GB2130058A

GB2130058A - Induction fluid heating apparatus

Info

Publication number: GB2130058A
Application number: GB08231528A
Authority: GB
Inventors: Robert Stanley Ellis
Original assignee: IPW Ltd
Current assignee: IPW Ltd
Priority date: 1982-11-04
Filing date: 1982-11-04
Publication date: 1984-05-23
Also published as: GB2130058B

Abstract

The apparatus comprises a double-loop magnetic core 1, of which the common limb 2 is upright and carries a primary input winding 3 and a secondary output winding 4 in the form of a tube for conducting the liquid or other fluid to be heated. The tube, which is self-draining of fluid, has a single high portion 6 and falls away on both sides of that portion to a region 9 where the tube sections at each end of the winding pass in close proximity to each other, separated by a small gap 10. On each side of this gap a tubular shorting link 12 is welded to the adjacent sections of the tube. The shorting link contains a through passage for conduction of a cooling medium and the gap 10 forms a further cooling passage. The welded length is preferably at least equal to the average circumference of the tubular link 12. <IMAGE>

Description

SPECIFICATION Fluid heating apparatus This invention is concerned with fluid heating apparatus of the kind which employs an electrical induction heating system comprising a primary input winding and a secondary output winding.

The output winding is formed of a tube for conducting the fluid, and in order to produce the necessary heating effect this winding is electrically short-circuited.

The aim of the present invention is to improve on previous proposals in various respects.

In one particular previous proposal a shorting link in the form of a heavy stainless steel gap is used, joining the two ends of the output winding. It has been found, however, that after a prolonged period of operation the strap can become excessively hot.

Now, according to one aspect of the present invention, fluid heating apparatus of the kind described in the opening paragraph above is characterised by the fact that the output winding is short-circuited by a shorting link which contains at least one through-passage for conduction of a cooling medium.

For optimum cooling the shorting link is preferably in the form of an elongate tube-like member.

The tube-like shorting link preferably extends in substantially the same direction as the adjacent portions of the tube that forms the output winding. The link is best joined to these adjacent portions by some form of metallic bonding such as soldering, brazing or preferably welding. The bonded length is preferably at least equal to the mean circumference of the tube forming the output winding to minimise heating in the bond.

In a particularly preferred configuration there are two such tube-like links located on each side of a gap between the adjacent portions of the tube that forms the output winding. With such an arrangement the gap itself may form a further cooling passage.

Where natural air cooling is employed the tube-like links are preferably disposed in an upright position to create a chimney effect.

According to a further aspect, the invention also provides fluid heating apparatus comprising a magnetic loop core having an upright limb which carries both a primary input winding and a secondary output winding, the output winding being formed of a tube for conducting the fluid, the tube having a high portion on both sides of which the tube falls away to a region where the tube sections at each end of the winding pass in close proximity to each other, where they electrically shorted together.

This arrangement has several advantages over the earlier proposal referred to above, namely compactness and much tighter inductive coupling between the input and output windings, together with the fact that the output winding may be selfdraining of liquid. This latter feature is particularly important because any liquid remaining in the tube can present dangers.

The core is preferably a double-loop core with the common limb carrying the primary and secondary windings.

The output winding may to advantage be short-circuited by means of the new shorting link arrangement described above.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a general view of the apparatus, including an enlarged view of the portion indicated, and Figure 2 is a sectional view taken on line Il-Il of Figure 1.

The apparatus comprises a laminated double loop magnetic core 1 arranged with its common limb 2 in an upright position. This limb 2 carries a primary input winding 3 of between ten and several thousand turns of copper wire, the lower end of the range being necessary for high power applications, and a co-axial secondary output winding 4. The core is split into two parts, I a and 1 b, for ease of assembly.

The output winding 4 is formed of a high temperature alloy tube which is wound in a single helix about the limb 2. The tube rises continuously from the lower end 5 of the winding to the upper end 6 which constitutes a high portion. At the lower end 5 the tube is directed downwardly to form a feed section 7. Similarly, at the upper end 6 the tube forms a downwardly directed return section 8. Both sections fall substantially vertically until they reach a region 9 where they deviate towards each other, though still with a continuous fall, and run substantially parallel for a short distance in close mutual proximity, separated by a small gap 10.

On each side of the gap 10 there is a shorting link in the form of a length of tube, 11 and 12.

Each link is disposed vertically and is seated against both the feed and return sections, 7 and 8, to which it is attached by welds 13. The welded length I (which may or may not be equal to the length of the link) is substantially equal to the mean circumference of the tube forming the output winding 4. For convenience the links 11 and 12 formed from the same stock tube as the winding 4, although they could be formed of different size tube if desired. The use of tubes of the same material simplifies welding and minimises stresses due to differential expansion, although again, different materials could be used.

The feed section 7 is connected to a suitable fluid pump (not shown).

In use, the input winding 3 is connected to a suitable mains supply (e.g. 415 volts 50 Hz in UK) via leads 14. A heavy current is induced in the short-circuited secondary winding 4, generating heat in the tube walls which is transmitted to the fluid flowing through the tube. The current flows circumferentially through the shorting links 11 and 12 generating heat in their walls and in the welds 13, but because of the vertical disposition of these links there is a natural chimney effect which draws air through the interior passages of the links to produce natural cooling. A similar effect also creates an air flow through the gap 10 between the links.

Forced cooling could be employed, for example using a blower. The ends of the links could be adapted for connection to a cooling system for pumping a cooling fluid through the links. It is envisaged that the ends of the links could be extended perpendicuarly to the feed and return sections (i.e. using generally U-shaped links) to facilitate coupling to such a system.

The co-axial arrangement of the windings results in tight mutual coupling, and in this regard the double-loop core configuration illustrated is superior to a single loop, although the latter could be used if desired. The configuration of the output winding makes it self-draining when the apparatus is used for heating liquids.

Instead of the single helix arrangement described the winding could continue from the upper end 6 in a further downward helix, i.e.

forming a double helix, and still be self-draining.

The important thing is that there should be only a single high portion with the tube dropping away on either side until it reaches the shorting links, and preferably beyond to the very ends of the tube. Although undesirable, the fall could incorporate horizontal portion if necessary.

The apparatus is particularly effective for generating very high pressure steam from water, although it is also suitable for heating a variety of liquids and gases.

Claims

1. Fluid heating apparatus comprising an electrical induction heating system having a primary input winding and a secondary output winding which is electrically short-circuited, the output winding being formed of a tube for conducting the fluid, and the apparatus being characterised by the fact that the output winding is short-circuited by a shorting link which contains at least one through-passage for conduction of a cooling medium.

2. Apparatus according to Claim 1, in which the shorting link is in the form of an elongate tube-like member.

3. Apparatus according to Claim 2, in which the shorting link extends in substantially the same direction as the adjacent portions of the tube that forms the output winding.

4. Apparatus according to Claim 3, in which the link is joined to the adjacent portions of the tube by a form of metallic bonding.

5. Apparatus according to Claim 4, in which the form of metallic bonding is used is welding.

6. Apparatus according to Claim 4 or 5, in which the bonded length is at least equal to the average circumference of the tube forming the output winding.

7. Apparatus according to any of Claims 2 to 6, in which there are two such tube-like links located on each side of a gap between the adjacent portions of the tube that forms the output winding.

8. Apparatus according to any of claims 2 to 7, in which the tubelike link/s is/are disposed in an upright position for natural air cooling.

9. Apparatus according to any preceding claim, which includes a magnetic loop core having an upright limb which carries both the primary input winding and the secondary output winding, the tube forming the output winding having a high portion on both sides of which the tube falls away to a region where the tube sections at each end of the winding pass in close proximity to each other, where they are electrically shorted together by the shorting link/s.

10. Apparatus according to Claim 9, in which the extreme ends of the tube beyond the shorting link/s are downwardly directed.

1 Apparatus according to Claim 9 or 10, in which the core is a double-loop core having a common limb which carries the primary and secondary windings.

12. Fluid heating apparatus comprising a magnetic loop core having an upright limb which carries both a primary input winding and a secondary output winding, the output winding being formed of a tube for conducting the fluid, the tube having a high portion on both sides of which the tube falls away to a region where the tube sections at each end of the winding pass in close proximity to each other, where they are electrically shorted together.

1 3. Apparatus according to Claim 12, in which the extreme ends of the tube beyond the region where they are shorted together are downwardly directed.

14. Apparatus according to Claim 12 or 13, in which the core is a double-loop core having a common limb which carries the primary and secondary windings.

1 5. Fluid heating apparatus which is substantially as described with reference to the accompanying drawings.