JPH05157240A - Heater device for hot air generating device - Google Patents

Abstract

PURPOSE:To provide a heater for a hot air generating device in which the temperature rising time when heated is short, it has a superior durability and further a hot air generating device can be made small in size. CONSTITUTION:A heater member of a hot air generating device 2 is formed by a belt foil electrical resistance heater 1 with a thickness of several tens mum and a width of several tens mm. Since its thermal capacity is low, its rising time when heated is short, a heat exchanging area is 4 to 10 times of the prior art heater element, resulting in that the surface temperature of the heater element is decreased to improve its durability and at the same time the hot air generating device 2 can be made small in size. In addition, since the foil electrical resistance heater element 1 is formed with some corrugations crossing at right angles with the air blowing directions 3 and 4, so that a disturbed flow can be generated at the air blowing at the surface of it to improve a heat exchanging rate and to reinforce it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element for a hot air generator used in electric cookers and electric heaters.

[0002]

2. Description of the Related Art Conventionally, most heating elements for hot air generators used in electric cookers, electric heaters, etc. have been linear or band-shaped heating wires or sheath heaters.

The structure of a heating element (hereinafter referred to as a heater) for a conventional hot air generator will be described below with reference to FIGS.

The linear heater is, as shown in FIG.
It is formed by winding a round wire-shaped heating wire 11 having a diameter of about mm into a coil shape. Then, cold air 12 is caused to flow through this, and hot air 13 is generated by forced convection heat transfer.

Further, the strip heater is, as shown in FIG.
It is formed by bending a band-shaped heating wire 14 having a thickness of 0.2 mm and a width of about 5 mm in a meandering shape. And cold wind 12
The hot air 13 is generated by forced heat exchange.

Further, as shown in FIG. 7, the sheathed heater comprises a heating wire 15, an insulating agent 16, a sealing material 17, and a protective tube 18 to form a rod-shaped sheathed heater. When the power is turned on, the surface temperature of the protection tube 18 is 700 to 800.
When the temperature reaches ℃, the cold air 12 is heated and hot air 13 is generated.

[0007]

In such a conventional heater, in order to obtain a certain amount of heat generation, for example, the surface area of a round wire heating wire 11 having a diameter of 1.1 mm per 1 m in length is 36 cm ² . Yes, a strip-shaped heating wire with a width of 5 mm and a thickness of 0.2 mm 1
The surface area per 1 m of 4 is 104 cm ² . The surface temperature of the heating wire is about 800 ° C. for the round heating wire 11 and about 700 ° C. for the strip heating wire 14,
There is a problem that the heating wires 11 and 14 are easily broken due to high temperature oxidation and thermal fatigue.

In order to prevent such high temperature oxidation and thermal fatigue, in order to prevent high temperature oxidation and thermal fatigue, if the cross-sectional areas of the heating wires 11 and 14 are increased and the length is increased to lower the surface temperature, a hot air generator is provided. There was a problem that became large.

Further, in the sheath type heater, the sheath heater stretches the heating wire 15 in the protective tube 18 and the insulating material 16
Since it has a structure in which the heat capacity is large, the surface area is small as well as the surface area of the protection tube 18 is as high as 700 to 800 ° C. Further, since the heat capacity is large, there is a problem that it takes time to rise. It was

The present invention is intended to solve the above problems, and an object thereof is to obtain a heating element for a hot air generating device, which has a short rise time of heat generation, excellent durability, and can be downsized. There is.

[0011]

In order to achieve the above object, the present invention provides a strip-shaped foil-shaped electric resistance heating element having a thickness of several tens of μm and a width of several tens of mm. In addition, a strip-shaped foil-shaped electric resistance heating element is formed with corrugated ridges orthogonal to the blowing direction.

[0012]

The present invention is configured as described above, and under the condition that a certain amount of heat is generated, it is about 1% as compared with a round wire heating wire.
It is possible to obtain a surface area, that is, a heat exchange area that is 0 times as large as that of the belt-shaped heating wire and is approximately 4 times as large as that of the heating wire.

By the way, the heat transfer amount Q (W) between the heating element and the air
Is the heat transfer coefficient α (W / m ² K) and the heat transfer area is A
(M ² ), where the temperature difference between the surface temperature of the heating wire and the air temperature is (Th−Ta) (k), it is expressed as follows.

Q is αA (Th-Ta) Therefore, in the case of generating the same amount of hot air, in the foil-shaped electric resistance heating element, the surface temperature should be lower than that of the round wire heating wire or the band heating wire. You can

Further, since the corrugated ridges are formed, the air flow becomes a turbulent flow on the surface of the foil-shaped electric resistance heating element, so that the heat exchange rate can be increased. Further, the corrugated ridges can reinforce the foil-shaped electric resistance heating element.

Further, since the foil-shaped electric resistance heating element is formed in a corrugated shape so as to be orthogonal to the air blowing direction, a turbulent flow is generated in the air flow on the surface, so that the heat transfer coefficient α is improved by about 10%. You can

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, reference numeral 1 is a foil-shaped electric resistance heating element (hereinafter referred to as a foil-shaped heating element), and 2 is a hot air generator constituted by the foil-shaped heating element 1.

The foil heating element 1 has a thickness of several tens of μm and a width of several tens.
mm, length is a few meters strip-shaped, Ni-Cr
Made of Fe-Cr-Al-based metallic material,
In order to reduce the size of the hot air generator 2, the hot air generator 2 is formed in a meandering shape so as to have a shape suitable for an air passage. And, for example, in the case of a hot air generator for a microwave oven of 1.2 kW, the thickness is 50 μm, the width is 20 mm, and the length is about 5 m, and the surface temperature when energized is about 600 ° C.
To heat the cold air 3 and generate hot air 4.

In the above structure, the foil-shaped heating element 1 has a very thin thickness of several tens of μm, so that the rising speed is very fast, about 5 seconds, and the surface temperature is the same as that of the sheathed heater shown in the conventional example. Alternatively, since it is lower than a linear or strip-shaped heating wire heater, high-temperature oxidation and thermal fatigue can be prevented, and the durability of the heating wire can be improved.

Next, in FIGS. 2 and 3, the foil-shaped heating element 1 is provided with a corrugated ridge 5 which is orthogonal to the blowing directions 3 and 4.

In the above structure, the blown cold air 3 becomes a turbulent flow on the surface of the foil-shaped heating element 1 formed in the corrugated shape, the boundary layer becomes thin and the heat exchange rate is improved by about 10%, and the foil-shaped heat generation The surface temperature of the body 1 can be further lowered. Thereby, the resistance value of the foil-shaped heating element 1 can be set small, and the hot air generator 2 can be downsized.

FIG. 4 shows an example of an oven range provided with the above-mentioned hot air generator 2 on its back side, and 1 is a foil-shaped heating element 6 which is a forced convection fan.

The air 8 in the oven chamber 7 is sent to the foil heating elements 1, 1 by the forced convection fan 6, and the foil heating element 1
The heated food 9 is heated to about 300 ° C. and becomes hot air 9 which is blown into the oven chamber 7 to heat the food 10. In the case of oven cooking, it is necessary to preheat the internal temperature to about 200 ° C, but in the past, the preheating time required more than ten minutes.
In the present invention, the time could be shortened by 20 to 30%.
Further, since the hot air generator 2 is small, the space on the back surface of the microwave oven can be reduced.

[0025]

As is apparent from the above description of the embodiments, according to the present invention, a strip-shaped foil-shaped electric resistance heating element having a thickness of several tens of μm and a width of several tens of mm is used for a hot air generator. Since the heat exchange area with the blast can be increased by using heat generation, the surface temperature of the foil-shaped electric resistance heating element is lowered to prevent high-temperature oxidation and thermal fatigue, improve durability, and improve the hot-air generation device. Can be miniaturized. Furthermore, since the foil-shaped electric resistance heating element is a foil of several tens of μm, it has a small heat capacity, the rise time of heat generation can be extremely shortened, and hot air of a required temperature can be obtained instantaneously.

Further, by forming the corrugated ridges in the foil-shaped electric resistance heating element at right angles to the blowing direction, turbulent flow can be generated in the blowing air to improve the heat exchange rate, and at the same time, the foil-shaped electric resistance heating element can be improved. Can be reinforced.

As described above, according to the present invention, it is possible to provide a heating element for a hot air generating device which has a short rise time of heat generation, is highly durable, and can be downsized.

[Brief description of drawings]

FIG. 1 is a perspective view of a heating element for a hot air generator according to an embodiment of the present invention.

FIG. 2 is a perspective view of a heating element for a hot air generator according to another embodiment.

FIG. 3 is a perspective view of the main part.

FIG. 4 is a plan cross-sectional view of a microwave oven incorporating a hot air generator having the heating element for the hot air generator.

FIG. 5 is a perspective view of a heating element for a conventional hot air generator.

FIG. 6 is a perspective view of another heating element for a hot air generator.

FIG. 7 is a perspective view of another heating element for a hot air generator.

[Explanation of symbols]

 1 foil-shaped electric resistance heating element 2 hot air generator 3 cold air (air blowing direction) 4 hot air (air blowing direction) 5 corrugations

Claims (2)

[Claims] 1. A heating element for a hot air generator, which comprises a strip-shaped foil-shaped electric resistance heating element having a thickness of several tens of μm and a width of several tens of mm. 2. The heating element for a hot air generating device according to claim 1, wherein a strip-shaped foil-shaped electric resistance heating element is formed with a corrugated ridge orthogonal to the air blowing direction.