ANGLE-PAIRED WAVEGUIDE VACUUM MICROWAVE DEHYDRATOR

FIELD OF THE INVENTION This invention relates to vacuum microwave dehydration. In particular, this invention relates to a device using angle-paired waveguides to diagnose and remedy microwave generator overheating.

BACKGROUND OF THE INVENTION

Dehydration is a common method of preserving food and other materials of biological origin. Dehydration is primarily used to increase product longevity for storage purposes, although many items are also used or consumed in their dehydrated forms. Conventional dehydration processes include sun-, air-, and freeze-drying. More recently, applying microwave energy to materials of biological origin in a partial vacuum has been utilized as a dehydration process. Vacuum-microwaving is an advantageous dehydration process, as it tends to be faster than the other conventional processes. Additionally, vacuum-microwaving may be performed at relatively low temperatures and in a reduced-oxygen environment, which reduces oxidation and thermal degradation of the product and generally produces a dried material with fewer alterations from the original biological material than the other conventional processes.

Conventional vacuum microwave dehydrators (VMDs) generally comprise a microwave generator (typically a magnetron), a waveguide, and a usually microwave-reflective vacuum chamber. Microwave energy propagates from the generator through the waveguide and into the chamber, where it is absorbed by the target material. Particularly where the target material is a food product, the microwave energy is dominantly absorbed by the water in that food product. Under the reduced pressure of the vacuum in the chamber, the energy absorbed by the water causes it to vaporize at temperatures below 100 °C, the boiling point of water at one atmosphere of pressure. As the water in the target material vaporizes, the target material absorbs less microwave energy, and the unabsorbed microwave radiation reflects within the chamber.

Additional generators and waveguides may be used to increase the overall power output of the VMD, thereby increasing the amount of target material which may be dehydrated, decreasing the amount of time required to dehydrate the target material, or both. However, microwaves produced by one generator may, depending on the conditions and topology involved, propagate to and along the waveguides associated with other generators to reach the other generators themselves. The coupling of radiation of one generator to another is referred to as “cross-talk”. If cross-talk is allowed to occur, the receiving generator may overheat to the point of damage.

Cross-talk may be avoided or mitigated in a number of ways. For example, U.S Patent No. 9,316,437 to Fu et al. discloses a VMD in which remaining microwave radiation is absorbed by a water load after it passes through the material to be dehydrated. However, this solution is less efficient because some of the microwave energy is wasted into the water load, whereas if the radiation is allowed to reflect within the vacuum chamber, then more of the microwave energy is transferred into the dehydrating material.

Alternatively, Russian Patent No. 2,832,964 to Andreevich et al. discloses a microwave dryer for timber in which magnetrons are cycled on and off. Magnetron overheating from cross-talk is much less likely to occur when the magnetron is not also operating. However, cycling magnetrons on and off increases the amount of time it takes to dehydrate material over a system in which the magnetrons are powered for the duration of the dehydration process.

A third way to partially mitigate cross-talk is disclosed in U.S. Patent No. 9,267,734 to Durance et al. in 734, the magnetrons and waveguides are mounted to a door, with each waveguide oriented at a different angle than the other waveguides on the door. Waveguides of different angles are less likely to cross-talk, since the radiation produced by each magnetron is initially oriented at a different angle. However, different waveguide orientations cannot prevent cross-talk entirely. Essentially randomized interactions between radiation produced by each magnetron and reflections inside the vacuum chamber may reorient the radiation produced by one magnetron sufficiently to allow it to crosstalk. When this occurs, it is impossible to tell which magnetron is causing the cross-talk due to the random nature of the interactions. As such, the only way to correct the cross-talk is through trial and error by selectively turning off magnetrons until the overheating stops, or by reducing the power to all magnetrons until the overheating subsides.

It is an object of this invention to provide a more efficient VMD with continuously-powered microwave generators directed into a reflective vacuum chamber. It is a further object of the invention to provide a system which allows the operator to more intelligently assess the source of generator overheating due to cross-talk and thereby stop the overheating by controlling the source.

These and other objects will be better understood by reference to this application as a whole. Not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims. SUMMARY OF THE INVENTION

In one aspect, the invention comprises a control system for a VMD with multiple, continuously-powered microwave generators. There will always be potential for randomized cross-talk arising from radiation reflection and interaction in a continuously-powered VMD with multiple generators. As this type of cross-talk is exceedingly difficult to predict and therefore mitigate, the invention instead relies on predictable cross-talk among pairs of generators to be able to diagnose the source of microwave generator overheating and thereby control it. Using the principle that cross-talk is much more likely to occur in generators with waveguides oriented at the same angle, the system harnesses cross-talk as a way to detect the source of the radiation causing the overheating in a generator.

At least one microwave generator waveguide is paired with the waveguide of another generator by orienting the two waveguides at the same angle, so that long sides of the cross-sections of those waveguides are parallel to each other. Accordingly, when that generator overheats, it can reasonably be assumed that the overheating of that generator is primarily due to the other generator of the pair. Therefore, stopping the overheating becomes a matter of reducing power only to the paired generators until the affected generator reaches a safe operating temperature, while the other generators continue to operate at the desired power output.

According to an embodiment, the VMD comprises multiple angle-paired waveguides, with each pair of waveguides oriented at a different angle than the other pairs of waveguides. Paired waveguides may be located on the same side of the vacuum chamber or a paired waveguide may be diametrically opposed to its angle-pair counterpart.

According to another embodiment, the VMD comprises a waveguide angle- paired to more than one other waveguide. The multi-paired waveguides may be located on the same side of the vacuum chamber or may be diametrically opposed to their angle-pair counterparts.

According to another embodiment, the VMD further comprises sensors to detect overheating in a microwave generator, a controller then automatically reducing power to the pair counterpart(s) in the event that overheating occurs.

According to an embodiment, the VMD dehydrates in a batch process whereby product is loaded into the vacuum chamber through a hatch, a vacuum is applied to the chamber and the microwave generators dehydrate the product, following which the chamber is vented to atmosphere and the dehydrated product is removed.

According to another embodiment, the VMD dehydrates in a continuous feed whereby the product is introduced to the chamber through a vacuum airlock, conveyed through the chamber on a conveyor system, and the dehydrated product is removed through a second vacuum airlock. In another aspect of the invention, an apparatus for dehydrating organic material comprises a vacuum chamber, a plurality of microwave generator assemblies connected to the vacuum chamber for radiating microwave energy into the vacuum chamber, each of the microwave generator assemblies comprising a microwave generator, a sensor for detecting overheating of the microwave generator, and a waveguide, each microwave generator assembly of the plurality of microwave generator assemblies being angle-paired to at least another microwave generator assembly by orienting their respective waveguides such that long sides of cross-sections of the respective waveguides are parallel to one another and are not parallel to the long sides of cross-sections of waveguides of other microwave generator assemblies of the plurality of microwave generator assemblies, respective sensors associated with each of the angle-paired microwave generator assemblies for detecting overheating in respective microwave generators of the angle-paired microwave generator assemblies, and a controller communicating with the respective sensors for selectively reducing or interrupting power supplied to at least one of the angle-paired microwave generator assemblies in response to respective sensors of the angle-paired microwave generator assemblies detecting overheating in respective microwave generators of the angle-paired microwave generator assemblies.

In a further aspect, respective microwave generator assemblies of the angle- pairs of microwave generator assemblies radiate microwave energy into the vacuum chamber from one side of the vacuum chamber.

In a further aspect, respective microwave generator assemblies of the angle- pairs of microwave generator assemblies radiate microwave energy into the vacuum chamber from opposing sides of the vacuum chamber.

In a further aspect, the invention comprises means to move the organic material around in the vacuum chamber.

In a further aspect, the invention comprises means to move the organic material through the vacuum chamber continuously.

In a further aspect, each of the waveguides includes a microwave isolator.

In a still further aspect, each of the microwave isolators comprises a microwave circulator connected to a microwave transparent tube through which a water supply circulates. In another aspect of the invention, a method for preventing damage to microwave generators due to overheating in a vacuum microwave dehydration apparatus comprises providing a vacuum microwave dehydration apparatus comprising a vacuum chamber, a plurality of microwave generator assemblies connected to the vacuum chamber for radiating microwave energy into the chamber, each of the microwave generator assemblies comprising a microwave generator, a sensor for detecting overheating of the microwave generator, and a waveguide, wherein each microwave generator assembly of the plurality of microwave generator assemblies is angle-paired to at least another microwave generator assembly by orienting their respective waveguides such that long sides of cross- sections of the respective waveguides are parallel to one another and are not parallel to the long sides of cross-sections of waveguides of other microwave generator assemblies of the plurality of microwave generator assemblies, detecting overheating in respective microwave generators of an angle-pair of microwave generator assemblies using respective sensors of the angle-pair of microwave generator assemblies, reducing or interrupting power supplied to respective microwave generators of the angle-pair of microwave generator assemblies.

In a further aspect, power supplied to respective microwave generators of other microwave generator assemblies of the plurality of microwave generator assemblies is also adjusted.

In another aspect of the invention, an apparatus for dehydrating organic material comprises a vacuum chamber, a plurality of microwave generator assemblies connected to the vacuum chamber for radiating microwave energy into the chamber, each of the microwave generator assemblies comprising a microwave generator, a sensor for detecting overheating of the microwave generator, and a waveguide, at least two microwave generator assemblies of the plurality of microwave generator assemblies being angle-paired to one another by orienting their respective waveguides such that long sides of cross-sections of the respective waveguides are parallel to one another and are not parallel to the long sides of cross-sections of waveguides of other microwave generator assemblies of the plurality of microwave generator assemblies, and a controller communicating with respective sensors of the at least two microwave generator assemblies for reducing or interrupting power supplied to at least one of the at least two microwave generator assemblies in response to a detection by one of the respective sensors of overheating in the one microwave generator assembly of the at least two microwave generator assemblies.

In a further aspect, a plurality of microwave-transparent windows is interposed between the vacuum chamber and the plurality of microwave generator assemblies for hermetically sealing the vacuum chamber from the plurality of microwave generator assemblies.

The foregoing may cover only some of the aspects of the invention. Other and sometimes more particular aspects of the invention will be appreciated by reference to the following description of at least one preferred mode for carrying out the invention in terms of one or more examples. The following mode(s) for carrying out the invention are not a definition of the invention itself, but are only example(s) that embody the inventive features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

At least one mode for carrying out the invention in terms of one or more examples will be described by reference to the drawings thereof in which:

Fig. 1 is a cutaway perspective view of the Vacuum Microwave Dehydrator (VMD), with one of the microwave generator assemblies removed to show the microwave transparent window;

Fig. 2a is a perspective view of a microwave generator assembly;

Fig. 2b is a bottom view of the microwave generator assembly;

Fig. 3 is a perspective view of the preferred embodiment of the VMD;

Fig. 4 is a front view of the preferred embodiment of the VMD;

Fig. 5a is a detailed perspective view of a port of the VMD with the associated microwave generator assembly removed; Fig. 5b is a detailed perspective view of the preferred embodiment of the microwave generator assembly;

Fig 5c is a side view of the preferred embodiment of the microwave generator assembly; Fig. 5d is a front section view of the preferred embodiment of the microwave generator assembly, taken along line D-D of Fig. 5c;

Fig. 6 is a section view of the preferred embodiment taken along line 6-6 of Fig. 4; in which each waveguide is angle-paired to another waveguide, forming 3 sets of angle pairs; Fig 7 is a perspective view of another embodiment of the VMD in which the first and second microwave port arrays are diametrically opposed;

Fig. 8 is a top view of the embodiment in Fig. 7, showing a possible configuration for cross-chamber pairing of waveguides;

Fig. 9 is a schematic representation of a control system for the VMD; Fig. 10 is an example flowchart of an algorithm for correcting overheating of a microwave generator in the VMD;

Fig. 11 is a perspective view of an embodiment of the VMD which operates in a continuous feed process; and

Fig. 12 is a side section view of the embodiment of Fig. 11 , taken along plane 12.

DETAILED DESCRIPTION OF THE PREFERRED AND OTHER

EMBODIMENTS

Referring to Fig. 1, a vacuum microwave dehydrator 100 comprises a vacuum chamber 102 having a first side 104, a second side 106, a first end 108, and a second end 110. An interior surface 112 of the vacuum chamber 102 is microwave-reflective. A first access port 114 is formed in the first end 108 to allow a product A to be introduced into and removed from the vacuum chamber. The first access port 114 is sealable against atmospheric pressure and conditions according to means described below, so that the vacuum chamber may efficiently operate at reduced pressure. A vacuum port 116 is formed in the vacuum chamber 102. A vacuum pump system (not shown) is connected to the vacuum port 116 in order to remove air from the vacuum chamber 102 prior to the dehydration process. Vacuum pressure is monitored within the chamber using a pressure sensor 119. Condensers (not shown) remove water vapour from the vacuum chamber 102 during the dehydration process. Product temperature sensors 117, preferably contact-free infrared temperature sensors, are mounted within the vacuum chamber 102 to measure the temperature of the product A and thereby monitor the dehydration process.

A plurality of microwave ports 118 are formed in the first side 104 and the second side 106 of the vacuum chamber 102. Each microwave port 118 is sealed with a microwave-transparent window 120. A microwave generator assembly 122 is mounted to each microwave port 118 (although in Fig. 1 one of the microwave generator assemblies is not shown so that the microwave- transparent window 120 is visible). Referring to Figs. 2a to 2b, each microwave generator assembly 122 comprises a microwave generator 124 and waveguide 125. As shown in Fig 2a, each waveguide 125 is rectangular in cross-section, having a short side 136 and a long side 138. Each microwave generator 124 preferably comprises a magnetron 126 and output antenna 128. The output antenna 128 couples microwave energy produced by the magnetron 126 into the waveguide 125. The microwave energy then propagates through the waveguide 125 and into the vacuum chamber 102. The magnetron 126 preferably further comprises a water-cooling system 130 (only the cooling coil portion of the system is shown for clarity). A thermocouple 132 or other suitable temperature sensor is inserted into an outlet feed 134 of the water-cooling system 130 to measure the temperature of coolant water exiting the magnetron 126. Sudden increases in the coolant water temperature at the outlet feed 134 indicate that the magnetron 126 is overheating. Such overheating can generally be attributed to cross-talk microwave energy from the other microwave generators 124.

Each waveguide 125 is angle-paired to at least one other waveguide. Waveguides are angle-paired when the cross-sectional long sides 138 of each waveguide 125 are parallel to each other. For example, the waveguides of microwave generator assemblies 122a and 122b seen in Fig. 1 are angle-paired. Microwave generator assemblies with angle-paired waveguides are much more likely to cross talk with each other than with a microwave generator assembly having a waveguide oriented at a different angle. Accordingly, when a magnetron 126 overheats, as indicated by a spike in temperature registered by the thermocouple 132 in the outlet feed 134 of that magnetron’s water-cooling system 130, the overheating can be attributed to cross-talk from that magnetron’s waveguide angle-pair counterpart(s). Power can then be reduced to the angle- pair counterpart, and to the overheating magnetron if necessary, so as to avoid damage to the overheating magnetron while allowing the other magnetrons not paired to the overheating magnetron to operate according to normal parameters.

Referring to Figs. 3 and 4, in the preferred embodiment the vacuum chamber 102 is cylindrical. A circumferential side wall 103 is divided into the first side 104 and the second side 106 by a plane 105 bisecting the vacuum chamber 102 along a longitudinal axis 117 of the vacuum chamber 102. Plane 105 is preferably substantially vertical. An access hatch 135 is mounted to the first access port 114 to alternately seal and provide access to the interior of the vacuum chamber 102 The plurality of microwave ports 118 are evenly distributed into a first array 136 and a second array 138 on the first side 104 and the second side 106, respectively. Each microwave port 118 in the first array 136 is preferably oriented orthogonal to a first array plane 137 passing through the longitudinal axis 117. Likewise, each microwave port 118 in the second array 138 is preferably oriented orthogonal to a second array plane 139 also passing through the longitudinal axis 107. The first array plane 137 and the second array plane 139 may be the same plane, in which case the first array 136 and the second array 138 are diametrically opposed. Alternatively, the first array plane 137 and the second array plane 139 may define an angle X between them. X may be any angle between 0 and 180 degrees. For example, in Figs. 3 and 4 X is approximately 90 degrees.

Microwaves from each microwave generator 124 interact with the microwaves from the other generators, producing areas of varying electromagnetic field strength within the vacuum chamber 102. Therefore, a product carousel 140 is preferably mounted within the vacuum chamber to rotate product through these areas of varying field strength, thereby limiting the product’s prolonged exposure to areas of high strength and mitigating the chances of the product getting burned. The product carousel 140 is preferably made from microwave- transparent materials. Other apparatus for moving the product within the vacuum chamber are possible without departing from the scope of the invention.

Referring to Figs 5a to 5d, each microwave port 118 is preferably circular. A transition horn 142 is mounted by flange clamps 144 to the microwave port. Microwave generator assemblies 122 are fixed to the transition horn 144. By loosening the flange clamps 144 and rotating the transition horn 142, the angle of the waveguide 125 can be re-oriented to allow for different angle pairings as described below. In another embodiment, each microwave generator assembly 122 further comprises a circulator 150 connected to the waveguide 125. The circulator has a first port 152, a second port 154, and a third port 156. The first port 152 is mounted to the waveguide 125. The second port 154 is mounted to the vacuum chamber 102. The third port 156 is connected to a water load 160.

Microwave energy entering the circulator 150 through any of the ports will exit primarily through the next sequential port. For example, microwave energy entering the circulator 150 from the waveguide 125 through the first port 152 will mostly exit through the second port 154. However, microwave energy coming from the vacuum chamber 102 through the second port 154 will be mostly diverted into the water load 160 through the third port 156. The circulator 150 thereby substantially isolates the magnetron 126 from cross-talk radiation, allowing it to operate longer without overheating.

Referring to Fig. 6, in the preferred embodiment waveguides are angle-paired to other waveguides in the same array. Fig. 6 shows an exemplary first array 136 in plan view. In this exemplary view, waveguide 125a has been angle-paired to waveguide 125f, waveguide 125b has been angle-paired to waveguide 125e, and waveguide 125c has been angle-paired to waveguide 125d. Other arrangements are possible without departing from the scope of invention. Additionally, waveguides may be angle-paired to more than one other waveguide. For example, the first array 136 may consist of two sets of angle-paired triplets. In practice, the physical parameters of the material being dehydrated will dictate which waveguides should be angle-paired to which other waveguides.

Referring to Figs. 7 and 8, in another embodiment the first array 136 and the second array 138 (hidden behind the vacuum chamber 102 in Fig. 7) are diametrically opposed as described above. In this embodiment, microwave generators may be angle-paired to generators in the same array as in the preferred embodiment. Microwave generators may also be paired cross-array, i.e. a waveguide 125 in the first array 136 may be paired to another waveguide in the second array 138. For example, as shown in Fig. 8 waveguides 125a and 125g are paired, waveguides 125b and 125h are paired, and waveguides 125c and 125i are paired. Many more possible configurations are available without departing from the scope of the invention.

Referring to Fig. 9, the VMD 100 further comprises a controller 146 to automate control over power output of the magnetrons 126. The product temperature sensors 117 and the thermocouples 132 input temperature data to the controller 146, which operates the magnetrons 126 according to that temperature data. In the event of sudden increases in the temperature data from one of the thermocouples 132, the controller 146 is programmed to reduce power to the pair counterpart(s) of the magnetron 126 associated with that thermocouple 132. The controller 146 may output readings to a display 148 for an operator. Preferably, manual override controls 162 are also provided. A single controller 146 may also be configured to operate multiple VMDs simultaneously.

The embodiments described above preferably operate in a batch process. Product is introduced into the vacuum chamber 102 through the access hatch 135. The access hatch 135 is closed and the controller 146 powers the vacuum pump 138 to reduce pressure in the vacuum chamber 102. The controller 146 operates the magnetrons 126 according to the programmed dehydration routine and the data received from the product temperature sensors 117. When dehydration is complete, the magnetrons 126 are powered off and the vacuum chamber 102 is vented to atmosphere so that the access hatch 135 can be opened and the dehydrated product removed. Referring to Fig. 10, the controller 146 initiates a separate routine in the event that a magnetron 126 overheats. At block 200, the controller 146 operates the regular programmed routine. At block 210, the controller 146 routinely checks the temperature data from the thermocouples 132. Where that data indicates that a magnetron 126 is overheating, the controller 146 proceeds to block 220 and shuts off or reduces power to the overheating magnetron’s angle-pair counterparts. The controller 146 may also proceed to block 230 and turn off or reduce power to the overheating magnetron as well. At block 240, the controller 146 checks to see if the other non-paired magnetron(s) are operating at maximum capacity. If they are not, the controller can increase power to those magnetrons at block 250 to compensate for the lack of power input from the angle-paired magnetrons. At block 260, the controller 146 monitors the temperature of the overheated magnetron(s). Once they return to a safe operating temperature, the controller 146 turns the angle pair counterparts on at block 270 and, if necessary, the overheated magnetron back on at block 280, at which point the controller 146 returns to the programmed routine at block 200.

Referring to Figs. 11 and 12, in another embodiment a VMD 500 comprises an elongate cuboid vacuum chamber 502 having a first wall 504 and a second wall 506. A plurality of microwave generator assemblies 122 are mounted in transverse rows on the first and second walls 504, 506. The microwave generator assemblies 122 on the first wall 504 may be longitudinally offset from the microwave generator assemblies 122 on the second wall 506 as shown in Fig. 12. The VMD 500 preferably operates in a continuous feed process. Product, preferably on trays, is loaded into the first airlock 510 and carried through the vacuum chamber 502 on conveyor 512. Preferably, the vacuum chamber 502 is divided by interior microwave baffles 514. The interior microwave baffles 514 allow the product through but minimize the transfer of microwaves. The interior microwave baffles 514 thereby establish “zones” 516 of largely independent microwave power levels. Microwave generators 124 and their associated waveguides are angle-paired within each zone 516, in either a same-array or cross-array configuration. Product exits the vacuum chamber 502 at the second airlock 518, where it may be unloaded by the operator.

A controller 520 for the VMD 500 operates in a similar manner as controller 146 described above. In addition to adjusting the power output of cross-talking magnetrons inside each microwave zone 516, the controller 520 may also adjust power to magnetrons in adjacent zones to compensate for the reduced power output within the zone 516 where the cross-talk was occurring.

In the foregoing description, exemplary modes for carrying out the invention in terms of examples have been described. However, the scope of the claims should not be limited by those examples, but should be given the broadest interpretation consistent with the description as a whole. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.