JPH0992448A - Induction heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evenly heat a fluid through induction heating by winding a coil around a conductor so formed that the fluid can pass through it. SOLUTION: A metallic body 6 is provided with a number of holes 7 through which a fluid passes vertically, and a heating element 1 is provided in which the opening area of the holes 7 gets smaller toward the center so as to increase its density. Thus crossing magnetic flux is increased even at the center of the heating element 1 and an eddy current generated is also increased, so the amount of heat generated is also increased.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an induction heater for heating a liquid or gas by electromagnetic induction heating.

[0002]

2. Description of the Related Art A heating element which is a conductor is placed in a fluid,
A heater is known that induction-heats a heating element by passing a high-frequency current through an external coil provided around the heating element. For example, Japanese Unexamined Patent Publication No. 7-35413 discloses an induction heater having a configuration as shown in FIG. In this induction heater, a cylindrical heating element 1 through which a fluid (liquid or gas) can pass is immersed in the fluid to be heated in a case 3 around which a coil 4 connected to an AC power supply 2 is wound. Is installed. A liquid (for example, water) or a gas (for example, air) is introduced into the case 3 so as to be in direct contact with the heating element 1, and passes through the heating element 1 and the gap between the heating element 1 and the case 3. When an alternating current flows through the coil 4, a magnetic flux 5 interlinking the heating element 1 is generated, and an eddy current is generated in the heating element 1 by the magnetic flux 5 to generate Joule heat. By transferring this heat to the fluid introduced into the case 3,
The fluid is heated.

FIG. 6 shows a heating element 1 installed in a case 3.
It is a figure which shows the specific example of the shape of. By providing a large number of holes 7 penetrating in the vertical direction in the cylindrical metal body 6, the surface area is increased and the fluid is heated when the fluid passes around the metal body 6 and in the holes 7. ing.

[0004]

However, in the induction heating, the eddy current generated by the magnetic flux is concentrated on the peripheral side of the conductor due to the skin effect. Therefore, even the heating element 1 having the structure as shown in FIG. A large amount of eddy current is generated in the peripheral portion, and the generation of eddy current is small in the central portion. The amount of heat generated by Joule heat is proportional to the square of the current. For this reason, almost no heat is generated in the central portion of the heating element 1, and uneven heating occurs.

The present invention has been made to solve the above problems, and an object thereof is to provide an induction heater capable of heating a fluid, which is an object to be heated, substantially uniformly.

[0006]

In order to solve the above-mentioned problems, the first invention is made such that a coil is wound around a heating element which is a conductor through which a fluid can pass, and the coil is wound around the heating element. An induction heater for heating the fluid by inducing an alternating current to heat the heating element is characterized in that the heating element has a structure having a high density in a central portion and a low density in a peripheral portion. That is, the heating element is composed of a conductor that generates heat by induction heating and a plurality of small spaces through which a fluid can pass. For example, the conductor occupies a large proportion on the central side of the heating element and relatively on the peripheral side. The heating element is formed so that the proportion of the conductor is small.

A second invention made to solve the above problems is to wind a coil around a heating element which is a conductor through which a fluid can pass, and to flow an alternating current through the coil. In an induction heater that heats the fluid by inductively heating the heating element, the flow rate of the fluid passing through the peripheral side of the heating element is increased and the flow rate of the fluid passing through the center side is decreased. In addition, in particular, for simplification of the configuration, a structure may be provided in which the fluid can pass only on the peripheral side of the heating element.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The density of eddy currents that generate Joule heat is proportional to the magnetic flux density that links conductors. Therefore, in order to increase the amount of heat generated inside the heating element, it is necessary to increase the magnetic flux density at the center of the heating element.
The heating element used in this type of heater is a substance having a uniform magnetic permeability, but in the first aspect of the invention, the density is increased in the central portion of the heating element so that the central portion of the heating element moves to the peripheral portion. The same effect as the magnetic permeability of the magnetic material is lowered. That is, the magnetic flux passing through the peripheral portion of the heating element decreases and the magnetic flux passing through the central portion increases. For this reason, eddy currents are easily generated even in the central portion, and the entire heating element is heated almost uniformly. As an example of a specific structure of the heating element, a plurality of holes or voids through which a fluid can pass are formed in the metal conductor, and the opening area of the holes or the size of the voids is made smaller toward the center.

Further, in the second aspect of the present invention, a large amount of fluid is provided in a portion having a large calorific value and a small amount of fluid is provided in a portion having a small calorific value so that the amount of heat supplied to a unit volume of fluid is made uniform. It is designed to guide. Therefore, as in the first aspect of the invention, the flow rate of the fluid passing therethrough can be adjusted by changing the ratio of the conductor to the small space in the heating element. Further, the ratio of the conductor to the small space in the heating element may be made uniform, and the amount of fluid introduced to the peripheral side and the center side of the heating element may be changed. The simplest version of the second invention is a structure in which the fluid is not introduced into a portion of the heating element having a small amount of heat generation. That is, a conductor or non-conductor member having no holes or voids is arranged in the center of the heating element, and a conductor member such as a metal conductor having holes or voids is arranged in the peripheral portion surrounding the member. . An eddy current is generated in the conductor member on the peripheral side due to the interlinking magnetic flux, and Joule heat is generated. By disposing a conductor member through which a fluid can pass only in a range where a large amount of eddy current is generated, the fluid can be heated substantially uniformly according to conditions such as frequency.

[0010]

As described above, in both the first and second inventions, the fluid to be heated can be heated almost evenly.

[0011]

Embodiments of the induction heater according to the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of the shape of a heating element in the induction heater according to the first invention. The heating element 1 is a cylindrical metal body 6 similar to that shown in FIG.
A large number of holes 7 penetrating in the vertical direction are formed.
The hole 7 is formed so that the diameter, that is, the opening area, increases from the central portion of the heating element 1 toward the peripheral portion. That is, the density of the metal body 6 is high in the central portion of the heating element 1 and low in the peripheral portion. This metal body 6 is a substance having a uniform magnetic permeability, but due to the difference in its density,
In fact, it has the same effect as the magnetic permeability is high in the central portion and low in the peripheral portion.

Therefore, when the heating element 1 having the above structure is used as the heating element 1 in FIG. 5, the magnetic flux is dense in the central portion of the heating element 1 and is sparse in the peripheral portion. Therefore, a large amount of eddy current induced by the magnetic flux also occurs in the central portion. As described above, this eddy current is biased to the peripheral portion of the heating element 1 due to the skin effect. However, since a large amount of eddy current is generated in the central portion, the amount of heat generated in the central portion is relatively increased. The depth of current penetration in the heating element 1 is
Since it depends on the material (resistivity and relative permeability) of the metal body 6 and the frequency of the alternating current flowing through the coil, the density of the central portion and the peripheral portion of the heating element 1 should be set to an appropriate ratio according to these parameters. By doing so, the fluid passing through the hole 7 can be heated almost uniformly.

FIG. 2 is a perspective view showing another embodiment of the shape of the heating element in the induction heater according to the first invention. In this embodiment, instead of the circular hole, the polygonal hole 7 is
It is formed so that the opening area increases from the central portion toward the peripheral portion. It is clear that the same effect as in the example of FIG. 1 can be obtained also by this.

It should be noted that the heating element 1 may not be integrally formed, but may be constituted by laminating a plurality of plate-shaped metal plates having openings as shown in FIGS. 1 and 2, for example. Also,
The density may be adjusted by compressing a metal sponge-like material strongly in the central part and gently compressing it in the peripheral part. Furthermore, the heating element 1 is formed by winding one or a plurality of wire nets, and the density may be adjusted by winding the wire mesh densely in the central portion and loosely in the peripheral portion.

FIG. 3 is a perspective view showing an embodiment of the shape of the heating element in the induction heater according to the second invention. In this embodiment, a member 8 made of a non-conductive material is embedded in the center of the conventional heating element 1 as shown in FIG. This non-conductor member 8
Does not generate eddy currents and therefore does not generate heat, and the fluid is heated when passing through the holes 7 formed in the surrounding metal body 6 which generates heat. That is, only the portion of the metal body 6 that generates heat almost uniformly due to the interlinking magnetic flux is used for heating the fluid.

As described above, the depth of current permeation in the heating element 1 depends on the material of the metal body 6 and the frequency of the alternating current flowing through the coil. By deciding the size appropriately,
The fluid passing through the holes 7 can be heated almost uniformly.

FIG. 4 is a perspective view showing another embodiment of the heating element in the induction heater according to the second invention. In this figure, only part of the case 3 and the coil 4 is shown in cross section. In this example, the non-conductive member 8 is used as a core rod when the wire net 9 which is a heating element is wound, and the wire net 9 is wound around this core.
The wire mesh 9 is kept at an appropriate interval by inserting the wire mesh 9 between them.
At this time, the density is also adjusted by winding the wire netting 9 so that the space between the wire nets 9 becomes narrower near the center and the space near the case 3 becomes wider. By combining the first and second inventions as in this example, uniform heating of the fluid can be achieved more easily.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an induction heater according to the first invention.

FIG. 2 is a perspective view showing another embodiment of the induction heater according to the first invention.

FIG. 3 is a perspective view showing an embodiment of an induction heater according to the second invention.

FIG. 4 is a perspective view showing another embodiment of the induction heater according to the second invention.

FIG. 5 is a general configuration diagram of an induction heater.

FIG. 6 is a perspective view showing a shape example of a heating element of a conventional induction heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Heating element 2 ... AC power supply 4 ... Coil 6 ... Metal body 7 ... Hole 8 ... Non-conductive member 9 ... Wire mesh

Claims (3)

[Claims] 1. An induction heating for heating a fluid by heating a fluid by winding a coil around a heating element which is a conductor through which the fluid can pass and applying an alternating current to the coil to inductively heat the heating element. The induction heater according to claim 1, wherein the heating element has a structure having a high density in a central portion and a low density in a peripheral portion. 2. An induction heating for heating the fluid by winding a coil around a heating element, which is a conductor through which the fluid can pass, and applying an alternating current to the coil to inductively heat the heating element. In an induction heater, the flow rate of the fluid passing through the peripheral side of the heating element is increased and the flow rate of the fluid passing through the central side thereof is decreased. 3. The induction heater according to claim 2, wherein the induction heater has a structure in which the fluid can pass only on the peripheral side of the heating element.