IE51043B1

IE51043B1 - Electrical heating element

Info

Publication number: IE51043B1
Application number: IE890/81A
Authority: IE
Original assignee: Braun Ag
Priority date: 1980-04-18
Filing date: 1981-04-16
Publication date: 1986-09-17
Also published as: HK64889A; IE810890L; DE3014935A1; EP0038414A1; ES266004U; DE3168230D1; ES266004Y; EP0038414B1

Abstract

1. Electrical wire heating element for heating an air flow, which has a heating conductor support receiving the heating conductor winding and which comprises rectangular support plates made from insulating material arranged in cross-like or star-like manner about the central axis of the air flow and parallel thereto, the inner edges of said plates being oriented parallel to the air flow and whereof in each case two further edges are at right angles to the air flow and onto whose four outer edges is spirally wound a heating conductor, whose longitudinal course is periodically deformed, i.e. in meander-like, zig-zag or wavy manner and whose turns are partly successively arranged in the air flow, characterized in that the portions (51, 52) of in each case two successive turns of the heating conductor winding supported and defined by two adjacent support plates (1, 2; 2, 3; 3, 4; 4, 1) differ from one another with respect to the number of their periodic undulations.

Description

The present invention relates to an electrical wire heating element for heating an air flow.

Different electrical wire heating elements are known in which a heating conductor is wound over support plates arranged in cross or star like formation. The support plates used may be rectangular or trapezoidal, in which case the trapezoidal shape has the advantage over the rectangular shape familiar from DE-B-1 540 731, for instance, that the heating conductor windings wound over it are not arranged precisely one behind the other within the flow of air but are instead staggered in steps. This prevents succeeding heating-conductor windings from entirely shielding one another, so that the air carried along the support plates from the blower does not come in contact solely with the first but also with the succeeding heating-conductor windings and can therefore flow past in a more heat efficient manner. Examples of such heating wire elements are described in the following printed publications, for instance: OS-A-1 490-088, DE-A-2 727 940, FR-A-2 056 541, GB-A-713 712 and US-A-1 467 667.

Although noticeable progress has already been achieved with trapezoidal support plates, it was found when using heating conductors deformed at regular intervals over their length (i.e. in meander, zig-zag or wave form), a particularly advantageous feature from the cost point of view, that the effect obtained with this shape of plate was still insufficient to avoid overheating of the heating conductor windings situated further back along the air flow and to avoid the defects thereby produced.

The existing requirements for increased output of heat and for efficiency of the heating element also contributed to the problem on which the present invention is based, that of producing an electrical wire heating element capable of being mass-produced at favourable cost, which would ensure optimum flow conditions for effective heating of air, given the purpose of its use e.g. in hair driers and the like - and the generally restricted installation dimensions prevailing in such equipment.

According to the invention, there is provided an electrical wire heating element for heating an air flow, which has a heating conductor support for receiving a heating conductor winding and which comprises rectangular support plates made from insulating material arranged in cross-like or star-like manner about the central axis of the air flow and parallel thereto, the inner edges of said plates being oriented parallel to the air flow and whereof in each case two further edges are at right angles to the air flow and onto whose four outer edges is spirally wound a heating conductor deformed at regular intervals along its length, i.e. in meanderlike, zig-zag or wavy manner and whose turns are partly successively arranged in the air flow, wherein sections of two successive turns of the heating conductor winding supported and defined by two adjacent support plates differ from one another with respect to the number of their periodic undulations.

The difference in number of undulations in adjacent and succeeding heating conductor sections as provided by the present invention prevents these sections from shielding one another at any time over their entire length, even when using rectangular support plates. This results in overall improvement of heat transfer from the heating conductor to the air flowing past; which means that heating output or capacity is increased or that a smaller heating element will suffice where greater heating capacity is not required.

It is worth noting in this context that the invention's contribution to optimisation of utilisation of heat is surprisingly simply and effectively achieved, without additional cost.

It is advantageous for the support plates of the heating conductor support to be shaped as unequal-edged rectangular trapezoids, in which the plates are arranged in Intersecting planes in cross or star-shaped form. In this case, the sloped outer edges of the support plates can all be mounted in like direction and also aligned alternately displaced by 180° in relation to the air flow.

To adapt the length of sections of the heating conductor as defined by the outer edge of the support plates to prevailing requirements (in order, for example, to distribute electrical voltage drop and heating capacity uniformly over the heating element by providing approximately equal length in all such sections). One version of the present invention provides for curved or, in particular, arcuate shaped design of these outer edges.

Another version of the invention can be used to advantage when the cross-section of flow at the side of the heating element facing the blower differs from that at the opposite end, for instance by being oval at the one end and circular at the other; optimum adaptation is achieved in this case in that the length of the support-plate edges perpendicular to direction of flow is different at the side facing the blower and and identical at the other end, or vice versa.

One further advantageous means of influencing the winding geometry of the heating element as specified in this invention is the continuous axial displacement by a small distance of the support plates running in parallel with direction of flow. In this way, it is possible to keep the support radius for the heating conductor and the free-span length of the heating conductor sections between support plates largely constant within each individual heating conductor winding.

As means of attachment of the support plates, it is preferred in accordance with the present invention to fix their inner edges, running in parallel with the central axis of the air flow, to the shell of a tubular body.

The attached drawings of a number of embodiments according to the invention demonstrate the essential characteristics of this invention.

Figure 1 shows in principle the arrangement of the heating element according to this invention.

Figure 2 shows the differing number of undulations in two succeeding windings of the heating element provided in accordance with this invention, as viewed in the direction of air flow.

Figure 3 shows the above-mentioned arrangement incorporating a tubular supporting body Referring to the drawings, Figure 1 shows four support plates 1, 2, 3 and 4 arranged together in cross like pattern, over the outer edges 11, 21, 31 and 41 of which is wound a wave-formed heating conductor 5. The wave shape shown is solely In schematic form and not to scale, thus making it impossible to identify from this drawing the inventive feature of differing number of undulations in succeeding sections of the heating conductor. The plate edges 12, 22, 32 and 42 perpendicular to direction L of air flow and facing towards the blower are of different length in the example shown, while the corresponding edges 13, 23, 33 and 43 at the other end are of equal length. In this way, this heating element is adapted over its length to a change in cross-section of flow from oval to round. Hatched lines are used to indicate that the support plates can have curved, e.g. arcuately shaped edges 14, 24, 34 and 44 - intended especially in order to provide a constant free voltage length a in heating conductor 5.

Fig. 2 graphically shows half of a heating conductor section 51 consisting of six undulations in total and, located behind it, the corresponding section 52 of adjacent winding of the heating conductor winding 5, which has a total of five undulations. It can clearly be seen that, in this example, hardly any shielding takes place even with a difference of no more than one undulation in the number of undulations in each section.

The heating element shown in Figure 3 includes a tubular supporting body 6, to which are attached trapezoidal support plates 1 to 4 with outer edges 11, 21, 31 and 41 ascending radially upwards in direction of flow L. Plate 2 is displaced by a slight amount b-c in the axial direction in relation to plate 1, while plate 3 is displaced likewise in relation to plate 2 and plate 4 to plate 3. Displacement b-c can especially be so designed in size that, within each individual heating conductor winding, as in winding 51 in this example, the support height d in all four support plates will be the same and the free span length a of the heating elements between the plates will remain approximately constant.

Claims

1. Electrical wire heating element for heating an air flow, which has a heating conductor support for receiving a heating conductor winding and which comprises rectangular support plates made from insulating material arranged in cross-like or star-like manner about the central axis of the air flow and parallel thereto, the inner edges of said plates being oriented parallel to the air flow and whereof in each case two further edges are at right angles to the air flow and onto whose four outer edges is spirally wound a heating conductor, deformed at regular intervals along its length i.e. in meander-like, zig-zag or wavy manner and whose turns are partly successively arranged in the air flow, wherein sections of two successive turns of the heating conductor winding supported and defined by two adjacent support plates differ from one another with respect to the number of their periodic undulations.

2. Electrical wire heating element according to Claim 1, wherein the support plates are constructed as unequal-sided, right-angled trapeziums.

3. Electrical wire heating element according to Claim 1, wherein the four, outer edges of the support plates are constructed in a curved and in a particular arcuate manner. .51043 - 10

4. Electrical wire heating element according to any one of claims 1 to 3, wherein the edges of the support plates facing the blower have different lengths, whilst the edges remote from the blower are of the same length 5. Or vice versa.

5. Electrical wire heating element according to any one of claims 1 to 4, wherein the support plates are axially staggered by a small distance with respect to one another.

6. 10 6. Electrical wire heating element according to any one of claims 1 to 5, wherein the inner edges of the support plates running parallel to the central axis of the air flow L are fixed to the circumferential surface of a tubular body.

7. 15 7. Electrical heating element, substantially in accordance with either of the embodiments as herein described with reference to and as shown in the accompanying drawings.