A system for generating mechanical waves into a device holding fluid

Abstract

The present invention relates to a system for introducing mechanical waves into devices (310) holding fluid such as heat exchangers, inlets of heat exchangers, reactors, inlets of reactors, pipes, and crystallization equipments. The system (300) comprises a mechanical wave generating means (301) such as an ultrasound transducer, a waveguide (302), and a contacting means (303) comprising plurality of protrusions (304) including one or more protrusions (304a) at acoustic axis (305) of the system. The protrusions are made of material softer than contact surface of the device.

Description

[0001] A system for generating mechanical waves into a device holding fluid

[0002] FIELD

[0003] The present invention relates to systems for generating mechanical waves, in particular ultrasound waves, into devices holding fluid such as heat exchangers, reactors, pipes, and crystallization devices.

[0004] BACKGROUND

[0005] Fouling within industry has an impact on both capital and operation costs. An increase in internal fouling results in poor thermal efficiency. This is coupled with poor heat and mass transfer to the metal surface of designed heat exchangers, pipes, and other equipment. The cleaning of fouled heat exchanges presents a significant challenge to the maintenance and operation of e.g., chemical, petroleum and food processes. Despite efforts in the design of processes and hardware to minimize fouling, eventually the intricate interior surface of the exchanger requires cleaning to restore the unit to the required efficiency.

[0006] Heat exchangers are typically cleaned onsite by removing the exchanger and by placing the unit on a wash pad for spraying with high pressure water to remove foulants. Cleaning heat exchangers in an ultrasonic bath requires specially designed vessels that allow coupling sound into them and that are capable of holding sufficient fluid to affect the cleaning, and that feature specific design to allow easy removal of the foulant material from the immersed device.

[0007] Also, systems for online ultrasound cleaning of heat exchanges have been proposed. Some of the systems include a belt of ultrasonic transducers clamped onto the external shell of heat exchanger. This approach permits fouling prevention and fouling cleaning, without process interruption. Since fouling build-up is thus prevented, maximal efficiency is maintained, and energy losses are reduced.

[0008] Figure 1 shows mechanical coupling of a transducer assembly 100 on a device such as a pipe 110 filled with water. The transducer assembly comprises an ultrasonic transducer 101 , a waveguide 102, and a contacting means 103 in contact with outer surface of the device. Axial displacement (uz) along the transducer center axis is shown also. Such a mechanical coupling results in mechanical loading of the transducer, and a displacement node is introduced at the transducer head. This, in turn, calls for perfect coupling between the transducer assembly and the device. For ideal coupling, various gels, and adhesives such as glues etc. between the device and the coupling means have been used. This approach, however, is not applicable in high-power applications since the adhesives may not stand the pressure and heat generated. One possibility is to grind contact surfaces to allow good contact. This is very difficult in practice, and even a small incompatibility causes the connection to deteriorate dramatically.

[0009] Figure 2 shows another mechanical coupling of a transducer assembly 200 on a device such as a pipe 210 filled with water. The transducer assembly comprises an ultrasonic transducer 201 , a waveguide 202, and a contacting means 203 comprising two protrusions 203a, b in contact with outer surface of the device, and space therebetween. This design minimizes the mechanical loading experienced by the transducer head and permits a free boundary condition at the head. As a result, the transducer features a half-lambda resonance, illustrated by the displacement graph. Thus, a natural resonance frequency of the transducer remains, despite mechanical contact to a device holding fluid. However, the protrusions have to be made of a hard material to withstand constant operation. This in turn may damage the target structure since the transducer assembly is able to transmit high power.

[0010] Accordingly, there is need for further ways to contact transducer assemblies to devices such as heat exchangers.

[0011] SUMMARY

[0012] The present invention is based on the observation that when an ultrasound transducer head was equipped with a contacting means comprising plurality of protrusions configured to be in contact with outer surface of the device at least at acoustic axis of the system, at least some of problems related to contact coupling can be avoided or at least alleviated. Accordingly, it is an object of the present invention to provide a system for introducing mechanical waves into a device holding fluid, the system comprising mechanical wave generating means; a waveguide comprising a first end in contact with the mechanical wave generating means and a second end; and a contacting means in contact with the second end of the waveguide, wherein the contacting means comprises plurality of protrusions made of material softer than outer surface of the device and wherein the contacting means is configured to be in contact with the outer surface of the device at least via one or more of the protrusion essentially at an acoustic axis of the system.

[0013] It is also an object of the present invention to provide a method for introducing mechanical waves into a device holding fluid using the system according to claim 1 , the method comprising the following steps a) contacting at least the one or more protrusion essentially at the acoustic axis of the system with outer surface of the device; and b) the mechanical wave generating means emitting, through the outer surface of the device, a succession of mechanical waves into the device.

[0014] It is still an object of the present invention to provide a use of the system of claim 1 for cleaning a device holding fluid.

[0015] It is still an object of the present invention to provide a use of the system of claim 1 for processing fluid within a device holding the fluid.

[0016] Further objects of the present invention are described in the accompanying dependent claims.

[0017] Exemplifying and non-limiting embodiments of the invention, both as to constructions and to methods of operation, together with additional objects and advantages thereof, are best understood from the following description of specific exemplifying embodiments when read in connection with the accompanying drawings.

[0018] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of unrecited features. The features recited in the accompanied depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e., a singular form, throughout this document does not exclude a plurality.

[0019] BRIEF DESCRIPTION OF DRAWINGS

[0020] The exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below with reference to the accompanying drawings, in which:

[0021] Figures 1 and 2 show ultrasound wave generating means according to prior art, figure 3 shows A: a side view of system for generating mechanical waves into a device for holding fluid according to an exemplary non-limiting embodiment of the present invention; B: an isometric view of part of the system of figure 3A; C: a side view of the contacting means of the system of figure 3A, figure 4 shows an exemplary system of the present invention wherein the system comprises a clamping means, figure 5 shows an isometric view of a contacting means of an exemplary system of the present invention, figure 6 shows an exemplary system of the present invention in contact with a crystallization device, and figure 7 shows A: electric impedances and B: phase curves experimentally measured from the electrodes of a piezoelectric power ultrasound transducer attached onto a heavily corroded iron pipe wall filled with water. Solid line: ultrasound transducer including contacting means made of titanium and wherein the contact surface is smooth; dotted line: ultrasound transducer including contacting means made of copper and wherein the contact surface is smooth; line with triangles: ultrasound transducer including contacting means made of copper and wherein the contact surface comprises plurality of protrusions.

[0022] DESCRIPTION

[0023] Figures 1 and 2 have been discussed in Background section of this document. According to one aspect the present disclosure concerns a system for introducing mechanical waves, in particular ultrasound waves, into a device for holding fluid. An exemplary system is shown in figure 3A. Isometric view and side view of the contacting means of the system is shown in figure 3B and 3C, respectively.

[0024] The system 300 of figure 3A is in contact with outer surface of a device 310 holding fluid. The system comprises mechanical wave generating means 301 ; a waveguide 302 comprising a first end 302a in contact with the mechanical wave generating means and a second end 302b; and a contacting means 303 in contact with the second end of the waveguide. The contacting means comprises plurality of protrusions 304, such as pins. The contacting means is configured to be in contact with the outer surface of the device at least via one or more protrusion 304a essentially at the acoustic axis 305 of the system.

[0025] The contacting means or at least the plurality of protrusions of the contacting means are made of material which is softer than the material of the outer surface of the device. For example, when the outer surface of a device for holding fluid is made of stainless steel or iron, the protrusions or the whole contacting means is made of aluminum, bronze, brass, or copper, preferably copper.

[0026] The contacting means includes typically at least 20 protrusions, preferably at least 50 protrusions. The protrusions can be distributed evenly or unevenly at the surface of the contacting means. The protrusions can be of different shape such as conical, cylindrical, and / or cubical.

[0027] The protrusions 304a in the center area of the surface 304b of contacting means essentially at the acoustic axis of the system 305 prevent the formation of a displacement antinode and form a rigid boundary condition at the surface of the contacting means. Typically, for a cylindrical waveguide, this can be accomplished if the diameter D’ of the center area of the surface of the contacting means at the base of the protrusions 304a is at least 1 / 4 of the diameter D of the second end of the waveguide. Average initial length I of a protrusion, i.e., the length of a protrusion before the protrusion is contacted with outer surface of the device and the mechanical wave generating means is turned on, is preferably less than 5%, more preferably 0.5- 1 % of wavelength of the mechanical waves generated by the mechanical wave generating means. An exemplary initial length of a protrusion is 0.1-5 mm, preferably 1 -2 mm. Distance d between the tips of the protrusions is preferably less than 1 / 5 of diameter D of the second end of the waveguide. An exemplary distance d is 1 -5 mm, preferably 2-4 mm.

[0028] According to a preferable embodiment the system comprises clamping means configured to hold the system in place on outer surface of the device. An exemplary system 400 including a clamping means 406 is shown in figure 4. The clamping means includes preferably springs 407 in order to sustain the contact between the protrusions and the outer surface of the device 410 while the system is in operation.

[0029] According to a preferable embodiment the contacting means is exchangeable. Thus, the contacting means can be tailored to produce ideal contact with the outer surface of a device for holding fluid whereas the rest of the system, i.e., the waveguide and the mechanical wave generating means can be used for various applications. For example, the contacting means shown in figure 3 is configured to be in contact with curved surfaces, whereas the contacting means 503 shown in figure 5 is configured to be in contact with flat surfaces.

[0030] According to one embodiment the mechanical wave generating is an ultrasound transducer such as a Langevin transducer. A Langevin transducer comprises a front mass (head), a back mass (tail) and piezoelectric ceramics. A Langevin transducer is a resonant transducer for high-power ultrasonic actuation. The transducer is typically composed by a stack of piezoelectric disks, e.g., 2, 4, 6 or 8 disks, clamped between two metallic bars, typically aluminum, titanium or stainless-steel, that feature a front mass and a back mass of the transducer, respectively. The length of the front mass and back mass of the transducer can be tuned so that the transducer behaves as a half-wavelength resonator featuring antinodes at both ends of the system. When the system is in operation and in contact with the outer surface of the device holding fluid, the mechanical wave generating means emits succession of mechanical waves towards the plurality of protrusions. Since there is a rigid boundary in the center area essentially at the acoustic axis, mechanical loading is introduced at the protrusions.

[0031] Since the protrusions are made of material softer than the outer surface of the device, the contact improves during operation since the force generated by the mechanical wave generating means molds the protrusions to the shape of the outer surface. This results in growing of the total contact area during operation. For example, if the initial contact area of the protrusions with the outer surface is 1 -30% of the area of the second end of the waveguide, the contact area could increase up to 50-60% or even higher, of the area of the second end of the waveguide. Although the contact surface of the system of the present invention is smaller than the contact surface of a system disclosed e.g., in figure 1 , the protrusions improve the contacting quality compared to prior art since in every realistic system there is unevenness on the surfaces and the protrusions on the present invention are molded to match these unevenness during operation.

[0032] According to another aspect the present disclosure concerns a method for introducing mechanical waves into a device holding fluid. The method is exemplified with the system shown in figure 3. The method comprises the following steps a) providing a system 300 comprising mechanical wave generating means 301 ; a waveguide 302 comprising a first end 302a in contact with the mechanical wave generating means and a second end 302b; and a contacting means 303 in contact with the second end of the waveguide, wherein the contacting means comprises plurality of protrusions 304, such as pins made of material softer than outer surface of the device, and configured to be in contact with the outer surface at least via one or more protrusion 304a essentially at acoustic axis 305 of the system; b) contacting at least the one or more protrusion essentially at the acoustic axis of the system with outer surface of the device 310; and c) the mechanical wave generating means emitting, through outer surface of the device, a succession of mechanical waves into the device.

[0033] According to an embodiment the outer surface of the device selected from outer surface of a heat exchanger, outer surface of an inlet of an exchanger, outer surface of a reactor, outer surface of an inlet to a reactor, outer surface of a pipe, and outer surface of a crystallization equipment.

[0034] According to one embodiment the method is used for sonocrystallization. An exemplary system suitable for sonocrystallization is shown in figure 6 which is used for demonstrating the method. The method comprises the following steps a) providing a device 610 holding fluid, wherein the fluid includes a solvent and a solute; b) providing a system 600 comprising mechanical wave generating means 601 ; a waveguide 602 comprising a first end 602a in contact with the mechanical wave generating means and a second end 602b; and a contacting means 603 in contact with the second end of the waveguide, wherein the contacting means comprises plurality of protrusions 604, such as pins made of material softer than outer surface of the device, and configured to be in contact with the outer surface at least via one or more protrusion 604a essentially at the acoustic axis 605 of the system; c) contacting at least the one or more protrusion essentially at the acoustic axis of the system with outer surface of the device; and d) the mechanical wave generating means emitting, through the outer surface of the device mechanical into the fluid thereby initiating crystallization of the solute.

[0035] According to yet another aspect the present invention concerns use of the system for cleaning a device holding fluid. Exemplary devices which can be cleaned using the system are heat exchanges, inlets for heat exchangers, reactors, inlets of reactors, and pipes. The mechanical waves, such as ultrasound waves remove and / or avoid formation of fouling within the device. According to still another aspect the present invention concerns use of the system is for processing fluids within a device holding fluid.

[0036] According to one embodiment the processing includes avoiding formation fouling in the fluid.

[0037] According to another embodiment the fluid includes a solvent and a solute, and the processing includes initiating crystallization of the solute.

[0038] Experimental

[0039] Design of the transducer assembly

[0040] The transducer assembly was composed of a piezoelectric ultrasonic stack transducer (Langevin transducer, sandwich transducer) and a waveguide. The transducer was either a commercially available model, or a custom made one. The transducer was a narrowband (featuring typically e.g., a 1 kHz bandwidth) resonant transducer, composed by a stack of piezoelectric disks (e.g., 2, 4, 6 or 8 disks), clamped between two metallic bars (typically aluminum, titanium, or stainless steel) that feature front mass and back mass of the transducer.

[0041] The transducer design was based on a chosen resonant frequency (e.g., 20 kHz) which determines the choice (material and dimensions) of the piezoelectric disks. The stack of piezoelectric disks features a narrowband resonator. The lengths of the front mass and back mass were tuned such that the coupled resonator (i.e., transducer) behaves as a half-wavelength (lambda / 2) resonator at the chosen frequency. This is the fundamental resonance of the transducer. The bandwidth remained narrow (e.g., 1 kHz). Transducer design was based on theoretical and / or numerical modelling (finite-element simulations).

[0042] A waveguide was fitted as an extension on the first end of the transducer. The length of the waveguide was chosen / tuned so as to maintain the fundamental resonance behavior of the transducer. To this end, the waveguide length must be a multiple of lambda / 2. A waveguide may be useful e.g., to increase the q- value of the transducer assembly, to provide thermal insulation between the transducer and a system to be cleaned, or to provide flexibility in transducer placement in situations when the transducer cannot directly fit against the device to be cleaned. Waveguide design is based on theoretical and / or numerical modelling (e.g., finite-element simulations).

[0043] The assembly also included a contacting means. Plurality of pins made of copper were machined as extensions on the contact surface. The contacting means was positioned at the second end of the waveguide of a transducer assembly. The shapes and positions of the contact pins were evaluated and optimized by theoretical and / or numerical modelling (finite-element simulations).

[0044] Figure 7 shows electric impedance (A) and phase curves (B) experimentally measured from the electrodes of a piezoelectric power ultrasound transducer attached onto a heavily corroded iron pipe wall (thickness 5 mm, diameter 300 mm). The pipe was filled with water. A contact coupler made from soft metal (copper) featuring its contacting surface textured by a matrix of protruding pins was compared to a contact coupler made from soft metal (copper) featuring a smooth contacting surface and another contact coupler made from titanium and featuring a smooth contacting surface. A 4500N compressional contacting force was applied to the transducer assembly in all cases.

[0045] The ultrasound transducer including contacting means according to the present invention exhibited a lower contrast between the impedance minimum (resonance) and the impedance maximum (antiresonance) than the ultrasound transducers according to state of art. Moreover, the contacting means according to the present invention resulted in a lower phase maximum than state of art coupling means. These results are indicative of better mechanical contacting quality. In particular, the lower phase maximum of the ultrasound transducer including contacting means according to the present invention was exactly 0 degrees, which improves the electro-mechanical power transmission as compared to the +30 degrees phase maximum featured of the state of art ultrasound transducers. Furthermore, the state of art ultrasound transducer with a contact coupler made of titanium exhibited strong frequency-dependent disturbances demonstrating the reduced contacting quality.

Claims

What is claimed is1 . A system (300, 400, 600) for introducing mechanical waves into a device holding fluid, the system comprising mechanical wave generating means (301 , 601 ); a waveguide (302, 602) comprising a first end (302a, 602a) in contact with the mechanical wave generating means and a second end (302b, 602b); and a contacting means (303, 603) in contact with the second end of the waveguide characterized in that the contacting means comprises plurality of protrusions (304, 604) made of material softer than outer surface of the device and wherein the contacting means is configured to be in contact with the outer surface of the device at least via one or more protrusion (304a, 604a) essentially at acoustic axis (305, 605) of the system.

2. The system according to claim 1 wherein average initial length I of the plurality of protrusions is less than 5%, preferably 0.5-1 % of wavelength of the mechanical waves generated by the mechanical wave generating means when the system is in operation.

3. The system according to claim 1 or 2 wherein distance d between the protrusions less than 1 / 5 of diameter D of the second end of the waveguide.

4. The system according to any one of claims 1 to 3 wherein the contacting means comprises at least 20 protrusions, preferably at least 50 protrusions.

5. The system (400) according to any one of claims 1 to 4 comprising clamping means (406) configured to hold the plurality of protrusions in contact with the outer surface of the device.

6. The system according to any one of claims 1 to 5 wherein the contacting means is exchangeable.

7. The system according to any one of claims 1 to 6 wherein the plurality of protrusions are evenly distributed in surface (304b) of the contacting means.

8. The system according to any one of claims 1 to 6 wherein the plurality of protrusions are unevenly distributed in surface (304b) of the contacting means.

9. A method for introducing mechanical waves into a device holding fluid using the system according to any one of claims 1 to 8, the method comprising the following steps a) contacting at least the one or more protrusion essentially at the acoustic axis of the system with outer surface of said device; and b) the mechanical wave generating means emitting, through the outer surface of the device, a succession of mechanical waves into the device.

10. The method according to claim 9 wherein the outer surface is selected from a group consisting of an outer surface of a heat exchanger, an outer surface of an inlet of a heat exchanger, an outer surface of a reactor, an outer surface of an inlet of a reactor, an outer surface of a pipe, and outer surface of a crystallization equipment.11 . Use of a system according to any one of claims 1 to 8 for cleaning a device holding fluid.

12. The use according to claim 11 wherein the device is selected from a heat exchanger, an inlet of a heat exchanger, reactor, an inlet of a reactor, and a pipe.

13. Use of the system according to any one of claims 1 to 8 for processing fluid within a device holding fluid.

14. The use according to claim 13 wherein the processing comprises avoiding formation of fouling in the fluid.

15. The use according to claim 13 wherein the fluid comprises a solvent and a solute and the processing comprises initiating crystallization of the solute.

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