CA1170251A

CA1170251A - Heat-exchanger element and process for its manufacture

Info

Publication number: CA1170251A
Application number: CA000385126A
Authority: CA
Inventors: Dieter Disselbeck; Dieter Stahl
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1980-09-04
Filing date: 1981-09-03
Publication date: 1984-07-03
Also published as: EP0047443A3; DE3167213D1; GR81401B; ES8206014A1; ES505058A0; FI812703L; DK389881A; EP0047443B1; EP0047443A2

Abstract

ABSTRACT

The heat-exchanger elements are composed of a two-ply woven fabric which is provided with spacer-fila-ments and is completely sealed against fluid heat transfer media. They are intrinsically rigid, preferably through the use of materials which are initially deform-able, but which are subsequently cured, such as curable synthetic resins. A textured surface gives the elements the appearance of other, conventional articles without a heat-exchanger element, for example the appearance of flat or corrugated roofing sheets.

Description

1 ~7(~5 e invention relates to a heat-exchanger ele-ment, compose~ o~ a two-pl~J ~70ven fabric which is pro_ ~ided with spacer-filaments and is completely sealed aga~nstfluid heat transfer media, and of inlet and outlet lines for the fluid heat transfer media.
With regard to economical energy~u~ilization and to new processes for utilizing regenerative energy sources, the object which is becoming increasingly impor-tan~ conce~ns the pro~ision of hea-t-exchangers which transfer heat with the lowest possibl losses, and which can be manufactured, in large areas, from corrosion-resistantma~erials. In conventional plate-type heat-exch~ngers, the heat transfer medium is led through tubes or channels, these tubes or channels being connected, in dif~erent ~esign-variants, with rlbs, or being integrated in the surface.
In this context, the quality~ of a plate-type heat-exchanger, in thermal engineering terms, is decisive-ly in~luenced by the heat transfer between the rib and the tube, and by the heat-transition which depends essen-tially~ on the tube spacing~, the thickness of the tubes and of the ribs, as well as on the thermal conductivity of the material. Particularly advantageous conditions ; are achieved when the area which is wetted by the~heat :
transfer'medium corresponds approxlmately to the size of the outer heat transfer surface, that is to say, when it ~ , .
is possibls ~o manufacture a hollcw body through wkich flow takes~lace over 'he entire area - a body without ribs, tubes, or channels.

l ~7~251 ~ 3 --A sy tem of this type is described in German Offenlegungsschrift 2,714,901, this system being in the form of a flexible heat-exchanger, composed of a web, coated on both sides, of two-ply woven fabric, this web being provided with inlet and outlet lines for a heat transfer medium. In the case of this construction of the heat-exchanger, the thermal conductivity of the mat-erial is of secondary importance, and it is even possible to employ corrosion-resistant plastics with advantage.
; 1~ Despite the significantly lower thermal conductivity of plastics, in comparison to metals, a more advantageous heat-transition results, since the heat need be trans-ported only over a very short distance, corresponding to the wall thickness of the heat-exchanger element.
The desire to impart the advantageous heat trans-fer characteristics of the heat-exchanger elements accor-ding to German Offenlegungsschrift 2,714,901, partic-ularly the through-flow over the entire area, even to intrinsically rigid heat-exchangers, fo~ ~hich this 20 ~ had previously been~impossible,~ never~heless remalned s~atis~ied, as did ihe~desire to;obtain flat and corrugated roof~covèrlngs having an;~integrated heat-ex-changer element e object~of the~invention lS accordingly to enable the advantageous principle;~o~ the~full-area through-flow heat-exchange~ to be used in as many fields of app-lication as possible~, as~vell~as~to oarry~out~the manu-. :
facture of these heat-e~-~hangers in~an economical manner.
mis ob~ect ls;aohieved aocording to the ~ ~ , ~ : .
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1 J 70~5 1 _ 4 _ inven~ion1 oy a heat-exchanger elemen~ o~
the ~ype desc~ibed above ~Jhich is irtrinsi-caIly rigid. Complete sealing o~ the two-ply woven fabric against fluid heat transfer media, and the intrin-sic rigidity, are advantageously brought abou-t by means of materials which are initially deformable, but which have subsequently become intrinsically rigid as a result of curing. A textured finish is advantageously impar-ted to at least one surface of the heat-exchanger ele-ment. According to a further preferred embodiment,the two-ply woven fabric of the heat-exchanger element is mechanically attached to a preformed sheet-like structure.
In order to manufacture the heat-exchangers accor-ding to the invention, use is made of a process in which the two-ply woven fabric is provided, on its upper and lower sides, with a layer of a sealing materlal, at least one~ of these layers bringing about ~he intrinsic rigidity of thè hea~-exchanger element, and in which process the .
upper~and lower layers are~bonded to one another, at the edges of the;two-ply w~ven~fabric, this bond being leak-proof~with respect to the fluid~heat~transfer medium, and in which process the inlet and outlet lines are a^ttzched.
; Materials which can~be cured are~employed as~sealing mat-erlal on at least~one~side, curing o~these materials be-ing effeoted in a~manner known per se7 A material which can be cured is preferably applied to~at least one side of the two-ply woven fabrio,~ ~he said fabric, thus treated,~is then formed into~the desired shape and is '`'' ~ ~
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: . . , , ' 1 1 7~25 1 subsequently cured in this shape According to another - varia~ of the process aocording to the invention, the intrinsic rigidity is brought about by bonding the two-ply woven fabric, on at least one side, to a pre-formed body.
The two-ply woven fabrics used for the manufac-ture o~ the heat-exchanger element are known. They are manufactured, for example, according to the process described in German Offenlegungsschrift, 1,535,736, or according to Melliand Textilberichte [Melliand Textile Reports] 711970, page 766. me spacer-filaments ~ are preferably monofilaments and thus give the two-ply `~ woven fabric the required compressive strength. The t~-o-ply woven fabric, Lncluding the spacer-filaments, is composed of polyesters, polyamides, polytetrafluoroethy-lene, glass, or other filamentary materials, depending on the requirements laid on its characteristics.
The inlet and outlet lines for ~the fluid heat trans~er medium which is intended to fIow~t~rough the heat-exchanger element are attached by known~methods, for example according to the abovementLoned German Offen-legungsschrlft 2~714,901 or~a~s~described in German Offenl~egungsschrlft 2,923,913~
e heat-transfer element~must be~leakproof~ on all sides~with respect to the fluid heat~tr~nsfer medium which is ut111zed. ~ ~ Possible seali~g materials are ~both plates~ and sheet-like~ bo ies, the former made o~ metals such~as, for example, copper or alumin~m, .
~ and the latter made of~the conventional thermoplastics :
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} 1 702~ 1 such as, for example, polyethyle~e, p~lypropylene, polyvinyl chloride or p~lystyrene; the side parts of the heat-exchanger element can then be closed by welding or gluing together.
- It has proved very convenient if the seal is composed, at least on one side, of a material which is initially deformable, but which is subsequently rendered rigid by means o~ curing. These curable materials are pre~er-ablythermo-settingsynthetic resins, such as unsaturated polyester resins, epoxy resins, methacryla~e resins, phenol-~ormaldehyde resins, melamine resins or furan resin~.
However, water-setting materials, such as, for example, cement or plaster can also be employed. All these materials can be reinforced with glass fibers or with a woven fabric. After applying the sealing material which is still deformable curirg is effected according to the known methods.
In order to achieve speciaT visual effects t a textured finish is imparted to at least one of the two surfaces of the heat-exchanger element. By this means, the heat-exchanger element receives the exter-nal texture of other, conventional ~materials~ for example of roofing tiles or slates By mechanically attaching the initially still deformable two-ply woven fabric to a preformed sheet-like structure, su~h as, for example, a corrugated asbes-tos-cement board or to a corrugated plas~ic ~oard inten-ded ts serve~as a roof-covering, a heat-exchanger elemen~
is obtained3 ~hich combines the advantageous mechanical ' ' " ' ' ' ~ ' , ' ' ~
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1 :1 7~2~ 1 ¢haracteristics of this above~entioned corruga~ed bGard with the advantageous heat transfer characteristics of the the two-ply woven fabric through which flow takes place over the entire area. Nevertheless, it is also suffi--cient, for many purposes, to form the two-ply woven fabri~
cQated w'~. the ~a~er~al which is lnitially deformable, into the desired shape on its own, and afterwards to carry out the c~ring treatment.
In the text which fol~ows, it is intended to describe the manufacture of the rigid,whole-area through-flow heat-exchanger elements in greater detail. A
two-ply woven fabric of the desired dimensions, for -ex~e 5 x 1 m, and having a separation of 2 mm between the upper and lower fabrics, is inserted between two ~iber ma-ts which have been impregnated with a curable synthetic resin and provided, on their rear sides, with a release-film, and the fabric is coated, on bot~ sides, by pressing lightly with a doctor-blade. In order to avoid welding and jointing operations for sealing the open edges of the two-ply woven fabric, it is advantageous if the dimensions of the synthetic resin laminate are larger than those of the web o~ two-ply woven fabric, so that the two synthetic resin laminates are bonded to one another outside the edge of the ~wo-ply wov-en fabric.
Pressure-tight sealing of the inserted two-ply woven fabric can also be achie~Jed by milling a peripheral groove in the edge regions o~ the two-ply woven fabric which has been provided with the synthetic resin laminate, this groove being milled, after the synthetic resin has 1 1 7~25 1 been cured, as far as the lower layer, and by running a synthetic resin into the groove thus obtained, prefer-ably until this resin is flush with the uppermost layer In performing the latter operation, the viscosity of the synthetic resin is adjusted to a value such that undesired running of the resin into the two-ply woven fabric is a~toided. In this way, after stripping off the re-lease-film, a sheet-like, pressure-tight and dimension-. ally stable hollow body element is obtained, which has a 10 glossy surface and, provided with inlet and outlet lines~ -can be employed in wide fields of technology as a plate-type heat-exchanger, or heat absor~er~ -- The inlet and outlet lines for the fluid medium are usually located diagonally opposite to one another.
m ey can, however, also be situated on the same side of the heat-exchanger element, In order to ensure, when the lines are thus located, that flow through the heat-exchanger element takes place over the entire area, a ; zone having an enhanced flow reslstance ls ~ormed in the center of the heat-exchanger element, between the inlet and outlet lines, this zone only partially subdividing the heat-exchanger element into two separate flow-chambers.
is~partial subdivision is~achieved,~for example, by ` milling a groove at right angles to the line joining the connections, this groove extending~over only a portion of this length, or of the wLdth, of the heat-exchanger ele-ment, and being filled by pouring ~in a synthetic rèsin.
In many applications, this arrangement of the connections ~- on one side of the heat-exchanger element leads to a ~' -,. ; . - .~

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2 5 1 _ g _ -saving in assembly costs~ and facilitates its integra-tion into existing systems~ This ~s the case, for example, when the heat-exchanger elements are employéd as heat absorbers in "energy-roof"~heat-pump systems ~or - -the utilization of heat from the .surroundings. When the single-sided arrangement is used, lt is possible, for example, to lay the inlet and outle~ pipes beneath the roof-ridge covering, without the risky routeing of pipes ~hrough the roof skin, and without pipes becoming visible on the roo~.
The heat-exchanger elements according to the invention are preferably used in the ~orm of flat or corrugated roofing sheets containing an integrated heat-exchanger element. - .
In order that the invention may be more clearly understood, reference will now be made to the accompanying drawlngs which lllustrate preferred embodiments of the invention by way of example, and in which:
Fig. 1 is a perspective view of a heat-exchanger - element in the~ form of a flat rooflng sheet, the element .
being shown partly broken away and partly in section; and, Fig. 2 is a vlew similar to Plg.~l showing a heat-exchanger element in~the form of a corrugated roo~fing~sheet.
Referring first to Fig.; 1, a heat-exchanger element of generally flat rectangular form is shown and includes a .
two-ply woven fabric 2 in which a closed space for receiving rar~3~cr a fluid heat ~s~e~ medlum is defined~between the plies.
Spaaer filaments are disposed bet~-een and ma~ddn the plles at the .
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required spacing. Inlet and outlet lines for permitting a fluid heat transfer medium to circulate through the space are denoted respectively by reference numerals 5 and 6 and, in this embodiment, extend through the top ply of fabric and communicate with the space between the plies.
Il~ 3 ; ~ Layers 1 and ~ respectively of sealing material are provided on each of the outer sides of the fabric. The fabric itself and the sealing layers are of the form referred to above in the description of the process by which the heat exchanger elements are manufactured. Thus, the sealing layers are formed by fiber mats which have been impregnated with a curable synthetic resin as discussed previously. These layers completely seal the fabric against permeation by said heat transfer medium and impart intrinsic rigidity to the element.
In this embodiment, the edges of the fabric are sealed to prevent leakage of heat transfer medlum by a bead of synthetic resin, denoted by reference numeral 4, formed in a peripheral groove inset slightly from the outer edges of the fabric. It will be seen that the peripheral groove is in fact formed by four rectilinear groove~s spaced inwardly from the respective outer edges of the fabric and overlapping adjacent the corners of the fabric. As discussed ahovel the groove is~formed after the sealing layers 1 and ~ have cured and extends~down through the fabric from the top sealing layer 1 as far as the lower layer 3. The resin bead fills the groove to the level of the top of layer 1.
As indicated above, the h~eat-exchanger element shown in Fig. 1 takes the form~of a flat roofing~sheet and is designed ' ' 1 37~51 to be incorporated in a roof surface. Fig. 2 shows a heat-exchanger element which has the same physical structure as the element shown in Fig. 1 except in that it is of corrugated shape and, accordingly, is adapted for incorporation in a corrugated roofing surface. The element is manufactured in this shape by forming the fabric to the desired shape after the sealing layers 1 and 4 have been applied to the fabric but before the layers have been cured. The layers are then cured with the fabric in this shape.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A heat-exchanger element comprising: a two-ply woven fabric in which a closed space for receiving a fluid heat transfer medium is defined between the plies of said fabric; spacer-filaments disposed between and spacing said plies; and inlet and outlet lines communicating with said space for permitting said fluid heat transfer medium to circulate through said space; said fabric being completely sealed against permeation by said medium and said element being intrinsically rigid.

2. An element as claimed in claim 1 further comprising at least one sealing material on the outer sides of both of said fabric plies, said material being selected to provide said complete seal-ing of the two-ply woven fabric against fluid heat transfer media and said intrinsic rigidity, and said material being initially deformable and curable to an intrinsically rigid form.

3. An element as claimed in claim 1 or 2, wherein a textured finish is imparted to at least one outer surface of said element.

4. An element as claimed in claim 1 or 2, further compris-ing a preformed sheet-like structure to which said two-ply woven fabric is mechanically attached.

5. A process for manufacturing a heat-exchanger element comprising; .
providing a two-ply woven fabric having spacer filaments defining a space between said plies;

providing on each outer side of said fabric a layer of a sealing material, at least one of said layers being adapted to provide intrinsic rigidity for the heat-exchanger element;
bonding the fabric plies to one another at the edges of the fabric, in a manner which is leakproof with respect to a fluid heat transfer medium to be circulated through the element; and attaching to said fabric inlet and outlet lines communicating with said space.

6. A process as claimed in claim 5, wherein said sealing material is curable, and wherein the process further comprises the step of curing said material.

7. A process as claimed in claim 6 wherein said curable sealing material is attached to at least one side of the two-ply woven fabric, and wherein the process further comprises the steps of forming the fabric into a desired shape, with said material thereon and subsequently curing the material with the fabric in said shape.

8. A process as claimed in claim 5, further comprising the step of bonding at least one side of the two-ply woven fabric to a preformed body adapted to provide said intrinsic rigidity for the heat exchanger element.