GB2076270A

GB2076270A - Electrical air-heating device

Info

Publication number: GB2076270A
Application number: GB8114072A
Authority: GB
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1980-05-14
Filing date: 1981-05-08
Publication date: 1981-11-25
Also published as: DE3119302A1; GB2076270B

Abstract

An air-heating device has flat heating elements (10) of positive temperature coefficient, each of which has an electrode (11) on each surface and metal heat-radiating structures (13) in contact with the electrodes (11). The heating efficiency is improved by the use of the radiating structures (13), and the number of PTC heating elements (10) may be reduced as compared with that used in conventional devices. Various forms of the radiating structures (13) are described. <IMAGE>

Description

SPECIFICATION Air heating device BACKGROUND OF THE INVENTION: The present invention relates to an air heating device using thermistor elements of positivetemperature coefficient.

Constant temperature air heaters of harmonica structure are conventionally known wherein a plurality of constant temperature heating elements having a flat shape and made of thermistor material of positive-temperature coefficient are arranged parallel to each other within a frame, and electrodes formed at the end faces of the respective elements are connected to each other and to a power source through a connecting wire.

Other constant temperature air heaters of honeycomb structure are also conventionally known wherein electrodes and connecting wires are arranged at both surfaces of a constant temperature heating element having a plurality of small holes and formed by extruding a thermistor material of positivetemperature coefficient into a cylindrical shape. Among them, the air heating device of the harmonica structure is more difficult and more expensive to manufacture as compared with that of the honeycomb structure because of many elements included and many steps required for assembly. However, the air heating device of the honeycomb structure is defective in that the pressure loss is great and clogging often occurs.

SUMMARY OF THE INVENTION: The primary object of the present invention is to provide an air heating device using thermistor elements of positive-temperature coefficient, which is efficient and simple in construction.

The present invention provides an air heating device of harmonica type which has flatshaped thermistor heating elements of positive-temperature coefficient, each of which has respective electrodes on both surfaces and metal radiating structures in contact with each of the electrodes. According to the present invention, the heating efficiency is improved by the use of the radiating structures, and the number of thermistor heating elements of positive-temperature coefficient to be used may be vastly reduced as compared with the conventional devices.

BRIEF DESCRIPTION OF THE DRAWINGS: Figures 1A and 1B are perspective views, respectively, of conventional air heating devices; Figures 2A and 2B are a perspective view and a sectional view, respectively, illustrating an embodiment of an air heating device according to the present invention; Figure 3A is a perspective view of an air heating device according to a second embodiment of the present invention; Figure 3B is a sectional view of the main part of Fig. 3A; Figure 3C is a perspective view of a radiating structure constituting part of the heating device shown in Figs. 3A and 3B; Figures 4 to 7 are perspective views, respectively, illustrating third to sixth embodi ments of the air heating device according to the present invention;; Figure 8 is a front view illustrating a modification of the radiating structure; Figures 9 to ii are perspective views, respectively, illustrating seventh to ninth embodiments of the air heating device according to the present invention; and Figure 12 is a perspective view illustrating a modification of the embodiment of Fig. 11.

DETAILED DESCRIPTION OF THE PRIOR ART: Constant temperature air heaters of harmon ica structure are conventionally known wherein, as shown in Fig. 1A, a plurality of constant temperature heating elements 1 having a flat shape and made of thermistor material of positive-temperature coefficient are arranged parallel to each other within a frame 2, and electrodes 3 formed at the end faces of the respective elements 1 are connected to each other and to a power source through a connecting wire 4. Other constant temperature air heaters of honeycomb structure are also conventionally known wherein, as shown in Fig. 1 B, electrodes 7 and connecting wires 8 are arranged at both surfaces of a constant temperature heating element 6 having a plurality of small holes 5 and formed by extruding a thermistor material of positive-tempera..

ture coefficient into a cylindrical shape.

Among them, the air heating device of the harmonica structure is more difficult and more expensive to manufacture as compared with that of the honeycomb structure because of many elements included and many steps required for assembly. However, the air heating device of the honeycomb structure is defective in that the pressure loss is great and clogging often occurs.

DESCRIPTION OF THE PREFERRED EMBODI MENTS: The present invention will be described by its embodiments with reference to the accompanying drawings.

As shown in Figs. 2A and 2B and Figs. 3A, 3B and 3C, electrodes 11 are respectively formed on both surfaces of a plurality of positive-temperature coefficient thermistor (to be referred to as PTC thermistor hereinafter) elements 10 formed by sintering in flat-rectangular shape to provide PTC thermistor heating elements 1 2. Conventionally known methods may be adopted for forming the electrodes 11, for example, such as coating of an electrically conductive material such as silver and copper; metalikon, vapor deposition, or sputtering of a metal such as aluminium and copper; plating of nickel or the like; and so on.From the viewpoint of the ease of mutual connection of the electrodes 11 of the respective elements 10 and connection of the connecting wires, the conventional structure of the electrodes 11 according to which they are formed at both end faces of the elements is advantageous. However, from the viewpoint of efficiency, it is vastly advantageous to form the electrodes 11 at both surfaces of the elements. As for the shape of the electrodes, it is preferably substantially square or round in shape from the viewpoint of ease of forming and processing. However, the shape of the elements may be selected according to the intended purpose.

Radiating structures 1 3 of metal are formed in contact with the surfaces of the respective electrodes 11 of the PTC thermistor heating elements 1 2. In other words, the PTC thermistor heating elements 1 2 are clamped between two radiating structures 1 3 through heat-resistant and thermally conductive silicon adhesive layers 14, and the protruding parts of the electrodes 11 of the heating elements 1 2 are connected by lead wires 1 5 with electrically- conductive adhesive layers 16.When a voltage is applied to the electrodes 11 of the PTC thermistor heating elements 1 2 and air is supplied in the direction shown by the arrow A, the air is warmed by the heating elements 1 2. This principle of obtaining warm air is also employed in the following embodiments.

The radiating structure 1 3 may comprise a conventional radiation fin of a material such as aluminium and shape allowing a better radiating efficiency. Favorable heating effects may be obtained with a radiating structure of a block shape formed by die casting as shown in Figs. 2A and 2B, or with a radiating structure of shape in which metal plates with excellent radiating characteristics are bent in the form of channels. Although the electrodes 11 formed at both surfaces of the heating elements 1 2 and the radiating structures 1 3 may be electrically insulated, they may be electrically coupled together for simplifying the connection of a connecting wire.In this case, as shown in Figs. 2A and 2B and in Figs. 3A, 3B, and 3C, a plurality of heating elements 12 may be aligned, and the com mon metal radiating structures 1 3 may be mounted between every pair of adjacent heat ing elements 1 2 in contact with the electrodes 11 formed thereon. With such a structure, the equivalent heating output may be obtained with about 1/3 to 1/4 of elements in a conventional air heating device of harmonica structure wherein the heating elements alone are arranged parallel to each other.

In order to obtain better heating effects and to minimize expense, a radiating structure of channel ype may be utilized in which metal plates of about 0.3 mm thickness are bent in a corrugated pattern as shown in Figs. 3A, 3B, and 3C instead of a radiating structure of metal blocks. In this case, since the elastic radiating structures may be combined to be adhered to the heating elements 12, the electrical connection may be easily attained and the structures serve both as connecting wires and as the radiating structures 1 3. Furthermore, the radiating structures 1 3 may be assembled into a frame 1 7 utilizing their elas- ticity, and the construction may be simplified.

In constructing these radiating structures 13, when the electrodes 11 at both surfaces of the elements 1 2 are formed by metalikon of aluminium and the radiating structures 1 3 are formed from aluminium plates, the overall structure is resistant to humidity and allows longer service life as a result of the use of a combination of the same kind of metal.

In order to obtain better heating effects, the pitch of radiating structures 1 8 must be decreased or the height h thereof must be increased to increase thereby the surface area of the radiating structures 18, referring to Fig.

4. However, with the radiating structures 1 8 obtained by bending metal plates, a smaller pitch results in a smaller height h, and a greater height h results in a greater pitch.

Referring to Fig. 4, reference numeral 1 9 denotes a PTC thermistor element and 20 denotes electrodes.

Thus, a structure as shown in Fig. 5 is conceivable. Referring to Fig. 5, reference numeral 21 denotes a PTC thermistor element; 22, electrodes; and 23 to 26, radiating plates bent in a corrugated pattern with a small pitch which are stacked in a number of stages to provide radiating structures. With such a structure, it is possible to increase the overally height ha of the radiating structure, to increase the surface area of the radiating structure, and to facilitate the heating effects.

However, this structure is disadvantageous in that the number of radiating plates and other parts increases, so that the number of assembly steps also increases and the manufactur ing cost becomes high.

In order to solve this problem, a structure as shown in Fig. 6 may be adopted.

Referring to Fig. 6, reference numeral 27 denotes a thin-plate PTC thermistor element, on both major surfaces of which are formed electrodes 28 by flame spraying. Reference numerals 29 and 30 are radiating plates which are formed by bending a single alumin ium plate in a corrugated pattern and in three stack type. These radiating plates 29 and 30 are securely adhered to both major surfaces of the PTC thermistor element 27.

With such an arrangement of the radiating structure, a one-piece radiating structure of a greater height hb may be formed with a multi stacked bent plate while attaining a small pitch of the radiating elements 29 and 30, thereby providing an air heating device with superior heating effects at less cost.

Fig. 7 shows another embodiment of the present invention. According to this embodiment, each of radiating plates 31 and 32 is made of a single aluminium plate which is bent in a corrugated pattern. Although this embodiment is similar to the former embodiment in that the radiating plates 31 and 32 of a small bending pitch are stacked in a number of stages, a layer of the same aluminium plate is interposed between each pair of adjacent stages.

With such a radiating structure, the metal plate material constituting the radiating plates 31 and 32 is interposed between the PTC thermistor element 27 and the radiating plates 31 and 32, increasing the area of thermal coupling. This results in better thermal transmission from the PTC thermistor element 27 to the radiating plates 31 and 32, allowing better heating effects. Thus, the surface area of the radiating plates 31 and 32 is supplemented by the area of the metal plates between the stages, so that more heat can be transmitted to the air. In order to further increase the output of the heating device, the surface area of the radiating structures 1 8 in Fig. 4 may be increased as much as possible.

However, when the height h of the radiating structures 1 8 is increased, the heating device becomes larger in size. Thus, it may be conceivable to make the width a of the protruding part smaller to obtain a radiating structure of as narrow a corrugated pattern as possible.

However, the smaller width a cannot be obtained beyond a certain limit during the processing of the aluminium thin plate.

Thus, another structure may be considered as shown in Fig. 8 wherein the radiating structure formed in a waveform is transversely pressed. In this case, with the width C the same as the width a of Fig. 4, the surface area of the radiating structure within the overall width I becomes twice that of the example shown in Fig. 4. The heating output also increases when such a radiating structure is used in combination with the PTC thermistor elements. However, in the case of the radiating structure of the shape shown in Fig. 8, the parts designated by letter A become narrow, resulting in clogging by waste threads, dust, etc. This disadvantageously interferes with the flow of air, thus causing a decrease in the output or an abnormal rise in the temperature of the air.

A structure as shown in Fig. 9 is proposed in consideration of these problems. Referring to Fig. 9, reference numeral 33 denotes a PTC thermistor element; 34, electrodes formed by metalikon of aluminium; and 35 and 36, radiating structures formed by processing thin plates of aluminium having crosssections in the form of continuously repeated S-shape. These radiating structures 35 and 36 are adhered to the PTC thermistor element 33 and also function as power supply terminals.

While the radiating structures having crosssections in the form of S-shape, the parts B of the radiating structures 35 and 36 become in the form of R-shape. Therefore, processing of the aluminium thin plates becomes easier, even when the width d is smaller than the width a of the case shown in Fig. 4, providing the radiating structures 35 and 36 with larger surface areas at less cost. When an air heating device as shown in Fig. 9 is constructed using the radiating structures 35 and 36, a heating device with a large output is obtained.

Furthermore, since the cross-sections of Sshape are adopted, the parts D of the radiating structures 35 and 36 include fewer narrow spaces, resulting in a heating device which is subject to less clogging of dust.

When the air heating device of the present invention is put into practice, however, in the event that a metal piece or the like which is longer than the thickness b of the PTC thermistor element 1 9 in Fig. 4 simultaneously contacts both the radiating structures 18, short-circuiting occurs, with a dangerously large flow of electrical current. In order to prevent this, it is possible to make the thickness b greater to make thereby the distance between the opposing electrodes greater.

However, such a structure results in significant resistance against the flow of air and thus interferes with the flow of air. This also results in a heavier PTC thermistor element and a higher cost.

Thus, a structure as shown in Fig. 10 is proposed.

Referring to Fig. 10, reference numeral 37 denotes PTC thermistor elements, on both of the major surfaces of which are formed electrodes (not shown) by metalikon of aluminium. Reference numeral 38 denotes radiating structures formed by bending aluminium thin plates which are adhered to the PTC thermistor elements 37 to alternate therewith and which also function as the power supply terminals. Reference numeral 39 denotes a silicon-type heat-resistant insulating paint which is painted on the PTC thermistor elements 37 and on the radiating structures 38 in the direction perpendicular to the direction of the flow of air shown by the arrow A.

With such an arrangement, contact of a conductor such as a metal piece with the heating device does not cause short-circuiting.

Furthermore, the thickness of the PTC thermistor elements 37 need not be made greater, so that an air heating device with little resistance against flowing air and which is inexpensive may be provided. Although it is advantageous that the insulating paint 39 be painted on the PTC thermistor elements 37 and the radiating structures 38 in the direction perpendicular to the direction of flow of air, it may be painted on the overall heating deviced depending upon the kind of the paint and the method of application.

For putting the present invention into practice, an arrangement as shown in Fig. 11 may be adopted for facilitating the insulation and mounting of the device. Referring to Fig. 11, reference numeral 40 denotes a PTC thermistor element in the form of a thin plate, on both major surfaces of which are formed electrodes 41 formed by metalikon of aluminium.

Radiating structures 42 and 43 of aluminium are adhered with an epoxy adhesive (not shown). Reference numerals 44 and 45 denote power supply lead wires which are adhered to the surfaces of the electrodes 41 of the PTC thermistor element 40 with an electrically conductive adhesive such as solder. Reference numeral 46 denotes a sheet-shaped insulator of silicon rubber or the like which encloses the overall device in the direction not to interfere with the flow of air therethrough.

Reference numeral 47 denotes grommets of brass or the like which secure the sheetshaped insulator 46.

According to this arrangement, since the radiating structures 42 and 43 are adhered with an adhesive, the exterior of the air heating device may be insulated with a simple structure and may not require complex steps for mounting of the device. Furthermore, since the sheet-shaped insulator 46 encloses the exterior of the device, the number of parts to be used for constructing the device is reduced, assembly is simplified and the device may be less expensive.

Fig. 1 2 shows a modification of the arrangement shown in Fig. 11, according to which the sheet-shaped insulator comprises a thermally shrunk tube 48. When such a tube 48 encloses the device and is thermally shrunk, the step of winding the sheet-shaped insulator may be eliminated, providing an air heating device which is less expensive and easier to mount the device.

In order to show the advantageous effects obtainable with the present invention, the description will further be made with reference to the data obtained by experiments conducted according to the embodiments shown in the accompanying drawings.

First, as shown in Fig. 2, the electrodes 11 are formed by a silver paint or aluminium metalikon on both surfaces of the plateshaped PTC thermistor elements 10 (switching temperature 220 C, and initial resistance 20 1) of dimensions 30 X 20 X 1.5 mm3 to provide the PTC thermistor heating elements 1 2. Using two commercially available radiating structures 1 3 of 100 mm length, 25 mm width, and 40 mm in the length of the projecting parts, together with the PTC thermistor heating elements 1 2 described above, the heating elements 1 2 are clamped between them through the heat-resistant and thermally conductive silicon adhesive layers 14.The projecting parts of the electrodes 11 of the heating elements 1 2 are mutually connected with the lead wires 1 5 with the conductive adhesive layers 16. By the same method, the electrodes 11 on both the front and rear surfaces of the elements are mutually connected to service connecting wires.

When an air heating device using five such heating elements was used as an air heater, a heating output corresponding to 360 W was obtained. The same air-heating effects were obtained as with a conventional device (as shown in Fig. 1A) using 18 to 20 heating elements of the same dimensions.

When a heat-resistant and electrically conductive adhesive is used for the heat-resistant silicon adhesive layers 14 in the embodiment shown in Figs. 2A and 25, since the radiating structures 1 3 also function to electrically connect the electrodes 11 of the heating elements 12, the lead wires 1 5 need not be mounted with the electrically conductive adhesive layers 16, so that the connecting wires may be directly connected to the radiating stuctures 1 3. For this reason, the width of the heating element 1 2 may be made the same as that of the radiating structure 13, resulting in a better heating efficiency and easier manufacture.

In the embodiment shown in Figs. 3A, 3B and 3C, the heating elements 1 2 are the same as those in Fig. 2. Next, an aluminium sheet of 20 mm width and 0.3 mm thickness is bent to have a plurality of corrugations of 5 mm height to form the radiating structures 13, as shown in Figs. 3A, 3B and 3C. The length of the radiating structure is made to equal length of the heating element 1 2 (30 mm). The heating elements 1 2 and the radiating structures 1 3 are inserted and secured with a heat-resistant insulator in the frame 1 7 having inner dimensions of 30 X 56 mm2 and 20 mm height.The numbers of the combined heating elements and of the radiating structures are determined according to the relationship between the radiating effects and the characteristics of the element 1 2. However, the same output as that obtainable with the device shown in Fig. 2 with four heating elements 1 2 is obtained when one heating element 1 2 is combined with two radiating structures 1 3.

The radiating structures 1 3 may be superposed as shown in Figs. 3A, 3B and 3C or according to another method, depending upon the elastic effects and the thermal and electrical conductivity characteristics of the material of the structure.

In summary, in accordance with the present invention, the heating efficiency may be improved by the incorporation of the radiating structures described above. The number of the PTC thermistor elements may be reduced and the radiating effects may be improved as compared with conventional devices. The radiating structure may also function as connecting wires for electrodes, resulting in a simpler construction, easier assembly, and lower manufacturing cost.

Claims

1. An air heating device characterized in that PTC thermistor heating elements of flat shape having respective electrodes on both surfaces of the PTC thermistor elements are provided and heat-radiating structures of metal are disposed in contact with the surfaces of the respective electrodes.

2. An air heating device according to claim 1, characterized in that both electrodes of the PTC thermistor heating elements and the metal radiating structures are directly electrically connected.

3. An air heating device according to claim 1 or 2, characterized in that the radiating structures formed by bending high radiative metal plates in a plurality of corrugations are used.

4. An air heating device according to claim 1, characterized in that the radiating structures comprise elastic metal plates of continuous corrugated cross-sections which clamp the PTC thermistor heating elements therebetween.

5. An air heating device according to claim 2, characterized in that the electrodes of the PTC thermistor heating elements and the radiating structures are made of the same metal.

6. An air heating device according to claim 5, characterized in that the electrodes of the PTC thermistor heating elements and the radiating structures are made of aluminium.

7. An air heating device according to claim 3, therein the metal radiating structures are securely adhered to the electrodes of the PTC thermistor heating elements, characterized in that the metal radiating structures are formed by bending a single metal plate in a corrugated form and are stacked in a number of stages.

8. An air heating device according to claim 7, characterized in that parts of the metal plates constituting the radiating structures are interposed respectively between stages of the metal radiating structures.

9. An air heating device according to claim 1 or 2, therein the metal radiating structures are securely adhered to the electrodes of the PTC thermistor heating elements, characterized in that the metal radiating structures comprise aluminium thin plates and have cross-sections of continuously repeated S-shape.

1 0. An air heating device according to claim 2, therein the metal radiating structures are securely adhered to the electrodes of the PTC thermistor heating elements, characterized in that an electrically insulating paint is painted on surfaces of the PTC thermistor heating elements and the metal radiating structures, the surfaces being at least in the direction perpendicular to the flow of air.

11. An air heating device according to claim 2, therein the metal radiating structures are securely adhered to the electrodes of the PTC thermistor heating elements, characterized in that a sheet-shaped insulator encloses the overall device in the direction not to interfere with the flow of air.

1 2. An air heating device substantially as hereinbefore described, by way of example, with reference to any one of Figs. 2A to 1 2 of the accompanying drawings.