WO2013093183A1

WO2013093183A1 - Ultrasonic cleaner for a heat exchanger

Info

Publication number: WO2013093183A1
Application number: PCT/FI2012/051227
Authority: WO
Inventors: Esko Jukkala
Original assignee: Vahterus Oy
Priority date: 2011-12-21
Filing date: 2012-12-12
Publication date: 2013-06-27

Abstract

A cleaning rod (150) for a heat exchanger (100), comprising a first end and a second end (164), an ultrasonic vibrator (185), and fastening means (172) for fastening the cleaning rod (150) to the heat exchanger (100). The fastening means (172) are left between the second end (164) of the cleaning rod and the ultrasonic vibrator (185), wherein the cleaning rod (150) is arranged to be fastened to the heat exchanger (100) in such a way that the ultrasonic vibrator (185) is placed outside the heat exchanger (100), and the second end (164) of the cleaning rod (150) is placed inside the heat exchanger. Thus, the ultrasonic vibrator (185) is not, in use, subjected to the operating conditions inside the heat exchanger (100), and the acoustic coupling from the ultra-sonic vibrator (185) to the inside of the heat exchanger (100) is good. Further a heat exchanger (100) comprising said cleaning rod (150). Further a method for cleaning a heat exchanger (100). In the method, the second end (164) of the cleaning rod (150) is arranged inside the heat exchanger in such a way that the ultrasonic vibrator (185) is left outside the heat exchanger (100). Furthermore the use of a cleaning rod (150) for cleaning a heat exchanger (100). In use, the cleaning rod (150) is arranged in a way corresponding to the method.

Description

ULTRASONIC CLEANER FOR A HEAT EXCHANGER

Field of the invention The invention relates to a heat exchanger cleaning rod, which is of the type presented in the preamble of the appended claim 1 . The invention relates to a heat exchanger which is of the type presented in the preamble of the appended claim 9. The invention relates to the use of a cleaning rod for cleaning a heat exchanger according to claim 13. The invention relates to a method for cleaning a heat exchanger according to claim 15. The heat exchanger can also be called a heat transfer device.

Background of the invention Heat exchangers are used, among other things, in energy technology and process engineering for recovering heat produced in processes. The heat is transferred with a first heat transfer medium to a heat exchanger, in which a second heat transfer medium circulates as well. The heat transfer media are insulated from each other in such a way that solely heat is exchanged between these substances while the substances themselves are not mixed. The inner structure of the heat exchanger may consist of, for example, pipes or sheets, through which heat is transferred from the first heat transfer medium to the second heat transfer medium. Heat exchangers are used, among other things, in energy, processing and construction industries, as well as in refrigeration apparatuses. The heat exchanger can also be called a heat transfer device.

The efficiency of the heat transfer between the heat transfer media is influenced particularly by the heat resistance between these substances. The heat resistance consists of the heat resistances of the surfaces and the heat resistance of the pipe or sheet between the substances. The heat resistance of the surfaces can be influenced, among other things, by patterning, which has an effect on the flow profile of the heat transfer medium and thereby the heat transfer coefficient. A problem with these surfaces is soiling. Impurities accumulated on the surface as such increase the heat resistance of the surface and thereby impair the function of the heat exchanger. Furthermore, impurities accumulated on the surfaces reduce the cross-sectional area of the flow, wherein the pressure loss caused by the heat exchanger increases. Therefore, the heat exchanger has to be cleaned regularly. The cleaning of the heat exchanger is a problematic operation. The production process has to be stopped for the time of cleaning of the heat exchanger, and furthermore, the inner parts of the heat exchanger are very complex in shape and thereby difficult to clean. Plate heat exchangers can be cleaned according to prior art, for example, by spraying a washing solution under pressure by means of nozzles onto the plate surfaces of the heat exchanger. Furthermore, it is known to use scrapers movable on the surfaces of the heat exchanger plates. From tube heat exchangers, it is also known to use movable brushes. In heat exchangers, it is known to use ultrasonic cleaners. Arrangements are known, in which the ultrasonic source is placed outside the heat exchanger, in the shell of the heat exchanger. In such arrangements, the coupling of the ultrasonic source to the heat transfer medium flowing in the heat exchanger becomes a problem. In another known arrangement, the ultrasonic source is placed inside the shell of the heat exchanger. In such arrangements, the sealed (hermetic) encapsulation of the ultrasonic source becomes a problem, because the ultrasonic source is subjected to moisture (liquid). Furthermore, the pressure inside the heat exchanger may be high, wherein the hermetic protection of the ultrasonic source is difficult. Furthermore, the temperature inside the heat exchanger may be high, whereby the high working temperature may reduce the service life of the ultrasonic source.

Brief summary of the invention It is an aim of the present invention to enable the use of an ultrasonic cleaner in the cleaning of a heat exchanger during the operation of the heat exchanger in such a way that the ultrasonic source is well coupled acoustically to the heat transfer medium in such a way that the operating environment of the ultrasonic source corresponds to the external operating environ- ment of the heat exchanger, for example the room or other space in which the heat exchanger is arranged. A cleaning rod according to the invention for a heat exchanger comprises an ultrasonic vibrator. The cleaning rod is arranged to be fastened to a heat exchanger in such a way that the ultrasonic vibrator is placed outside the heat exchanger and the second end of the cleaning rod is placed inside the heat exchanger.

Thus, the ultrasonic vibrator is not subjected to the operating conditions inside the heat exchanger, and the acoustic coupling from the ultrasonic vibrator to the inside of the heat exchanger is good. The cleaning rod according to the invention for a heat exchanger is described in claim 1 . Other characteristics of the cleaning rod according to the invention for a heat exchanger are described in the independent claims 2 to 8. The heat exchanger according to claim 9 comprises a cleaning rod according to the invention. Other characteristics of the heat exchanger according to the invention are described in the independent claims 10 to 12.

The cleaning rod according to the invention can be used in several heat exchangers, one at a time. Thus, the cleaning rod can be arranged in a heat exchanger to be cleaned. The cleaning rod is arranged partly inside the heat exchanger in such a way that the ultrasonic vibrator remains outside the heat exchanger. The use according to the invention is described in claim 13, and one feature of the use in claim 14. When cleaning the heat exchanger, the ultrasonic vibrator is controlled to generat ultrasonic waves. The method according to the invention is described in claim 15. Other features of the method according to the invention are described in claims 16 and 17.

Description of the drawings

In the following, the invention will be described in more detail with reference to the appended drawings. The drawings illustrate the invention.

Fig. 1 a shows a plate heat exchanger of prior art in a side view, Fig. 1 b shows the plate heat exchanger of Fig. 1 a in the sectional plane lb-lb of Fig. 1 a,

Fig. 1 c shows a tube heat exchanger of prior art in a side view,

Fig. 1 d shows the tube heat exchanger of Fig. 1 b in the cross-sectional plane Id-Id of Fig. 1 c,

Fig. 2a shows a plate heat exchanger according to the invention in a side view,

Fig. 2b shows a plate heat exchanger according to the invention in a side view, Fig. 2c shows a tube heat exchanger according to the invention in a side view,

Fig. 3a shows a cleaning rod for a heat exchanger in a side view, Fig. 3b shows a cleaning rod for a heat exchanger in an end view,

Fig. 3c shows the generation of an ultrasonic wave in a cleaning rod for a heat exchanger in a side view, Fig. 3d shows the generation of an ultrasonic wave in a cleaning rod for a heat exchanger in a side view,

Fig. 4a shows a cleaning rod for a heat exchanger in a side view, Fig. 4b shows the second end of a cleaning rod for a heat exchanger in a side view,

Fig. 4c shows the second end of a cleaning rod for a heat exchanger in a side view, shows the vibrating rod of a cleaning rod for a heat exchanger in an end view,

shows the vibrating rod of a cleaning rod for a heat exchanger in an end view, shows a vibrating rod of a cleaning rod for a heat exchanger, extendable in length, shows a cleaning rod fastened to the shell of a heat exchanger in a side view, shows a cleaning rod fastened to a through-hole in the shell of a heat exchanger in a side view, is a perspective view showing a cleaning rod fastened to a through-hole in the shell of a plate heat exchanger and placed in a channel formed by holes in the heat transfer plates,

Fig. 6 shows a cleaning rod and a control unit for a heat exchanger.

In Figs. 1 to 6, corresponding numerals or symbols refer to corresponding elements.

Detailed description of the invention

Heat exchangers can be used, for example, for recovering waste heat from processing industry. A heat exchanger is also commonly called a heat transfer device. In this description, a heat exchanger refers to a closed structure in which the flow of both heat transfer media through the heat exchanger can be adjusted. Semi-open heat exchangers are also known, in which for example a heat transfer pipe is led through the second heat transfer medium, such as sea water, without controlling the flow of the second heat transfer medium in any way.

Figure 1 a shows a plate heat exchanger of prior art in a side view. Figure 1 b shows the plate heat exchanger of Fig. 1 a in the cross-sectional plane lb-lb according to Fig. 1 a. The heat exchanger 100 of Fig. 1 a comprises a shell 102 which encloses the inner parts of the heat exchanger 100. The shell 102 of the heat exchanger of Figs. 1 a and 1 b can have the shape of, for example, a cylinder with a circular bottom, or the shell 102 of the heat exchanger may comprise a part having the shape of a cylinder with a circular bottom. The external structure of the heat exchanger may differ from that shown in Figs. 1 a and 1 b even to a significant extent.

The heat exchanger 100 comprises a first inlet pipe 1 10 for supplying first heat transfer medium 1 1 1 to the heat exchanger 100. The first heat transfer medium is illustrated with an arrow in the figures. The heat exchanger 100 comprises a first outlet pipe 1 15 for removing first heat transfer medium 1 1 1 from the heat exchanger 100. The first heat transfer medium 1 1 1 is arranged to flow through the heat exchanger 100 by means of, for example, a pressure difference. The flow of the first heat transfer medium through the heat exchanger 100 can be adjusted, for example, by a pressure difference or the cross-sectional area of the pipe (1 10, 1 15). The cross-sectional area of the pipe (1 10, 1 15) can be influenced by, for example, a valve or valves (not shown in the figure).

The heat exchanger 100 comprises a second inlet pipe 120 for supplying second heat transfer medium 121 to the heat exchanger 100. The second heat transfer medium is illustrated with an arrow in the figures. The heat exchanger 100 comprises a second outlet pipe 125 for removing second heat transfer medium 121 from the heat exchanger 100. The second heat transfer medium is arranged to flow through the heat exchanger 100 by means of, for example, a pressure difference. The flow of the second heat transfer medium through the heat exchanger 100 can be adjusted, for example, by a pressure difference or the cross-sectional area of the pipe (120, 125). The cross-sec- tional area of the pipe (120, 125) can be influenced by, for example, a valve or valves (not shown in the figure).

This first heat transfer medium refers to the substance, from which heat is recovered, and the second heat transfer medium refers to the substance, in which heat is stored. Consequently, the first heat transfer medium 1 1 1 is cooled when flowing from the inlet pipe 1 10 to the outlet pipe 1 15 in the heat exchanger. In a corresponding manner, the second heat transfer medium 121 is heated when flowing from the inlet pipe 120 to the outlet pipe 125. In view of the invention, it is not significant, which one of the heat transfer media is heated and which one is cooled.

In the processing industry, in which heat exchangers are often used, the temperature of the first heat transfer medium 1 1 1 can often be several hundreds of degrees (°C) in the inlet pipe 1 10. The first heat transfer medium 1 1 1 used can be, for example, oil, water, air, steam, or a mixture of water and steam. The second heat transfer medium 121 used can also be, for example, oil, water, air, steam, or a mixture of water and steam. It is also possible that the first heat transfer medium 1 1 1 and the second heat transfer medium 121 are different substances. The heat exchanger 100 can be pressurized, for example when water is used as at least the second heat transfer medium at high temperatures. The pressurization may be advantageous when the temperature is so high that the heat transfer medium would be in a gaseous form (for example, steam) if unpressurized. When pressurized, the same heat transfer medium may be in liquid form (for example, water). With water, a higher heat flow can be achieved than with steam.

The plate heat exchanger shown in Figs. 1 a and 1 b comprises heat transfer plates 130 in its inner parts. There may be, for example, first heat transfer medium 1 1 1 and second heat transfer medium 121 alternating between the plates, whereby heat is transferred through the heat transfer plate 130 from the first heat transfer medium 1 1 1 to the second 121 . The heat transfer plates 130 are typically provided with two holes 132 and 132a which act as a flow channel for the second heat transfer medium 121 . Of the holes, the first one 132a is arranged to transfer the unheated second heat transfer medium from the inlet pipe 120 in between the heat transfer plates 130. In a corre- sponding manner, the second one of the holes, 132, is arranged to collect the heated heat transfer medium from between the heat transfer plates 130 and to convey it to the outlet pipe 125. The heat transfer plate 130 may also comprise another number, typically an even number, of holes 132. Typically, the heat transfer plates 130 are placed in parallel to each other and in such a way that the holes 132 are aligned. Thus, the row of holes 132 forms a channel 133 inside the plate heat exchanger. In the heat exchanger shown in Figs. 1 a and 1 b, there are two such channels 133. The row of holes, that is, the channel 133, is formed of the holes 132 of adjacent heat transfer plates 130. The inlet pipe 120 is not necessarily on the same side of the heat exchanger as the outlet pipe 125, but said pipes can be, for example, on opposite sides of the heat exchanger with respect to each other. Even in such a case, the holes of the heat transfer plates form channels 133 inside the heat exchanger.

Figure 1 c shows a tube heat exchanger in a side view, and Fig. 1 d shows a cross-section of the tube heat exchanger in the cross-sectional plane Id-Id of Fig. 1 c. The tube heat exchanger of Figs. 1 c and 1 d comprises heat transfer pipes 135 in its inner parts. The second heat transfer medium 121 flows in the heat transfer pipes, and the first heat transfer medium 1 1 1 flows outside them. Thus, heat is transferred through the wall of the heat transfer pipe 135 from the first heat transfer medium 1 1 1 to the second 121 . Free areas 138 are left between the heat transfer pipes 135, extending in the heat exchanger. The inlet pipe 120 is not necessarily on the same side of the heat exchanger as the outlet pipe 125, but said pipes can be, for example, on opposite sides of the heat exchanger with respect to each other. Also in such a case, free areas 138 are left between the heat transfer pipes 135, extending in the heat exchanger.

A common problem in heat exchangers is the accumulation of impurities onto the surfaces of the inner structures, such as heat transfer plates 130 or heat transfer pipes 135, of the heat exchangers. The impurities increase the heat resistance between the heat transfer media and thereby impair the function of the heat exchanger. According to prior art, the heat exchanger can be arranged to be opened for removing impurities, so that a brush or another corresponding tool can be used for removing the impurities mechanically, or the heat exchanger can be equipped with a cleaning apparatus which mechanically cleans the heat transfer plates of the plate heat exchanger. It has been found that ultrasound can be used for the cleaning of heat exchangers. Ultrasonic cleaning is very suitable for use in heat exchangers, because the cleaning effect extends to such places inside the heat exchanger 100 which would otherwise be difficult to access, and furthermore, the cleaning effect also extends behind the walls, such as heat transfer plates 130 or pipes 135.

The ultrasonic cleaning is based on the phenomenon of cavitation. Ultra- sound refers to a high-frequency sound which is inaudible to the human ear. The frequency of the ultrasound may be, for example 17 kHz to 150 kHz, advantageously at least 20 kHz. A low-frequency sound can also be used for cleaning objects, but the cleaning may then cause harmful noise. In ultrasonic cleaning, the sound waves cause strong pressure variations in a liquid. When the pressure drops below the pressure of saturated vapour, the liquid boils. This phenomenon is called cavitation. In ultrasonic cleaning, steam bubbles formed in cavitation clean the objects in the liquid. Furthermore, the collapsing, or condensation, of the cavitation bubbles causes cleaning waves in the liquid. As the cavitation bubbles collapse, pressure waves are gener- ated which exert shearing forces on unclean surfaces. The size and number of the cavitation bubbles will depend on the frequency of the ultrasound. At a low frequency (for example, 20 kHz), bubbles fewer in number but larger in size are obtained than at a high frequency (for example, 100 kHz). Furthermore, in the design it should be noted that a high-frequency sound is attenu- ated faster than a low-frequency sound in a medium.

Cleaning of the heat exchanger during the process has several economic benefits. The process does not need to be stopped, which entails significant cost savings. It is not necessary to introduce a separate washing solution into the heat exchanger, but the cleaning can be implemented with a conventional heat transfer medium. Advantageously, ultrasonic cleaning is performed under normal conditions during running of the process within the range of a service program designed in advance or whenever a drop in the heat transfer properties is detected in the heat exchanger. The invention is especially suit- able for plate heat exchangers, which are difficult to clean by other methods. The internal structure of plate heat exchanges may make it possible to install the cleaner to be presented even in a heat exchanger with a conventional design. Thus, the fitting of the ultrasonic cleaner does not necessarily require modifications in the internal structure of the heat exchanger. A problem in such cleaning is the coupling of the sonic source to at least one heat transfer medium. In an embodiment of the invention, an ultrasonic vibrator is connected, directly or by means of at least one intermediate piece, to at least one heat transfer medium inside the shell 102 of the heat exchanger. Said at least one heat transfer medium is in liquid form. Said intermediate pieces are advantageously made of a hard material, such as metal, glass or ceramics, wherein the acoustic coupling of the ultrasonic source to the intermediate pieces is good. Furthermore, in an embodiment, the ultrasonic vibrator is left outside the heat exchanger, wherein it is not subjected to the operating conditions inside the heat exchanger, such as the liquid, the pressure, or the heat that may prevail inside the heat exchanger.

Figure 2a shows a heat exchanger 100 according to an embodiment of the invention. The heat exchanger 100 comprises a shell 102. The interior and the exterior of the heat exchanger 100 are limited inside and outside the shell 102, respectively. The heat exchanger also comprises a cleaning rod 150. Part of the cleaning rod 150 is arranged inside the heat exchanger. That end of the cleaning rod which is arranged inside the heat exchanger is called the second end 164 of the cleaning rod. Thus, the acoustic contact of the clean- ing rod 150 with the heat transfer medium in the heat exchanger is good. The cleaning rod 150 comprises an ultrasonic vibrator 185 which is arranged outside the heat exchanger. Thus, the ultrasonic vibrator is not subjected to the operating conditions inside the heat exchanger 100. The ultrasonic vibrator is arranged to vibrate by means of an electric stimulus. It has been found that such a cleaning rod 150 is acoustically well connected to the heat transfer medium inside the heat exchanger. The acoustic coupling refers to the transfer of vibration energy. When the coupling is good, a great part of the energy of the ultrasonic vibrator 185 is transferred to the heat transfer medium.

The heat exchanger 100 shown in Fig. 2a is a plate heat exchanger. The heat exchanger of Fig. 2a is provided with two cleaning rods 150. In Fig. 2a, the second ends of the cleaning rods are arranged precisely in the channels 133 of the plate heat exchanger (Fig. 1 a). Figure 2b shows a plate heat exchanger 100 according to an embodiment. The plate heat exchanger 100 of Fig. 2b is provided with a particular tubular bushing 140 for the cleaning rod 150. The plate heat exchanger 100 of Fig. 2b is also provided with a second tubular bushing 140. However, the second bushing in Fig. 2b is not used for inserting a cleaning rod into the heat exchanger. Figure 2c shows a tube heat exchanger according to an embodiment of the invention. The tube heat exchanger of Fig. 2c is provided with a cleaning rod 150 in such a way that part of the cleaning rod 150 is arranged inside the heat exchanger and the ultrasonic vibrator 185 is arranged outside the heat exchanger.

Figure 3a shows a cleaning rod 150 in more detail. The figure shows conductors 182, 184 for supplying energy to the ultrasonic vibrator 185. The ultrasonic vibrator 185 can be controlled by, for example, AC power. The ultrasonic vibrator is arranged to vibrate by means of an AC signal. Most commonly, piezoelectric ultrasonic vibrators 185 are used. A piezoelectric material, such as ceramics, is deformed when it is subjected to an electric field. The frequency and the strength of the AC signal determine the frequency and the strength of the ultrasound to be generated. The strength of the alternating current power refers to the voltage in the case of a piezoelectric ultrasonic vibrator. Ultrasonic vibrators whose operation is based on an alternating magnetic field are also known. An alternating magnetic field can be produced, for example, by alternating current power, for example by means of a coil. When the magnetic field is generated by means of a coil, the strength of the magnetic field is influenced by the electric current running through the coil. The magnetic field can be used to generate, for example, the vibration of a magnetostrictive ultrasonic vibrator. The strength of the AC signal can also refer to the current. Advantageously, the frequency of the generated ultrasound is 20 to 100 kHz, and 20 kHz in an embodiment of the invention.

In Fig. 3a, the vibration of the cleaning rod is illustrated with arrows 187. In solid substances, sound can propagate in both transverse mode and in longitudinal mode. In thin rigid pieces, sound normally propagates in the form of transverse vibration. The transverse vibration takes place in a direction perpendicular to the direction of propagation of the sound; that is, in a direction perpendicular to the longitudinal direction of the rod. Thus, the vibration transverse to the surface of the cleaning rod is well transferred to the surrounding liquid. The cleaning rod 150 can be hollow or solid. Advanta- geously, the cleaning rod 150 is solid, in which case the ultrasound propagates in the form of transverse vibration in the cleaning rod 150. The second end 164 of the rod can be shaped for directing the ultrasound. The conical shape of the second end 164 of the rod shown in Fig. 3a also directs vibra- tions slightly parallel to the rod in the heat transfer medium.

The cleaning rod 150 of Fig. 3a further comprises fastening means 172 for fastening the cleaning rod 150 to the heat exchanger 100. The cleaning means 172 are located at such a point that the second end 164 of the cleaning rod can be fitted inside the heat exchanger, while the ultrasonic vibrator 185 can be fitted outside the heat exchanger. The fastening means 172 are left between the ultrasonic vibrator 185 and the second end 164 of the cleaning rod. The fastening means 172 are left between the ultrasonic vibrator 185 and the second end 164 of the cleaning rod in the longitudinal direction of the cleaning rod. The fastening means 172 of the cleaning rod can be formed by, for example, a protrusion. According to Fig. 3b, the protrusion 172 can be provided with holes 175. Figure 3b shows the cleaning rod 150 of Fig. 3a for a heat exchanger in an end view. The heat exchanger may comprise corresponding bolts or threaded bars fitted in the holes 175 in the protrusion of the cleaning rod. Thus, the cleaning rod 150 can be fastened to the heat exchanger by means of, for example, nuts. The cleaning rod 150 can be fastened tightly to the heat exchanger 100. The cleaning rod 150 can be fastened to the heat exchanger so tightly that the heat transfer medium cannot leak from the fastening point. The heat exchanger 100 can be pressurized. Various gaskets can be used in the fastening.

Figure 3c illustrates the formation of an ultrasonic wave 192, 194 between the ultrasonic vibrator 185 and the second end 164 of the cleaning rod 150. The first one of the waves, 192, illustrates sound propagating from the ultra- sonic vibrator 185 to the second end 164. The second one of the waves, 194, illustrates reflected sound, that is, sound propagating from the second end 164 to the ultrasonic vibrator 185. In Fig. 3c, the ultrasonic vibrator 185 is farther away from the second end 164 of the cleaning rod 150 than from the first end of the cleaning rod 150. The cleaning rod 150 is in resonance with the vibration frequency of the ultrasonic vibrator 185, wherein the cleaning rod 150, particularly that area of the cleaning rod which is left between the ultrasonic vibrator 185 and the second end 164 of the cleaning rod 150, is acoustically coupled to the ultrasonic vibrator 185 in an efficient way.

In Fig. 3c, the ultrasonic wavelength is indicated with the symbol λ. In a known way, the speed v, frequency f and wavelength λ of sound depend on each other: v = f λ The speed of sound, in turn, depends on the medium in which the sound propagates. In a known way, the speed of transverse sound in thin rigid bars is

where Y is Young's modulus for the material, and p is the density of the material . The cleaning rod may comprise, for example, titanium or an alloy that contains titanium, whereby Young's modulus can be about 1 10 GPa and the density about 4500 kg/m³, whereby the speed of sound c_s can be about 4900 m/s. Thus, the wavelength corresponding to a frequency of, for example, 20 kHz is about 25 cm. When the rod is heated, its density, Young's modulus and length may change. The cleaning rod may also comprise another material, such as another metal, glass, or ceramics. The wavelength in another material can be calculated in a corresponding way. For the sake of illustration, a considerably short cleaning rod 150 is shown in Figs. 3a to 3d. Typically, the length of the cleaning rod is several wavelengths.

As shown in Fig. 3c, the ultrasonic wave is generated between the ultrasonic vibrator 185 and the second end 164 of the cleaning rod 150 when the distance L_vp between these points is fitted to the wavelength λ in such a way that L_vp = (½ Ni + ¼) λ, where Ni is a positive integer or 0. In an embodiment of the invention, the fastening means 172 in the cleaning rod 150 are provided between the ultrasonic vibrator 185 and the second end 174 of the rod, wherein Ni > 0. In a corresponding manner, the length L_vp of the cleaning rod 150 from the ultrasonic vibrator 185 to the second end of the cleaning rod 150 can be fitted with the frequency of the ultrasonic vibrator 185, to produce resonance. It has been found that in some arrangements, a great part of the vibration energy is transferred to the heat exchanger 100, particularly its shell 102, via the fastening means 172 of the cleaning rod. Furthermore, it has been found that when the fastening means 172 of the cleaning rod is arranged substan- tially in the nodal point 300 of the ultrasonic wave in the cleaning rod 150, the cleaning rod 150 is weakly connected acoustically to the heat exchanger 100. This point is also illustrated in Fig. 3c. The nodal point 300 of the ultrasonic wave is formed at distances of ½ N₂ λ from the ultrasonic vibrator, where N₂ is a positive integer. In a corresponding manner, a nodal point is formed at the distance of (½ Ν₃ + ¼) λ measured from the second end 164 of the cleaning rod, where N₃ is a positive integer or 0. The fastening means 172 of the cleaning rod is arranged substantially at the nodal point 300 of the ultrasonic wave in the cleaning rod 150, when the location of the centre of the fastening means 172 of the cleaning rod deviates from the location of the nodal point 300 by not more than 1/8 of the wavelength. The centre of the fastening means 172 refers to the centre of the projection of the fastening means 172 on the longitudinal central axis of the cleaning rod 150, where said projection is the projection on the plane that comprises the longitudinal central axis of the cleaning rod. In Figs. 3a, 3c and 3d, the centre of the fas- tening means 172 is the centre of the cleaning rod in the longitudinal direction, at which the fastening means 172 is fastened to the rest of the cleaning rod 150. That point of the fastening means 172 for the cleaning rod, at which the fastening means 172 is fastened to the rest of the cleaning rod 150, is arranged in the cleaning rod 150 substantially at the nodal point 300 of the ultrasonic wave in the longitudinal direction of the cleaning rod 150. In Figs. 3a, 3c and 3d, particularly the centre of the fastening means 172 is left between the second end 164 of the cleaning rod and the ultrasonic vibrator 185 in the longitudinal direction of the cleaning rod 150. Figure 3d illustrates an embodiment of the cleaning rod 150. The cleaning rod 150 of Fig. 3d comprises an ultrasonic source 180 and a vibrating element 310. The ultrasonic source 180 comprises an ultrasonic vibrator 185. Ultrasonic sources 180 according to Fig. 3d are commercially available, wherein the cleaning rod 150 is easy to manufacture. In the ultrasonic source 180, the ultrasonic vibrator 185 is arranged at a distance of a quarter wavelength from the surface 189 of the ultrasonic source 180. The surface 189 is arranged to transmit the ultrasound from the ultrasonic source 180 to the vibrating element 310. In addition, the ultrasonic source 180 comprises means for supplying energy, such as AC power, to the ultrasonic vibrator 185 (cf. Fig. 3a, not shown in Fig. 3d). The vibrating element 310 comprises fas- tening means 172 for fastening the cleaning rod 150 to the heat exchanger 100. The fastening means 172 are arranged substantially at the nodal point 300 of the ultrasound. Thus, the distance of the centre of the fastening means 172 from the first end L_kpi of the vibrating rod is about (½ N + ¼) λ, where N is a positive integer or 0. In the above-described way, a small deviation from the nodal point can be allowed. Advantageously, the ultrasonic source 180 is arranged close to the fastening means 172, wherein N = 0. The vibrating element 310 is arranged to resonate with the ultrasonic source 180, wherein, as shown in the figure, the length L_s of the vibrating element 310 is (½ Ν₅)λ, where N₅ is a positive integer or 0. Figure 3d also shows the distance L_kp2 of the fastening means 172 from the second end of the vibrating rod. On the basis of the figure, it is obvious that L_kpi + L_kp2 = L_s. As stated above, L_kp2 is advantageously about (½ N₃ + ¼)λ. Said lengths correspond to the length of the cleaning rod 150 under operating conditions. The temperature inside the heat exchanger may be higher than, for example, when the rod is worked. The thermal expansion of the rod can be taken into account in the dimensioning of the rod, as well as the change in the density and Young's modulus.

In Fig. 3d, the vibrating element 310 is fastened to the ultrasonic source 180. The vibrating element 310 is thus configured to be fastened to the ultrasonic source 180. The vibrating element 310 is configured to be fastened to the ultrasonic source 180 by a fastening means 152, such as a threaded bar.

Figure 4a shows a cleaning rod 150. The cleaning rod 150 of Fig. 4a com- prises a vibrating element 310 and an ultrasonic source 180. The vibrating element 310 comprises a vibrating rod 160 and an amplifier flange 170. The vibrating rod 160 is connected to the amplifier flange 170 mechanically by a fastening means 154, such as a threaded bar. The amplifier flange 170 and thereby the vibrating element 310 are connected to the ultrasonic source 180 mechanically by a fastening means 152, such as a threaded bar. In Fig. 4a, the ultrasonic source 180 is connected to the first end of the cleaning rod. The second end 164 of the cleaning rod, which is simultaneously the second end 164 of the vibrating element, is arranged to be placed inside the heat exchanger. The ultrasonic source 180 is connected to the amplifier flange 170 and further to the vibrating rod 160 in such a way that the acoustic cou- pling between the ultrasonic source 180 and the vibrating rod 160 is good.

Figure 4b shows the second end 164 of a cleaning rod in more detail. The second end is shaped to be advantageously conical, wherein sound waves are also directed partly in parallel with the rod, as shown in Fig. 3a. The opening angle a of the conical second end 164 can be, for example, between 10° and 180°. The end 164 is not necessarily conical, but it can also be straight, wherein the opening angle is 180°. Sound can also be directed in parallel with the vibrating rod in such a way that the shape of the end 164 is a cone opening towards the end, as shown in Fig. 4c. In this case, the opening angle a may be, for example, 180° to 350°. In the advantageous embodiment shown in Fig. 4a, the opening angle a is about 90°. In the embodiment shown in Fig. 4b, the opening angle a is about 45°. The opening angle could be, for example, about 270° or about 315°, corresponding to the above-presented angles, but having the shape of a cone opening towards the end. In the embodiment shown in Fig. 4c, the opening angle a is about 315°.

Figure 4d shows the vibrating rod 160 of a cleaning rod 150 seen from its first end. The second end of the vibrating rod 160 forms the second end 164 of said cleaning rod. The vibrating rod 160 of Fig. 4c has a circular cross-sec- tion, and its diameter is indicated with the symbol d. The diameter d can be, for example, between 1 cm and 20 cm. The diameter d is a factor affecting the vibration frequency of the rod: a small diameter can be used at high frequencies, whereas large diameters can be used for a lower frequency. At the frequency of 20 kHz, the diameter d can be, for example, 5 cm. As described above in connection with Fig. 3c, the length of the cleaning rod and the wavelength used are correlated when the cleaning rod 150 is in resonance with the ultrasonic vibrator 185. Because the speed of sound only depends on the material of the cleaning rod (and slightly on the temperature, too), the length of the rod also affects the ultrasonic frequency. A given length can be represented by several frequencies, depending on the number of waves corresponding to the length, for example the number Ni . Advantageously, the diameter d is small compared with the ultrasonic wavelength. The diameter can be, for example, smaller than ½ λ or smaller than ¼ λ. In an embodiment of the invention, the wavelength λ is about 25 cm. A fastening means 162 is provided at the first end of the vibrating rod 160. Corresponding to Fig. 4a, the fastening means 162 can be, for example, a hole provided with threads, into which the fastening means 154, such as a threaded bar, can be fastened.

Figure 4e shows another vibrating rod 160 for a cleaning rod 150, seen from its first end. The vibrating rod 160 of Fig. 4e has a cross-section of a regular triangle, wherein it has two orthogonal dimensions: for example the height 02 and the side length di . Also these dimensions can be in the above-mentioned range. On the side of such a cleaning rod, an angle β is formed, whose size is 60°. The cleaning rod could also have another polygonal shape, in which case the size of the angle β would deviate from that mentioned above. An angle of another polygon can be, for example, within the above-mentioned angle range; for example, the angle could be a right angle, and the polygon could be a quadrangle. All the angles of the polygon are not necessarily equal. The polygon can be, for example, a parallelogram. The width, the largest dimension of the cross-section of the polygon, can be for example in the above-mentioned range relating to the diameter. The second dimension, the smallest dimension of the cross-section of the polygon can be for example in the above-mentioned range relating to the diameter. The coupling between the vibrating element 310 and the ultrasonic source 180 or between the vibrating element 160 and the amplifier flange 170 is advantageously implemented with threaded bars. The coupling can be purely mechanical, wherein the vibrating bar 160 or the vibrating element 310 is fitted in the ultrasonic source 180 or in the amplifier flange. The coupling can also be implemented by welding. One way of coupling is to utilize heat expansion: for example, the amplifier flange 170 can be provided with a protrusion, such as a pin or the like, and the vibrating rod 160 can be provided with a hollow that is slightly smaller than this protrusion. When the rod 160 is heated, the rod and thereby said hollow increases in size, wherein the pro- trusion of the amplifier flange 170 can be fitted in said hollow. When the vibrating rod 160 is cooled, the amplifier flange 170 is fitted in the vibrating rod 160.

Figure 4f shows a vibrating rod 160. The vibrating rod 160 comprises an extension piece 166. The extension piece 166 is connected to the other parts of the vibrating rod 160 by fastening means 168. The extension piece 166 can be used for adjusting the length of the vibrating rod 160. By using the extension piece 166 or extension pieces 166, the length of the vibrating rod 160 can be easily fitted to the heat exchanger used. Advantageously, the length of the vibrating rod used is such that the vibrating rod extends substantially all the way inside the heat exchanger, as shown in Figs. 2a to 2c. However, the length of the vibrating rod is primarily adjusted to resonance with the frequency of the ultrasonic vibrator 185. The length of the extension piece 166 can thus be, for example, a multiple of the half of the wavelength. In a correspondingly obvious manner, the length of the vibrating element 310 can be adjusted even if the vibrating element did not comprise a separate vibrating rod 160 (cf. Fig. 3d). In a correspondingly obvious manner, the length of the cleaning rod 150 can be adjusted even if the cleaning rod 150 did not comprise a separate vibrating element 310 (cf. Figs. 3a and 3c).

The cleaning rod 150 can be arranged in even a great length, substantially in the length of the heat exchanger. Long cleaning rods may have to be supported inside the heat exchanger, for example to heat transfer plates 130 or pipes 135. Such supports are advantageously arranged in a nodal point or nodal points of the ultrasound. Figure 3c shows one such support 330 and another ultrasonic nodal point 300b. With reference to Fig. 3c, the second end 164 of the cleaning rod is not such a nodal point, wherein the second end 164 is advantageously freely vibrating, that is, free. The cleaning rod 150 shown in Fig. 4a comprises a throttling area 151 . With respect to the fastening means 172, the throttling area 151 is placed on the side of the second end 164 of the cleaning rod 150 of the vibrating element. The throttling area can be placed in the vibrating element 310. In particular, the throttling area 151 can be placed in the amplifier flange 170, as shown in Fig. 4a. The cross-section of the cleaning rod 310 in the throttling area 151 is smaller than outside the throttling area 151 . The cross-sections of the clean- ing rod 150 and the throttling area 151 may be substantially circular in shape. The diameter of the throttling area 151 can be, for example, 50 to 90% of the diameter of the cleaning rod outside the throttling area 151 . The diameter of the throttling area 151 can be in said range, compared with e.g. the diameter of the vibrating rod 160. If the throttling area 151 and/or the cleaning rod 150 is not circular in cross-section, the cross-sectional area of the throttling area can be, correspondingly, for example 25 to 80% of the cross-sectional area of the part of the cleaning rod outside the throttling area. The length of the throttling area 151 , indicated with the symbol L_k in the figure, may vary, for example between ¼ and ½ λ, where λ is the ultrasonic wavelength. In an embodiment, the length L_k of the throttling area 151 is about 6 cm. By means of the throttling area 151 , it is possible to amplify the vibration of the cleaning rod 150. In particular, it is possible to amplify the vibration in the area between the throttling area 151 and the second end 164 of the cleaning rod 150. For example, if the aim is to transfer high ultrasonic power by means of a short cleaning rod 150 to the heat transfer medium, it may be necessary to arrange the throttling area 151 in the cleaning rod 150, for example in the vibrating element 310 or in the amplifier flange 170. As shown in Figs. 3a and 3d, the cleaning rod 150 does not necessarily comprise a throttling area.

With reference to Figs. 1 a, 2a and 2b, in an advantageous embodiment of the invention the cleaning rod 150 is arranged partly inside the plate heat exchanger. In particular, the cleaning rod 150 is arranged partly in a channel 133 formed by a row of holes 132 in heat transfer plates 135. One cleaning rod 150 can be arranged partly in each channel 133; for example, two cleaning rods can thus be arranged partly inside the heat exchanger. Thus, the cleaning rod (or cleaning rods) can be installed in an existing heat exchanger. Alternatively, the cleaning rod can be installed in a plate heat exchanger at the stage of manufacturing the plate heat exchanger without a need to re-design the inner structure of the plate heat exchanger.

With reference to Figs. 2a and 2b, that part of the cleaning rod 150 which is inside the heat exchanger 100 may extend substantially in the length of the heat exchanger 100 in said direction. Thus, that part of the cleaning rod 15 which is inside the heat exchanger 100 extends substantially through the whole heat exchanger 100. For example, the length L_t of the part of the cleaning rod inside the heat exchanger (Figs. 5a and 5b) can be 50 to 100% of the corresponding inner dimension of the heat exchanger. The length can also be slightly below 100%, for example 50 to 95%, wherein the flow in the heat exchanger, for example in its channel 133, is enhanced. The length of the cleaning rod 150 can be smaller, for example by at least the diameter d of the cleaning rod, than the inner dimension of the heat exchanger corresponding to the length of the cleaning rod 150. However, the length of the cleaning rod 150 is primarily adjusted to resonance with the frequency of the ultrasonic vibrator 185. The conical shape of the second end 164 of the cleaning rod may guide the flow in the channel 133. The second end 164 of the cleaning rod is advantageously not fastened to the heat exchanger 100, wherein the second end 164 of the cleaning rod is free, and the second end 164 of the cleaning rod can vibrate freely. Figure 5a illustrates the fastening of the cleaning rod 150 to the shell 102 of the heat exchanger in more detail. The cleaning rod 150 is arranged partly inside the heat exchanger. The second end 164 of the cleaning rod 150 is arranged inside the heat exchanger. Thus, when the heat exchanger is used, either one of the heat transfer media surrounds the second end 164 of the cleaning rod 150. At least the heat transfer medium surrounding the second end of the cleaning rod is a liquid, wherein this liquid heat transfer medium can be utilized in ultrasonic cleaning of the heat exchanger. In the case shown in Fig. 5a, the second end 164 of the cleaning rod 150 is surrounded by the second heat transfer medium 121 . Moreover, the second heat trans- fer medium 121 surrounds that part of the cleaning rod 150 which is inside the heat exchanger. Part of the cleaning rod 150 is inside the heat exchanger. The length of the part of the cleaning rod 150 inside the heat exchanger is indicated with the symbol L_t in Fig. 5a. Said length can be in the same order as the length L_kp2 shown in Fig. 3d. Said length L_t can be, for example, 3 cm to 10 m. In this way, the cleaning rod 150 and particularly its second end 154 is in contact with at least one heat transfer medium. The ultrasonic vibrator 185 at the first end of the cleaning rod is arranged outside the heat exchanger. Figure 5a also shows a fitting flange 410, by means of which the cleaning rod 150 can be fitted in the shell 102 of the heat exchanger. Figure 5a also shows a fastening device 104, by means of which the fitting flange 410 is arranged to be fastened to the shell 102 of the heat exchanger. The fastening device 104 can comprise, for example, a threaded bar or a bolt connected to the shell 102, and a corresponding nut. In a corresponding manner, the fitting flange 410 can comprise holes, through which said threaded bar or bolt is arranged to be introduced. Furthermore, the assembly comprises a fastening device 175, by which the amplifier flange 170 is arranged to be fastened to the fitting flange 410. The fastening device 175 can consist of, for example, a threaded bar and a nut. The fitting flange 410 may comprise a threaded hollow, in which the fastening device 175 is arranged to be screwed. The fitting flange 410 can comprise a threaded bar or bolt for fastening the amplifier flange to the fitting flange.

In some embodiments of the invention, the ultrasonic source 180 or the ultra- sonic vibrator 185 does not need to be protected from moisture. The ultrasonic source 180 may thus be at least one of the following: uncoated, unshielded, and unencapsulated. In a known way, each of these - a coating, a shield, and an encapsulation - increases the heat resistance from the ultrasonic source 180 to the environment. Thus, an unshielded ultrasonic source 180 is easier to control thermally than a moisture-proofed one.

In Fig. 5a, the first end of the cleaning rod 150 is provided with a cooler 420 for cooling the ultrasonic vibrator 185. In Fig. 5a, the cooler 420 is arranged in the ultrasonic source 180. In Fig. 5a, the cooler 420 comprises cooler plates 425 which increase the surface area of the ultrasonic source 180 and thereby improve the heat transfer from the ultrasonic vibrator 185 to the environment. The cooler 420 can also be active, comprising refrigeration apparatuses or thermoelectric elements known as such. It may be necessary to control the temperature of the ultrasonic vibrator 185 so that the ultrasonic vibrator 185 itself would operate at a desired frequency. The ultrasonic vibrator may be particularly tuned to operate at a given operating frequency which can be influenced by the thermal expansion of the ultrasonic vibrator.

Figure 5b shows the placement of a cleaning rod 150 with respect to the shell 102 of the heat exchanger, when the heat exchanger is equipped with a bushing 140. The bushing 140 is further provided with fastening means 142 for fastening the cleaning rod 150 to the heat exchanger. The fastening means 142 may comprise, for example, a nut and a bolt, by means of which the amplifier flange 170 can be compressed into the fitting flange 410 and the fitting flange 410 further to the bushing 140, as shown in the figure. In the joint, it is possible to use gaskets to seal the joint and to prevent leaking of the heat transfer medium.

Figure 5c illustrates the situation of Fig. 5b, in which the plate heat exchanger 100 is equipped with a bushing 140. The assembly is shown in a perspective view. The plate heat exchanger comprises heat transfer plates 130 equipped with a hole 132, the holes 132 constituting a flow channel 133. A cleaning rod 150 comprises a vibrating rod 160, an amplifier flange 170, and an ultrasonic source 180. The vibrating rod 160 is arranged partly in the channel 133 formed by the holes 132 in the heat transfer plates 130. The cleaning rod 150 is arranged in the bushing 140.

Figure 6 illustrates the control of the cleaning rod 150. The ultrasonic vibrator 185 can be controlled, for example, by alternating current power, which is supplied to the vibrator 185 along, for example, conductors 182, 184. The AC signal for controlling the ultrasonic vibrator 185 can be generated by, for example, a control unit 500. The control unit 500 is supplied with electric power by a conductor 530. The control unit 500 comprises means 520 for controlling the cleaning rod, for example a keypad. The control unit 500 comprises a display 510 arranged to provide the user with information about the cleaning state. The display 510 can be arranged to display information about, for example, the duration of the cleaning program, the applied power of the AC signal, and/or the applied frequency of the AC signal. The control unit 500 also comprises means for generating an AC signal. A piezoelectric ultrasonic vibrator 185 constitutes a primarily capacitive load. The control unit may comprise an inductive element which is arranged with said capacitive load to form an electric LC vibrator (LC oscillator), known as such, having a desired ultrasonic frequency. The frequency may be arranged adjustable. The frequency can be adjusted to the specific frequency of the cleaning rod. The frequency can be, for example, 20 kHz ± 0.5 kHz. The specific frequency of the cleaning rod can slightly change as a result of thermal expansion. A coil for controlling a magnetostrictive vibrator constitutes a primarily inductive load. Thus, the control unit can comprise a corresponding capacitive element.

The control unit is arranged to control the ultrasonic vibrator 185 according to the cleaning program applied. The power of the AC signal used can be, for example, dependent on time. The heat exchanger can be cleaned, for example, for the time of a cleaning cycle. The cleaning cycle can comprise, for example, a first cycle, in which the ultrasonic vibrator 185 is controlled at a first power level; a second cycle in which the ultrasonic vibrator 185 is con- trolled at a second power level; and a third cycle in which the ultrasonic vibrator 185 is controlled at a third power level. The duration of the first cycle can be, for example, 3 min and the first power level can be 0% of the maximum power. The duration of the second cycle can be, for example, 3 s and the second power level can be 50% of the maximum power. The duration of the third cycle can be, for example, 30 s and the third power level can be 100% of the maximum power. The power can be affected by the voltage applied. The voltage for attaining the maximum power is fully dependent on the ultrasonic vibrator 185. With some commercial ultrasonic sources 180, the maximum power is achieved at a voltage of about 500 V. After the cleaning cycle, the heat exchanger can be in operation in such a way that the vibration of the cleaning rod 150 is not maintained; in other words, no alternating current power is supplied to the ultrasonic vibrator. The cleaning rod 150 can be arranged partly inside the heat exchanger even though the vibration of the cleaning rod is not maintained. The maximum power used in cleaning may depend on the size of the heat exchanger used. The ratio between the maximum power and the volume of the heat exchanger can range from 0.1 W/l to 100 W/l and be, for example, about 2 W/I. Advantageously, the power is sufficient for achieving cavitation in the heat transfer medium inside the heat exchanger 100.

The cleaning rod 150 is not necessarily an integral part of the heat exchanger 100. Thus, the heat exchanger 100 can be cleaned by arranging the cleaning rod 150 partly inside the heat exchanger in such a way that the ultrasonic vibrator 185 is left outside the heat exchanger 100; and by controlling the ultrasonic vibrator to generate ultrasonic waves. In particular, the second end 164 of the cleaning rod 150 is arranged inside the heat exchanger. The cleaning rod can be arranged partly inside the plate heat exchanger 100 in such a way that the second end 164 of the cleaning rod 150 is inserted through a hole 132 in at least one heat transfer plate 130. The cleaning rod 150 can also be integrally welded in the heat exchanger 100. Thus, in the cleaning rod 150, the fastening point of the cleaning rod 150 is advantageously selected as described in connection with the fastening means 172. Thus, the cleaning rod 150 does not necessarily comprise fastening means 172. The cleaning rod 150 may comprise a mark of an advantageous fastening point, for example a welding point, which mark may be arranged, for example, substantially in a nodal point 300 of the ultrasonic wave.

The cleaning result is influenced, among other things, by the temperature and pressure of the heat transfer medium. At a high temperature, the heat transfer medium cavitates more easily, wherein a high temperature improves the cleaning efficiency. Furthermore, it has been found that the cleaning result is improved at a high pressure. The pressure inside the heat exchanger can be, for example, 10 bar. The heat exchanger can be unpres- surized, in which case the pressure inside the heat exchanger can be about 1 bar. Furthermore, the application of a washing agent or agents improves the cleaning result. However, the use of cleaning agents in heat exchangers is not always possible. In particular, the use of cleaning agents can be difficult in cleaning during the process. The use of cleaning agents is facilitated if the heat exchanger is removed from the process for the time of the cleaning. The cleaning agent is advantageously non-foaming and environmentally friendly. For impurities of incrustation type, an acidic cleaning agent is advantageously suitable, whereas for fatty impurities, an alkaline cleaning agent is advantageously suitable. Also in case the heat exchanger is removed from the process for the time of the cleaning, it is important for the operation of the ultrasonic cleaner that the heat exchanger is filled with a liquid that can be cavitated by ultrasound. In view of the continuity of the process, however, it is not advantageous to remove the heat exchanger.

Claims

Claims:

1 . A cleaning rod (150) for a heat exchanger (100), comprising

- a first end and a second end (164),

- an ultrasonic vibrator (185), and

- fastening means (172) for fastening the cleaning rod (150) to the heat exchanger (100),

characterized in that

- the fastening means (172) are left between the second end (164) of the cleaning rod and the ultrasonic vibrator (185), wherein the cleaning rod (150) is arranged to be fastened to the heat exchanger (100) in such a way that the ultrasonic vibrator (185) is placed outside the heat exchanger (100), and the second end (164) of the cleaning rod (150) is placed inside the heat exchanger (100),

wherein the ultrasonic vibrator (185) is not, in use, subjected to the operating conditions inside the heat exchanger (100), and the acoustic coupling from the ultrasonic vibrator (185) to the inside of the heat exchanger (100) is good.

2. The cleaning rod (150) according to claim 1 for a heat exchanger (100), characterized in that

- the fastening means (172) for fastening the cleaning rod (150) to the heat exchanger (100) are arranged substantially at a nodal point (300) of the ultrasonic wave in the cleaning rod (150),

wherein the cleaning rod (150) is weakly coupled acoustically to the heat exchanger (100).

3. The cleaning rod (150) according to claim 1 or 2 for a heat exchanger (100), characterized in that

- the length (L_vp) of the cleaning rod (150) from the ultrasonic vibrator (185) to the second end (164) of the cleaning rod (150) is fitted to the frequency of said ultrasonic vibrator (185)

to produce resonance.

4. The cleaning rod (150) according to any of the claims 1 to 3 for a heat exchanger (100), characterized in that - the cleaning rod (150) is arranged to be extended in length by an extension piece (166).

5. The cleaning rod (150) according to any of the claims 1 to 4 for a heat exchanger (100), characterized in that the cleaning rod (150) comprises

- an ultrasonic source (180) comprising said ultrasonic vibrator (185), and

- a vibrating element (310) fastened to the ultrasonic source (180).

6. The cleaning rod (150) according to claim 5 for a heat exchanger (100), characterized in that the vibrating element (310) comprises

- said fastening means (172) for fastening the cleaning rod (150) to the heat exchanger (100), and

- a throttling area (151 ) on the side of the second end (164) of the cleaning rod (150) with respect to said fastening means (172), in which throttling area (151 ) the cross-section of the vibrating element (310) is smaller than outside the throttling area (151 ).

7. The cleaning rod (150) according to claim 5 or 6 for a heat exchanger (100), characterized in that the vibrating element (310) of the cleaning rod (150) comprises

- a vibrating rod (160) and

- an amplifier flange (170) comprising said means (172) for fastening the cleaning rod (150) to the heat exchanger (100).

8. The cleaning rod (420) according to any of the claims 1 to 7 for a heat exchanger (100), characterized by a cooler (420) for cooling the ultrasonic vibrator (185).

9. A heat exchanger (100) comprising

- a shell (102), which limits the interior of the heat exchanger (100) inside the shell (102), and the exterior of the heat exchanger (100) outside the shell (102),

characterized in that the heat exchanger (100) comprises

- a cleaning rod (150) according to any of the claims 1 to 8 for a heat exchanger (100), wherein - the second end (164) of the cleaning rod (150) is arranged inside the heat exchanger (100), and

- the ultrasonic vibrator (185) of the cleaning rod (150) is arranged outside the heat exchanger (100).

10. The heat exchanger according to claim 9, characterized in that the heat exchanger (100) comprises

- heat transfer plates (130), each of which limits at least one hole (132),

- at least part of the holes (132) of the heat transfer plates (130) constitute a channel (133), and

- the second end (164) of the cleaning rod (150) is arranged in the channel (133).

1 1 . The heat exchanger (100) according to claim 9 or 10, characterized in that that part of the cleaning rod (150) which is inside the heat exchanger

(100) extends substantially in the whole length of the heat exchanger (100).

12. The heat exchanger (100) according to any of the claims 9 to 1 1 , characterized in that the heat exchanger (100) comprises a control unit (500) for controlling the ultrasonic vibrator (185).

13. The use of a cleaning rod (150) for cleaning a heat exchanger (100), the cleaning rod (150) comprising

- an ultrasonic vibrator (185), and

characterized in that in use,

- the ultrasonic vibrator (185) is arranged outside the heat exchanger (100), and

- the second end (164) of the cleaning rod (150) is arranged inside the heat exchanger (100).

14. The use according to claim 13, characterized in that

- the second end (164) of the cleaning rod (150) is arranged in a channel (133) formed by holes (132) in heat transfer plates (130).

15. A method for cleaning a heat exchanger (100), in which

- a cleaning rod (150) is provided, which comprises an ultrasonic vibrator (185),

characterized in

- arranging the second end (164) of the cleaning rod (150) inside the heat exchanger in such a way that the ultrasonic vibrator (185) is left outside the heat exchanger (100), and

- controlling the ultrasonic vibrator (185) for generating ultrasonic waves.

16. The method according to claim 15, characterized in

- controlling the ultrasonic vibrator (185) for generating ultrasonic waves at a frequency fitted to the specific vibration frequency of the cleaning rod (150).

17. The method according to claim 15 or 16, wherein the heat exchanger (100) comprises heat transfer plates (130), each of which limits at least one hole (132), wherein at least part of the holes (132) constitutes a channel (133),

characterized in

- inserting the second end (164) of the cleaning rod (150) in the channel (133).