of the plurality of transducers according to the invention has a surprising effect in that the flow along the length of the member was enhanced.

It has been further found in tests that the invention has a surprising effect of showing an improvement in the uniformity of temperature distribution within the vessel when compared with prior art devices.

It should be noted that any of the various features of the above subject of the application can be combined as suitable and desired.

Brief description of the drawings

In order that the present invention may be more clearly ascertained, embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective schematic view of an ultrasound device for treating a pumpable or flowable medium in accordance with an embodiment of the invention; Figure 2 is a perspective view of a portion of the ultrasound device shown in Figure 1 and depicting the angular shape of the transducer cavity and the helical distribution thereof;

Figure 3 is a side view of a transducer cavity into which is mounted a transducer, and depicts the range of possible angles of elevation;

Figure 4 is a cross section view of the portion of the ultrasound device shown in Figure 2, depicting the angular distribution of the transducer cavities across the hollow longitudinal member and the angular deviation of the transducer at the horizontal cross sectional plane of the hollow longitudinal member;

Figure 5 is a longitudinal view of the helical distribution of wall cavities along a portion of the vessel; Figure 6a shows a portion of the exterior of the ultrasound device in an experimental set-up, the device having a luminol medium contained therein;

Figure 6b is a graphical representation of a photograph of the luminol medium in the device, in the absence of ultrasound;

Figure 6c is a graphical representation of a photograph showing the luminol medium in the device, and the resulting sonoluminescence from the application of ultrasound; Figure 7 is a schematic view of a first configuration of an ultrasound device used for treating corn kernels; and

Figure 8 is a schematic view of a second configuration of an ultrasound device used for treating corn kernels.

Detailed description

One skilled in the art will readily recognize from the following discussion that alternative embodiments and applications of the device illustrated herein may be employed without departing from the principles of the invention described herein. Figure 1 illustrates a schematic perspective view of an ultrasound device 10 for treating a pumpable or flowable medium in accordance with an embodiment of the invention. The ultrasonic device 10 includes a treatment vessel or pipe 12 having the form of a hollow longitudinal member. The treatment vessel 12 has an entrance aperture 14 and an exit aperture 16. The entrance aperture 14 of the pipe is provided with an inlet fitting or flange 18 and the outlet aperture 16 of the pipe is provided with an outlet fitting or flange 18 to enable like pipes 12 to be positioned together and thereafter fluidly secured together by a suitable means. All transducer cavities are formed in the wall of the pipe 12 and are distributed in a helical path around an axial length or axis A- A' of the pipe 12. With reference to Figures 2 and 3, each transducer cavity 20 is formed in the sidewall of the pipe 12 and each transducer cavity 20 is defined by a bottom wall 22, a sidewall 26 and a cavity mounting element or bolt 28. The transducer cavity 20 is formed such that its bottom wall 22 is angled with respect to the sidewall of the pipe 12. The transducer cavity 20 is a receptacle so as to be able to receive a transducer element therein. Each transducer element 24 is screwed into the transducer cavity 20 through an internal thread and bolt 28 joined for final attachment. The transducer element 24 includes a housing manufactured from a piezo-ceramic material 33 and includes an upper housing section defined by a circular cylinder 32 and a lower housing section 34 defined by a lower cylinder that includes the threaded section for transducer attachment. The upper and lower housing sections connect together to enclose and seal the transducer element 24 from exposure to the pumpable or flowable medium. The lower housing section 34 presents its face to the pumpable or flowable medium for transmission of acoustic energy from the transducer element and into the pumpable or flowable medium. An ultrasonic generator (not shown) and associated circuitry is provided for driving each of the transducers elements 24 at the frequency and an amplitude to impart energy into and to produce cavitation to the pumpable or flowable medium within the interior of the pipe 12. The transducer element transmits acoustic energy in a conventional manner which will be appreciated by those of skill in the art.

The sidewall of the pipe 12 is substantially enveloped in a sheath (not shown) to protect the transducer elements 24 and associated circuitry.

Depending on the desired application, the produced cavitation is able to be optimized according to three parameters: the angle of elevation 'a' of each cavity and thus transducer mounted therein as depicted in figure 3, the angular separation between neighboring cavities and thus transducers as depicted in figure 4, and the longitudinal separation 'c' between neighboring cavities and thus transducers as depicted in figure 5. Referring again to Figure 3, the bottom wall 22 of each cavity and hence the subsequent angle of elevation of the transducer therein may be formed to be anywhere between 3 degrees and 87 degrees, or preferably between 5 degrees and 30 degrees. With reference to Figure 4, the angular separation between neighboring transducers 24a and 24b, 24b and 24c, 24c and 24d etc, may be anywhere between 1 degree and 179 degrees. The angular separation '6' between respective pairs of transducers (for instance between transducers 24a and 24b, and between 24b and 24c) may be the same. The tilt of the cavity forming angle in Figure 4 can vary anywhere from -30 degrees to 30 degrees. The longitudinal separation 'cf between neighboring cavities and thus transducers as depicted in figure 5 can vary between 3 mm and 300mm.

Experimental prototype

The invention is illustrated by the following non-limiting examples. Example 1: Sonoluminescence trials with luminol

A sonoluminescence trial was performed to demonstrate the uniformity of the acoustic field produced with a device configured in accordance with the invention. A luminol solution was placed in a treatment vessel in the form of an acrylic tube with a plurality of transducer cavities positioned therein in a helical arrangement. Figure 6a shows a portion of the wall of the ultrasound device utilized for the experiment. The bottom wall of each transducer cavity and hence the subsequent angle 'a' of elevation of each transducer element therein was established at 15°, the angular separation ^l V between neighboring transducer elements 24a and 24b was established at 50°, and the tilt of the cavity forming angle 'c' was established at 0°.

Results showed that sonoluminescence occurred when the ultrasound was turned on (compare figures 6b and 6c where in Figure 6b the ultrasound is turned off). Figure 6c notably shows the uniform color of the luminol solution, which represents the uniformity of the acoustic field created by the helical arrangement of the transducer elements.

Example 2: Inactivation of natural flora from raw corn kernels

An ultrasound device configured in accordance with the invention was used in a pilot scale volume of 20 L to demonstrate the application of the invention for enhanced sanitation of fresh produce. In this particular experiment, raw corn kernels were selected due to the innovation of this process to address challenges currently faced by this industry. Figure 7 shows the experimental set-up utilized that consisted of suspending corn kernels in a 100 ppm HCIO sanitizsanitizer solution. This set-up included establishing the bottom wall of each cavity and hence the subsequent angle 'a' of elevation of the transducer therein at 12°, the angular separation '6' between neighboring transducers at 50°, and the tilt of the cavity forming angle 'c' at 0°.

The enhancement of the sanitation efficiency was determined in two scenarios each conducted at room temperature: (a) sanitizer solution with the ultrasound switched off; (b) sanitizer solution with the ultrasound switched on. Each transducer element was operated at a frequency of 28 kHz and 80 W. The ultrasound device in each case consisted of a helical arrangement of 12 transducer elements. In each instance, the sanitation time was set at 10 min. Table 1 summarizes the inactivation achieved in terms of total counts of bacteria and yeasts and moulds. In this case, mould counts were below the detection limit after application of the sanitizer. Additional microbial reduction was achieved when using a combination of the sanitizer and the application of ultrasound in accordance with the invention.

Table 1. Microbial inactivation after application of sanitizer with and without ultrasound.

Example 3: Inactivation of natural flora from raw corn kernels

A further study was conducted to demonstrate the sanitation effectiveness of an ultrasound device in accordance with the invention compared with a conventional sanitation method. The medium in this study was a quantity of supermarket bought corn kernels.

The treatment vessel of the ultrasound device consisted in a short length of pipe, and the ultrasound device was configured in two different ways in an attempt to confine the corn kernels in the active section of the pipe. In a first configuration, configuration A, as schematically illustrated in Figure 7, the ultrasound device was arranged such that the treatment vessel 12 was manually twistable in the vertical plane by way of handle 40. In the second configuration, configuration B, as schematically illustrated in Figure 8, a separation mesh was incorporated and the medium was vigorously pumped to maintain the corn kernels suspended in the active zone. For both configurations, all of the transducers were driven at 28 kHz. The temperature of the sanitizer was maintained at an ambient temperature and the sanitizer, a solution of lOOppm chlorine, was pumped through the ultrasound device for a period of between 5 to 10 minutes.

For comparison, a portion of the quantity of supermarket bought corn kernels was additionally sanitized conventionally using a solution of lOOppm chlorine. As for the experiments involving the ultrasound device, the temperature of the sanitizer in the conventional trial was maintained at an ambient temperature and the corn kernels were washed for a period of between 5 to 10 minutes. Table 2 below shows the results of the study.

Table. 2 Log Reduction in corn kernels after sanitation with and without ultrasound

As is evident from the tabled results, the relative number of live microbes (bacteria and yeast) eliminated from the surface of the quantity of corn kernels using the ultrasound device according to configuration A is a 0.16-log reduction, and according to configuration B is a 0.57-log reduction, respectively.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Whilst the invention has been described with respect to its application to cleaning a product such as a food product, it should be appreciated that the invention has more wide reaching applications. In one application, the device is able to be used in a pretreatment step in the process of air drying of fruit. Some types of tropical fruit present significant losses due to decomposition after harvesting because they are extremely perishable and do not allow the use of freezing for conservation. As such, these fruits can be dried in order to provide an extension of shelf life. Drying techniques involve immersion of pieces of fruit in water or a hypertonic aqueous solution and subjecting the immersed fruit to ultrasound. An advantage in using ultrasound is that the process is able to be carried out at ambient temperature thereby reducing the potential of thermal degradation. After pre-treatment the dehydrated samples would typically be drained, blotted with an absorbent paper to remove excess solution and transferred to a forced circulation air-drying oven.

In another application, the device is able to be used in the production of olive oil. In the processing of olives to produce olive oil, harvested olives are typically cleaned, crushed and de-pitted to produce an olive paste. The olive paste is then passed through a malaxation process which determines the balance between the quality and quantity of oil extracted. Thereafter the oil is centrifuged and clarified. The device of the invention is able to be used prior to the step of malaxation. The application of ultrasound at this stage in the process significantly reduces the pre-heating state of the malaxation, therefore reducing ultimate energy demands.

It should be appreciated that the device can be used outside food technologies in applications such as flow mixers of chemical substances.