Radio frequency generator

Abstract

A radio frequency generator (1) for thermal treatment comprising a plurality of compartments (3) for containing at least one triode (2), a grid feedback circuit (20, 21), the grid inductance (4) of the triode (2), an LC oscillating circuit (5), a variable capacitor (6), a filament transformer (7) for the triode (2) and at least one high direct voltage generator (8). Each containment compartment (3) has a differentiated atmospheric pressure in order to avoid the presence of air flows which can spread particles from the external environment to the compartments (3) and avoid air ionization phenomena and / or the generation of unwanted thermal electric arcs.

Description

RADIO FREQUENCY GENERATORDESCRIPTIONField of the invention

[0001] The present invention generally relates to the technical field of radio frequency treatment devices and it particularly relates to radio frequency generator for thermal treatment.Background art

[0002] The use of alternating electromagnetic fields having a more or less high frequency has been long known in the radio frequency treatment devices industry.

[0003] In particular, there are known plants that operate with electromagnetic fields in the range of microwaves and radio frequency, used for drying or desiccating relatively moist products, such as for example leather or even varnished products.

[0004] Further uses of electromagnetic fields are provided in the field of food plant engineering, for example for pasteurising products containing milk or eggs, and in general for the conditioning and / or sanitisation treatment of any food product.

[0005] Generally, these treatment plants comprise a high voltage generator which supplies a radio frequency oscillator connected to a pair of electrodes adapted to produce the electromagnetic field designed to be passed through by the products to be treated.

[0006] A capacitor provided with a pair of opposite plates, whose distance can be adjusted mechanically to vary the capacity of the capacitor, is connected to the electrodes, with the resulting change in the current for supplying the electrodes and correspondingly the power for emitting the electromagnetic field.

[0007] Adjusting the power enables to change the value of the heating temperature generated by the electromagnetic field on the products to be treated.

[0008] One of the most common drawbacks of such radio frequency treatment devices lies in the fact that the various components of the generator operate under high voltage and they are subject to phenomena relating to partial ionisation of the surrounding air and / or thermal electric arcs.

[0009] Such phenomena are accentuated by the level of dirt of the surrounding air and, therefore, by the presence of external particles (dust) in the compartment for generating the high voltage and high frequency electromagnetic field.

[0010] In particular, the components with high risk of generating electrical discharges are the generator, triode, capacitors and similar components.

[0011] Such drawback, results in the need to compartmentalize each member or device of the plant at risk of discharge through mechanical structures adapted to block the movement of particles with resulting need to strengthen them.

[0012] Another drawback of high voltage generators known in the prior art lies in the fact that it comprises a large number of components that need to be cooled with air during the operation thereof.

[0013] Last but not least, a drawback of such generators lies the fact that it has a magnetic coupling of the various magnetic fields of the various elements that form it.

[0014] Such particular phenomenon makes the generator unstable under the high powers.

[0015] As a matter of fact, under high load conditions, given that the power is proportional to the square of the current, and given that the magnetic field generated by the individual inductance of the members that form the generator is proportional to the current, the induced voltages, for mutual coupling on the individual inductive components, are significant at high frequency.

[0016] Therefore, there arises the need to minimise such problems, while maintaining the high efficiency of the radio frequency treatment device.Technical problem

[0017] In the light of the prior art, the object of the present invention is to solve the technical problem of providing a radio frequency generator that maximises the dissipation of heat, minimises the risk of generating an electric arc and which has a high ability to screen electromagnetic fields.Summary of the invention

[0018] The object of the present invention is to solve the aforementioned problem by providing a radio frequency generator for the thermal treatment which is highly effective and cost-effective.

[0019] A particular object of the present invention is to provide a radio frequency generator of the type indicated above which is highly effective to the detriment of generating electric arcs that are detrimental to its operation.

[0020] Another object of the present invention is to provide a radio frequency generator of the type indicated above that is easy to manufacture.

[0021] A further object of the present invention is to provide a radio frequency generator of the type indicated above that allows to simultaneously and efficiently cool the cathode and anode of the triode.

[0022] Another object of the present invention is to provide a radio frequency generator of the type indicated above which minimises the diffusive transport of particles from the external environment.

[0023] The objects mentioned above and others which will be more apparent hereinafter, are achieved by a radio frequency generator for thermal treatment, according to claim 1 , comprising a plurality of containment compartments for at least one triode, the grid inductance of the triode, an LC oscillating circuit, a variable capacitor, a filament transformer for the triode and at least one high direct voltage generator.

[0024] According to a peculiar aspect of the invention, each containment compartment has a differentiated atmospheric pressure in order to avoid the presence of air flows which can spread particles from the external environment to the containment compartments and avoid air ionisation phenomena and / or the generation of unwanted thermal electric arcs.

[0025] This combination of characteristics allows to control and minimise the entry of unwanted external particles, such as for example dust, into the compartment for generating the high voltage and high frequency electromagnetic field.

[0026] Advantageous embodiments of the invention are attained according to the dependent claims.Brief description of the drawings

[0027] Further characteristics and advantages of the invention will be more apparent in the light of the detailed description of a preferred but not exclusive embodiment of a radio frequency generator for thermal treatment like the one mentioned above, shown by way of non-limiting example with reference to the drawings below, wherein:FIG. 1 is a top view of the radio frequency generator according to the invention;FIG. 2 is a lateral view of a particular component of the generator of Fig. 1 ;FIG. 3 is a schematic representation of the energy analysis of the generator of Fig. 1 ;FIG. 4 is a concentrated parameter circuit diagram of the generator of Fig. 1.Detailed description of a preferred embodiment

[0028] With particular reference to the figures, there is shown a radio frequency generator, indicated in their entirety with reference numeral 1 , for the thermal treatment of products by means of radio frequency.

[0029] In a per se known manner, the radio frequency generator 1 comprises one or more triodes 2 and it may be set up to generate an alternating electromagnetic field with a substantially constant frequency or, alternatively, with variable frequency within a predetermined band.

[0030] Furthermore, the generator 1 may be applied onto any system for the thermal treatment of products by means of radio frequency.

[0031] A general system incorporating the generator 1 of the present invention, may be used in the food industry, for example for sterilising, pasteurising and / or treating food products in general, in particular food products based on milk and / or eggs, flours, grain and the like.

[0032] Other possible applications are in the tanning industry and treatment of industrial leather in general, for example so as to reduce the initial content of relative humidity of leather coming from tanning baths or other treatments typical of the industry.

[0033] A further application of a similar plant may be the one for treating and drying polymeric materials, such as profiles or the like treated on the surface with aqueous-based coatings.

[0034] As better shown in the arrangement shown in FIG. 1 , the generator 1 comprises a plurality of containment compartments 3 adapted to embed and contain the members and the devices that form the generator 1.

[0035] By way of non-limiting example, the members and devices that form the generator 1 are, at least one triode 2, a grid inductance 4 for the triode 2, an LC oscillating circuit 5, a variable capacitor 6, a filament transformer 7 for the triode 2 and at least one high direct voltage generator 8.

[0036] Each of such devices is contained in a respective containment compartment 3, as clearly shown in FIG. 1.

[0037] The object and the function of such members and devices for operating the generator 1 is per se known and will not be addressed below unless when strictly necessary for the intelligibility of the solution to the technical problem outlined above.

[0038] Preferably, the triode 2 is of the type cooled with air and self-oscillating in “class C”, as better described below.

[0039] In an embodiment, the generator 1 comprises a substantially closed structure 9 partitioned into a first section called radio frequency generation section 10 which contains the LC oscillating circuit 5, the variable capacitor 6, the triode 2, the grid inductance 4 and the filament transformer 7 and a secondhigh voltage generation section 11 in which there is present the high direct voltage generator 8 as schematically shown in FIG. 1.

[0040] Preferably, the first radio frequency generation section 10 comprises a first inspection door 12 and the second high voltage generation section 11 comprises a second inspection door 13.

[0041] In a per se known manner, the components of the generator 1 such as the LC oscillating circuit 5, the triode 2, and the various capacitors present in the first generation section 10 can be subjected to phenomena relating to partial ionisation of the surrounding air and / or thermal electric arcs due to the voltages involved and the level of cleanliness / filtering the air which touches the components of the generator 1.

[0042] According to a peculiar aspect of the invention, each compartment 3 of the plurality of compartments has a differentiated atmospheric pressure in order to avoid the presence of air flows which can spread particles from the external environment to the containment compartments 3 and avoid air ionisation phenomena and / or the generation of unwanted thermal electric arcs.

[0043] In other words, each compartment 3 is over-pressurised with respect to the atmospheric pressure present outside the compartments 3, and therefore the atmospheric pressure of the external environment.

[0044] Hereinafter, the expression external environment will be used to indicate the space at atmospheric pressure present outside the containment compartments 3 of the generator 1 as well as the space outside the first 10 and second generation section 11.

[0045] Therefore, the entire generator 1 is over-pressurised with respect to the external environment with the specific purpose of controlling and minimising the entry of unwanted external particles, such as for example dust, into the compartment for generating the high voltage and high frequency electromagnetic field.

[0046] As a matter of fact, according to Fick's law, the foreign particles dispersed in the air of the external environment, considered a dirty environment and at atmospheric pressure, can move freely in a diffusedmanner proportionally to the relative pressure gradient and to the constant diffusivity of the air of the external environment.

[0047] Therefore, the overpressure of the containment compartments 3 with respect to the external environment hinders the diffusive immigration of the foreign particles from the low-pressure environment towards the overpressurised environment.

[0048] The absence of unwanted particles minimises phenomena relating to partial ionisation of the surrounding air and / or thermal electric arcs.

[0049] Obviously, the inspection doors 12, 13 will be configured to withstand the overpressure present in the various containment compartments of the generator 1.

[0050] Advantageously, the generator 1 comprises an intake system 14 for introducing air into a first containment compartment 3A of the triode 2.

[0051] As better shown in FIG. 1 , in the first compartment 3A there may be provided the components of the triode 2 such as an anode 15, the grid 16, a cathode 17 and a filament 18, as well as an anode inductance 19 and a grid feedback circuit 20, 21.

[0052] In particular, the grid feedback circuit 20, 21 consists of a feedback block capacitor 20 and of a grid feedback inductance 21.

[0053] Furthermore, in the first compartment 3A there may be present an anode block capacitor 22 between the anode 15 of the triode 2 and the LC oscillating circuit 5.

[0054] Preferably, the triode 2 comprises a plurality of cooling fins, not shown in the figures, and the intake system 14 is configured to directly introduce air on such plurality of fins, as well as to convey air from the cathode and from the filament towards the anode.

[0055] In other words, the air intake system 14 allows to introduce cold air into the first containment compartment 3A to touch the hot surfaces of the triode 2.

[0056] The air is subsequently directed through suitable dissipators obtained on the grid 16 and on the cathode 17 of the triode 2, to pass through the coolingfins of the triode 2, maximising the turbulent behaviour of the air introduced by the system 14 and therefore maximising the coefficient of air-surface convective exchange.

[0057] A first part of the air generated by the air intake system 14 and which passed through the triode 2 increasing the enthalpy thereof, is discharged into a drying cabin comprising at least one electrode. Such drying cabin is directly connected to the generator 1 using the variable capacitor 6 and it is not shown in the figures.

[0058] Furthermore, a second part of the air generated by the air intake system 14 is conveyed into a second compartment 3B for containing the LC oscillating circuit 5 so as to cool the latter and dissipate the heat generated by its components.

[0059] As better shown in FIGS. 1 -2, in the second compartment 3B there may be provided the components of the LC oscillating circuit 5 such as an output system with parallel capacitor 23, an input TEM mode conductor 24 for supplying the LC oscillating circuit 5 and connected to the anode block capacitor 22, a high voltage capacitive system 25.

[0060] The second part of the air introduced into the second containment compartment 3B of the LC circuit 5 is subsequently conveyed towards a third containment compartment 3C of the variable capacitor 6 connected to the output of the LC oscillating circuit 5 and delivery also in a drying cabin.

[0061] Advantageously, a portion 3D of the second containment compartment 3B of the LC oscillating circuit 5 is maintained at atmospheric pressure.

[0062] In a per se known manner, in a radio frequency generator 1 , the LC oscillating circuit 5 is the site of at least 90% of the resistor leaks by Joule effect.

[0063] Therefore, in order to minimise such leaks, the second containment compartment 3B comprises one or more cooling holes 26 adapted to cool the LC oscillating circuit 5.

[0064] In order to demonstrate how the compartmentalization of the generator 1 according to the invention allows to maximise the dissipation of heat whilemaintaining high efficiency, an energy analysis of the generator 1 will be subsequently earned out.

[0065] With reference to FIG. 3, the useful radio frequency power PRF-T [%] supplied by the triode 2 corresponds to the useful supply power PHVDC [%] supplied by the high direct voltage generator 8 multiplied by the efficiency r|T [%] of the triode 2:PRF-T=PHVDCXT1T wherein r|T is comprised between 75% and 80%.

[0066] The power supplied to the radio frequency electrode PRF-EL [kW] is the useful radio frequency power PRF-T [%] supplied by the triode 2 net of the leaks PO-LC on the reactive components of the LC oscillating circuit 5:PRF-EL=PRF-TXT1RF-GEN=PRF-T'PO-LC whereinD_ (Va-RMs)20-LC ~ nKO-LC where RO-LC is the parallel resistance of the LC oscillating circuit 5 at the resonance condition, which physically consist in the actual behaviour of the inductive components of the resonant LC oscillating circuit 5 and wherein RO- LC = 104Q and where VaRMS [V] is the voltage in effective value at the heads of the LC oscillating circuit 5.

[0067] As a result, the power transferred from the radio frequency electrode PRF-EL [kW] is the product of the transfer efficiency of the high frequency power circuit:

[0068] Lastly, the power transferred to the load PRF-LOAD, generated by the interaction between the electric field generated by the electrodes is proportional to the electrode-load transfer efficiency HRF-LOAD [%]:PRF-LOAD=PRF-ELXT1RF-LO D

[0069] Therefore, the total net power transferred to the radio frequency electrode PRF-EL [kW] is proportional to the product of the efficiency of each transmission stage:

[0070] As a result, the total power dissipated PL-TOI and not transferred to the load is:P L-Tot=P HVDC X (1 — 1]TX ^RF-GENX^RF-LOAD)

[0071] The power dissipated on the triode 2 can be expressed with PL-T and as shown below:P L-T=P HVDCx(1 — T]T)

[0072] Therefore, the air intake system 14 enables to exploit the broad thermal exchange surface of the finned assembly of the triode 2 to exchange thermal power with the cooling airflow conveyed into the first containment compartment 3A of the triode 2.

[0073] Furthermore, exploiting the convective exchange enables to obtain high-enthalpy air.

[0074] The power dissipated on the LC oscillating circuit 5 may be expressed with PO-LC and as shown below:

[0075] Therefore, the air intake system 14 enables to exploit the broad thermal exchange surface of the LC oscillating circuit 5 to exchange thermal power with the cooling airflow conveyed into the second containment compartment 3B of the LC oscillating circuit 5.

[0076] Also in this case, exploiting the convective exchange enables to obtain high-enthalpy air.

[0077] The over-temperature with respect to the environment of the air conveyed into the first containment compartment 3A of the triode 2 is:wherein Taj-out is the temperature of air at the outlet of the triode2, Tenv is the temperature of the air of the external environment, which is used to cool the triode 2, rriT is the volumetric flow rate of the air for cooling the triode 2, pais the density (of specific weight) of the air for cooling the triode 2 and CP,ais the thermal capacity of the dry air at constant pressure.

[0078] The over-temperature with respect to the environment of the air conveyed into the second containment compartment 3B of the LC oscillating circuit 5 is:wherein Ta,i_c-out is the temperature of the cooling air at the outlet of the LC oscillating circuit 5 and mi_c is the volumetric flow rate of the air for cooling the LC oscillating circuit 5.

[0079] As a result, the energy recovery system provides cooling air directly to the drying / heating system in the form of heated air.

[0080] The thermal excursion that the cooling air is subjected to is strictly bound to the power absorbed by the system for generating radio frequency power.

[0081] With reference to FIG. 3, the air is mixed in the drying cabin. Therefore, the available mean over-temperature ATrec is basically the weighted mean of the over-temperatures with respect to the environment of the two convective flows:

[0082] According to a further particular aspect of the invention, each containment compartment 3 of the plurality of compartments has walls made of high magnetic permeability material so as to obtain a mutual magnetic decoupling.

[0083] Preferably, the high magnetic permeability material of such walls is aluminium which allows to avoid any magnetic coupling of the magnetic fields.

[0084] Therefore, the compartmentalization of the generator 1 also carries out the passive screen function for the various electromagnetic components.

[0085] FIG. 4 shows a typical concentrated parameter circuit diagram of a radio frequency generator 1 with self-oscillating triode 2 in Class C.

[0086] The distributed parameter analysis shows that there are mutual magnetic couplings or mutual inductances between different inductivecomponents of the generator 1 which, in the figure, are shown with solid line arrows.

[0087] As a result, through the magnetic decoupling, the generator 1 is more stable in the high power operation.

[0088] As a matter of fact, as known, under high load working conditions, given that the power is proportional to the square of the current, and given that the magnetic field generated by the individual inductances of the components of a generator 1 is proportional to the current, the induced voltages, for mutual coupling on the individual inductive components, are significant at high frequency.

[0089] Therefore, the magnetic decoupling carried out by means of walls made of high magnetic permeability material enables to improve the stability of the generator 1 and oscillation at high powers.

[0090] In the light of the description above, it is clear that the radio frequency generator according to the invention achieves the pre-established objects and in particular maximises the dissipation of heat, minimises the risk of generating an electric arc and it has a high ability to screen electromagnetic fields.

[0091] The generator according to the invention is susceptible to numerous modifications and variants all falling within the inventive concept outlined in the attached claims.

[0092] Although the generator has been described with particular reference to the attached figures, the reference numerals used in the description and in the claims are meant for improving the intelligibility of the invention and they do not limit the claimed scope of protection in any manner whatsoever.

[0093] Throughout the description, reference to “an embodiment” or “the embodiment” or “some embodiments” indicate that a particular characteristic, structure or element described is comprised in at least one embodiment of the object of the present invention.

[0094] Furthermore, the particular characteristics, structures or elements may be combined in any appropriate fashion in one or more embodiments.Industrial applicability

[0095] The present invention can be applied at industrial level because it can be manufactured on industrial scale by industries belonging to the field of radio frequency treatment devices.

Claims

CLAIMS1. A radio frequency generator (1) for thermal treatment, comprising a plurality of compartments (3) for containing at least one triode (2), a grid feedback circuit (20, 21), a grid inductance (4) for said triode (2), an LC oscillating circuit (5), a variable capacitor (6), a filament transformer (7) for said triode (2) and at least one high direct voltage generator (8), characterised in that each compartment (3) of said plurality is over-pressurised with respect to the atmospheric pressure present outside said compartments (3) thereby avoiding the presence of air flows which can spread particles from the external environment into said compartments (3) and air ionization phenomena and / or the generation of unwanted thermal electric arcs.

2. Generator as claimed in claim 1 , characterised in that it comprises an intake system (14) for introducing air into one first containment compartment (3C) of said triode (2).

3. Generator as claimed in claim 2, characterised in that said triode (2) comprises a plurality of cooling fins, said intake system (14) being configured to introduce air directly on said plurality of fins.

4. Generator as claimed in claim 2, characterised in that a first part of the air generated by said intake system (14) is discharged into a drying cabin to which said generator (1) is connected.

5. Generator as claimed in claim 4, characterised in that a second part of the air generated by said intake system (14) is discharged into a second containment compartment of said LC oscillating circuit (5).

6. Generator as claimed in claim 5, characterised in that a portion (3D) of said second containment compartment (3B) of said LC oscillating circuit (5) is maintained at atmospheric pressure.

7. Generator as claimed in claim 4, characterised in that said second containment compartment (3B) comprises one or more holes (26) for cooling said LC oscillating circuit (5).

8. Generator as claimed in claim 1 , characterised in that each compartment (3) of said plurality has walls made of high magnetic permeability material to obtain a mutual magnetic decoupling.

9. Generator as claimed in claim 8, characterised in that said high magnetic permeability material is aluminium.

10. Generator as claimed in claim 1 , characterised in that said grid feedback circuit (20, 21) comprises a feedback block capacitor (20) and a grid feedback inductance (21).

11. Generator as claimed in claim 1 , characterised in that it comprises a substantially closed structure (9) partitioned into a first radio frequency generation section (10) and a second high voltage generation section (11), said first (10) and second section (11) comprising a respective inspection door (12, 13)

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