Heat exchanger
A heat exchanger is formed with tessellating conduits 4 passing therethrough. The tessellating conduits having transverse cross-sectional shapes which together substantially completely cover the transverse plane to the heat exchange 2. The tessellating conduits may be the outer conduits 18 within conduit pairs formed of an outer conduit 18 and an inner conduit 22. The outer conduits may have a cross-section that is a regular hexagon and the inner conduits may have a cross-section that is a circle. The heat exchanger can advantageously be formed by selective remelting of material with an energy beam.
This invention relates to the field of heat exchangers.
Published PCT Patent Application WO-A-2006/064202 describes a compact heat exchanger and reactor (CHXR) that can be manufactured by energy beam methods, such as selective laser remelting (SLR). Compact heat exchangers formed in this way are capable of providing large numbers of fine conduits with associated complex manifolding arrangements in a way that produces a high heat exchange surface area to volume ratio. However, a problem with such heat exchangers is that the manufacturing process can be disadvantageously slow and expensive. The remelting of material to form the conduits takes a significant amount of time and accordingly the greater the wall material requiring remelting that is present within the heat exchanger design, the longer it will take to manufacture that heat exchanger. A further problem is that whilst it is desirable to have thin conduit walls so as to promote high levels of heat transfer, significant pressure differentials can exist between different sides of the walls resulting in it being necessary to provide a greater wall thickness in order to withstand the forces resulting from such pressure differences. Such thickened conduit walls again take longer to manufacture and reduce the level of heat transfer.
Viewed from one aspect the present invention provides a heat exchanger comprising:
a body with a portion having a plurality of substantially parallel fluid carrying tessellating conduits passing therethrough, wherein
said tessellating conduits have transverse cross-sections with one or more shapes that substantially completely cover a plane through said portion of said body transverse to said tessellating conduits by repeated use of said one or more shapes.
The present invention recognises that tessellating conduits having cross-sections with shapes that fit together substantially to completely cover a plane transverse to those conduits result in a heat exchanger with a reduced amount of wall material. This makes manufacturing quicker and less expensive as well as providing other advantages. The tessellating shapes provide arrangements in which at least some neighbouring conduits can have the same contained fluid pressure and accordingly reduces the forces exerted on the conduit walls in a way which enable such conduit walls to be advantageously thinner.
Whilst it will be appreciated that there are many shapes, and combinations of shapes, which have the property of tessellating to cover a plane, design of the heat exchanger is advantageously simplified when the tessellating conduits have one shape which regularly tessellates to cover the plane.
Whilst regular tessellation can be achieved by a variety of shapes, a particularly preferred shape is that of a regular hexagon. Regular hexagons have internal angles which are not too sharp (i.e. reducing potential stress risers) and tend toward a circular cross-section which is able to provide a good degree of strength against internal or external pressure.
The tessellating conduits may each form an outer conduit of a conduit pair with an inner conduit being disposed within the outer conduit along at least a part of the outer conduit. Such a pipe-in-pipe arrangement is capable of providing a high level of heat transfer area to volume ratio. The tessellating outer conduits substantially completely fill the plane of a transverse cross-section of the heat exchanger body in a way that avoids redundant “dead spaces” which might reduce the heat transfer surface area to volume ratio and might also reduce the surface porosity. If these “dead spaces” were to be filled with material that material would require remelting and increase manufacture time. Simultaneously, the inner conduits are surrounded by the fluid contained within the outer conduits in a way which gives a high degree of heat transfer.
The inner conduits can have a variety of different shapes, but a circular cross-section provides a good degree of strength for the amount of material used.
The inner conduits may be held in position by arms extending from the inner conduits to the outer conduits. This arrangement is capable of providing a high degree of strength in the heat exchanger body.
Returning to consideration of the tessellating conduits themselves, the tessellating conduits may be arranged in concentric rings with adjacent rings being connected to receive different fluids. Thus, rings of tessellating conduits can together give rise to a collection equivalent to a pipe-in-pipe arrangement, even though conduit pairs are not being-used. It would also be possible to use conduit pairs in combination with such a concentric ring arrangement.
The efficiency of the present embodiments in reducing the amount of material needed to form the body of the heat exchanger are such that a tessellating conduit completely surrounded by neighbouring tessellating conduits will share all of its walls with respective tessellating conduits. These shared walls will be monolithic (formed of a single piece of material).
It will be appreciated that at the edges of the heat exchanger body, the tessellating conduits will not be surrounded by neighbouring tessellated conduits. Such edge conduits can have a different shape to those within the main body of the heat exchanger and may also have thickened exterior walls to better resist pressure differences.
The conduits may be further strengthened by having thickened walls proximal to their vertices and having curved vertices rather than sharp corners.
Whilst heat exchangers having the structural form described above are advantageous however manufactured, they are particularly well suited to manufacture from remelted material, that is layers of material remelted with an energy beam to form part of the body prior to addition of a successive layer of material that will be remelted.
It will be appreciated that manifolds are needed to connect to the conduits formed within the heat exchanger body and these will have a complex form given the detailed and complex form of the heat exchanger body. The use of remelted layers of material to manufacture such manifolds is highly convenient.
Whilst the heat exchangers formed in accordance with the present technique can have a high surface area to volume ratio compared to conventional heat exchangers, this can in some embodiments of the invention be made to exceed 5000 m2/m3, or in more preferred embodiments 10000 m2/m3 or in still more preferred to embodiments 15000 m2/m3. Some of these gains may be counteracted by an associated increase in pressure drop through the heat exchanger, although this may be addressed by the use of a larger number of shorter conduits.
Viewed from another aspect the present invention provides a method of malting at least a portion of a heat exchanger, said portion having a plurality of tessellating conduits passing therethrough, said method comprising the steps of:
providing a plurality of successive layers of a material to be remelted; and
energy beam remelting predetermined regions of each layer in accordance with a predetermined design, said energy beam remelting of each layer being performed prior to addition of a successive layer;
wherein said predetermined regions of each layer subjected to energy beam remelting form solid structures within said layer and said energy beam remelting of each layer fuses said predetermined regions of each layer to remelted regions of a preceding layer; and
said tessellating conduits have transverse cross-sections with one or more shapes that substantially completely cover a plane through said portion of said body transverse to said tessellating conduits by repeated use of said one or more shapes.
Example embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Within the body of the heat exchanger 2, a tessellating conduit 4 will be completely surrounded by neighbouring tessellating conduits. Each wall forming such a tessellating conduit is shared with one of its neighbouring tessellating conduits 4. The walls are thickened towards the vertices of the cross-section so as to better resist stress. Furthermore, the vertices are curved rather than having sharp corners so as to reduce stress risers.
At the edge of the heat exchanger body 2 the tessellating conduits 4 are not completely surrounded by neighbouring tessellating conduits. Accordingly, the shapes of these edge tessellating conduits 5 can differ from those within the main body of the heat exchanger 2. Furthermore, the outermost walls of these edge conduits may be thickened relative to the walls within the main body of the heat exchanger so that these edge conduit 5 can better resist higher pressure differences across the outermost walls.
As previously mentioned, the alternating concentric rings are connected by appropriate manifolds (not shown) to pass fluid in different directions. These fluids may be different fluids, such as a combusting air gas mixture in one set of rings and water to be heated in another set of rings. The inner surfaces of the tessellating conduits 4 containing the combusting air gas mixture may be coated with an appropriate catalyst to promote such combustion.
It will be appreciated that many other forms of tessellating shapes and patterns are possible and that the use of such patterns reduces the amount of wall material required since there will not be “dead spaces” between the conduits needing to be filled with excessive wall material.
In the example shown, the outer conduits 18, 20 carry fluid in one direction (e.g. up from the plane of the drawing), whereas the inner conduits 22, 24 carry fluid in the opposite direction (e.g. down into the plain of the drawing). As the outer conduits 18, 20 neighbour other outer conduits carrying the same fluid in the same direction they will tend to have the same internal pressure on either side of the walls forming the boundary between those outer conduits 18, 20. This reduces the stress on these walls an enables them to be thinner requiring less material to be used. It will be appreciated that heat transfer also occurs due to heat conduction through the walls and the arms 26, as well as directly from the fluid within the conduits across the wall of the inner conduits 22, 24.
The inner conduits 22, 24 are parallel with and pass along at least a portion of the outer conduits so as to form a pipe-in-pipe arrangement.
The dimensions given in
Claims
1. A heat exchanger comprising:
- a body with a portion having a plurality of substantially parallel fluid carrying tessellating conduits passing therethrough, wherein
- said tessellating conduits have transverse cross-sections with one or more shapes that substantially completely cover a plane through said portion of said body transverse to said tessellating conduits by repeated use of said one or more shapes.
2. A heat exchanger as claimed in claim 1, wherein said tessellating conduits have transverse cross-sections with one shape that regularly tessellates to cover said plane.
3. A heat exchanger as claimed in claim 2, wherein said tessellating conduits have regular hexagonal transverse cross-sections.
4. A heat exchanger as claimed in claim 1, wherein said tessellating conduits are outer conduits of respective conduit pairs, each conduit pair being an outer conduit and an inner conduit disposed within said outer conduit over at least a part of said outer conduit.
5. A heat exchanger as claimed in claim 4, wherein said outer conduit and said inner conduit within a conduit pair are connected to receive respective different fluids.
6. A heat exchanger as claimed in claim 4, wherein said inner conduits have a substantially circular transverse cross-section.
7. A heat exchanger as claimed in claim 4, wherein within a conduit pair a plurality of arms extend from said inner conduit to said outer conduit to hold said inner conduit in position.
8. A heat exchanger as claimed in claim 1, wherein said tessellating conduits are arranged in concentric rings with tessellating conduits in adjacent rings being connected to receive respective different fluids.
9. A heat exchanger as claimed in claim 1, wherein neighbouring tessellating conduits have polygonal transverse cross-sections and walls between neighbouring tessellating conduits are shared such that all walls of a tessellating conduit completely surrounded by neighbouring tessellating conduits are shared walls.
10. A heat exchanger as claimed in claim 1, wherein an edge conduit being a tessellating conduit not completely surrounded by other tessellating conduits has a transverse cross-section differing from said one or more shapes.
11. A heat exchanger as claimed in claim 10, wherein said edge conduit has at least one wall shared with a neighbouring tessellating conduit and at least one wall not shared with a neighbouring tessellating conduit and thicker than said at least one wall shared with a neighbouring tessellating conduit.
12. A heat exchanger as claimed in claim 1, wherein conduit walls of said tessellating conduits thicken proximal to vertices of said one or more shapes.
13. A heat exchanger as claimed in claim 12, wherein said conduit walls are curved at said vertices.
14. A heat exchanger as claimed in claim 1, wherein said body is formed of remelted material being layers of material remelted with an energy beam to form part of said body prior to addition of a successive layer.
15. A heat exchanger as claimed in claim 1, comprising one or more fluid manifolds connected to said tessellating conduits, said one or more fluid manifolds being formed of remelted material being layers of material remelted with an energy beam to form part of said manifold prior to addition of a successive layer.
16. A heat exchanger as claimed in claim 1, wherein said heat exchanger has surface area to volume ratio of greater than one of:
- 5000 m2/m3;
- 10000 m2/m3; and
- 15000 m2/m3.
17. A method of making at least a portion of a heat exchanger, said portion having a plurality of tessellating conduits passing therethrough, said method comprising the steps of:
- providing a plurality of successive layers of a material to be remelted; and
- energy beam remelting predetermined regions of each layer in accordance with a predetermined design, said energy beam remelting of each layer being performed prior to addition of a successive layer;
- wherein said predetermined regions of each layer subjected to energy beam remelting form solid structures within said layer and said energy beam remelting of each layer fuses said predetermined regions of each layer to remelted regions of a preceding layer; and
- said tessellating conduits have transverse cross-sections with one or more shapes that substantially completely cover a plane through said portion of said body transverse to said tessellating conduits by repeated use of said one or more shapes.
Type: Application
Filed: Oct 16, 2007
Publication Date: Dec 2, 2010
Inventors: Drummond Watson Hislop (London), Stephen David Joseph (Saratoga)
Application Number: 12/311,851
International Classification: F28F 9/02 (20060101); F28F 1/10 (20060101); B21D 53/02 (20060101);