GB1590697A

GB1590697A - Heat exchanger

Info

Publication number: GB1590697A
Application number: GB46406/77A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1977-11-08
Filing date: 1977-11-08
Publication date: 1981-06-10

Description

(54) HEAT EXCHANGER (71) We STANDARD TELEPHONES AND CABLES LIMffED, a British Company of 190 Strand, London WC2, England, 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 state ment This invention relates to a heat exchanger, particularly to one suitable for heating liquid such as water by capturing solar radiation.

Many proposals for heat exchangers of this kind have been put forward over recent years but most are relatively expensive. One arrangement aimed at providing a relatively cheap heat exchanger is described in our published specification No. 1 516 262 in which the heat exchanger is formed by an elongate tubular element which is either coiled up or cut into lengths and connected parallel to each other between top and bottom headers.

According to the present invention there is provided a heat exchanger, including a sealed hollow radiation absorbant cell having an inlet and an outlet for a liquid whose temperature is to be changed, a support structure for the cell formed from a foamed plastics material, said support structure including rigid strip members extending through the foamed plastics material and whereby the support structure can be secured to a surface, and a transparent cover which covers the front of the cell with an air gap between the cover and the front, whereby solar radiation will heat liquid passed through the cell and the support structure acts not only to support the cell but also acts as thermal insulation for the cell.

Preferably the support structure comprises a single integral moulded block of foamed plastics material. We have found a suitable material is polyisocyanurate foam. Preferably also this is coated with a resin gel coat to give environmental protection and also protection against the deleterious effect of ultra-violet rays.

Very preferably the sealed hollow cell comprises polypropylene which is extruded to form a multi-channel membrane. Preferably this is of rectangular form and made matt black by the inclusion of carbon black, with a header moulded to it at two opposite parallel edges.

The support structure preferably has corresponding recesses to accommodate the headers, one of them fitting one header accurately, the other recess being wide enough to accommodate movement of the other header caused by expansion and contraction of the sealed cell due to temperature changes.

Preferably the cover is supported on side walls of the foamed plastics support structure.

Plastic straps can be used to secure the cover to the support of structures. A pair of extruded metal sections can be moulded into the foam adjacent opposite edges to stiffen the foam and form carrying and mounting devices to mount the heat exchanger on the roof of a building.

In order that the invention can be clearly understood reference will now be made to the accompanying drawings, in which Figures 1A and 1B show respectively a lengthwise and crosswise section through a heat exchanger according to an embodiment of the present invention, Fig. 1A being a section along the line A-A of Figure 1B and Figure 1B being a section along the line B-B of Figure 1A, Figures 2A and 2B show part-sections of the support structure of Figure 1 and Figures 3A, 3B and 3C show part sections and a part-plan view of the cover of the embodiment of Figure 1.

Referring to Figure 1 the heat exchanger comprises a single glazed modular polypropylene sealed cell 1 formed by a polypropylene extrusion having a large number of parallel flow channels. It is matt black by the inclusion of carbon black and has a front wall 2 and a rear wall 3 spaced from the front wall by an amount which is small in comparison with the length and breadth of the sealed cell and with the length of the channels. Conveniently the extrusion is like packaging board, the spacing between the front and rear wall being about 4 mm. and the channel width being about 5 mm. In this particular embodiment the length of the cell is approximately 2 metres and the width 11/4 metres. Inlet and outlet tubular headers polypropylene 4 and 5 extend the breadth of the cell 1 and are sealed to the cell by propropylene sealer.The walls of the cell are about l/2 mm. thick.

The bottom wall 3 of the sealed cell is supported by a support structure 6 made of an integral moulding of foamed plastics material, in this embodiment polyisocyanurate foam.

This has a thickness, in the embodiment described, between the ground and the bottom wall 3 of between 4 and 5 cm. and has recesses 7 and 8 in which the headers 4 and 5 are seated.

As can be seen recess 8 is wide enough to allow movement of the header 5 backwards and forwards caused by contraction and expansion of the sealed cell 1 when the temperature changes.

A pair of extruded aluminium channels 19 and 20 are moulded into the support structure and act as stiffeners and securing points where they protrude at each end, for plastics securing straps 17, to be described later, and for mounting the exchanger on an external structure.

The protruding ends also are useful as handles to carry the exchanger. The structure is coated with a white resin gel coat which gives environmental protection, particularly against moisture and ultra-violet rays.

A transparent cover 9, in this embodiment made of polymethylmethacrylate, covers the front wall of the sealed cell with an air gap 10 which varies betwen 1 and 2 cm. at the edges to 2 to 4 cms. at the centre. The edges 11 and 12 of the cover are formed as shallow depending walls which fit around the upstanding walls such as 13 and 14 of the support structure 6.

As shown in Figure 1B the lengthwise edge regions of the cover have a shallow channel 15 and 16 to accommodate long plastics straps, one being shown in Figure 1A and referenced 17. There would be two such straps one in each of the channels 15 and 16 and secured at their ends to the ends of the aluminium channels 19 and 20. These channels are used also to secure the heat exchanger in position on, for example, the roof of a building.

Figure 2 shows in greater detail and on a different scale the support structure 6. Figure 2A is a section along the line D-D of the part section shown in Figure 2B, and Figure 2B is a part-section along the line C-C of Figure 2A.

The recesses 7 and 8, as shown in Figure 2A, extend out through the far side wall 13 to provide access for connection pipes to the headers 4 and 5.

Referring now to Figure 3 there is shown in greater detail a corner area of the cover 9, Figure 3A being a section along the line F-F of Figure 3B and Figure 3B being a part-section along the line E-E of Figure 3A. Figure 3C is a plan view of part of the corner area. This particular comer provides an outlet recess 18 which co-operates with the aperture through the wall 13 for th connection of the header 4.

A feature of the heat exchanger described resides in the moulded foamed plastics support structure 6 which not only supports the heat exchanger but also provides excellent thermal insulation. As can be seen the heat exchanger comprises only three basic elements, that is to say the support structure 6, the sealed cell 1 and the cover 9. Thus it is simple to manufacture, is light and has inherent strength.

Although not shown there is provided a reflective layer in the form of aluminium foil interpersed between the rear wall 3 of the cell 1 and the structure 6.

We have successfully carried out tests using this heat exchanger to pre-heat water to 60"C for factory washing facilities. Water is pumped through the heat exchanger to a header tank by a pump which is controlled by a temperaturedifferential thermostat arrangement, whereby the pump is stopped when the differential between the heat exchanger and the header tank falls below a preset value, which could be zero. The headers could open at opposite edges of the exchanger instead of the same edge shown.

WHAT WE CLAIM IS: 1. A heat exchanger, including a sealed hollow radiation absorbent cell having an inlet and an outlet for a liquid whose temperature is to be changed, a support structure for the cell formed from a foamed plastics material, said support structure including rigid strip members extending through the foamed plastics material and whereby the support structure can be secured to a surface, and a transparent cover which covers the front of the cell with an air gap between the cover and the front, whereby solar radiation will heat liquid passed through the cell and the support structure acts not only to support the cell but also acts as thermal insulation for the cell.

2. A heat exchanger according to Claim 1, wherein the support structure comprises an integrally moulded block having a base and an upstanding peripheral wall.

3. A heat exchanger according to Claim 1 or 2 wherein the support structure is made of polyiscyanurate foam.

4. A heat exchanger according to any preceding claim wherein the sealed cell comprises an extruded multi-channel plastics member with inlet and outlet headers sealed to it at two opposite edges, and the support structure has corresponding recesses accommodating the headers.

5. A heat exchanger according to Claim 4, wherein the recess fits the head and the other recess provides a gap to allow lateral movement of the other header caused by expansion and contraction of the sealed cell when the temperature changes.

6. A heat exchanger according to any preceding claim comprising a reflective layer interposed between the cell and the support structure.

7. A rectangular heat exchanger comprising a sealed hollow rectangular cell formed by a multi-channel plastics member of laminar configuration extending between and sealed to two tubular plastics headers so as to define for liquid to be heated a flow path extending into one header, through the channels and out through the other header, a substantially rigid

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. integral moulding of foamed plastics material, in this embodiment polyisocyanurate foam. This has a thickness, in the embodiment described, between the ground and the bottom wall 3 of between 4 and 5 cm. and has recesses 7 and 8 in which the headers 4 and 5 are seated. As can be seen recess 8 is wide enough to allow movement of the header 5 backwards and forwards caused by contraction and expansion of the sealed cell 1 when the temperature changes. A pair of extruded aluminium channels 19 and 20 are moulded into the support structure and act as stiffeners and securing points where they protrude at each end, for plastics securing straps 17, to be described later, and for mounting the exchanger on an external structure. The protruding ends also are useful as handles to carry the exchanger. The structure is coated with a white resin gel coat which gives environmental protection, particularly against moisture and ultra-violet rays. A transparent cover 9, in this embodiment made of polymethylmethacrylate, covers the front wall of the sealed cell with an air gap 10 which varies betwen 1 and 2 cm. at the edges to 2 to 4 cms. at the centre. The edges 11 and 12 of the cover are formed as shallow depending walls which fit around the upstanding walls such as 13 and 14 of the support structure 6. As shown in Figure 1B the lengthwise edge regions of the cover have a shallow channel 15 and 16 to accommodate long plastics straps, one being shown in Figure 1A and referenced 17. There would be two such straps one in each of the channels 15 and 16 and secured at their ends to the ends of the aluminium channels 19 and 20. These channels are used also to secure the heat exchanger in position on, for example, the roof of a building. Figure 2 shows in greater detail and on a different scale the support structure 6. Figure 2A is a section along the line D-D of the part section shown in Figure 2B, and Figure 2B is a part-section along the line C-C of Figure 2A. The recesses 7 and 8, as shown in Figure 2A, extend out through the far side wall 13 to provide access for connection pipes to the headers 4 and 5. Referring now to Figure 3 there is shown in greater detail a corner area of the cover 9, Figure 3A being a section along the line F-F of Figure 3B and Figure 3B being a part-section along the line E-E of Figure 3A. Figure 3C is a plan view of part of the corner area. This particular comer provides an outlet recess 18 which co-operates with the aperture through the wall 13 for th connection of the header 4. A feature of the heat exchanger described resides in the moulded foamed plastics support structure 6 which not only supports the heat exchanger but also provides excellent thermal insulation. As can be seen the heat exchanger comprises only three basic elements, that is to say the support structure 6, the sealed cell 1 and the cover 9. Thus it is simple to manufacture, is light and has inherent strength. Although not shown there is provided a reflective layer in the form of aluminium foil interpersed between the rear wall 3 of the cell 1 and the structure 6. We have successfully carried out tests using this heat exchanger to pre-heat water to 60"C for factory washing facilities. Water is pumped through the heat exchanger to a header tank by a pump which is controlled by a temperaturedifferential thermostat arrangement, whereby the pump is stopped when the differential between the heat exchanger and the header tank falls below a preset value, which could be zero. The headers could open at opposite edges of the exchanger instead of the same edge shown. WHAT WE CLAIM IS:

1. A heat exchanger, including a sealed hollow radiation absorbent cell having an inlet and an outlet for a liquid whose temperature is to be changed, a support structure for the cell formed from a foamed plastics material, said support structure including rigid strip members extending through the foamed plastics material and whereby the support structure can be secured to a surface, and a transparent cover which covers the front of the cell with an air gap between the cover and the front, whereby solar radiation will heat liquid passed through the cell and the support structure acts not only to support the cell but also acts as thermal insulation for the cell.

rectangular foamed plastics support structure encasing the member and the headers, and a transparent plastics cover positioned over the member and seated on the support structure with an air gap between the member and the cover, the headers opening at one or opposite edges of the exchanger and there being at least two elongate stiffening elements extending through the support structure for mounting the exchanger on an external structure, the support structure acting as the main thermal insulation around the cell apart from the cover.

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