GB1565092A

GB1565092A - Making heat exchangers

Info

Publication number: GB1565092A
Application number: GB12407/76A
Authority: GB
Original assignee: T I Ltd
Current assignee: T I Ltd
Priority date: 1977-03-25
Filing date: 1977-03-25
Publication date: 1980-04-16

Description

(54) MAKING HEAT EXCHANGERS (71) We, T.I. (GROUP SERVICES) LIMITED, a British Company, of T.I.

House, Five Ways, Birmingham, B16 6SQ, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the manufacture of heat exchangers. Where heat is to be exchanged between a fluid flowing through a pipe and another medium, which may be a second fluid or it could be radiated heat, it is desirable to increase the effective surface area of the pipe and countless proposals have been made for adding fins or more extensive sheet metal surfaces. For example in solar heating panels used for picking up solar heat and conducting it to a liquid, usually water, flowing through a coiled or meandering pipe, it is known to solder, braze or weld the edges of sheet metal surfaces to the pipe. However this only produced a thermally conductive path of limited cross-section. Another solution is wrap the metal sheet partially around the pipe, with or without a soldered or brazed connection to improve the conduction, but with known techniques this is only practical where the pipe is straight.

Roll-bonded pairs of sheets sandwiched together with integral passages formed between them by fluid pressure are also known but are expensive to make.

In the field of solar heaters even conventional sheet metal radiators are used, but cannot have the same heat absorption for a given weight and water volume as more refined structures. Likewise even moulded plastics structures are known, but plastics have a limited thermal conductivity.

The aim of the invention is to provide an improved method of manufacturing heat exchangers, especially though by no means exclusively solar heating panels. According to the invention we propose a method of manufacturing a heat exchange assembly, comprising a pipe or array of pipes in thermal contact with a sheet of ductile, heat-conducting metal comprising placing the sheet on the opposite side of a pipe or array of pipes from a forming surface and subjecting the sheet to a fluid pressure differential to cause the sheet to be deformed about the pipes or array of pipes and against the forming surfaces, so that the sheet wraps itself partially around the pipes or array of pipes, and the portions of the sheet not in contact with the pipe or array of pipes conform substantially to the forming surface.

The process can be, in fact, very like the known vacuum-forming and blow-moulding techniques used on sheet plastics materials, and used for packaging. The invention is applicable primarily to those metals known as superplastic alloys, which are already known to be capable to being shaped by the use of fluid pressure, usually air pressure, but it may be possible also to use other sheet metals if they are sufficiently ductile.

In particular it is possible to use steel sheet rolled from steel having transformation - induced plasticity.

The invention will now be further described by way of example with reference to the accompanying drawings. in which: Figure 1 illustrated diagrammatically a forming bed with the parts ready to be formed; and Figure 2 is a vertical section through a bed similar to that of Figure 1 with the parts shown in the position they occupy after the forming operation.

The forming bed, shown at 1. is in the form of a shallow tray with vertical sides and a flat floor in the example illustrated. It has a horizontal outwardly directed flange 2 at its rim, provided with means (not shown) for clamping a flat sheet in an air-tight manner across its open top. The sheet is shown at 3 ready to be dropped into position but first there is placed on the floor of the bed a length of tube 4, for example aluminium alloy or copper tube, bent to a meandering or serpentine shape. The shape can be of any other form to suit requirements, for example spiral or in a series of parallel tubes forming a grid. The two ends of the tube are turned downwards to protrude through holes in the floor of the bed, or they extend through notches (not shown) in the side walls of the bed.

When the tube 4 has been placed in position and the sheet 3 clamped across the top of the bed, the sheet is heated to the temperature required to give it the necessary ductility and then air is withdrawn from the interior of the bed, allowing atmospheric pressure to force the sheet down to engage floor of the bed and at the same time to wrap itself at least partially around the tube 4. As explained earlier, the sheet must be of sufficiently ductile metal, for example an aluminium-based or zinc-based superplastic alloy or a transformation-inducedplasticity steel. The degree to which the sheet wraps itself around the tube will depend on its ductility and on the pressure differential applied, but the greater the degree of wrapping the better will be the thermal contact between the sheet and the tube. In a typical example the sheet may embrace 270 of the circumference of the tube. If desired, instead of using atmospheric pressure one could employ a pressure above atmospheric, and it is within the scope of the invention to employ hydrostatic, i.e. liquid, pressure instead of gas pressure.

Figure 2 shows the sheet 3 wrapped around two runs of tube 4. It will be appreciated that the apparatus described is verv flexible in use. in that the same forming bed can be used regardless of the shape to which the tube is bent. no special jigs or dies being required to ensure that the sheet fits closely around the tube.

In the example shown, the sheet wraps itself around more than 1800 of the circumference of the tube and so the tube is securely locked in place in the tube to form a unitary structure that is ready for handling and for installation in solar planel heat exchanges. However, in a modification it would be possible to arrange that the sheet only extends about 1800, or slightly less, around the tube, allowing the tube to be removed for the insertion of a heatconducting cement, the tube then being replaced and thereby bonded by this cement to the sheet in a manner that ensures a high degree of heat transfer.

After the cement has been applied and the tube re-inserted, the resulting assembly could be put back in the bed and subjected to a higher pressure differential than before to increase the degree of wrap-around and lock the tube in place, as well as squeezing out any voids in the cement. It may also be possible to do the whole thing in a single operation, that it to say, to apply a cement to the tube after it is first placed in the bed, and to form the sheet around the tube, locking the tube in place, without the intermediate step.

By the provision of bars, placed on the floor of the bed between the runs of tube, as indicated in broken lines at 5 in Figure 1 one can produce corrugations or ridges in the finished body as shown at 6 in Figure 2.

These ridges help to accommodate the thermal strain differential that may arise with certain combinations of material for the sheet and the tube.

It will be appreciated that the floor of the forming bed need not be flat; on the contrary one can produce heat-exchange panels having a single or even compound curvature.

By means of the invention solar panels of any desired shape and size can be made, with the heat-absorbing surface in intimate contact with the greater part of the total surface area of the tube. and with the surface simultaneously forming the means for mounting and locating the tube.

Moreover there are no restrictions on the shape to which the tube can be bent, and no tolerances are required in the bending process. Two or more separate lengths of tube may be secured simultaneously to the same panel.

The tooling can be so arranged that a raised or otherwise shaped edge is provided on the panel for the attachment of facing glass or backing insulation. In addition auxiliary items such as attachment fixings may be located in the tooling and 'captured' by the sheet in the same manner as the tubes.

WHAT WE CLAIM IS: 1. A method of manufacturing a heat exchange assembly, comprising a pipe or array of pipes in thermal contact with a sheet of ductile, heat-conducting metal comprising placing the sheet on the opposite side of a pipe or array of pipes from a forming surface and subjecting the sheet to a fluid pressure differential to cause the sheet to be deformed about the pipe or array of pipes and against the forming surface. so that the sheet wraps itself partially around the pipe or array of pipes, and the portions of the sheet not in contact with the pipe or array of pipes conforms substantially to the forming surface.

2. A method according to claim 1 in which the pipe or array of pipes is resting against the forming surface.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. manner across its open top. The sheet is shown at 3 ready to be dropped into position but first there is placed on the floor of the bed a length of tube 4, for example aluminium alloy or copper tube, bent to a meandering or serpentine shape. The shape can be of any other form to suit requirements, for example spiral or in a series of parallel tubes forming a grid. The two ends of the tube are turned downwards to protrude through holes in the floor of the bed, or they extend through notches (not shown) in the side walls of the bed. When the tube 4 has been placed in position and the sheet 3 clamped across the top of the bed, the sheet is heated to the temperature required to give it the necessary ductility and then air is withdrawn from the interior of the bed, allowing atmospheric pressure to force the sheet down to engage floor of the bed and at the same time to wrap itself at least partially around the tube 4. As explained earlier, the sheet must be of sufficiently ductile metal, for example an aluminium-based or zinc-based superplastic alloy or a transformation-inducedplasticity steel. The degree to which the sheet wraps itself around the tube will depend on its ductility and on the pressure differential applied, but the greater the degree of wrapping the better will be the thermal contact between the sheet and the tube. In a typical example the sheet may embrace 270 of the circumference of the tube. If desired, instead of using atmospheric pressure one could employ a pressure above atmospheric, and it is within the scope of the invention to employ hydrostatic, i.e. liquid, pressure instead of gas pressure. Figure 2 shows the sheet 3 wrapped around two runs of tube 4. It will be appreciated that the apparatus described is verv flexible in use. in that the same forming bed can be used regardless of the shape to which the tube is bent. no special jigs or dies being required to ensure that the sheet fits closely around the tube. In the example shown, the sheet wraps itself around more than 1800 of the circumference of the tube and so the tube is securely locked in place in the tube to form a unitary structure that is ready for handling and for installation in solar planel heat exchanges. However, in a modification it would be possible to arrange that the sheet only extends about 1800, or slightly less, around the tube, allowing the tube to be removed for the insertion of a heatconducting cement, the tube then being replaced and thereby bonded by this cement to the sheet in a manner that ensures a high degree of heat transfer. After the cement has been applied and the tube re-inserted, the resulting assembly could be put back in the bed and subjected to a higher pressure differential than before to increase the degree of wrap-around and lock the tube in place, as well as squeezing out any voids in the cement. It may also be possible to do the whole thing in a single operation, that it to say, to apply a cement to the tube after it is first placed in the bed, and to form the sheet around the tube, locking the tube in place, without the intermediate step. By the provision of bars, placed on the floor of the bed between the runs of tube, as indicated in broken lines at 5 in Figure 1 one can produce corrugations or ridges in the finished body as shown at 6 in Figure 2. These ridges help to accommodate the thermal strain differential that may arise with certain combinations of material for the sheet and the tube. It will be appreciated that the floor of the forming bed need not be flat; on the contrary one can produce heat-exchange panels having a single or even compound curvature. By means of the invention solar panels of any desired shape and size can be made, with the heat-absorbing surface in intimate contact with the greater part of the total surface area of the tube. and with the surface simultaneously forming the means for mounting and locating the tube. Moreover there are no restrictions on the shape to which the tube can be bent, and no tolerances are required in the bending process. Two or more separate lengths of tube may be secured simultaneously to the same panel. The tooling can be so arranged that a raised or otherwise shaped edge is provided on the panel for the attachment of facing glass or backing insulation. In addition auxiliary items such as attachment fixings may be located in the tooling and 'captured' by the sheet in the same manner as the tubes. WHAT WE CLAIM IS:

1. A method of manufacturing a heat exchange assembly, comprising a pipe or array of pipes in thermal contact with a sheet of ductile, heat-conducting metal comprising placing the sheet on the opposite side of a pipe or array of pipes from a forming surface and subjecting the sheet to a fluid pressure differential to cause the sheet to be deformed about the pipe or array of pipes and against the forming surface. so that the sheet wraps itself partially around the pipe or array of pipes, and the portions of the sheet not in contact with the pipe or array of pipes conforms substantially to the forming surface.

3. A method according to claim 1 or

claim 2 in which the meandering pipe or the array likes in one plane.

4. A method according to any one of claims 1 to 3 in which the sheet is of a superplastic alloy.

5. A method according to claim 4 in which sheet is of a superplastic aluminium alloy.

6. A method according to any one of claims 1 to 3 in which the sheet is of a steel having transformation induced plasticity.

7. A method according to any one of the claims 1 to 6 in which the sheet is caused to wrap itself around more than 180C of the circumference of the pipe or each of the array of pipes, so as to lock the pipe or pipes in the sheet.

8. A method according to any one of claims 1 to 7 in which a heat-conducting cement is incorporated between sheet and the or each pipe.

9. A method according to any one of claims 1 to 6 in which the sheet is caused to wrap itself around not substantially more than 1800 of the circumference of the or each pipe, so as to allow the or each pipe to be detached subsequently from the sheet.

10. A method according to claim 9 in which, after formation of the assembly, the or each pipe is detached from the sheet, a heat-conducting cement is applied to one of the mutually engaging surfaces, and the sheet and pipe or pipes are reassembled.

11. A method according to any one of claims 1 to 10 in which the fluid pressure is air pressure.

12. A method according to claim 11 in which the pipe or array of pipes is laid in the floor of a tray-like forming bed, the sheet is clamped across the open top of the bed, and air is withdrawn from the interior of the resulting closed space to cause atmospheric pressure to deform the sheet around the pipe or array of pipes.

13. A method of manufacturing a heat exchanger assembly substantially as described with reference to the accompanying drawings.

14. A heat exchanger assembly made by the method of any one of claims 1 to 13.