THIN FILM GAS HEAT EXCHANGER

Abstract: A heat exchanger for essentially counterflow heat exchange between two air flows comprises inside a housing (9) essentially parallel partitions (3) of in the air flow direction extended and stretched each with a substantial tension force (P) membranes (3', 3'') of high tensile strength, that pairwise (3', 3'') essentially gas tight enclose first channels (4) for a warmed, first air flow (1). In alternating second channels (5), surrounding said first channels (4), is propelled a second, cooled air flow (2). The membranes (3', 3'') are formed into deflated segments (31) by supporting strips (8) inside said first channels (4), by local static pressure differences ( DELTA p) between said air flows (1, 2) and by said tension force (P).

Description: THIN FILM GAS HEAT EXCHANGER The present invention refers to a neat exchanger for essentially countorflou neat exchange betueen tuo air flous, com p rising insiαe a housing a numoer o f essentially parallel partitions of flexible membranes forming first channels for a first, warmed air flou an al ernating second cnannels for a second, cooled air flou, further a first inlet and first outlet in said housing for said first air flou and a second inlet and outlft f or said second air flou. A prime use for the invention is heat recovery in domestic and inoustrial buildigs ventilation system and specifically for .heat recovery from very polluted and corrosive exhaust air. A first purpose uith t e invention, using thin plastic memoranes as heat exchanger surface, is to achieve uith simple means full control over flftu channel geometry, simplified joining of the separate channel systems to inlets and outlets for the separate air flous and simplified sealing along the rim of the apparatus betueen the separate air flous. A second purpose is to provide flou channels for a polluted, moist ana corrosive exhaust αii fluu. , cooled in the apparatus, that are smooth, unobstructed by spacing elements, that have a high corrosive resistance and that are exceotionally ea y to clean. A thir purpose, is to combine reasonable, small flou resistance for the air uith a uell extended channel length needed for high heat exchange-; efficiency. A forth purpose is a heat exchanger, that acts as an exceptionally good absorber of fan noise. 5aid purposes are met uith a heat exchanger further chara terized in that it comprises said membranes made of a high tensile plastic film such as polyester film, exten d ed and stretched in the main air flou direction uith a substaπsial tension force, further compri r. » ~, pairs of said mempranes enclosing essentially gas tight said first channels, further comprises the ends o τ" said mem b ranes enclosing and laminated to air penetrable tension pla t es, preferably of corrugated carddoard, further com¬ prises a strapping αevice for strapping said tension p lates 9acfι uith double said tension force, yuv * m - ~~ PCI7SE90/00584 further comprises said tension plates connected to said first inlet ami first outlet and further comprises uithin said first channels as spacing elements strips of corru¬ gated material, preferably corrugated cardboard, that are positioned essentially at right angle to air flou, are laminated to one of said pair of membranes and that alternate uith deflated segments of said membranes, formed by local, positive static pressure differances betueen said second and first air flou. Elastic sheets as partitions in a gas heat exchan¬ ger are known from SU,A, 1200114. This document shous elastic sheets separated from each other by thin uire spacers, thus forming separate channel systems. This solution is not fitted to a. corrosive and dusty exhaust air, since the uire would quickly lug uith dust and corrode. Further no pro¬ visions- are shoun to cope uith the local, differing pressure gradients on the sheets, due to flou resistance in the channels, or the rim pcoblems of the apparatus concerning well separated inlets and outlets of the separate gas flous. and their connections to the channel systems. Other documents on thin film heat exchangers show tubular sections in thin film construction, the tubes being formed and stabilized by media pressure and used as spacers as well as heat exchange surface. FR,A, 2289870 and US 4 411 310, figure 15 represent such a principle. These constructions require intriηuate welding and the use of a weldablε film, which may lack other desired qualities like high tensile strength. They furthermore pose difficult topolαgical problems along the rim of the apparatus in connecting the channel systems to inlets and outlets and efficient sealing. The invention is in the following described more in detail in relation to -ithe drawings. Figure 1 shous a plan section and figure 2 a longitudinal cross section. Figures 1a and 2a show in plan and cross section an alternative strapping device. In cross sections show figure 3 a package of tension plates, figure 4 flou chan¬ nels and figure 5 flnw channels being cleaned. Figure 6 shows a detailed plan section of flou channels and figure 7 illustrates an example of pressure loss, pressure load on membranes and spacing of supporting strips in a flow channel . In referance to figures 1-4 are within a housing 9 arranged a number of essentially parallel partitions 3, forming first channels 4 for a first, warmed air flou 1 and alternating second channels 5 for a counterflow driven second, cooled air flow 2. In the air flow direction the par ¬ titions are well extended and comprise in the air flow di- i rection stretched plastic film membranes 3' and 3" of high tensile strength. Each membrane is stretched with a substansial tension force P and the pair of membranes 3' ,3" enclose essentially gas tight the first channels 4. The membranes 3', " are at their ends pairwise laminated to and enclosing a gas penetrable tension plate 6 preferably of corrugated cardboard. In referance to fig. 3 adjacent tension plates are packed to each other and against the housing 9, using suitable intermediate sealing 61. The tension plates 6 are connected to a first inlet 11 and a first outlet 12 for the first, warme air flow 1. ihey are further by a strapping device 7, secured to the hou iπo 9, each affected by a tension force 2P. The second channels 5 are open in the housing 9 to a second inlet 21 and second outlet 22 for the second air flow 2. The first channels 4 comprise as spacing ele ents gas penetrable strips 8 of corrugated aterial, positioned at intervalls "a" along the channels at essentially right angles to flow direction. The strips alternate with deflated segments 31 of the membranes 3',3", formed by local positive pressure differances A p between the second 5 and first chan¬ nels 4.. A positive value for dp is ensured at all points by the coupling of the first outlet 12 to the suction side of a fan for propelling first air flow 1 and the coupling of the second inlet 21 to the pressure side of a fan for the second air flow 2. The second channels lack spacing elements and has a smooth, unobstructed surface with high corrosive resistance and small dust collecting potential. * 1,υwι PCT/SE90/00584 4 Climate inside the first channels 4 for a warmed , first air flou is dry. The strips 8 may therefore like the tension plates 6 be cut out of corrugated cardboard and laminated to one of the membranes 3' or 3". As membrane material is preferred a polyester film, type "Ilelinex" from ICI, in a standard thickness o 75 or 125 for tough conditions. This film is utterly stable in dimension, has high tensile strength and high chemical stability to moisture and corrosive gases. In said thickness heat resistance in the film is negligable. It can be laminated to cardboard with a very strong bond using for instance a vinyleacetateacrylate dispersion. By folding a rectangular sheet of polyester fi and enclosing and laminating a each and a tension plate and along the channel appropriate number of strips 8 an element "A" or "B" is formed, which in the apparatus be added to any desired flow capacity. The elements may a small marginal cost be extended in length for increase heat exchange efficiency. Longitudinal open edges of the join by suction in the elements but may further be seale by a glue bond. The elements "A" and "B" alternate in the exc ger and differ in that strips in either are displaced half of mentioned interval "a" inrelation to the strips in the other element. In this manner, obvius from figure 1 and 6, the channel 5 aquires a fairly even height and gently wavy extension uith good flou properties. In order to preserve flow areas, flou velocit and to minimize flow resstance in the channels 4 and 5 in the flow direction the intervals "a" decrease towards the suction end of first channels 4 according to figures 6 and 7 and the following. The pressure difference Δ p between second a first channels will increase from first inlet 11 to firs outlet 12. The membrane segments 31 form cylindric surfa with radius = R from the combination of intervall "a", tensiπn P and pressure differens A p. Calling depth of deflated segments 31 = h, following applies: P = R-dp 2Rh= a 2 /4 a 2 = 8hP / Δ p SUBSTITUTE SHEET Depth "h" should be kept constant. It follows: <- A P = constant An exemple, evaluated in practice, illustrates according to figure 7 a spacing of the strips 8 in accord to this rela ¬ tion. The example, showing corresponding membrane tension, flou resistance, channel dimensions etc. uill make the invention more clearly understood. Follouiπg applies: membranes 3', " length = 18U0 mm " width = BOO mm number of strips 8 = 13 strip height = 13 mm height of tension plate 6 = 17 mm tension force P = 0,075 kp/cm mean height of channel 4 and 5 = 8 mm mean air velocities 3.5 m/s depth »h" = 3.0 mm flow resistance in channel 4 =-16 mm wp = p 1 " " 5 = -f-7 mm wp = p 2 pressure difference Δ p = p ? — P, 7 as figure 7 intervals "a" , calculated, as figure 7 total tension force on each tension plate = 12 kp Further assuming pressure difference P remaining constant, following applies : • h = constant Increasing tension P thus reduces depth "h", will increase flou area in channel 4 and correspondingly decrease flow area in channel ' 5. Thus a doubling of tension P uill in above related example change flou area ratio from 1:1 to 1.8:1. Warying the tension P is thus a simple tool to optimize the geometry of the flou channels to varying proportions of mass flous of first and second air. A strapping device 7 may according to figures 1 and 2 comprise straps 71 anchored to the tension plates 6 and further anchored to the housing directly at one end and indirectly at the other end via an adjustable spring de¬ vice 72. This spring device may comprise a rectangular plate 721, to uhich four or eight straps 71 are anchored at the corners. The centre of the plate is pulled by a spring 722. In this manner four or eight tension plates 6 may equally teπsioned by one adjustable spring 722. An alternate spring device may accordinπ to fi¬ gures 2a and 1a comprise a rubber bag 73, reacting on all said plates 721 and a box 74, anchored to the housing 9. Expanded by pneumatic or hydraulic means the rubber bag will react uith the same force on all plates 721 and thus stretch any number of membranes with equal tension P adjustable uith the meriiapressure in the rubber bag. A mainly horizontal gas flow direction is prefered for drainage out of the bottom 92 of condensate 35 precipitated from the cooled, second air flow 2. From a polluted such flow dust will deposit, specially on moist membranes 3' ,3". There are cases, where dust clogging is so severe, for instance in pig stables, that knoun heat exchangers are practically worthless. Even a fatty dust from a pig stable is however readily cleaned from an apparatus according to the invention, as illustrated in figure 5. The air flows are cut off and an uppεr lid 91 of the housing 9 is removed. Over the package of membranes is sprinkled a suitable detergent 3b. Lacking a pressure load Δ p , the membranes 3 ' , " facing second channels 5 will adhere to each other. I he detergent will readily wot and by capillary action spread over all membrane surface, soak the dirt and make it loosen. A following water rinsing will readily remove deposits out of bottom 92 and a drain 93. The apparatus has proven to be an exceptional¬ ly good sound absorber. The different, strung segments 31 with separate lengths self oscillate at separate tones and will thus constitute an efficient wide-spectrum noise absorber. Uith the apparatus connected with first inlet 11 and second outlet 22 to the outside of a building and with first outlet12 and second inlet 21 via air fans to the interior, fan noise to the outside, very often a severe nuisance, is practically totally eliminated. As appears from the description the invention, using simple means such as corrugated cardboard and thin poly¬ ester film, constitutes a useful, versatile tool for heat recovery between air, including very polluted and corrosive exhaust air. The invention solves by simple means the difficult, often neglected tαpological problems along the rim of the apparatus of well sealed, functional connections

Claims: 91/04451 C L ftl FIS PCT/SE 1. A heat exchanger for essentally counterflow heat exchange between tuo air flous, comprising inside a housing (9) a number of essentially parallel par¬ titions (3) of flexible membrane (3' , 3") , forming first channels (4) for a first, uarmed air flow (1) and alternating second channels (5) for a second cooled air flow (2), further a first inlet (11) and first outlet (12) in said housing for said first air flow and a second inlet (21) and outlet (22) for said second air flow c h a r a c t e r i z e d i n that it comprises said membranes (3", ") made of a high tensil plastic film such as poly¬ ester film, extended and streched in the main air flow direction with a substaπsial tension force (P), further comprises pairs (3' ,3") of said mem¬ branes enclosing essentially gas tight said first channels (4), further comprises the ends of said pair of membranes (3 ' , ") enclosing and laminated to air penetrable tension plates (6), preferably of corrugated car board, furt er comprises a strapping device (7) for strapping said tension plates (6) to said housing (9) each uith double said tension force (2P), further comprises said tension plates (6) connected to said first inlet (11) and first outlet (12) and further comprises uithin said first channels (4) as spacing elements strips (8) of corrugated material, preferably corru¬ gated cardboard, that are positioned essentially at right angle to air flow, are laminated to one of said pair of membranes (3 1 ,3") and that alter¬ nate with deflated segments (31) of said membranes (3 1 ,3") , formed by local positive pressure diffe¬ rences ( Λ p ) between said second (2) and first air flow ( 1 ) . 2. A heat exchanger according to claim 1 c h a r a c t e r i z e d i n that it comprises said membranes (3' ,3") facing said second channels (5) adhering to each other, when said air flows (.1,2) are shut off. > . A heat exchr._.ιger according to claim 1 -2 c n a r a c-» t e r i z e d i n that it co prises said strips (O) distributed in any said first channel (4) essen¬ tially in the middle between corresponding said strips (8) within surrounding said first channels (" J. 4. A heat exchanger according to claims 1 -3 c a r a c t e r i z e d i n that it comprises said strips (0) distributed along said first chan¬ nels (4) with intervals (a) chosen in such a rela¬ tion ( a-N = constant ) to said pressure difference ( A p) that depth (h) of said segments (31) is kept constant. 5. A heat exchanger according to claims 1 - 4 c h a r a c t e r i z e d i n that it comprises said laminated tension plates (6) of each said end packed against each other and said housing (9) to¬ gether wi h intermediate seals (61). 6. A heat exchanger according to claims ■ _ 5 c h a r a c t e r i z e d i n that said strapping device (7) comprises straps (71) anchored to each said tension plate (6), said straps further being anchored directly to said housing (9) at one end and indirectly at opposite end via a spring device (72) transmitting to all said tension plates (6) each essentially said double tension force (2P). -. A heat exchanger accorciing to claims 1 - 6 c h a r a c t e r i z e d i n that said spring device (72) comprises means to vary said tension force (p) and consequently said depth (h) and flow area ratio between said channels (4,5). B. A heat exchanger according to claims 1 - 7 c h a r a c t e r i z e d i n that said spring device [_!'?) "inpι ist_s a pneumatically or hydrau- lically expandable rubber bag (73), reacting on a fixed housing support (74) and flexible strap supports (721.) . 9. A heat exchanger according to claims 1-8 c h a r a c t e r i z e d i n that it comprises said first air flow (1) being sucked from said first outlet (11) and said second air flow (2)

Inventors: ZEILON STEN, ZEILON, STEN
Applicants: ZEILON STEN, ZEILON, STEN
Application year: 1990
Main classification: F28D9
IPC codes: F28D9, F28G9