GB2199647A

GB2199647A - Heat exchangers

Info

Publication number: GB2199647A
Application number: GB08700195A
Authority: GB
Inventors: Nicholas Julian Jan F Macphail
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-01-07
Filing date: 1987-01-07
Publication date: 1988-07-13
Anticipated expiration: 2007-01-07
Also published as: GB8700195D0; GB2199647B

Abstract

Within a boiler heat exchanger formed by a water jacket wall 10 and held loosely in random orientation by a support plate and spacing box are short pieces of metal tube 14. These cause turbulent flow of the flue gases in flue gas passage 12 while effectively increasing the surface area of the water jacket and transfer their heat by multipath point contact via the water jacket 10 to the water in the water passage 11. The pieces 14 may be secured to one another and wall 10 by solder or adhesive cement. <IMAGE>

Description

"Improvements in Heat Exchangers" I, NICHOLAS JULIAN JAN FRANCIS MacPHAIL, a British Subject of La Girouette, Grandes Rocques, Guernsey of the Channel Islands, do hereby declare the invention for which we pray that a patent may be granted to me and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a heat exchanger.

In general, a heat exchanger comprises a flow passage for a first medium and a flow passage for a second medium, the flow paths being separated by a thermally conductive wall structure. It is common to employ in heat exchangers some method of increasing the effective surface area of the wall structure in order to obtain a greater rate of transfer of heat energy between the media. For example, in a heat exchanger in which water to be heated is passed through a boiler water jacket of which the inside is subject to the products of combustion of a liquid, solid or gaseous fuel, fins or baffles may be provided on the inside of the water jacket to increase their effective surface area and turbulence.However, the provision of such finning is relatively expensive, and demands complex and accurate assembly procedures of the heat exchanger while baffles produce high gas flow resistance or low efficiency.

It is an object of the present invention to provide an improved heat exchanger in which the above stated disadvantages are avoided or reduced.

According to the present invention there is provided a heat exchanger comprising a flow passage for a first medium, a flow passage for a second medium, a thermally conductive wall structure separating said flow passages, and in at least one of the said flow passages a plurality of thermally conductive ring like elements, at least some of said elements contacting said wall structure.

Preferably said ring like elements are of tubular form, each having approximately the same length as diameter, and are disposed in random orientation in said flow passage. Said ring like elements may have their surface extended by, for example, fins or corrugations. The ring like elements in random orientation may be loose or fixed to each other and to the thermally conductive wall at their point contacts by dip bath soldering or where temperatures allow by adhesive cement coating.

The preferred embodiment comprises an inner flow passage for hot products of combustion of a fuel as the first medium, a thermally conductive wall structure forming said flow passage for the first medium and affording a second flow passage for liquid to be heated, said ring like elements being disposed in the first flow passage with at least some of them in contact with the said thermally conductive wall structure.

The heat exchanger preferably comprises a water jacket, concentric to the said inner flow passage, which is provided with inlet and outlet connections for the liquid.

In the inner flow passage is provided support brackets supporting a support plate and a spacing box.

The space between the spacing box and the thermally conductive wall is loosely filled with ring like elements.

The spaces between the support plate and the thermally conductive wall structure are large enough to allow the passage of the hot products of combustion but small enough to retain the ring like elements.

Said water jacket, support plate, spacing box and ring like elements may be formed from mild or stainless s;eel.

The invention will now be described by way of example with reference to the accompanying drawings in which: FIGURE 1 is a diagramatic representation of a heat exchanger embodying the invention, FIGURE 2 is a diagramatic cross-sectional elevation of a preferred form of heat exchanger, and FIGURE 3 is a diagramatic cross-sectional plan of the heat exchanger of Figure 2.

Referring firstly to Figure 1 there -is illustrated diagramatically part of a heat exchanger having a thermally conductive wall structure 10 which separates passages 11 and 12, along which respective heating or cooling media may flow. For example, a relatively hot medium may flow along the passage 12 and a relatively cool medium along the passage 11, in which case energy is transferred from the medium in passage 12 to that in passage 11 through the wall structure 10. In the flow passage 11 the effective area of the surface of the wall structure 10 which is presented'to-the medium, and at which surface heat transfer may occur, is that of the plain surface of the wall structure only.

In the flow passage 12, there is provided a plurality of ring like elements 14 arranged in random orientation, so that some of the ring like elements 14 contact the wall structure 10. The elements 14, which are made of heat conductive material, each having approximately the same length as diameter and are conveniently produced by suitable cutting up of tube stock. The random arrangements of the elements 14 is such that the effective surface area of the wall structure 10 which is presented to the medium in the passage 12 is increased over that of the plain surface presented to the passage 11, and thus heat energy may be transferred more easily to or from the medium in passage 12.

In addition to providing a greater effective surface area of the wall structure, the elements 14 also serve to cause turbulence of the flow of the medium in the passage 12 and thus increase further the rate of heat transfer. The elements 14 are loosely packed. Any suitable retaining means (not shown) may be provided for retaining these elements in the required position.

In Figures 2 and 3 there is illustrated an cpplication of such a heat exchanger to the heating of water, such as would be employed in a domestic hot water boiler or similar application. The apparatus comprises a water jacket 20 within which are dispose water entry and exit openings 21 and 22 respectively. Through one wall of the water jacket 20 a mounting for a fuel burner assembly 23 and flame tube 24 entry are provided. From the fuel burner assembly 23 a flame enters the combustion chamber 25, the base of which is protected from heat by a ceramic felt pad 26.

The hot products of combustion then flow arcund the support plate 27 through the space between the water jacket 20 and the spacing box 28 before exiting at 29 to an exhaust flue or the like.

The water jacket 20 thus forms a flow passage for a first medium in the form of the products of combustion, and with the water inlet and outlet openings 21 and 22 a flow passage for the second medium in the form of water, with the material of the inner face of the water jacket 20 constituting the thermally conductive wall structure of the heat exchanger.

Between the outside of the spacing box 28 and the water jacket 20 there is provided a plurality of ring like elements 30 which increase the rate of heat transfer from the products of combustion by increasing the effective surface area of the water jacket and providing turbulent flow of the products of combustion as before described. The ring like elements 30 may again be formed of tube, and are loosely packed in random orientation in the space between the spacing box 28 and the water jacket 20.

The space in or around the support plate 27 is such as to retain the rings above it.

In one typical construction of a boiler unit as Figures 2 and 3, the water jacket is approximately .3m x .3m x .75m internally and the ring like elements are approximately 15mm diameter x 15mm long. The ring like elements are conveniently made of mild or stainless steel, as are the water jacket, support plate and spacing box. The support plate and combustion chamber base may be conveniently protected against the effects of exposure to excessive heat by ceramic fibre pads.

Claims

AT I CLAIM IS:

AEAT I CLAIM IS: 1. A heat exchanger comprising a flow passage for a first medium, a flow passage for a second medium, a thermally conductive wall structure separating said flow passages, and in at least one of said flow passages a plurality of thermally conductive ring like elements, at least some of said elements contacting said wcll structure.

2. A heat exchanger according to claim 1 wherein said ring like elements are disposed in random orientation in said flow passage.

3. A heat exchanger according to claim 1 or claim 2 wherein each of said ring like elements is of generally tubular form, having a length substanti & ly equal to its diameter.

t. h heat exchanger according to any one of the preceding claims comprising a first flow passage for ambient atmospheric air or hot products of combustion of a fuel constituting said first medium, a second flow passage for receiving a liquid or gas to be cooled or heating constituting said second medium, and said ring like elements being provided in at least one flow passage with at least some of them contacting the said wall structure.

5. A heat exchanger substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Amendments to the claims have been filed as follows WHAT I CLAIM IS: 1. A heat exchanger comprising a flow passage for a first fluid, a flow passage for a second fluid, a thermally conductive wall structure separating said flow passages, and in at least one of said flow passages a plurality of thermally conductive ring like elements forming thermally conductive paths to the wall structure by contact between elements disposed generally across the flow passage from each other.

2. A heat exchanger according to claim 1 wherein said ring like elements are disposed in random orientation in said flow passage.

3. A heat exchanger according to claim 1 or claim 2 wherein each of said ring like elements is of generally tubular form, having a length substantially equal to its diameter.

4. A heat exchanger according to any one of the preceding claims comprising a first flow passage for ambient atmospheric air or hot products of combustion of a fuel constituting said first fluid, a second flow passage for receiving a liquid or gas to be cooled or heating constituting said second fluid, and said ring like elements being provided in at least one flow passage with at least some of them contacting the said wall structure.

5. A heat exchanger substcntially as hereinbefore described with reference to and as shown in the accompanying drawings.