JPH0226357B2 - - Google Patents

Abstract

1. Electrical heater for heating a gaseous or liquid medium, with a holding device for receiving a resistance-wire coil (8, 9), the holding device consisting of individual heater elements (1) of circular cross-section, which are placed on top of one another in the axial direction and in which there are, in regions located opposite one another, recesses (7) in which the resistance-wire coil (8, 9) is located, and the outer walls (4) of the heater elements (1), when these are placed on top of one another, complementing each other to form a closed cylindrical outer wall of the holding device, characterized in that in the heater elements (1) there are webs (5) which extend radially inwards from the outer walls to a central region and have the recesses (7) for receiving the resistance-wire coil (8, 9), and which between themselves determine axial flow channels (10) for the medium to be heated, in that in the central region of the heater there is at least one further axial flow channel (14a, 14b, 14c) which is closed at the downstream end of the heater, and in that on at least one of the downstream heater elements (1e, 1f) at least one radially extending passage (17) is formed between the further axial flow channel (14a, 14b, 14c) and the axial channels (10) located between the webs (5).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric heater for heating a fluid, and more particularly to an electric heater made of a refractory material and having support means extending axially relative to a passageway. A hollow cylindrical outer shell is provided,
Furthermore, the present invention relates to an electric heater in which a helical resistance-wound coil mounted in the support means is configured to be blown through by a fluid passing through the passage.

Generally, electric heaters of this type are employed in high-power air heaters, for example for hair dryers, hair brushes or paint coatings, and for soldering operations. Such electric heaters heat an air stream and include a cylindrical body of ceramic material with a plurality of passages extending along an axis, each passage containing a resistive coil. A section is included. The holes encompassing the sections of these coils also act as passageways for the air to be heated. Through this passage, cold air is injected by a blower from one end of the ceramic body, and warm air is blown out from the other end. Resistance coils, which are usually manufactured in one-piece construction, can be quite cumbersome to incorporate into this type of heater. The reason for this is that the coils must be drawn through the respective associated pores, taking care not to stretch them unnecessarily. In this case, if it stretches, the heating effect will change and it will no longer be possible to control it. Another drawback is that the holes formed in the ceramic body exhibit relatively large fluid resistance, so the blower used must have a high output to flow the heated air sufficiently. That's true. However, such high power blowers have the disadvantage that not only are they expensive, but they are also often very noisy, which can be a nuisance, especially in home appliances and hobby craft tools. On the other hand, the above-mentioned drawbacks can be solved by increasing the hole diameter of this air flow path, but this increases the size of the heater body, and as a result,
The disadvantage is that the amount of resistance wire that can be wound per unit volume is reduced, and the efficiency of fluid flow around these resistance wires is reduced. In the known heater bodies mentioned above, the windings of the resistance wire coils are placed against the walls of the holes formed in the ceramic body, so that the fluid, e.g. air, flows through the holes in the axial direction. There is a drawback that it tends to flow. In this case, if the diameter of this winding were increased, a relatively large part of the cross section of the air flow would not be in direct contact with this resistance wire coil, leading to unsatisfactory results in heat transfer. Become.

In other known heaters, the ceramic body is comprised of plate-like sections, each of which has a helical groove portion for accommodating a resistance wire coil. Although this helical groove is open towards the outer circumference of the cylindrical ceramic body, it has the disadvantage that the flow of the air to be heated around the resistance wire coil, and therefore the heat transfer, are extremely unsatisfactory. Since the temperature at which this resistance wire coil can be operated is limited depending on its own characteristics, heaters of this configuration have a relatively low thermal efficiency for a given size.

The object of the invention is to eliminate the various drawbacks of the prior art mentioned above and to provide a heater of the type described in the introduction.

In order to achieve the above object, it is necessary to implement a heater embodying claim 1.

The heater according to claim 1 has the following features. That is, the fluid to be heated, for example a gas, a mixture of gases, air or a fluid, flows through the resistance wire coil in a plane in which it is aligned approximately at right angles. In contrast, conventional heaters have fluid flow in the axial direction of the resistance wire coil, and this feature allows for improved fluid flow around the resistance wire coil. Improvements are therefore also achieved in heat exchange. As a result of this, the heater has the characteristic of increasing the heat output at a given maximum temperature of the resistance wire coil, so that the size of the heater can be considerably reduced for a given heat output. The fluid flowing through the resistance wire coil of the heater according to the invention provides the advantage of increasing the diameter of the flow channel, which has the effect of reducing the flow resistance.
This reduction in flow resistance makes it possible to achieve low noise and use a low-output blower, and this effect will be particularly noticeable when the heater of the present invention is used in home appliances and hobby tools. Become.

Embodiments of the present invention are characterized in that the installation of the resistance wire coil is extremely simple. These resistance wire coils no longer need to be pulled through a relatively long and narrow distribution channel, but instead can simply be placed in a mounting recess.
Coils can be easily placed in these recesses during assembly. In addition, in conventional heaters, a resistance wire coil is arranged in an axial distribution channel, so that a portion of this wire coil is
If it were cut, it would protrude outside the ceramic body, and there was a risk that part of the housing would come into contact with the power supply. On the other hand, according to the present invention, such drawbacks can be avoided. That is, the resistance wire coil can be completely enclosed, and the two ends of this wire coil are not enclosed, but in any case suitable terminals are connected, so that the above-mentioned dangers are avoided. Furthermore, the heater according to the present invention has the advantage of being extremely simple to assemble.

According to embodiments of the invention, portions of the resistance wire coil can be easily inserted into recesses formed in the webs of adjacent heater body elements, and the connecting portion can be inserted into the space between two such webs. through until the successive cross-section (cross-section between next adjacent heater body elements). Since the space between the two heating elements is open, this installation of the resistance wire coil is extremely simple.

In an electric heater according to the invention, cold fluid flows into the heater device from one end and is gradually heated by contacting a continuation of the resistance wire coil along the length of the heater. As a result, the downstream portion of the resistance wire coil (the coil portion near the air outlet) is less cooled than the upstream portion (the coil portion near the air inlet). The downstream portion of the coil will therefore typically be heated to a higher temperature than the upstream portion. Generally, the maximum temperature of the resistance wire coil is limited so that the upstream section can be used less effectively than the downstream section. Furthermore, the downstream portion is heated to a substantially higher temperature than other portions. However, it surrounds the heater body. It is desirable to achieve a nearly constant temperature over the entire length of the heater body, if overheating of the housing part can be avoided, especially if this housing part is made of something like a synthetic resin. has been done. By varying the winding pitch of the resistance wire coil, the flow of fluid around sections of the wire with greater pitch per unit length is increased, resulting in more effective cooling of these sections and this This makes it possible to suppress the temperature rising toward the downstream portion of the coil. This ensures a constant temperature over the entire length of the resistance wire coil. In principle, the above design concept was applied to conventional heater structures, but considerable difficulties arose in practice. On the other hand, when applied to the heater of the present invention, the variable pitch of the resistance wire coil has the advantage that it can be easily realized by expanding and contracting the downstream portion of the coil.

Further, according to the embodiment of the present invention, one end of the resistance wire coil can be guided through one hole and returned to the other end, which has the effect of solving the insulation problem.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

Embodiments of the heater of the present invention are illustrated in FIGS. 1-4.

FIG. 1 shows the heater in assembled form, which consists of seven identical heater body elements 1 stacked on top of each other, one of which is shown enlarged in FIG. do. The heater body element 1 is made of a refractory material, such as a ceramic material, and includes a hollow cylindrical outer ring 2 and a cylindrical inner part 3.
and twelve radial webs 4, which extend between the aforementioned portions 2 and 3 while maintaining equal spacing. This web 4 is formed as a thin wall, which has parallel main surfaces and extends in the radial and axial directions.

The inner part 3 has a central opening 6 with a rectangular cross section, into which a clamping element 7 with a rectangular cross section is inserted. The clamping elements 7 axially clamp the individual heater main body elements 1 and act to prevent these elements 1 from rotating relative to each other. In order to perform such a clamping action, a thread groove is formed at the end of the clamp element 7, and the clamp element 7 is locked with a clamp nut as shown in FIG. In addition, three axial holes 5a and 5b spaced apart by 120 degrees in the inner part 3 are provided.
and 5c, and a pair of grooves 5d and 5f connected to one end of the hole 5a are formed on both sides of the adjacent web 4 together with channels or passages through which air flows.

A recess 8 is provided at each axial end of the web 4. The reason for providing this recess 8 has been explained in detail above.

A resistance wire coil 9 having a structure as shown in FIG. 2 is held between the individual disc-shaped heater body elements 1. In the present example, this resistance wire coil 9 consists of a plurality of coil sections 9a, which are arranged in a cross section between two adjacent heater body elements and are arranged in a straight line extending axially. multiple connected parts 9 of
They are connected to each other by b. Coil part 9
a extends in an arc of 330° and is located in the recess 8 of the web 4. Resistance wire coil 9
has two terminals 10a for connection to the power supply.
and 10b. This terminal 10
a through the aligned holes 5a of the stacked heater body elements 1 for connection to the last part 9a of the resistance wire coil 9. (Left side of Figure 2). From the opening of the hole 5a, the terminal 10a is guided outward toward one of the two channels along one of the two grooves 5e or 5f. The first coil section 9a is placed in the recess 8 of the web 4 so that it extends across the flow channel. A connecting portion 9b connected to the first coil portion 9a facing the terminal 10a extends from the left side in FIG. 1 through the first axial passage of the second heater body element 1. The second coil portion 9a is
The shaft-shaped connecting portion 9b connected to the coil portion 9a of is passed through the passage following the third heater main body element 1. Such an offset configuration is repeated from one heater main body element to the next element until the other terminal 10b passes through the hole 5b of the last heater main body element 1. The other terminal 10c shown in FIG. 2 serves as a current take-off for the blower power supply and guides this terminal 10c to the outside of the assembled heater through a hole 15c in the last heater body element. The outer peripheral surface of the heater body element 1 is formed with alignment notches 20.

Fluid (usually air) is passed through the fully assembled heater body shown in FIG. 1 in the direction of arrow P so that the air flows along the path defined between the webs 4. As a result of this, the air passes around the continuous section of the resistance wire coil 9 and as a result becomes heated. In the annular space formed between the outer ring 2 and the inner part 3 there is a web 4 and a resistance wire coil 9 which acts only as a "resistance" to the flow of fluid.
Only that part will be stored. During assembly of the heater, the webs 4 of successive heater body elements 1 are aligned with each other so as to form a continuous wall. Accurate alignment can be verified by using alignment notch 20. As a result, the fluid flow resistance is relatively small and optimum conditions for the flow around the resistance wire coil 9 are obtained.

In the embodiment shown in Figure 1, cold air flows into the heater body from the right end, so that the upstream portion of the resistance wire coil (the portion that receives the incoming air first) typically (outflow part). The reason for this is that the air flowing around the downstream section is already preheated. This results in the downstream portion of the resistance wire coil 9 being heated to a higher temperature than the upstream portion. In order to avoid this phenomenon, the windings of the resistance wire are wound relatively densely in the upstream section, and the air passing through this section is made to flow less per unit length than in the downstream section. . This results in the characteristic that the resistance wire coil is heated at a substantially constant temperature over its entire length.

In the embodiment of FIG. 1, the number of turns of the individual sections 9a of the resistance wire coil 9 is as follows, which decreases towards the downstream section.

Part 1 53 times 2nd 40th 3rd 32nd 4th 26th 5th 21st 6th 17th

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the electric heater of the present invention;
Figure 2 is a perspective view of the resistance wire coil in Figure 1, Figure 3 is an enlarged view of the heater main body element in Figure 1,
FIG. 4 is a diagram showing the heater main body element and resistance wire coil portion of FIG. 3. DESCRIPTION OF SYMBOLS 1... Heater main body element, 2... Hollow cylindrical outer ring, 3... Cylindrical inner part, 4... Web, 5a-5c... Axial hole, 5e-5f...
Groove, 6...Central opening, 7...Clamp element, 8...Recess, 9...Resistance wire coil.

Claims (1)

[Claims] 1. In heating the fluid, means for supporting the helically wound resistance wire coil 9 is provided, and the supporting means has a circular cross-sectional shape and is stacked on top of each other in the axial direction. The support means are comprised of separate heater body elements 1 and have recesses 8 formed at mutually opposite positions, thereby supporting the electrical resistance wire coil 9 therein. In the heater body, in the stacked state of the heater body elements 1, the outer walls 2 of these elements form a continuous cylindrical outer wall of the support means; The webs 4 extend radially inwardly from the outer wall 2 and cooperate with the recess 8 to form the resistance wire coil 9.
an electric heater, characterized in that the radial webs define an axial flow channel between which a fluid flow is formed. 2. The sections 9a of the resistance wire coils 9 are arranged in a substantially closed circular configuration in cross section between two sets of adjacent elements of the heater body element 1, and the two sets of the sections 9a of these wire coils are interconnected. Shaft section 9
2. An electric heater as claimed in claim 1, characterized in that the webs (b) are guided by one web (4) along paths that are radially offset from each other. 3. The electric heater according to any one of claims 1 to 2, wherein the central core portion 3 is formed with axial holes 5a, 5b, and 5c.