JP7653149B2 - Microwave Dryer - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act Food and Development Vol. 56 No. 12 (Issue 767) December 2021 Issue Published on December 1, 2021, Pages 11-16

The present invention relates to a microwave dryer that irradiates microwaves onto a dielectric material to be dried to a predetermined dry state, and in particular to improvements in the mounting position and mounting angle of a waveguide that guides microwaves generated by a microwave oscillator into the drying chamber body.

Conventionally, microwave dryers have been used as devices for drying dielectric materials to a predetermined dry state, and as drying devices that can obtain a high-quality dry state without damaging the components contained in the raw materials of the materials to be dried.
As a structure for improving the productivity of such microwave dryers, a microwave dryer has also been developed in which microwave irradiation devices each consisting of a microwave oscillator and a waveguide are provided on one side of a side wall of a drying chamber body and the devices are stacked in multiple tiers in the vertical direction, as shown in Patent Document 1 listed below.

Also, as shown in Figures 16 and 17, a microwave dryer 101 has been developed that is equipped with a turntable 111 that rotates the loading tray 109 contained in the drying chamber main body 105 so that the temperature distribution of the material A to be dried on the loading tray 109 becomes uniform. Furthermore, a prototype has been made in which multiple waveguides 107A, 107B are installed at different horizontal mounting angles in order to reduce uneven drying caused by uneven heating of the microwaves.

JP 2013-113448 A

However, even when the above-mentioned turntable 111 is adopted and multiple waveguides 107A, 107B are installed at different horizontal installation angles, when the temperature distribution of the objects A to be dried is examined when multiple objects A to be dried are arranged side by side on the loading tray 109 as shown in Figures 16 and 17, the results show that the temperature is higher on the outer periphery of the loading tray 109 close to the opening 108 of the waveguide 107 and lower on the central portion.
This is thought to be related to the fact that the electric field strength acting on the object A to be dried by the microwaves radiated from the opening 108 of the waveguide 107 changes depending on where the object A to be dried is placed on the loading tray 109.

That is, the electric field of the microwave acts on the object A to be dried, which is a dielectric material containing moisture, and the object A to be dried is heated.
The microwaves attenuate as the distance from the opening 108 of the waveguide 107 increases, and are reflected by colliding with the side wall surface 113 of the drying chamber body 105, which is a metal surface.
As a result, within the drying chamber main body 105, microwaves traveling in the propagation direction and microwaves traveling in the reflection direction interfere with each other, causing the electric field strength to vary depending on the position on the loading tray 109 on which the material to be dried A is placed.

The electric field strength varies, causing uneven heating of the object A to be dried, which in turn causes uneven temperature of the object A after drying, thereby causing a decrease in the drying quality of the object A to be dried.
Specifically, it is considered that a strong electric field is locally generated near the opening 108 of the waveguide 107 and near the side wall surface 113 of the drying chamber body 105, and that this strong electric field acts on the objects A to be dried on the outer periphery of the loading tray 109, increasing the temperature of the objects A to be dried. On the other hand, it is considered that at the center of the loading tray 109, the microwave energy is absorbed by the objects A to be dried on the outer periphery, and a weaker electric field acts on the objects A to be dried on the outer periphery, decreasing the temperature of the objects A to be dried.

The present invention was made based on these points, and its purpose is to provide a microwave drying device that can be used for mass production and can dry all the objects on the loading tray well without temperature unevenness, regardless of the position of the objects on the loading tray in the drying chamber body.

In order to achieve the above object, a microwave dryer according to a first aspect of the present invention is a microwave dryer comprising: a microwave oscillator for oscillating microwaves; a waveguide for guiding the oscillated microwaves into a drying chamber body; and a drying chamber body having at least one opening for setting a loading tray on which an object to be dried is placed and for carrying the object in and out,
The waveguide has an extension protrusion such that the opening protrudes inward from one of the side wall surfaces of the drying chamber body , and the vertical mounting angle of the waveguide with respect to the side wall surface is set upward so that the opening faces the ceiling surface of the drying chamber body. The loading tray is set on a turntable provided in the drying chamber body so that the material to be dried can be dried while rotating. The vertical mounting angle of the waveguide is set to an angle such that the incident angle between the ceiling surface and a propagation center line passing through the center of the opening of the waveguide and extending along the central axis of the waveguide is equal to the reflection angle between the ceiling surface and a reflection center line extending from the intersection where the propagation center line intersects with the ceiling surface of the drying chamber body toward the center of rotation of the turntable. The microwaves radiated from the extension protrusion are reflected once by the ceiling surface and irradiated to the center of rotation of the turntable .

A microwave dryer according to claim 2 is the microwave dryer according to claim 1 , characterized in that the vertical mounting angle of the waveguide is set to an angle such that the incidence angle is in the range of 30° to 50°.

Further, the microwave dryer according to claim 3 is the microwave dryer according to any one of claims 1 and 2 , characterized in that the torsional mounting angle of the waveguide about the central axis with respect to the vertical axis is set within an angle range that allows the electric field action surface of the waveguide to be directed toward the opposing side wall surface of the drying chamber main body or the inner wall surface of the opening and closing door.

Further, a microwave dryer according to claim 4 is the microwave dryer according to claim 3 , characterized in that the twist mounting angle of the waveguide is set to be in the range of -20° or more and +20° or less with respect to a vertical axis, when the clockwise direction is defined as "+" as viewed in the propagation direction.

Further, a microwave dryer according to claim 5 is the microwave dryer according to any one of claims 1 to 4 , wherein the waveguide is attached to the side wall surface in a direction such that a central axis of the waveguide passes through a rotation center of the turntable in a plan view, and a horizontal attachment angle of the waveguide with respect to the side wall surface is set to be perpendicular to the side wall surface and such that left and right deflection angles with respect to a horizontal center line passing through the rotation center of the turntable are each in a range of 5° or more and 25° or less.

Further, a microwave dryer according to claim 6 is the microwave dryer according to claim 5 , characterized in that a plurality of the waveguides are provided for a single drying chamber body, and a horizontal mounting angle between two adjacent waveguides where the central axes of the waveguides intersect at the rotation center of the turntable is set to be in the range of 10° to 50°.

Further, the microwave dryer according to claim 7 is the microwave dryer according to any one of claims 1 to 6 , characterized in that the waveguide is a rectangular waveguide attached so that its electric field action surface faces the left and right direction, and the waveguide is attached so that no material to be dried and no structures including other side wall surfaces and inner wall surfaces of the opening and closing door are present in the vicinity of the electric field action surface of the waveguide protruding from the side wall surface into the drying chamber body.

Further, a microwave dryer according to claim 8 is the microwave dryer according to any one of claims 1 to 7 , characterized in that the waveguide has a split structure that can be split into an outer side and an inner side of a side wall surface to which the dryer body is attached.

Further, a microwave dryer according to claim 10 is the microwave dryer according to any one of claims 1 to 8 , characterized in that the drying chamber body has a stacked structure formed by stacking a plurality of stages in the vertical direction, and the one or a plurality of sets of microwave oscillators and waveguides are attached to the drying chamber body of each stage.

The above means can provide the following effects:
First, the microwave dryer of the present invention comprises a microwave oscillator that oscillates microwaves, a waveguide that guides the oscillated microwaves into the drying chamber body, and a drying chamber body in which a loading tray on which an object to be dried is placed is set and which has at least one opening for loading and unloading the object.
Furthermore, the waveguide is provided with an opening protruding inward from the side wall surface of the drying chamber body, and the vertical mounting angle of the waveguide with respect to the side wall surface is set upward so that the opening faces the ceiling surface of the drying chamber body.

As a result, the items to be dried placed on the loading tray are not only exposed to the direct microwave waves emitted from the opening of the waveguide, which have a strong electric field strength and tend to heat up the items, but also to the reflected waves, which have a weaker electric field strength as the direct waves are reflected off the ceiling surface, reducing uneven heating. This helps to keep the variation in drying quality caused by uneven temperatures of the items to be dried after drying to a minimum.

In addition, the above-mentioned loading tray is set on a turntable provided in the drying chamber body so that the material to be dried can be dried while rotating. When the vertical mounting angle of the above-mentioned waveguide is set to an angle such that the angle of incidence formed by the propagation center line that passes through the center of the opening of the waveguide and extends along the central axis of the waveguide and the ceiling surface is equal to the angle of reflection formed by the reflection center line that extends from the intersection point where the propagation center line intersects with the ceiling surface of the drying chamber body toward the rotation center of the above-mentioned turntable and the ceiling surface, the microwaves radiated from the opening of the waveguide spread out so as to diffuse around the path that passes through the above-mentioned propagation center line and reflection center line to the rotation center of the turntable. Therefore, the material to be dried on the loading tray set on the turntable is prevented from being excessively heated at the outer periphery of the turntable, and insufficient heating at the center of the turntable is improved, resulting in a uniform temperature distribution in the radial direction based on the rotation center of the turntable.

Furthermore, when the vertical mounting angle of the waveguide is set to an angle such that the incident angle is in the range of 30° or more and 50° or less, the propagation of microwaves expanding from the center of rotation of the turntable is carried out in an optimal state.
Furthermore, when the torsional mounting angle of the waveguide about its central axis with respect to the vertical axis is set within a range in which the electric field action surface of the waveguide can be directed toward the opposing side wall surface of the drying chamber body or the inner wall surface of the opening and closing door, it becomes possible to correct the positional deviation of the radiation position of the microwaves on the loading tray caused by differences in the vertical or horizontal mounting position of the waveguide and structural factors such as the shape and size of the drying chamber body by adjusting the torsional mounting angle of the waveguide about its central axis without changing the vertical or horizontal mounting position of the waveguide.
Furthermore, by adjusting the twist mounting angle within a range that enables the electric field action surface of the waveguide to be directed toward the opposing side wall surface of the drying chamber body or the inner wall surface of the opening and closing door, it is possible to suppress the temperature rise caused by the increased amount of microwave radiation toward the material to be dried outside the loading tray, which is caused by excessive twisting of the waveguide, and to achieve a uniform temperature distribution over the entire surface of the loading tray.
Furthermore, when the twist mounting angle of the waveguide is set to be in the range of -20° or more and +20° or less with respect to the vertical axis, where "+" is the clockwise direction as viewed in the propagation direction, the propagation of the microwaves spreading out based on the center of rotation of the turntable is kept within an optimal range without bias.

In addition, when the waveguide is attached to the side wall surface in a direction such that the central axis of the waveguide passes through the center of rotation of the turntable in a plan view, and the horizontal attachment angle of the waveguide to the side wall surface is set so that the left and right deflection angles with respect to a horizontal center line that is perpendicular to the side wall surface and passes through the center of rotation of the turntable are in the range of 5° to 25°, it becomes possible to attach multiple waveguides to the same side wall surface, and the propagation of microwaves radiated from the opening of the waveguide is also carried out smoothly without affecting the horizontal attachment angle.

In addition, if multiple waveguides are provided for a single drying chamber body and the horizontal mounting angle between two adjacent waveguides, where the central axes of the two waveguides intersect at the rotation center of the turntable, is set to a range of 10° to 50°, the microwave output can be increased to improve the drying efficiency of the objects to be dried. In addition, the phase difference between the microwaves radiated from the openings of the two waveguides changes, and because these interfere with each other, the standing waves are not fixed, which causes variations in the temperature distribution of the objects to be dried on the loading tray. Therefore, by fine-tuning the horizontal mounting angle between the above-mentioned waveguides within the above angle range, the adverse effects on the propagation of the microwaves radiated from the openings of the two waveguides can be minimized, and drying can be carried out smoothly.

In addition, if the waveguide is a rectangular waveguide attached so that the electric field acting surface faces left and right, and the waveguide is attached so that there are no structures, including the material to be dried and other side walls and the inner wall surfaces of the opening and closing door, near the electrolytic acting surface of the waveguide protruding from the side wall surface into the drying chamber body, the strong electric field that is locally generated near the opening of the waveguide and near the side wall surface of the drying chamber body is prevented from adversely affecting the temperature of the material to be dried itself and the temperature inside the drying chamber body, thereby achieving uniform, even, and high-quality drying of the material to be dried.

In addition, if a waveguide with a split structure that can be split into an outer and inner part of the side wall surface to which the waveguide is attached in the drying chamber body is used, maintenance becomes easier, and if a malfunction or problem occurs in only one of the parts, it is possible to resolve the malfunction or problem by replacing, repairing, cleaning, or otherwise maintaining only that part.

In addition, when a drying chamber body having a stacked structure formed by stacking multiple tiers vertically is adopted and one or more sets of microwave oscillators and waveguides are attached to the drying chamber body of each tier, a large amount of material to be dried can be dried at once, improving the drying productivity of the material to be dried.
Furthermore, since the waveguide is attached to the side wall surface of the drying chamber body of each stage, the microwave oscillator and the waveguide do not get in the way when stacking the drying chamber bodies.

FIG. 1 is a diagram showing a first embodiment of the present invention, and is a conceptual diagram showing an outline of the overall configuration of a microwave dryer. FIG. 1 is a perspective view showing a main part of a microwave dryer according to a first embodiment of the present invention. FIG. 1 is a diagram showing a first embodiment of the present invention, and is a front view showing a main part of a microwave dryer. FIG. 1 is a left side view showing a main part of a microwave dryer according to a first embodiment of the present invention. FIG. 1 is a diagram showing a first embodiment of the present invention, and is a plan view showing a main part of a microwave dryer. FIG. 2 is a perspective view showing the first embodiment of the present invention, illustrating the relationship between the vertical mounting angle of the waveguide and the angle of incidence and the angle of reflection. FIG. 2 is a perspective view showing the twist mounting angle of the waveguide according to the first embodiment of the present invention. FIG. 2 is a diagram showing the first embodiment of the present invention, and is a plan view showing the relationship between the horizontal installation angle and the left and right deflection angle when two waveguides are installed. FIG. 1 is a diagram showing the first embodiment of the present invention, and is a plan view showing the electric field distribution in a waveguide, the propagation direction of microwaves radiated from the waveguide, and the attenuation curve of the electric field of the microwave. FIG. 2 is a plan view showing the first embodiment of the present invention, in which the propagation directions of microwaves radiated from two waveguides are overlapped. FIG. 11 is a front view showing a microwave dryer according to a second embodiment of the present invention, in which drying chamber bodies are stacked in three tiers in the vertical direction. FIG. 2 is a diagram showing the measurement results of the first embodiment of the present invention, illustrating the temperature distribution of the material to be dried on the turntable and the variation in the temperature distribution. FIG. 1 is a front view showing the main parts of a microwave dryer, illustrating a case in which a first waveguide is installed in the manner of the present invention, a second waveguide is horizontal, and the central axis of the waveguide does not pass through the center of rotation of the turntable. FIG. 1 is a plan view showing the main parts of a microwave dryer, showing a case in which a first waveguide is installed in the manner of the present invention, a second waveguide is horizontal, and the central axis of the waveguide does not pass through the center of rotation of the turntable. FIG. 1 shows a case where a first waveguide is installed in the manner of the present invention, a second waveguide is horizontal, and the central axis of the waveguide does not pass through the center of rotation of the turntable, and is an explanatory diagram showing the temperature distribution of the material to be dried on the turntable and the variation in the temperature distribution. FIG. 1 is a diagram showing the structure of a conventional microwave dryer, and is a front view showing a main part of the microwave dryer. FIG. 1 is a diagram showing the structure of a conventional microwave dryer, and is a plan view showing a main part of the microwave dryer.

Hereinafter, the microwave dryer of the present invention will be specifically described by taking as examples two embodiments, a first embodiment shown in FIGS. 1 to 10 and a second embodiment shown in FIG.
In the following description, first, the first embodiment shown in FIGS. 1 to 10 is taken as an example, and an outline of the overall configuration of the microwave dryer of the present invention is described based on FIG. 1. Then, the configuration of the main parts of the microwave dryer of the present invention is specifically described based on the first embodiment shown in FIGS. 1 to 10.

Next, a microwave dryer according to a second embodiment shown in FIG. 11 will be described, focusing on the differences from the first embodiment. Then, measurement results will be described with reference to FIGS. 12 and 15 for the case where two waveguides are provided in the embodiment of the present invention and the case where two waveguides are provided in the embodiment shown in FIGS. 13 and 14.
Finally, another embodiment of the present invention having a partially different configuration from the above two embodiments will be mentioned.

(1) Overview of the overall configuration of a microwave dryer (see Figure 1)
The microwave dryer 1 of the present invention is basically composed of a microwave oscillator 3 that oscillates microwaves M, a waveguide 7 that guides the oscillated microwaves M into the drying chamber main body 5, and a drying chamber main body 5 in which a loading tray 9 on which the material to be dried A is placed is set and which has at least one opening 6 for loading and unloading.
In the present invention, the waveguide 7 is provided with the opening 8 protruding inward from the side wall surface 13 of the drying chamber main body 5, and the vertical mounting angle θ of the waveguide 7 with respect to the side wall surface 13 is set upward so that the opening 8 faces the ceiling surface 15 of the drying chamber main body 5.

The microwave dryer 1A according to this embodiment further includes a turntable 11 that supports the set loading tray 9 while rotating it, an opening/closing door 17 that is attached to the opening 6 of the drying chamber body 5 in an openable/closable state and forms a shielded space inside the drying chamber body 5 when closed, a pressure reducing device 19 that is connected to the drying chamber body 5 and is configured as a vacuum pump or the like to reduce the pressure inside the drying chamber body 5, an air inlet pipe 21 for introducing air Q from the outside, an air adjustment introduction valve 23 for switching between introducing and blocking the air Q and adjusting the flow rate of the introduced air Q, a temperature sensor 25 that is configured as a radiation thermometer or the like to measure the temperature inside the drying chamber body 5 during drying, and a control device 29 that controls various aspects of the microwave dryer 1A.

A microwave leakage prevention mechanism (not shown) is provided on the back of the opening/closing door 17 so as to surround the opening 6 of the drying chamber body 5, thereby preventing the microwaves M radiated into the drying chamber body 5 from leaking to the outside. As an example of the microwave leakage prevention mechanism, a sealing structure (not shown) made of a rubber packing or the like is provided on the outside to ensure sealing when the opening/closing door 17 is closed.

(2) Configuration of Main Parts of Microwave Dryer (See Figures 1 to 10)
The material A to be dried using the microwave dryer 1 of the present invention can be various solid or liquid items, such as food items such as vegetables and fruits, as well as industrial materials or additive materials for foods and cosmetics, and dispersions of cellulose nanofibers (CNF) used for various purposes.
Here, cellulose nanofiber (CNF) is a biomass material obtained from plant fibers such as wood, and is a fibrous material with a fiber width of about several nm to several tens of nm. CNF is known to have the properties of being more than five times stronger than steel and having a low expansion coefficient of about 1/50th that of glass, and is a new material that is expected to be applied in various fields.

In this embodiment, a large number of petri dish-like containers filled with water were prepared as the objects to be dried A, and these were aligned and placed on a loading tray 9 that was circular in plan view and set on a disc-shaped turntable 11, as shown in Figures 2 and 5.
The turntable 11 receives power from a drive device not shown, and the power is transmitted through rollers 31, of which four are provided, for example, on the underside of the outer periphery of the turntable 11, causing the turntable 11 to rotate at a predetermined rotational speed in a predetermined rotational direction around its rotation center C.
The temperature of the objects A to be dried arranged on the loading tray 9 can be measured, for example, by a product temperature sensor (not shown) provided in each container.

In this embodiment, the drying chamber body 5 is, as an example, a flat box-shaped member having a width W of 1128 mm, a depth D of 1000 mm, and a height T of 499 mm. The ceiling surface 15 and bottom surface 16 constituting the drying chamber body 5, as well as the three side walls 13A, 13B, and 13C and the inner wall surface of the opening and closing door 17 are, as an example, all formed from metal plates.

In addition, in this embodiment, as an example, two waveguides 7A, 7B are provided on one side wall surface 13A of the drying chamber main body 5, and these waveguides 7A, 7B are rectangular waveguides that are long in the propagation direction Y, and are attached to the one side wall surface 13A so that the opposing electric field action surfaces 33L, 33R face in the left-right direction X.
In addition, these waveguides 7A, 7B have a split structure that can be divided between the outside and inside of the above-mentioned one side wall surface 13A, and the part located outside the drying chamber main body 5 is the main body portion 35, and the part located inside the drying chamber main body 5 is the extended protrusion portion 37.

The vertical mounting angle θ of the waveguide 7 is set to an angle (θ1=θ2, θ=90°-θ1) at which the incident angle θ1 formed by the propagation center line L, which passes through the opening center O of the opening 8 of the waveguide 7 and extends along the central axis of the waveguide 7, and the ceiling surface 15, is equal to the reflection angle θ2 formed by the reflection center line R, which extends from the intersection point B where the propagation center line L intersects with the propagation center line L toward the rotation center C of the turntable 11, and the ceiling surface 15, as shown in Figures 3 and 6.
The vertical mounting angle θ of this waveguide 7 is set so that the incident angle θ1 is in the range of 30° to 50°, preferably so that the incident angle θ1 is approximately 40°.

In addition, the torsional mounting angle α of the waveguide 7 about the central axis thereof with respect to the vertical axis V is an adjustment angle used mainly for the purpose of correcting a positional deviation when a positional deviation occurs in the radiation position on the loading tray 9 of the microwaves M radiated from the opening 8 of the waveguide 7.
The torsional mounting angle α is set to an angle within a range that allows the electric field action surface 33 of the waveguide 7 to be directed toward the opposing side wall surface 13B of the drying chamber main body 5 or the inner wall surface of the opening/closing door 17 (including structures within the drying chamber main body 5, such as the driving device of the turntable 11).
Theoretically, by reducing the twisted mounting angle α (tilting the electric field action surface 33 of the waveguide 7 vertically), the amount of microwaves M radiated to the material A to be dried in the outer area A2 on the loading tray 9 set on the turntable 11 is reduced, and the temperature of the material A to be dried in the outer area A2 is lowered. As a result, the energy of the microwaves M is less likely to be absorbed by the material A to be dried in the outer area A2, and the temperature of the material A to be dried in the central area A1 near the rotation center C of the turntable 11 is relatively higher.

However, in reality, the temperature is not necessarily highest at the center of rotation C of the turntable 11 due to structural factors such as the mounting positions of the waveguides 7A, 7B in the left-right direction X and the up-down direction Z relative to the side wall surface 13A of each of the waveguides 7A, 7B and the shape and size of the drying chamber body 5.
In such a case, the deviation of the radiation position of the microwave M on the loading tray 9 can be corrected by adjusting the twisted mounting angle α of the waveguide 7. This makes it possible to adjust the temperature difference between the outer area A2 and the central area A1 of the turntable 11, so that the temperature distribution in the radial direction r based on the rotation center C of the turntable 11 becomes more uniform, and the drying quality of the dried object A after drying is further improved.

Specifically, the torsional mounting angle α is set to be in the range of -20° or more and +20° or less, with clockwise rotation being "+" and counterclockwise rotation being "-" with respect to the vertical axis V.
Therefore, in practice, the twist mounting angle α is adjusted and determined so that the temperature distribution in the radial direction r of the material A becomes most uniform while observing the temperature distribution of the material A. Incidentally, in this embodiment, the twist mounting angle α of the waveguide 7 is set to 10.5° clockwise, and the twist mounting angles α of the two waveguides 7A and 7B are set to be in the same direction and at the same angle as shown in FIG.

Further, the waveguide 7 is attached to the side wall surface 13A of the drying chamber main body 5 in such a direction that the central axis of the waveguide 7 passes through the rotation center C of the turntable 11 in a plan view.
The horizontal mounting angle of the waveguide 7 relative to the side wall surface 13A is set so that the left and right deflection angles β1, β2 relative to a horizontal center line H that is perpendicular to the side wall surface 13A and passes through the rotation center C of the turntable 11 are in the range of 5° or more and 25° or less.

Here, a procedure for setting the horizontal installation angle of the waveguide 7 when two waveguides 7 are provided will be described with reference to Fig. 10. The microwaves M radiated from the first waveguide 7 are simply reflected by the inner wall surfaces of the drying chamber body 5 and the opening/closing door 17 and the structures within the drying chamber body 5 (including the drive system of the turntable 11 and the second waveguide 7), so that the standing wave of the microwaves M is fixed.
On the other hand, since the microwave M radiated from the second waveguide 7 is asynchronous with the microwave M radiated from the first waveguide 7, a phase difference occurs between these two microwaves M, and these two microwaves M interfere with each other, so that the standing wave of the microwave M is not fixed.

Here, by determining the positional relationship between the opening center O of the opening 8, which is the radiation position of the microwave M radiated from the first waveguide 7, the intersection B between the propagation center line L extending from the opening center O and the ceiling surface 15, and the rotation center C of the turntable 11, the positional relationship between the direction of the reflection center line R extending from the intersection B toward the rotation center C of the turntable 11 and the object to be dried A on the turntable 11 is determined.
Theoretically, the temperature distribution in the radial direction r of the object A on the turntable 11 is determined by the reflection angle θ2 between the reflection center line R and the ceiling surface 15. However, when an analysis of electromagnetic waves and heat conduction is actually performed considering the reflection of microwaves M in the drying chamber body 5, there are cases where the temperature distribution of the object A located at the rotation center C of the turntable 11, particularly the rotation center C of the turntable 11 cannot be heated. Therefore, when heating of the rotation center C cannot be confirmed, the swing angles β1 and β2 of the horizontal installation angle are changed to 0°, ±5°, ±10° to adjust the rotation center C of the turntable 11 so that it can be heated well.

Similarly, for the second waveguide 7, without changing the positional relationship between the opening center O of the opening 8, which is the radiation position of the microwaves M radiated from the second waveguide 7, the intersection B of the propagation center line L extending from the opening center O and the ceiling surface 15, and the rotation center C of the turntable 11, the second waveguide 7 is rotated around the rotation center C to determine the above-mentioned positional relationship and positioned.
However, the positional relationship of the second waveguide 7 with respect to the drying chamber body 5 is different from that of the first waveguide 7. Therefore, an analysis of electromagnetic waves and heat conduction is actually performed again to confirm whether the rotation center C of the turntable 11 can be heated, and if heating of the rotation center C cannot be confirmed, the deflection angles β1 and β2 of the horizontal mounting angle are changed to 0°, ±5°, and ±10°, and adjustments are made so that the rotation center C of the turntable 11 can be well heated.

Based on the values of the deflection angles β1 and β2 of the horizontal mounting angle of the waveguide 7 set by such a procedure, in the present invention, the horizontal mounting angle β between two adjacent waveguides 7A, 7B where the respective central axes of the waveguides 7A, 7B intersect at the rotation center C of the turntable 11 is set to be in the range of 10° or more and 50° or less.
Incidentally, in this embodiment, as shown in Figures 5 and 8, the left deflection angle β1 of the waveguides 7A and 7B is set to 11.8°, the right deflection angle β2 is set to 16.8°, and the horizontal mounting angle β between the two waveguides 7A and 7B is set to β = β1 + β2 = 28.6°, as an example.

As shown in Figures 5, 9 and 10, the waveguide 7 is attached so that there are no structures, including the material to be dried A, other side wall surfaces 13B, 13C and the inner wall surface of the opening and closing door 17, in the vicinity of the electric field action surface 33 of the extension protrusion 37 of the waveguide 7 protruding into the drying chamber body 5 from the side wall surface 13A to which the waveguide 7 is attached.
This makes it possible to prevent excessive heating from occurring locally on the object A to be dried or the structure located in the outer peripheral area A2 of the turntable 11 close to the extension protrusion 37.
In addition, by using the reflected wave M2 of the microwave M directed toward the center of rotation C of the turntable 11 whose electric field strength has been weakened by hitting the ceiling surface 15 once, instead of the direct wave M1 of the microwave M directed toward the propagation direction Y which is directly radiated from the opening 8 of the waveguide 7, the temperature distribution of the objects A to be dried arranged in the radial direction r of the turntable 11 becomes uniform, making it possible to realize high-quality drying without temperature unevenness.

[Second embodiment] (see FIG. 11)
The microwave dryer 1B according to the second embodiment of the present invention is a microwave dryer having a configuration in which the microwave dryer 1A according to the first embodiment described above is stacked in a plurality of stages in the vertical direction Z.
Therefore, the description here will be omitted for the configuration of the microwave dryer 1A alone described in the first embodiment above, and will focus on the changes in configuration that arise when the microwave dryers 1A are stacked.

That is, the microwave dryer 1B according to this embodiment is configured by stacking drying chamber bodies 5A, 5B, and 5C in three stages in the vertical direction Z as shown in FIG. 11, and each stage of the drying chamber bodies 5A, 5B, and 5C is provided with the above-mentioned two sets of microwave oscillators 3A, 3B, two sets of waveguides 7A, 7B, one set of turntable 11, and a temperature sensor 25.
In addition, the three drying chamber bodies 5A, 5B, and 5C are provided by dividing the internal space of a large, vertically elongated housing body 39 into three rooms, and a large sliding door 43 is provided to close the front opening 41 of the housing body 39.

Therefore, in this embodiment, no opening/closing door 17, microwave leakage prevention mechanism, or sealing structure is provided for each drying chamber body 5A, 5B, 5C, and instead, a set of microwave leakage prevention mechanism and sealing structure is provided between the opening/closing door 43 and the back surface thereof, surrounding the front opening 41 of the single housing body 39.
Like the microwave dryer 1A according to the first embodiment described above, the microwave dryer 1B according to the present embodiment configured in this manner can prevent excessive heating that occurs locally around the opening 8 of the waveguide 7, and can achieve uniform drying of the material A to be dried without uneven heating that is not affected by the location of the material A placed on the loading tray 9.
Furthermore, in this embodiment, since the amount of the object A to be dried at one time can be increased, the drying productivity of the object A to be dried is significantly improved.

[Measurement results]
Next, two measurement results will be described, which were obtained using a microwave dryer 1A shown in FIGS. 9 and 10 in which two waveguides 7 are provided in the embodiment of the present invention, and a microwave dryer 10A shown in FIGS. 13 and 14 in which the first waveguide 7 is installed in the embodiment of the present invention and the second waveguide 7 is horizontal and installed such that the central axis of the waveguide 7 does not pass through the rotation center C of the turntable 11.
In this measurement, 69 containers arranged on a loading tray 9 were filled with water and dried for 10 minutes with a microwave output of 1000 W, and the temperature of the water (substance A) to be dried was measured.
The measurement results are shown in Figures 12 and 15, where Figure 12 shows the temperature distribution and the variation in temperature distribution of the material A to be dried when using the microwave dryer 1A according to the first embodiment of the present invention shown in Figures 9 and 10. Meanwhile, Figure 15 shows the temperature distribution and the variation in temperature distribution of the material A to be dried when using the microwave dryer 10A shown in Figures 13 and 14.

First, referring to FIG. 15, a temperature distribution was obtained in which the temperature was highest in the outer peripheral area A2 of the loading tray 9, was low in the intermediate portion, and rose again to a somewhat higher temperature in the central area A1.
In this case, the initial temperature was 23.0° C., the average temperature was 39.4° C., the average temperature rise was 16.4° C., the standard deviation was 3.7° C., and the relative standard deviation was 0.228.

Next, looking at FIG. 12, a temperature distribution was obtained in which the temperature was highest at the center of the loading tray 9, then decreased in the intermediate portion toward the outer peripheral area A2, and then increased again in the outer peripheral area A2 to become somewhat higher.
In this case, the initial temperature was 23.0° C., the same as in FIG. 15, the average temperature was 44.9° C., the average temperature rise was 21.9° C., the standard deviation was 1.8° C., and the relative standard deviation was 0.080.
As a result, it was found that when the microwave dryer 1A according to the first embodiment shown in Figures 9 and 10 in which two waveguides 7A, 7B are installed in the manner of the present invention is used, the variation in temperature distribution in the radial direction r of the material A to be dried is smaller, and the required drying quality can be obtained regardless of where the material A to be dried is placed on the loading tray 9.

On the other hand, when the microwave dryer 10A having two waveguides 7A, 7B installed as shown in Figures 13 and 14 was used, it was found that the variation in temperature distribution in the radial direction r of the material to be dried A was greater, and in particular, localized excessive heating affecting the drying quality of the material to be dried A occurred in the outer peripheral area A2 of the loading tray 9 close to the openings 8 of the waveguides 7A, 7B.
Therefore, when two waveguides 7 are installed in the same drying chamber body 5, it has become clear that when both waveguides 7 are installed in the manner of the present invention, the variation in temperature distribution of the material to be dried A is smaller, and good drying can be achieved without localized excessive heating.

[Other embodiments]
The microwave dryer 1 of the present invention is not limited to the above-mentioned two embodiments, and can be modified within the gist of the invention.
For example, the number of waveguides 7 is not limited to two, but may be one, or three or more. In addition, when the temperature distribution in the circumferential direction of the loading tray 9 is made uniform by arranging a plurality of waveguides 7 at equal intervals with respect to the center of the loading tray 9, the turntable 11 can be omitted.
Moreover, the pressure reducing device 19 provided in the above embodiment may be omitted.

Furthermore, when multiple drying chamber bodies 5 are stacked in the vertical direction Z as in the second embodiment described above, the configuration is not limited to the three-tiered configuration described in the second embodiment described above, and the drying chamber bodies 5 may be stacked in two tiers or four or more tiers.
Furthermore, the waveguide 7 is not limited to a divided structure divided into an outer portion and an inner portion of the side wall surface 13, and it is also possible to use a waveguide 7 having an integral structure.
In addition to providing a temperature sensor for measuring the temperature of the material A to be dried on the container set on the loading tray 9, it is also possible to provide a temperature sensor on the loading surface of the loading tray 9. Also, it is possible to provide the above-mentioned multiple temperature sensors only on the experimental machine in order to know the temperature distribution on the loading tray 9, and to provide, for example, one temperature sensor on the actual machine designed based on the information obtained from the experimental machine in order to measure only the temperature at the position with the highest temperature.

The microwave dryer of the present invention can be used in the field of drying various solid or liquid materials to be dried, and is particularly applicable when it is desired to provide a microwave dryer that can always obtain a stable drying state for the material to be dried regardless of the position of the material on the loading tray and can also accommodate a stacked structure.

1 Microwave dryer 3 Microwave oscillator 5 Drying chamber body 6 Opening 7 Waveguide 8 Opening 9 Loading tray 11 Turntable 13 Side wall surface 15 Ceiling surface 16 Bottom surface 17 Opening and closing door 19 Pressure reducing device 21 Air inlet pipe 23 Air adjustment introduction valve 25 Temperature sensor 29 Control device 31 Roller 33 Electrolytic action surface 35 Main body 37 Extension protrusion 39 Housing body 41 Front opening 43 Opening and closing door 101 Microwave dryer 105 Drying chamber body 107 Waveguide 109 Loading tray 111 Turntable 113 Side wall surface A Material to be dried A1 Outer peripheral area A2 Central area M Microwave M1 Direct wave M2 Reflected wave θ Vertical mounting angle θ1 Incident angle θ2 Reflection angle B Intersection Q Air C Rotation center X Left-right direction Y Propagation direction Z Up-down direction O Opening center L Propagation center line R Reflection center line V Vertical axis α Torsional mounting angle r Radial direction β Horizontal mounting angle β1 (Left side) deflection angle β2 (Right side) deflection angle H Horizontal center line W Width D Depth T Height

Claims (9)

A microwave dryer comprising: a microwave oscillator that oscillates microwaves; a waveguide that guides the oscillated microwaves into a drying chamber body; and a drying chamber body having at least one opening for setting a loading tray on which an object to be dried is placed and for carrying the object in and out,
a vertical mounting angle of the waveguide relative to the side wall surface of the drying chamber body is set upward so that the opening of the waveguide projects inward from one of the side wall surfaces of the drying chamber body, and the vertical mounting angle of the waveguide relative to the side wall surface is set upward so that the opening of the waveguide faces the ceiling surface of the drying chamber body; the loading tray is set on a turntable provided in the drying chamber body so that the material to be dried can be dried while rotating; the vertical mounting angle of the waveguide is set at an angle such that an incident angle formed by a propagation center line passing through the center of the opening of the waveguide and extending along the central axis of the waveguide and the ceiling surface is equal to an angle formed by a reflection center line extending from an intersection point where the propagation center line intersects with the ceiling surface of the drying chamber body toward the center of rotation of the turntable and the ceiling surface; and the microwaves radiated from the extended projection are reflected once by the ceiling surface and irradiated to the center of rotation of the turntable . 2. The microwave dryer according to claim 1 , wherein the vertical mounting angle of said waveguide is set to an angle such that said incident angle is in the range of 30 degrees to 50 degrees. The microwave dryer according to any one of claims 1 to 2, characterized in that a torsional mounting angle of the waveguide about a central axis with respect to a vertical axis is set to an angle within a range that allows an electric field action surface of the waveguide to be directed toward an opposing side wall surface of the drying chamber body or an inner wall surface of an opening/ closing door. 4. The microwave dryer according to claim 3, wherein a twist mounting angle of the waveguide is set to be in the range of -20° or more and +20° or less with respect to a vertical axis, when the clockwise direction is defined as " +" when viewed in the propagation direction. The microwave dryer according to any one of claims 1 to 4, characterized in that, in a plan view, the waveguide is attached to the side wall surface in a direction such that a central axis of the waveguide passes through a rotation center of the turntable, and a horizontal attachment angle of the waveguide with respect to the side wall surface is set so that the waveguide is perpendicular to the side wall surface and has left and right deflection angles with respect to a horizontal center line passing through the rotation center of the turntable in a range of 5° or more and 25° or less. 6. The microwave dryer according to claim 5, wherein a plurality of the waveguides are provided for a single drying chamber body, and a horizontal mounting angle between two adjacent waveguides where their central axes intersect at the rotation center of the turntable is set to be in the range of 10 ° to 50°. The waveguide is a rectangular waveguide attached so that the electric field acting surface faces in the left-right direction,
The microwave dryer according to any one of claims 1 to 6, characterized in that the waveguide is attached so that there are no objects to be dried and no structures, including other side wall surfaces and inner wall surfaces of the opening and closing door, near the electric field action surface of the waveguide protruding from the side wall surface into the drying chamber body. The microwave dryer according to any one of claims 1 to 7 , characterized in that the waveguide has a split structure that allows it to be divided into an outer side and an inner side of a side wall surface to which the dryer body is attached. The microwave dryer according to any one of claims 1 to 8, characterized in that the drying chamber body has a stacked structure formed by stacking a plurality of stages in the vertical direction, and the one or more sets of microwave oscillators and waveguides are attached to the drying chamber body of each stage.

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