Abstract:
A heat exchange device of a type for affecting an exchange of heat between a first and second fluid is characterized by a plurality of heat exchange cells in a stacked arrangement wherein each cell includes inlet and outlet manifold rings which define inlet and outlet manifolds, respectively. Adjacent heat exchange cells are bonded to one another via metallurgical bonds between the contacting surfaces of the manifold rings. In a further aspect, a method for the manufacture of a heat exchange device is provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119(e) to U.S. provisional application Ser. No. 60/927,532 filed May 3, 2007. The aforementioned provisional application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     This disclosure relates generally to heat exchangers with features directed to various innovations including ones relating to the gas turbine recuperators. 
     The recuperation of the gas turbine engine has been proven to increase thermal efficiency. However, the technical challenges associated with surviving the severe environment of a gas turbine exhaust while meeting the equally severe cost challenges has limited the number of viable products. A gas turbine recuperator is typically exposed to a thermal gradient of up to 600 degrees C., pressures of 3 to 16 bar, and may operate at a gas temperature of over 700 degrees C. Moreover, developers of advanced recuperated Brayton (gas turbine) systems are considering applications with pressures of up to 80 bar and temperatures ranging to 1000 degrees C. 
     The successful design must tolerate severe thermal gradients, and repeated thermal cycling, by allowing unrestricted thermal strain. The structural requirements to manage very high pressures tend to work against the normal design preferences for structural flexibility, which is important to tolerating large and rapid thermal transients. 
     Child, Kesseli, and Nash (U.S. Pat. No. 5,983,992) describe a flexible heat exchanger design as shown in  FIGS. 1A-1C . This design is composed of stamped parting sheets A, B, each formed with “substantially S-shaped” raised flanges C, D. These stamped hoops form an integral manifold in the plate. When welded cell to cell, the stack of manifolds becomes a flexible bellows-like structure. This feature represents the principal novelty of this prior art design over heat exchangers embodying a more rigid structure. While the flexibility of the manifold represents an advantage in environments of high thermal-induced strain, the thickness of the sheet and the manifold geometry limits its capacity for pressure. The inventors state that the light gauge sheet metal construction is critical to the performance and integrity of this design and superior to other designs employing edge bar or closure bar construction. 
     As exemplified by U.S. Pat. No. 4,073,340 to Garrett, other traditional manufacturers have produced heat exchangers formed of individual cells, brazed together employing stamped edge conditions and integral cut-out manifolds cut-out from the parting plate, principally similar to Child et al. (U.S. Pat. No. 5,983,992).  FIGS. 2A and 2B  illustrate the heat exchange apparatus of Garrett and shows stamped formed edge sheets E and manifold cutouts F and G. The complete heat exchanger core of this configuration is formed by coating the various elements with braze alloy, stacking the plates and secondary fin surfaces, and brazing the complete assembly in a furnace. Due to the sturdy edge bars, this design construction is likely to tolerate considerably higher pressures than the apparatus of Child et al. (U.S. Pat. No. 5,983,992). However, due to the monolithic structure formed as all contacting plate and fin surfaces are brazed, the rigid heat exchanger construction is prone to stress cracking caused by repeated thermal cycling. 
     British Patent No. 1,197,449 to Chausson shows a formed header like Child et al. (U.S. Pat. No. 5,983,992) and Garrett (U.S. Pat. No. 4,073,340) and the raised sheet metal manifold integral with the parting plates. Referring to  FIG. 3 , there appears the heat exchanger of GB1,197,449, which has a formed dish-shaped edge K, a high-density fin M between the parting plates, communicating with the formed manifold cutout L, configured to carry the first fluid. The second fluid, flowing on the outer surface of the parting plates passes through high-density fin matrix elements N and O, configured to carry the second fluid. The high-density fin matrix elements N, O are brazed to the parting plates, but not to one another, in a manner similar to Child et al. (U.S. Pat. No. 5,983,992). In addition, as with the device of Child et al., the construction is of light gauge sheet metal and best suited for low to moderate pressures. 
     Lowery (British Patent No. 1,304,692) discloses a cellular heat exchanger concept as shown in  FIG. 4 . Like Child et al. and GB1,197,449, this design uses a unit cell with light gauge external fin elements R and S bonded to the outside of an envelope forming a flow path for a first fluid, with internal passages inside the envelope forming passages for a second fluid. Also, as with the devices of Child et al. and GB1,197,449, the fin elements R and S of neighboring cells bear upon one another at crests T. A unique feature of this design relates to the heavy “pressings” forming the passages of the second fluid. These heavy pressings located in a hot gas stream tend lag in thermal response and consequently are prone to buckle when exposed to high temperature and steep thermal gradients. This design is most suitable for lower temperature air-water “radiator” applications. 
     U.S. Pat. No. 3,460,611 to Folsom et al. describes a plate-fin heat exchanger incorporating formed parting plates and strip fin. Quoting from this specification, “These parts are bonded or soldered together to make an integral unit or module and before that unit is incorporated in a stack or modules it conveniently may be tested and proven without leaks or cause to attain that condition.” See Folsom et al. at column 2, lines 51-55. See also claims 1 through 6 of U.S. Pat. No. 6,305,079 to Child et al. The heat exchange cell of Folsom et al., like that of Child et al, has formed lands around the perimeter. The apparatuses of Folsom et al. and Child et al. both incorporate formed lands around the header, thereby creating a cell not suitable for high internal pressure. Also, Folsom&#39;s formed semi-circular manifold requires an additional welding operation to attach the cell to a pipe or collector. 
     Based upon the foregoing limitations known to exist in plate-fin heat exchangers, it would be beneficial to provide a heat exchanger having a rigid manifold section capable of operation at elevated pressure, connecting to a light gauge, flexible sheet metal structure imposing limited mechanical constraints on and between neighboring cells. 
     SUMMARY 
     In one aspect, the present disclosure relates to a heat exchange device for transferring heat between a first fluid and a second fluid and comprising a plurality of heat exchange cells in a stacked arrangement and defining an inlet manifold and an outlet manifold. Each of the heat exchange cells comprises an upper cell plate having an exterior facing surface and an interior facing surface opposite the exterior facing surface. The upper cell plate has an inlet aperture, an outlet aperture, a central upper cell plate portion extending between the inlet aperture and the outlet aperture, and an upper peripheral edge bounding the inlet aperture, outlet aperture, and the central upper cell plate portion. A lower cell plate has an exterior facing surface and an interior facing surface opposite the exterior facing surface. The lower cell plate has an inlet aperture, an outlet aperture, a central lower cell plate portion, and a lower peripheral edge bounding the inlet aperture, outlet aperture, and the central lower cell plate portion. The lower cell plate is juxtaposed with the upper cell plate so that the inlet aperture of the lower cell plate is aligned with the inlet aperture of the upper cell plate, the outlet aperture of the lower cell plate is aligned with the outlet aperture of the upper cell plate, and the central lower cell plate portion is aligned with the central upper cell plate portion. The upper peripheral edge is joined to the lower peripheral edge to define a cell peripheral edge. The interior facing surface of the upper cell plate faces and is spaced apart from the interior facing surface of the lower cell plate to define an interior volume therebetween. The interior volume has a cell inlet and a cell outlet and defining a fluid passageway for the second fluid between the cell inlet and the cell outlet, wherein the cell inlet is adjacent the inlet aperture of the upper cell plate and the inlet aperture of the lower cell plate, and the cell outlet is adjacent the outlet aperture of the upper cell plate and the outlet aperture of the lower cell plate. A first heat transfer matrix is positioned within the interior volume, a second heat transfer matrix is attached to the exterior surface of the upper cell plate, and a third heat transfer matrix is attached to the exterior surface of the lower cell plate. An upper inlet manifold ring is attached to the exterior surface of the upper plate and circumscribes the inlet aperture of the upper cell plate. An upper outlet manifold ring is attached to the exterior surface of the upper plate and circumscribes the outlet aperture of the upper cell plate. A lower inlet manifold ring is attached to the exterior surface of the lower plate and circumscribes the inlet aperture of the lower cell plate. A lower outlet manifold ring is attached to the exterior surface of the lower plate and circumscribes the outlet aperture of the lower cell plate. 
     In a second aspect, the present disclosure relates to a method of manufacturing a heat exchange device of a type for transferring heat between a first fluid and a second fluid, the method including assembling a plurality of heat exchange cells. Each heat exchange cell comprises an upper cell plate having an exterior facing surface and an interior facing surface opposite the exterior facing surface. The upper cell plate has an inlet aperture, an outlet aperture, a central upper cell plate portion extending between the inlet aperture and the outlet aperture, and an upper peripheral edge bounding the inlet aperture, outlet aperture, and the central upper cell plate portion. A lower cell plate has an exterior facing surface and an interior facing surface opposite the exterior facing surface. The lower cell plate has an inlet aperture, an outlet aperture, a central lower cell plate portion, and a lower peripheral edge bounding the inlet aperture, outlet aperture, and the central lower cell plate portion. The lower cell plate is juxtaposed with the upper cell plate so that the inlet aperture of the lower cell plate is aligned with the inlet aperture of the upper cell plate, the outlet aperture of the lower cell plate is aligned with the outlet aperture of the upper cell plate, and the central lower cell plate portion is aligned with the central upper cell plate portion. The upper peripheral edge is joined to the lower peripheral edge to define a cell peripheral edge. The interior facing surface of the upper cell plate faces and is spaced apart from the interior facing surface of the lower cell plate to define an interior volume therebetween. The interior volume has a cell inlet and a cell outlet and defining a fluid passageway for the second fluid between the cell inlet and the cell outlet, wherein the cell inlet is adjacent the inlet aperture of the upper cell plate and the inlet aperture of the lower cell plate, and the cell outlet is adjacent the outlet aperture of the upper cell plate and the outlet aperture of the lower cell plate. A first heat transfer matrix is positioned within the interior volume, a second heat transfer matrix is attached to the exterior surface of the upper cell plate, and a third heat transfer matrix is attached to the exterior surface of the lower cell plate. An upper inlet manifold ring is attached to the exterior surface of the upper plate and circumscribes the inlet aperture of the upper cell plate. An upper outlet manifold ring is attached to the exterior surface of the upper plate and circumscribes the outlet aperture of the upper cell plate. A lower inlet manifold ring is attached to the exterior surface of the lower plate and circumscribes the inlet aperture of the lower cell plate. A lower outlet manifold ring is attached to the exterior surface of the lower plate and circumscribes the outlet aperture of the lower cell plate. The plurality of heat exchange cells are stacked such that a contacting surface of the lower inlet manifold ring of one of the plurality of the heat exchange cells contacts a contacting surface of the upper inlet manifold ring of an adjacent one of the plurality of heat exchange cells and a contacting surface of the lower outlet manifold ring of the one of the plurality of the heat exchange cells contacts a contacting surface of the upper outlet manifold ring of the adjacent one of the plurality of heat exchange cells. The plurality of heat exchange cells are metallurgically joined at the contacting surfaces of the upper and lower inlet manifold rings and the contacting surfaces of the upper and lower outlet manifold rings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
         FIGS. 1A-1C  illustrate a prior art heat exchanger, showing an elemental heat exchanger disclosed in U.S. Pat. No. 5,983,992 to Child, Kesseli, and Nash. 
         FIGS. 2A and 2B  illustrate another prior art heat exchanger as shown in U.S. Pat. No. 4,073,340 to Garrett. 
         FIG. 3  illustrates a heat exchanger design as shown in British Patent No. 1,197,449. 
         FIG. 4  illustrates yet another heat exchanger of the prior art, as disclosed in British Patent No. 1,304,692. 
         FIG. 5  is an exploded view of an elemental heat exchanger in accordance with an exemplary embodiment of the present invention. 
         FIGS. 6A and 6B  are enlarged, fragmentary, side cross-sectional views illustrates two exemplary options for edge conditions. 
         FIG. 7A  illustrates the assembled elemental heat exchanger cell shown in  FIG. 5 . 
         FIG. 7B  is a side cross-sectional view taken along the lines  7 B- 7 B in  FIG. 7A . 
         FIG. 7C  is a side cross-sectional view taken along the lines  7 C- 7 C in  FIG. 7A . 
         FIG. 8A  illustrates the heat exchanger core, formed of multiple elemental cells. 
         FIG. 8B  is a side cross-sectional view taken along the lines  8 B- 8 B in  FIG. 8A . 
         FIG. 9  illustrates the flow path of the first and second fluids through the elemental cell. 
         FIG. 10  is a side cross-sectional view of an alternative embodiment of an alternative embodiment having hollow manifold rings. 
         FIG. 11A  is a partially exploded view with the upper plate removed for ease of exposition, illustrating an alternative embodiment wherein the elemental cell includes an additional reinforcing cut-ring captured within the cell envelope. 
         FIG. 11B  is a side cross-sectional view taken along the lines  11 B- 11 B in  FIG. 11A . 
         FIG. 11C  is a side cross-sectional view taken along the lines  11 C- 11 C in  FIG. 11A . 
         FIG. 12A  illustrates an embodiment similar to the embodiment appearing in  FIG. 11A , wherein is a porous reinforcing ring is captured within the cell envelope. 
         FIG. 12B  is a side cross-sectional view taken along the lines  12 B- 12 B in  FIG. 12A . 
         FIG. 12C  is a side cross-sectional view taken along the lines  12 C- 12 C in  FIG. 12A . 
         FIGS. 13A and 13B  illustrate an alternative embodiment, tolerant to extreme pressures, where the matrix elements outside the cell envelope are compressively loaded upon one another. 
         FIGS. 14A and 14B  illustrate a “C-flow” embodiment of the heat exchange unit cell, which is composed of hoop rings, optional cut-rings, parting plates, and external and internal fin segments, similar to the embodiments appearing in  FIGS. 5-13B . 
         FIGS. 15A and 15B  illustrate an alternative version of the C-flow unit cell embodiment appearing in  FIGS. 14A and 14B . 
         FIG. 16  is a fragmentary, isometric view of an alternative C-flow cell with an external gas fin configured to allow single side manifold for the external fluid. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 5  shows an exploded view of an elemental counter-flow heat exchange element  20  with cross-flow header sections. The cell  20  includes upper and lower sheets  1  and  2 , respectively, which are a mirror image of one another and are assembled to form an envelope with interior  60  and exterior  61  volumes. A high surface area matrix  3  is located between the plates  1  and  2  in the interior volume  60 . Another high surface area matrix element  4  is affixed to the exterior surface of plate  1  in the volume  61 , while yet another high surface area matrix  5  is affixed to the exterior surface of plate  2  in an exterior volume  67 . The high surface area matrix elements  3 ,  4 ,  5  may be, for example, a folded or corrugated sheet metal material, dimpled sheet, sintered porous media, expanded metal foam, a screen pack, or any other type of secondary surface fin material common to the industry. Some favorable properties of the matrix elements  3 ,  4 ,  5  include a large surface to volume ratio, high thermal conductivity, and low manufacturing cost. 
     The parting plates  1  and  2  may be cut from sheet stock with a profile similar to that shown in  FIG. 5 . The features on the parting plate  1  are a mirror image of those of parting plate  2 . The parting plates  1 ,  2  depicted in  FIG. 5  are designed to accommodate the generally rectangular counter-flow matrix  3  and two cross-flow header matrix elements  6 ,  7  within the interior volume  61  defined between the two juxtaposed parting plates  1 ,  2 . The cross-flow area occupied by the header matrix elements  6  and  7  may have a tapering triangular shape as shown in  FIG. 5 , and functions to distribute the fluid uniformly across the leading edge of the counter-flow matrix element  3 . 
     Manifolds serve as a means for collecting the fluid flow from the headers. The manifolds for each cross-flow header are formed by cutting holes  15  and  97  in each parting plate  1  and cutout apertures  25  and  27  in each plate  2  intersecting the area occupied header matrix elements  6  and  7 . A circular manifold ring  10  is affixed on the exterior facing surface of the flat sheet  1 , in substantial alignment and circumscribing the diameter of cutout  15 . Similarly, a manifold ring  11  is affixed to the exterior surface of the flat sheet  1  surrounding the cutout  97 . Although the manifold rings and the corresponding cutout portions in the upper and lower cell plates are shown herein as being generally circular in cross-sectional shape, other manifold shapes are contemplates, such as inlet and outlet manifolds having a generally D-shaped cross section (see, e.g.,  FIG. 2A , reference character G), among others. 
     As plate  2  is a mirror image of plate  1 , manifold rings  12  and  13  are affixed to the exterior facing surface of the flat plate  2 , surrounding manifold cutouts  25  and  27 , respectively. The manifold rings  10 ,  11 ,  12 ,  13  provide structural reinforcement of the manifold defined thereby and serve as a weldable flange when joining the elemental heat exchanger cell to like cells or termination flanges, e.g., when forming an assembled heat exchange unit comprising a stacked plurality of heat exchange cells  20 . The thickness of the manifold rings is substantially equal to that or the counter-flow matrix element  4  or  5 , also affixed to the exterior surface of the envelope formed by the respective parting plates  1  and  2 . 
     The perimeter of the parting plates  1  and  2  may be formed, for example, by either option illustrated in  FIGS. 6A and 6B .  FIG. 6A  illustrates a dish-shaped edge  8 , as is typical in the forming industry. The dish-shaped edge  8  forms a raised flange  19  around the complete perimeter of the sheet, concaved towards the interior volume  60  of the envelope. The elevation of the raised flange  19  relative to the lower plate  2  is sized to be nominally equal to one-half of the thickness of the internal matrix  3  element. 
     An alternative perimeter configuration is shown in  FIG. 6B  wherein a metallic ring  9  having a thickness matching that of the interior matrix  3  is positioned around the perimeter of the cell  20  to be secured via metallurgical bonding, e.g., via welding, brazing, diffusion bonding, etc., to the edges of the flat parting plates  1 ,  2 . This relatively thick bar  9  or the dish-shaped edge  19  represent conventional but competing alternatives for sealing and spacing the parting plates  1 ,  2 . When production quantities are small, the edge bar  9  method represents the cost-effective alternative, requiring minimal tooling. When production volumes justify greater tooling investment, the dish-shaped edge  8  may reduce product cost by reducing labor. 
     In alternative embodiments, the heat exchanger embodiments herein may be constructed from materials other than metals or metallic alloys. Such alternative materials include, for example, ceramic materials and high-temperature polymers. In these cases, the cell elements may be joined by sintering, cementing, adhesive bonding, or other surface-surface fusing or solid state joining processes. 
       FIG. 7A  is an isometric view of the assembled heat exchange envelope of cell  20  formed by plates  1  and  2  with reinforcing rings  10  and  12 .  FIGS. 7B and 7C  are cross-sectional views through proximal and distal portions, respectively, of the rings  10 ,  12 . The inner diameter of the reinforcing rings  10  and  12  are in substantial alignment with the diameter cutouts  15  and  25 . The manifold reinforcing ring  10  is affixed to the outer surface of the parting plate  1  while the reinforcing manifold ring  12  is affixed to the outer surface of parting plate  2 . Similarly, the reinforcing rings  11 ,  13  are affixed to plates  1  and  2 , respectively, surrounding respective manifold cutouts  97  and  27 , with the ring  11 ,  13  inner diameters being in substantial alignment with the apertures  97  and  25 . The thickness of the reinforcing rings  10 ,  11 ,  12 , and  13  are equal to the height of the counter-flow matrix  4 ,  5 . 
     In a preferred embodiment, to create the heat exchanger cell  20  embodiment as shown in  FIGS. 7A-7C , the parting plates  1 ,  2  are coated with braze alloy at all of the contact points between the cell&#39;s components. The internal elements of the heat exchanger cell are assembled with the counter-flow matrix  3  and the cross-flow matrix headers  6  and  7  between the parting plates  1 ,  2  so that the circular headers  15 ,  25  are in close alignment. The adjacent counter-flow matrix elements  4  and  5  are positioned on the exterior surfaces of the respective plates  1 ,  2  in the respective adjacent exterior regions  61 ,  67  of the envelope  20 . When the mirror image parting plates  1  and  2  are in substantial alignment, the dish-shaped flanges  19  of the plates contact one another, forming a continuous contact surface around the perimeter of the cell  20 . 
     The heat exchange cell  20  may be formed by a typical oven-braze operation, joining the cell elements consisting of parting plates  1 ,  2 , inner counter-flow matrix  3 , header matrix elements  6  and  7 , the edge bar  9  or flange  19 , the external counter flow matrix segments  4 ,  5  and the circular reinforcing rings  10 , 11 ,  12 ,  13 . 
     Stacking a plurality of individual heat exchange cells  20  as shown in  FIGS. 8A and 8B  may form a heat exchanger of any reasonable size. Each cell  20  is positioned in substantial alignment with the other like cells, each contacting its neighbor at the external counter-flow matrix surfaces  4  and  5  and with reinforcing rings  10  and  11  of one cell  10  contacting reinforcing rings  12  and  13 , respectively, the neighboring cell. 
     The final assembly of a heat exchanger core  21 , comprising a plurality of cells  20  is produced by metallurgically bonding, e.g., welding, brazing, soldering, or diffusion bonding, the plurality of cells  20  at the surface of contact between contacting reinforcing rings  10  and  12  and between the surface of contact between contacting rings  11  and  13 . The counter-flow matrix segments  4  contacting its neighbor  5  are not bonded, but may bear on one another. The conduit formed by the reinforcing rings  10  and  12 , cutouts  15  and  25  in parting plates  1  and  2  serves as a manifold  22  for the fluid entering the heat exchanger core. Likewise, the conduit formed by the reinforcing rings  11  and  13 , and cut-outs  97  and  27  in parting plates  1  and  2  serves as a manifold  23  for fluid exiting the heat exchanger core. Because the contact surface between the matrix element  4  and  5  of adjacent cells is not bonded, the cells  20  present little resistance to the independent thermal growth between the two manifold stacks  22  and  23 . The assembled heat exchanger including the heat exchange core  21  further includes external ducting  24  (see  FIG. 8B ) surrounding the core for directing the flow of the low pressure heat exchange medium through the external heat exchange matrices  4 ,  5 . The external ducting  24  receiving the heat exchange core  21  may be of any known or conventional type as would be understood by persons skilled in the art. 
     The heat exchanger  21  in  FIGS. 8A and 8B  functions as a first fluid  30  enters a flange  31 , attached to the manifold stack  22 . The fluid  30  enters the header matrix element  6  of each cell  20  that is in communication with the conduit formed by the manifold stack  22 . The fluid  30  travels from the header matrix  6  to the counter-flow matrix  3  and then to the header matrix  7  and into the manifold stack  23 . The first fluid  30  exits through a flange  32 . The flanges  31  and  32 , or alternatively “V”-band connections or other method of mechanical attachment are welded, brazed, soldered, diffusion bonded, or the like, to the top cell  20  to facilitate ducting the first fluid  30  in and out of the core  21 . A second fluid  33  passes through the exterior, low-pressure matrices  4 ,  5  on the exterior surfaces of the plates  1 ,  2 . 
     In operation, the first fluid  30  may be a low temperature, high-pressure fluid and the second fluid may be a high temperature, low-pressure fluid. By way of example, waste heat in a relatively low-pressure fluid  33  can be recovered via thermal transfer to a high-pressure fluid passing through the interior counter flow matrices  3  within the interior volumes  61  of the heat exchange cells  20 . In a preferred embodiment, the first fluid  30  may be a working fluid such as compressed air for expansion through the turbine stage of a turbomachine, for example, to generate electrical and/or rotary shaft power and the second fluid  33  may be high-temperature, low-pressure turbine exhaust gas. 
       FIG. 9  illustrates the flow path of the first fluid  30  within the cell  20  and the flow path of the second fluid  33  between the cells  20 . The fluid  30  enters the header matrix  6 , flows through the matrix header  6 , and turns into the counter-flow matrix  3  sandwiched between the parting plates  1  and  2 . The fluid exiting the counter-flow matrix  3  collects in header matrix  7  and flows toward the exit manifold  23 . 
     The second fluid  33  flows across the outer surface of the cross-flow header region  64  and enters the counter-flow matrix segments  4  and  5 . The second fluid  33  exits the heat exchanger core  21 , flowing over the outer cell surface of the cross-flow header region  65 . The high surface area of the matrix elements  3 ,  4 , and  5  and the small hydraulic diameters within such matrix segments enhance heat exchange between the first fluid  30  and the second fluid  33 . 
     According to another embodiment, illustrated in  FIG. 10 , a heat exchange cell may be as described above, but where the reinforcing manifold rings  10 ,  11 ,  12 , and  13  may be fabricated from a rolled section of rectangular cross-section tubing. 
     According to yet another embodiment, illustrated in  FIGS. 11A-11C , a heat exchange cell may be may be as otherwise described above in connection with the embodiments of  FIG. 5  or  10 , but wherein a cut-ring  51  is inserted into the dish-shaped form  8  surrounding the manifold cut-outs  97  and  27  of plates  1  and  2 , respectively. The cut or open section  59  of cut-ring  51  is positioned at the opening of the header  7  to permit the unrestricted flow of the first fluid  30  out of the cell  20 . Similarly, a cut-ring  50  is inserted into the envelope between the plates  1  and  2 , surrounding the manifold cut-outs  15  and  25 , with an open portion  58  of the ring oriented adjacent the header matrix  6  to permit the unrestricted flow of the first fluid  30  into the header  6  of the cell  20 . The cut-rings  50  and  51  contact the corresponding aligned portions of the interior-facing surfaces of the plates  1  and  2 , and are bonded thereto, for example by coating with a braze alloy and brazing. After the oven brazing process, the result is a further reinforcing of the brazed manifold stacks  22  and  23 , thereby increasing their pressure capacity. 
     According to still another embodiment, illustrated in  FIGS. 12A-12C , porous rings  52  and  53  substitute for the cut-rings  50  and  51  appearing in  FIGS. 11A-11C . The embodiment of  FIGS. 12A-12C  may otherwise be as described herein. In  FIGS. 12A-12C , the porous ring  53  is inserted into the dish-shaped form  8  surrounding the manifold cutouts  97  and  27  of the plates  1  and  2 . Similarly, the porous ring  52  is inserted into the envelope between the plates  1  and  2 , surrounding the manifold cutouts  15  and  25 . The porous rings  52  and  53  contact the corresponding aligned portions of the interior-facing surfaces of the plates  1  and  2 , and are bonded thereto, for example by coating with a braze alloy and brazing. After the oven brazing process, the result is a further reinforcing of the brazed manifold stacks  22  and  23 , thereby increasing their pressure capacity. The porous rings  52  and  53  need not have a cut out section; rather, the first fluid  30  permeates through the porous material of the rings  52 ,  53  with minimal resistance. The rings  52 ,  53  may be formed of any porous matrix or material that permits fluid to permeate through the rings to allow the fluid to pass from the inlet manifold to the cell interior volumes and from the cell interior volume to the outlet manifold. 
     The purpose of the porous-rings  52  and  53  are two-fold. First, the porous rings provide structural hoop strength to the manifold stacks  22  and  23 . Second, when brazed to the surfaces of plates  1  and  2  at the intersection of the headers  6  and  7  with the manifold cutouts  15 ,  25  and  97 ,  27 , the porous rings  52 ,  53  work in tension to resist a pressure force acting to separate plate  1  from plate  2 . 
     According to an alternative embodiment, shown in  FIGS. 13A and 13B , the counter-flow matrix element  3  may be formed of two equal-thickness matrix elements  54  and  55 . All other features of the heat exchanger design and assembly as described in the aforementioned description may be preserved with this embodiment. 
     A further enhancement of the  FIGS. 13A and 13B  embodiment extends the counter-flow matrix segments  4  and  5 , affixed to the outer surfaces  61 ,  67  of the cell envelope  20 , to the edges  56  and  57  of the plates  1  and  2 . The purpose of this modification is to allow the matrix elements  54  and  55  to bear the compressive load that may occur as a result of pressurizing the interior  60  of the cell  20 . 
     An variation of the Z-flow concept shown in  FIGS. 5-13B  is shown in  FIGS. 14A and 14B . This design incorporates a so-called “C-flow” fluid arrangement. Rather than the “Z-flow” path taken by the internal cell fluid in  FIGS. 5-13B , the arrangement described in  FIGS. 14A and 14B  has an internal flow path that is largely parallel to the side edges  70  of the core. This shortens the path of the internal fluid  79 , permitting high-density fin  71  to extend between the two equal sized cutouts, forming the integral manifolds  72 . The high-density fin  71  provides greater tensile strength and pressure capacity of the cell while the straight (non-Z-flow) path results in lower pressure drop. In the depicted preferred embodiment, as shown in  FIG. 14B , the high surface area fin  71  extends all the way to the edge of the aperture defining the integral manifolds  72  and is cut to the radius or contour of the inner diameter of the manifolds  72  and the inner diameter of the reinforcing rings. Thus, the ends of the fin  71  extend between the reinforcing rings on opposite sides of the parting plates  1 ,  2  as the reinforcing rings. 
     The external fluid  73 , needing no header fin, flows in a cross-counter flow manner, with a prevailing “C-flow” direction after entering and exiting the counterflow matrix. In certain embodiments of this arrangement, the external fluid  73  may enter and exit the header from both sides of the core, as shown. Alternatively, a flow arrangement wherein the external fluid  73  enters and exits the header from the same transverse side of the heat exchange core is also contemplated. The external fin arrangement shown in  FIG. 14A  includes open space  77  on the outer cell surface to provide space for the external fluid  73  to distribute across the frontal entrance and exit of the external heat exchange matrix  75 . As shown in  FIG. 14B , the internal fluid  79  flows parallel to the parting plate edges directly between the circular manifolds  72 . 
     A variation on the embodiment shown in  FIGS. 14A and 14B  offers an alternative flow path for the external fluid  73  and associated header geometry. In  FIGS. 15A and 15B , the external gas fin  75  is cut in a shape to provide a gas entrance region  76  to permit entrance and exit of the external fluid from one side of the heat exchange core only. This arrangement may have packaging advantages in some applications. The region  76  also provides space for the external fluid to distribute across the frontal entrance and exit of the external heat exchange matrix  75 . As shown in  FIG. 15B , the internal fluid flows parallel to the parting plate edges directly between the circular manifolds  72 . As shown in  FIG. 15A , the external fluid  73  is required to make a “Z-path”, entering and exiting the heat exchange core on opposite transverse sides. As shown in  FIG. 15B , the high surface area fin  71  extends all the way to the edge of the aperture defining the integral manifolds  72  and is cut to the radius or contour of the inner diameter of the manifolds  72  and the inner diameter of the reinforcing rings as described above by way of reference to  FIG. 14B . 
       FIG. 16  illustrates an isometric view of a multi-cell heat exchange core wherein the heat exchange cells include an external fin  75  with a curved edge  76  defining an entrance region  77  to enable entrance and exit of the heat exchange fluid on opposite transverse sides of the core. 
     The invention has been described with reference to the preferred embodiments. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.