EP0007929B1

EP0007929B1 - Heat transfer elements and method for the manufacture of such elements

Info

Publication number: EP0007929B1
Application number: EP19780300275
Authority: EP
Inventors: Maxwell Wingate Davidson
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-08-10
Filing date: 1978-08-10
Publication date: 1983-01-12
Also published as: EP0007929A1; DE2862149D1

Description

The present invention relates to heat transfer elements, and particularly to heat transfer panels or tubes serving for the conduction of heat between zones on either side thereof.
Heat transfer elements in the form of plain or curved panels are known, which panels alone or in combination serve to form a barrier between zones of hot and cold fluids while being adapted to transmit heat by conduction from the hot zone to the cold zone. Elements in the form of tubes or pipes operate similarly. For satisfactory heat conduction, these elements are made of a material having a suitably high coefficient of thermal conductivity. Where there is a large boundary between the zones, as is usually the case for effective heat transfer, a large element area is required and since material of high thermal conductivity are relatively more expensive it is a disadvantage of these barriers that they can be costly.
It is an object of the present invention to obviate or mitigate this disadvantage.
The present invention is characterised by having a plurality of apertures extending through a base wall member of the heat transfer element to the opposed outer surfaces of the wall member, said apertures widening as they approach the outer surfaces of the wall member, so as to have a waisted middle part, said apertures being filled with a material of higher thermal conductivity than the material of the wall member, and a layer of higher thermal conductivity than the base wall material on at least one outer surface of the wall member.
Preferably the transversely extending portion has parts projecting from at least one outer surface of the wall portion: these parts can constitute protuberances for creating turbulent fluid flow at said one outer surface of the wall portion.
The panel should be made of materials permitting operation at elevated temperature. The higher thermal conductivity part can be made of a noble metal, silver, copper or other material of suitably high thermal conductivity.
The outer surfaces of the wall member can be of any suitable configuration, but preferably at least one surface is of undulating form with the material filled bores extending from the troughs and crests of the undulations. The base wall member is preferaby made from a plastics material for cheapness, for example a polymer.
Preferably, the bore fillings project as rods from at least one outer surface of the wall.
By having a major portion of the heat transfer element made from relatively cheap plastics material rather than a more expensive heat conducting metal e.g. copper, a considerable saving in cost is possible with the element, and particularly in accordance with the present invention by having the metal-filled through- apertures in the plastics panel waisted form and by providing a thin layer of heat conducting metal on the outer surfaces of the panel, efficient heat transfer is possible at particularly low cost.
According to a further aspect of the present invention a method of making a heat transfer element comprises forming a base wall member from one material, forming apertures in the wall member extending transversely between the outer surfaces thereof arranging that said apertures widen as they approach the outer surfaces of the wall member so as to have a waisted middle part, filling said apertures with another material of higher thermal conductivity than the material of the base wall member and additionally applying a layer of material to at least one surface of the wall member, said layer being formed from material of higher thermal conductivity than the base wall material. In a preferred embodiment layers of higher thermal conductivity material are formed on both outer wall surfaces.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:-

Fig. 1 shows a sectional end view of a heat transfer panel according to a first embodiment of the present invention;
Fig. 2 shows a sectional end view of a heat transfer panel according to a second embodiment of the present invention.

Referring to figs. 1 and 2, a heat transfer panel 1 of wall part is fabricated from a sheet of plastics material 2 (thermosetting or thermoplastic), polymerised material, acetylene, vinyl or similar, glass or ceramic material. The panel can be moulded to the required form, and in the embodiment shown has a corrugated form, but the surfaces 3 could be outer surfaces of flat or of other configuration. In particular the panel 1 has a corrugated form having equal corrugation pitch P and equal corrugation amplitude A. Alternatively the corrugations may have unequal pitch and unequal amplitude. The corrugations 3 extend longitudinally but could extend transversely or may be inclined. Further, the panel 1 could be provided with dimples or recesses, on one or both sides, and these may extend in parallel rows or may be arranged in a reverse or alternating manner.
A series of through-bores 4 is provided in the panel 1 and extending transversely at predetermined intervals and spacings between desired parts of the outer surfaces of the panel 1. In the example shown, the through-bores 4, can be provided at the crests and troughs of the corrugated panel. These through-bores 4 are fully filled with material which has a high thermal conductivity and which is capable of resisting corrosion (i.e. is a noble material). The through bores widen adjacent the outer- surfaces. The filling material can be a noble metal such as silver (with the base panel suitably a polyamide sheet) which metal has a coefficient of thermal conductivity (1.00 (gramme) calories cm per sec cm² per degree C) very many times greater than plastics materials (polymers: 4.0-6.0 x 10-⁴ calories cm per sec per cm² per degree (C).
In the use of a heat exchange panel 1, relatively hot fluid passes on one side of the panel 1 while relatively cold fluid passes on the other side and heat transfer is substantially via the metal filled bores 4. A serious barrier to the transfer of heat occurs in the boundary layers of the hot fluid in contact with the panel and in the relatively slower moving laminer flow regions close to the boundary layer. There is a similar barrier to heat transfer at the cold fluid/panel interface. Conductance of heat which has reached the panel surface is relatively unimpeded transversely across the panel to the other outer wall surface. For any heat transfer, the temperature difference between the main body of the heating fluid and the adjacent outer surface of the heat transfer panel 1 is normally much greater than the temperature difference across the panel itself. The cold fluid/panel temperature differential is also greater than this latter difference. Therefore, for improved efficiency of heat transfer a layer 5 of high thermal conductivity and non-corrosive material is provided on at least one outer surface of the panel as shown in Fig. 3, and preferably on both outer surfaces. Such a layer 5 may be a silver layer. Further, since the metal filled bores 4 widen adjacent the panel outer surfaces instead of being plain cylindrical more efficient heat transfer is possible. The filled bores 4 and layers 5 can be formed for example by electro-plating or dipping etc.
The above heat transfer panel according to the present invention has the high thermal conductivity material 4, 5 positioned at the most useful locations in the panel 1. Since plastics materials are considerably cheaper and more easily worked than noble metals, and stainless steels, the above panel will be cheaper than a panel made solely of the metal, but the panel will have higher efficiency of heat transfer than a pure plastics panel.
In the embodiment shown in Fig. 2, the material of the bores 4 is arranged to extend as rods 6 from one or both outer surfaces of the panel 1. These projecting rods serve as turbulence promoters, droplet promoters for condensing vapours and thermal collectors or distributors to the fluids in contact or "en passant".

Claims

1. A heat transfer element comprising a base wall member (2), a plurality of apertures (4) extending through the base wall member to the opposed outer surfaces of said wall member, said apertures being filled with a material of higher thermal conductivity than the material of the base wall member, characterised in that said apertures (4) widen as they approach the outer surfaces (3) of the base wall member (2), so as to have a waisted middle part, and in that a layer (5) of higher thermal conductivity than the base wall material is present on at least one outer surface (3) of the base wall member (2).

2. A heat transfer element as claimed in claim 1, characterised in that the aperture fillings project from at least one outer surface of the base wall member (2).

3. A heat transfer element as claimed in claim 1 or 2, characterised in that the higher thermal conductivity material is a metal capable of resisting corrosion.

4. A heat transfer element as claimed in any one of the preceding claims, characterised in that the layer (5) of high thermal conductivity material is provided on each outer surface (3) of the base wall member (2).

5. A heat transfer element as claimed in any one of claims 1 to 3 characterised in that at least one surface (3) is of undulating form with the material filled apertures extending from the troughs and crests of the undulations.

6. A heat transfer element as claimed in any one of the preceding claims, characterised in that the base wall member (2) is made of plastics material.

7. A heat transfer element as claimed in claim 6, characterised in that the plastics material is a polymer.

8. A heat transfer element as claimed in any one of the preceding claims, characterised in that the higher thermal conductivity material is a noble metal.

9. A heat transfer element as claimed in claim 8, characterised in that the noble metal is silver.

10. A method of making a heat transfer element comprising forming a base wall member (2) from one material, forming apertures (4) in said wall member extending transversely between the outer surfaces thereof, filling said apertures with another material of higher thermal conductivity than the material of the base wall member, characterised in that said apertures widen as they approach the outer surfaces of the base wall member so as to have a waisted middle part, and additionally applying a layer (5) of material to at least one surface (3) of the base wall member (2), said layer (5) being formed from material of higher thermal conductivity than the base wall material.

11. A method as claimed in claim 10, characterised in that said layers of material are formed on both outer surfaces.

12. A method as claimed in claim 10 or 11 characterised in that the higher thermal conductivity material is applied by electro-plating or by dipping.