JPS5925938B2 - microwave heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microwave heating furnace that heats substances using microwaves, and in particular relates to improvements for efficiently achieving high temperature heating, for example, related to prior art used for making pottery such as pottery. There is a microwave heating furnace shown in Fig. 1 of &A.

In the figure, a microwave generator 1 is coupled to a microwave open 3 via a waveguide 2 . A heated object 4 is placed inside the microwave opener 3 . The object to be heated 4 is first surrounded by the inner container 5. The inner container 5 is made of a material that generates heat by microwaves, such as a metal oxide whose main component is zinc oxide. The inner container 5 is surrounded by an intermediate container 6. This intermediate container 6 is made of a fireproof insulating material with low microwave loss, such as JIS standard A.
It consists of 7 species. Next, the operation will be explained.

Microwaves generated by a microwave generator 1 are guided to a microwave open 3 by a waveguide 2. At this time, resonant electromagnetic fields of various modes are formed within the microwave opener 3. This resonant electromagnetic field is transmitted through the intermediate container 6 to uniformly heat the inner container 5 with microwaves. A uniform heat radiation field is formed inside the inner container 5, which has reached a high temperature due to this microwave heating, and the object to be heated 4 is heated uniformly. Next, consider thermal efficiency in a state of thermal equilibrium. The intermediate container 6 has an outer diameter of 2γ, ■0.2
The sphere of [M], the inner container 5 has an outer diameter 2 of 0 = 0.1 [M]
The temperature of the inner container 5 is θ when the inner container 5 is a spherical body whose outer peripheral surface is in close contact with the inner peripheral surface of the intermediate container 5.

[°C], the surface temperature of the intermediate container 6 is θ, [°C], and its ambient temperature is θ. Cc], the surface area of the intermediate container 6 is ACM2]
, the amount of heat dissipated from its surface is QCKca/H], then the surface temperature θ1 of the intermediate container 6 is, where h is the overall heat transfer coefficient considering thermal radiation, and the heat transfer coefficient due to convection is Hc. To. , ε is the thermal emissivity of the intermediate container 6.

Next, the surface temperature θ of the inner container 5. where k is the thermal conductivity [Kcal/MHdeg] of the intermediate container 6.

Therefore, in order to increase θo, θ1 is increased, and for this purpose, the overall heat transfer coefficient h is decreased, and for this purpose, the intermediate vessel 6 is
It can be seen that it is sufficient to reduce the thermal emissivity ε of . Since the intermediate container 6 is made of the above-mentioned fireproof heat insulating material, ε
The value of is about 0.8 to 0.9, and no substance with a particularly small ε has been found.

Next, regarding a specific example, the surface temperature θ of the inner container 5 is determined based on the above formula.

We will explain the results of the trial calculation. Now, Q2429 [Kcal
/H], that is, converted to electric power, P=Q/0.86=50
00, Hc=5 [Kcal/M2Hdegl, k=
0.5 [Kcal/M2Hdeg], ε=0.9, θ
If o=20 [°C], θo+870 [°C], θ
It becomes 1+190 [°C].

In this example, the temperature of the inner container 5 is low for firing pottery, etc., and 700 [W] of microwave power is required to raise the temperature to 1200 [° C.] required for firing, which is not economical.

This invention was made based on the above considerations.
The purpose of this furnace is to provide a microwave heating furnace that can heat the inner container to a higher temperature when the same microwave is input. The container is placed inside the outer container, and microwaves are irradiated through an opening provided in the outer container.

An embodiment of the present invention will be described below with reference to the drawings. Second
The figure is a sectional view of an embodiment of the present invention, and FIG. 3 is a sectional view taken along the line in FIG. It is placed inside the outer container 7. Note that 8 is an opening provided so that microwaves can be emitted to the person. Next, the operation of this invention will be explained.

Now, assuming that the microwave frequency is 2450 MHz, the shape of the outer container 7 is cylindrical, and the dielectric constant inside the outer container is 1, if the diameter of the outer container 7 is 0.0717 [M] or more, Resonant electromagnetic fields of various modes are generated, and this resonant electromagnetic field passes through the intermediate container 6 and uniformly microwaves the inner container 5. Next, the temperature θ of the inner container 5 in the thermal equilibrium state in this example. We will explain the results of the trial calculation. The inner container 5 and the intermediate container 6 are the same spheres as in the above calculation example, and the outer container 7 is also assumed to be a copper sphere with an inner diameter of 0.2 [M] for convenience of calculation, and its thermal emissivity ε
-0.05, and assuming that the amount of heat dissipated from the surface of the outer container 6 is 500 [W] in terms of electric power, the surface temperature of the outer container 7 is θ2 + 510 [°C], θ1 + 510 [°C]
, θo-1200 [°C], and θ at the same microwave radiation power.

will be heated to a high temperature of approximately 330°C. In addition, Fig. 4 shows the miterro wave power P (W) and the temperature θ of the inner container.
o (°C) in the prior art and the present invention. In the figure, characteristic A indicates the temperature of the inner container according to the prior art, and characteristic B indicates the temperature according to the present invention. In the above embodiment, a cylinder made of copper is used as the outer container 7, but metals such as brass, aluminum, stainless steel, gold, etc., which have a small thermal emissivity ε, or materials plated with these metals may also be used. According to the present invention, an inner container made of a substance that generates microwave heat and contains an object to be heated, an intermediate container made of a fireproof heat insulating material with low microwave loss and which contains the inner container, and this intermediate container. An outer container made of a material with a low thermal emissivity that houses the container, and equipped with an opening that allows microwaves to be radiated into the interior, and a microwave irradiation device that irradiates the inside with microwaves from the opening. Thus, a microwave heating furnace capable of heating the inner container to a higher temperature is obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a microwave heating furnace according to the prior art, FIG. 2 is a sectional view of an embodiment of the present invention, and FIG. 3 is a sectional view of a microwave heating furnace according to the prior art.
FIG. 4 is a characteristic diagram comparing the temperature of the inner container of the heating furnace according to the prior art and the present invention. In the figure, 1 is a microwave generator, 2 is a waveguide, and 3 is a microwave generator.
is a microwave oven, 4 is an object to be heated, 5 is an inner container,
6 is an intermediate container, 7 is an outer container, and 8 is an opening.

Claims (1)

[Scope of Claims] 1. An inner container made of a substance that generates heat by microwaves and configured to accommodate an object to be heated, an intermediate container having fireproof and heat-insulating properties with low microwave loss, and a material with low thermal emissivity. an outer container that accommodates the intermediate container and is provided with an opening for irradiating microwaves through the intermediate container to an inner container accommodated therein, and radiating microwaves from the opening of the outer container. A microwave heating furnace equipped with a microwave irradiation device. 2. The microwave heating furnace according to claim 1, wherein the outer container has a surface covered with a metal having a low thermal emissivity. 3. The microwave heating furnace according to claim 1 or 2, wherein the material forming the outer container or the metal covering the surface thereof is copper, aluminum, stainless steel, or gold.