PANEL FOR REGENERATIVE HEAT-EXCHANGERS

Abstract: A heat exchange panel or element is adapted for use in a regenerative or recuperative type heat exchanger and is particularly suitable for use in a gas to gas, vapour bearing gas to gas, or gas or vapour bearing gas to air heat exchanger of the Ljungstrom or similar type. The panel or element comprises a composite wall member (9) made of metal mesh (10) and an encapsulating layer (11) of a material of lower thermal conductivity which envelopes and extends through the mesh, the layer thickness outside the mesh being thin and substantially less than the thickness of the mesh so that the mesh extends substantially to, and conducts heat from, the outer surfaces of the wall member. The mesh (10) may be interwoven metal strands or strips or be of pierced and expanded, preferably flattened, metal sheet. In one form immediately next to the mesh (10) the encapsulating layer is a filled plastics material to promote heat capacity and outside the mesh (10) the layer is of a corrosion resistant inert material.

Description: PANEL FOR REGENERATIVE HEAT-EXCHANGERS The present invention relates to a heat exchange panel or element adapted for use in a regenerative or recuperative type heat exchanger and such as may be used in packages of many such panels or elements within a regenerative or recuperative gas to gas, vapour bearing gas to gas or gas or vapour bearing gas to air heat exchanger of the well known Ljungstrom or similar type. Within Ljungstrom and such heat exchangers a body of sheet elements or panels is alternately exposed to passage through the interstitial spaces between the individual elements of a hotter flow of gas or gas and vapour and a cooler flow of gas,gas and vapour or air. It is the purpose of the elements or panels to accept and store heat energy as rapidly as possible from the hotter flow and when after a time interval a cooler flow is directed through the same interstitial spaces to give out the stored heat energy to the cooler flow thus raising the temperature of that flow. The elements or panels may be rotated or translated in such a way that they proceed alternately through the hotter and cooler flows. Alternatively the elements or panels may be stationary and the hotter and cooler flows respectively directed by means of dampers to pass alternately through the elements or panels. This invention has application for such regenerative and recuperative gas to gas or gas to air heat exchangers particularly, but not exclusively, where one or both of the gas flows, or the gas flow, contains vapours at or near their condensing temperatures or dew point and which vapours are corrosive to certain metals and other materials and which may be in a particular instance oxides of sulphur and of nitrogen as produced during the combustion of fossil and other fuels. According to a first aspect the present invention consists in a heat exchange panel or element adapted for use in a regenerative or recuperative type heat exchanger characterised in that it comprises a heat storage and transfer member which includes a composite wall member made from portions of different thermal conductivity, one said portion of higher thermal conductivity comprising a metal mesh of strips or strands and a second said portion of lower thermal conductivity constituting an encapsulating layer enveloping and extending through the mesh so that the portions are intimately interlocked together against separation and the composite wall member is enabled to operate at higher temperatures than could the material of the encapsulating layer alone, the thickness of the encapsulating layer outside the mesh being substantially less than the transverse extent of the mesh across the total thickness of the wall member and said transverse extent of the mesh being substantially to outer surfaces of the wall member whereby the mesh conducts heat from the outer surfaces to promote the heat absorption of the wall member, and at least some of the mesh continuing longitudinally and directly throughout the major part of the length and breadth of the wall member such that differential temperature between any two diverse locations in the wall member is minimised by the transfer of heat energy laterally of the wall member through such strips or strands. It is also proposed that at least immediately next to the mesh the encapsulating layer be composed of a material, such as a plastics, which may or may not be filled with particulated mineral or other substance to provide as high a heat capacity as possible for any given volume or mass of the filled material. It is further proposed that at least outside the mesh the encapsulating layer on both sides of the wall member be composed of a plastics or other material which is inert and resistant to corrosive effects of condensing vapours of acid gaseous oxides or vapours which may condense upon it. Preferably the thickness of the material of the encapsulating layer outside the mesh is of the order of 0.1-0.3mm. The average density of such a metal mesh and plastics composite wall member is considerably less than that of the equivalent metal or glass enamelled metal elements presently in use in the aforementioned heat exchangers whereas the specific heat capacity of the wall member is for any given volume as good as for metal or glass enamelled metal elements. Surfaces of the wall member of a panel or element in accordance with the present invention which are corrosion resistant as described above may be chosen from preferred plastics such as to reduce the adherence and building up of dust or scales on the surfaces, and, as taught in UK Patent Number 1 372 680, could be made to be non-fouling in respect of organic and other agents or growths. The encapsulating layer may be made of another suitable material of lower thermal conductivity than the metal mesh, if desired, for example glass. The metal mesh which forms the heat conducting material within the proposed panel or element also operates as a reinforcing grid within the panel or element imparting structural stability to the panel or element. That stability would not be present if a panel or element of purely plastics material were to be used, and it enables greater rigidity and stability to be imparted to any preferred ridging, folding or other profile forming of the panel or element for it to present undulating surfaces for enhanced heat transfer at those surfaces. The mesh may comprise interwoven or overlaid discrete metal strips or strands of wire or filament, for example of steel, aluminium, copper or brass, or it may comprise a sheet of metal, for example of one of the metals just mentioned, which has been pierced and expanded such that the sheet whilst retaining its unity effectively presents a network of strip or strand portions. In the latter form a preferred material is that known as EXPAMET which is metal sheet which has been pierced, expanded and subsequently flattened. The percentage open area of such a sheet between the strip or strand portions may vary, typically between 5 and 25% of the total area of the mesh. The thickness of the metal of the mesh may vary with the size of the panel but typically will be 0.3-1.0mm thick, resulting in a typical total, or laminate, thickness, of the wall member between 0.5 and 1.5mm. Since the encapsulating layer extends through the mesh as well as over it, it fully envelopes and bonds mechanically to the mesh so that the two are interlocked together to prevent separation of the layer from the mesh. According to a second aspect of the present invention a regenerative or recuperative type heat exchanger is provided which includes a heat exchange panel or element in accordance with the first aspect of the invention herein set forth. Further, according to a third aspect of the present invention there is provided a regenerative or recuperative heat exchanger of the Ljungstrom or similar type containing a body of heat exchange panels or elements each in accordance with the heat exchange panel or element as set forth in the first aspect of the invention herein. Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 shows schematically a side elevation of a regenerative heat exchanger with heat exchange elements according to the present invention, part sectioned through section A-A of Figure 2; Figure 2 shows a plan view through section B-B of Figure 1; Figure 3 shows a perspective view of part of a heat exchange element; Figure 4 shows a side view of an alternative form of heat exchange element, and Figure 5 shows a perspective view of part of yet another form of heat exchange element in accordance with the invention. Referring to the drawings, a regenerative heat exchanger 1 comprises a drum 2 carried by a rotating shaft 3 and including peripheral pockets 4 housing removable heat exchange panels or elements 5. The heat exchange panels or elements 5 are arranged in packs in the pockets 4 with the panels or elements of each pack in contiguous relationship but with passages defined between them for the flow of gas, gas and vapour or air for heat exchange with the panels or elements. The panels or elements are corrugated, ridged or otherwise suitably profiled for the passages to be defined and for there to be turbulent flow of the gas, gas and vapour or air between the panels or elements. The heat exchanger 1 has a heat input side IA and a heat output side IB, and suitable ductings 6, 7 are provided for gas, gas and vapour or air flows (shown arrowed) through the drum 2 at these sides for heat exchange with the panels or elements 5. The drum 1 is rotated very slowly, e.g. less than 1 r.p. ., by the shaft 3. Each heat exchange panel or element 5 includes, as shown in Figures 3 and 4, a composite wall member 9 made from portions of different thermal conductivity, one portion of higher thermal conductivity comprising a metal mesh 10 of interwoven wire strands while a further wall portion 11 of lower thermal conductivity constitutes an encapsulating layer which completely covers and extends through the mesh. The two portions of the wall are thus soundly mechanically bonded together and so intimately interlocked that delamination of the portions is prevented. Outside the mesh the covering of the encapsulating layer over the strands of the mesh is reduced to a very thin skin, preferably 0.1-0.3mm thick, which is substantially thinner than the thickness of the mesh and its strands, the skins outside the mesh being fused together by the material of the encapsulating layer through the openings between the strands of the mesh. The mesh 10, therefore, has a transverse extent across the depth of the wall member 9 substantially to the opposite outer surfaces or the wall member so that the mesh is able to conduct heat from the outer surfaces of the wall member into the body of the wall member to promote the heat absorption capacity of the wall member. The wall member 9 is incorporated, applied and fashioned into the panel or element to be suitable for application to the heat exchanger 1. Particularly for this purpose some of the mesh 10 continues longitudinally and directly throughout the major part of the length and breadth of the panel or element 5 such that differential temperature between any two diverse locations in the element 5 is minimised by the lateral transfer of heat energy through strands of the mesh. The panel or element 5 includes a peripheral bead 5A around the wall member 9. The bead 5A may be omitted, if desired. The mesh may be made of strands of copper, aluminium, nickel, bronze or other strand material of high thermal conductivity. The encapsulating layer 11 immediately enveloping the mesh strands is composed of a plastics material 12 filled with particulated mineral or other substance to provide as high a heat capacity as possible for any given volume or mass of the filled plastics material. The plastics material 12 may be un-filled. The encapsulating layer also includes thin outer layers 13 on both sides of the wall member 9 composed of a plastics or other material which inseparably bonds with the plastics material 12, is inert and unaffected by corrosive effects of any condensing vapours or acid gaseous oxides or vapours which may condense upon it. The outer layers 13 may be omitted so that the encapsulating layer is composed entirely of the plastics material 12, filled or un-filled, which not only extends through the mesh but provides the thin skins over the strands of the mesh outside the mesh. The material of the encapsulating layer 11 may be a thermoplastic or thermosetting plastics having suitable flexibility to permit thermal stressing during use of the panel. It must be able to withstand the highest operational temperatures of the panel. With the mesh contained within it the plastics material is able to operate satisfactorily at temperatures in excess of those at which the material might be expected to function on its own. A urethane or other elastomer is, for example, suitable. Depending upon the type of plastics material used for the encapsulating layer, the material may be applied molten to the mesh, sprayed in the form of a powder on to the mesh or the mesh may be dipped into a bed of the powder fluidised by compressed air to be covered by that material. Glass may be used to form the encapsulating layer 11 instead of plastics material. Instead of the mesh 10 being of interwoven wire strands it may comprise an arrangement of cross-laid strands 10* as shown in Figure 4. The mesh may be made of interwoven or cross-laid sheet metal strips. Another form of the composite wall member 9 is shown in Figure 5 of the accompanying drawings. In this case there is the encapsulating layer 11 as before but the mesh 10 is formed from pierced and expanded metal sheet which though a unitary piece of material presents a network of strip or strand portions 10" across the length and breadth of the wall member. Preferably this mesh is formed from pierced, expanded and flattened metal sheet, for example steel or aluminium EXPAMET. Again the mesh is completely covered, as in the previously described form of the composite wall member, by the encapsulating layer 11 which also extends through the openings of the mesh to fuse together through the mesh the portions of the encapsulating layer at opposite sides of the mesh sheet and interlock the mesh and encapsulating layer inseparably together. The encapsulating layer 11 may include thin outer layers, as in the other embodiments described and illustrated.

Claims: 10 CLAIMS 1. A heat exchange panel or element (5) adapted for use in a regenerative or recuperative type heat exchanger (1) characterised in that it comprises a heat storage and transfer member which includes a composite wall member (9) made from portions of different thermal conductivity, one said portion of higher thermal conductivity comprising a metal mesh (10) of strips or strands and a second said portion of lower thermal conductivity constituting an encapsulating layer (11) enveloping and extending through the mesh so that the portions are intimately interlocked together against separation and the composite wall member is enabled to operate at higher temperatures than could the material of the encapsulating layer alone, the thickness of the encapsulating layer outside the mesh being substantially less than the transverse extent of the mesh across the total thickness of the wall member and said transverse extent of the mesh being substantially to outer surfaces of the wall member whereby the mesh conducts heat from the outer surfaces to promote the heat absorption of the wall member, and at least some of the mesh continuing longitudinally and directly throughout the major part of the length and breadth of the wall member such that differential temperature between any two diverse locations in the wall member is minimised by the transfer of heat energy laterally of the wall member through such strips or strands. 2. A heat exchange panel or element according to Claim 1 characterised in that at least immediately next to the mesh the encapsulating layer (11) is composed of plastics material (12) . 3. A heat exchange panel or element according to Claim 1 characterised in that the encapsulating layer (11) is made of glass. 4. A heat exchange panel or element according to any preceding claim characterised in that the encapsulating layer (11) at least immediately next to the mesh is of a material filled with particulated mineral or other substance which promotes the heat capacity of the material. 5. A heat exchange panel or element according to any preceding claim characterised in that at least outside the mesh (10) the encapsulating layer (11) on both sides of the wall member (9) is comprised of material which is inert and resistant to corrosive effects of condensing vapours or acid gaseous oxides or vapours which may condense upon it. 6. A heat exchange panel or element according to Claim 5 characterised in that said inert and corrosion resistant material of the encapsulating layer (11) is a plastics which reduces the adherence and building up of dust or scales on the wall member. 7. A heat exchange panel or element according to any preceding claim characterised in that the mesh (10) comprises interwoven or overlaid discrete metal strips. 8. A heat exchange panel or element according to any of Claims 1 to 6 characterised in that the mesh (10) comprises interwoven or overlaid discrete metal strands of wire or filament (10'). 9. A heat exchange panel or element according to any of Claims 1 to 6 characterised in that the mesh comprises pierced and expanded sheet metal material which presents in effect a network of strip or strand portions (10* ') . 10. A heat exchange panel or element according to Claim 9 characterised in that the sheet of metal material is of a kind which has been flattened after it has been pierced and expanded. 11. A heat exchange panel or element according to Claim 10 characterised in that the open area of the mesh (10) between the strip or strand portions (10') is 5-25% of the total area of the mesh. 12. A heat exchange panel or element according to any preceding claim characterised in that it is profiled to present undulating surfaces for enhanced heat transfer at those surfaces. 13. A heat exchange panel or element according to any preceding claim characterised in that the thickness of the metal of the mesh (10) is 0.3-1.0mm thick. 14. A heat exchange panel or element according to any preceding claim characterised in that the thickness of the material of the encapsulating layer (11) outside the mesh (10) is of the order of 0.1-0.3mm. 15. A heat exchange panel or element according to any preceding claim characterised in that the total thickness of the wall member (9) is of 0.5-1.5mm. 16. A heat exchange panel or element according to any preceding claim characterised in that a peripheral bead (5A) is provided around the wall member(9). 17. A regenerative or recuperative type heat exchanger characterised in that it includes a heat exchange panel or element (5) as claimed in any preceding claim. 18. A regenerative or recuperative heat exchanger of the Ljungstrom or similar type characterised in that it contains a body of heat exchange panels or elements (5) each in accordance with the heat exchange panel or element as claimed in any of Claims 1 to 16. 19. A regenerative or recuperative heat exchanger according to Claim 18 characterised in that the heat exchange panels or elements (5) are removably housed in pockets (4) of a rotatable drum (2) . 20. A regenerative or recuperative heat exchanger according to Claim 18 or Claim 19 characterised in that the heat exchange panels or elements (5) are arranged in packs in contiguous relationship and having passages defined between them for flow of gas, gas and vapour or air for heat exchange with the panels or elements. 21. A regenerative or recuperative heat exchanger according to Claim 20 characterised in that the heat exchange panels or elements (5) are profiled for the passages to be defined and for there to be turbulent flow between the panels or elements.

Inventors: DAVIDSON MAXWELL WINGATE, DAVIDSON, MAXWELL, WINGATE
Applicants: DAVIDSON MAXWELL WINGATE, GLYNWED PLASTICS, DAVIDSON, MAXWELL, WINGATE, GLYNWED PLASTICS LIMITED
Application year: 1993
Main classification: F28D19
IPC codes: F28D19, F28F19, F28F21