United States Patent [191 Bathla [451 July 23,1974
[ LEAK PROTECTED HEAT EXCHANGER  Inventor: Pritam S. Bathla, Dayton, Ohio  Assignee: United Aircraft Products, Inc.,
' Dayton, Ohio 22 Filed: May 13, 1971 21 Appl.No.:143,027
 US. Cl. 165/70, 165/166  Int. Cl F28f 17/00, F28f 3/00  Field of Search 165/148, 150, 1, 154, 5,
 References Cited UNITED STATES PATENTS 2,365,515 12/1944; Baudry 165/70 2,743,089 4/1956 Gardner et al 165/70 X 3,165,152 1/1965 Jones 165/166 3,451,473 6/1969 Urie et a1 165/70 X 3,469,623 9/1969 Rawlings 165/70 Primary Examiner-Manuel A. Antonakas Assistant ExaminerTheophil W. Streule, Jr. Attorney, Agent, or Firm-J. E. Beringer 57 ABSTRACT A fluid to fluid heat exchanger in which facial surfaces of the heat exchanger are defined by headers forming drained leak chambers in such separating relation to different flowing fluids asto obviate mixing of a leaked fluid with another-fluid in the event of joint failure or the like. l
5.Claims,13 Drawing Figures PATENTEDJUL23l974 INVENTOR PRITAM S. BATHLA HIS ATTORNEY 1 LEAK PROTECTED HEAT EXCHANGER BACKGROUND OF THE INVENTION The heat exchanger art has recently been characterized by notable advances productive of a compact, high performance form of heat transfer device. These devices have particular utility when at least one of the fluids has a pressured flow therethrough. Component parts of the device are bonded to one another, usually by brazing, and this unites the parts into an integrated assembly as well as seals separated flow passages from one another. Present day bonding processes have a high degree of reliability. Occasionally, however, a heat exchange application presents itself in which failure of a bonded joint, with consequent mixing of separated fluids, cannot be tolerated even though only minor amounts of a fluid are leaked. It has been the view heretofore that compact, all brazed or like heat exchangers may be unsuited for those applications as not offering the required reliability.
SUMMARY or THE INVENTION The present invention deals with improvements in the described form of compact heat exchanger whereby positive separation of fluids in the heat exchanger, and at entrance and exit ends thereof, is established and maintained. A feature of the invention resides in a use of tubes, forming a tube and fin construction eliminating the need interiorly of the heat exchanger for bonded joints to separate different flowing fluids. In another feature a tube sheet or header construction at the tube ends provides separated collection chambers into which fluid leaked past a joint failure at facial ends of the heat exchanger may be trapped and suitably drained without mixing with other fluid. The construction lends itself to simplified assembly and mounting, the means forming the header construction comprising plural apertured plates mounted on the tubes of the heat exchanger and adapted for bonding and sealing to the tubes and to one another.
It is an object of the invention to provide a leak protected heat exchanger substantially of the class described.
Other objects and structural details of the invention will appear from the following description when read in connection with the accompanying drawings, wherein:
changer in accordance with the illustrated embodiment of the invention comprises a series of superposed, flattened tubes 10. These are devices made of a good heat conductive material each having upper and lower-fiat surfaces 11 and 12 interconnected along opposite margins by integrally curving surfaces 13. Opposite ends of the tube are open. The tube may be initially round and flattened to the configuration illustrated and described. It is, in any event, a one-piece article providing for through flow of a fluid from end to end thereof and is v in a fully confining relation to such fluid. In the illustrated instance, secondary heat transfer surface in the form of corrugated fin material 14 is placed within each tube 10.
Above and below each tube 10, in contacting relation to surfaces 11 and 12, are fin strips 15. These are, in the illustrated instance, disposed at right angles to the tubes 10 and define flow passages whereby a second fluid may pass in cross-flow heat transfer relation to a first fluid passing through the tubes. Defining upper and lower walls of the superposing assembly of tubes 10 and fin strips 15 are core sheets 16 and 17.
From side to side, core sheets 16 and 17, fin strips 15 and tubes 10 are, or may be, similarly dimensioned. From end to end, however, the parts have a relationship as illustrated in FIG. 3 with tubes 10 in a relatively projecting relation to other elements of the assembly.
At their ends, the tubes mount in header assemblies of which, since they are identical, only one will be described. Thus, each header assembly comprises inner and outer plate elements 18 and 19 and an intermediate plate 21. Plate 18 is a flat one-piece device having a series of apertures 22, one for each tube 10, contained within its margins. Bent outwardly from the margins of the apertures 22 are flanges 23. The plate 18 is oriented to project flanges 23 outwardly or toward intermediate plate element 21. The plates 19 and 21 are similarly constructed. They provide respective apertures 24 and 25 corresponding in number and location to the apertures 22. The apertures 24-25 may have projecting flanges like the flanges 23 but in the illustrated instance do not. At their outer margins the plate elements 19 and 21 are formed with turned over peripheral flanges 26 and 27 respectively. The plate elements 19 and 21 are oriented to cause flanges 26 and 27 to face inwardly or toward plate 18.
In the assembly of the heat exchanger, the tubes 10 and fin strips 15 are stacked in an alternating relation withupper and lower ends of the assembly defined by core sheets 16 and 17. The header plate elements 18, 19 and 21 are slipped over the projecting ends of the tubes 10 which are received in registering plate apertures 22, 24 and 25. The telescoping movement of the parts is continued until the plate elements 18 achieve a contacting, compressive relation to ends of the fin strips 15 and until the following plate elements 21 and 19 achieve the contacting spaced relation shown in FIG. 3. While the parts are held so assembled, the heat exchanger is subjected to a brazing or like operation in which joints defined by the mutually contacting header plate elements and between the header plate elements and the tubes 10 and core sheets 16 and 17 are closed by means constituting a seal and a bond. A self contained, integrated core unit is in this manner defined which may be used in any suitable manner. By way of example, manifolds may be welded or otherwise attached to opposite ends of the heat exchanger to enclose projecting ends of the tubes 10 and provide for flow of a fluid therethrough Another fluid may be suitably directed transversely and externally of the tubes 10, with the different fluids being in heat transfer relation through the tube walls.
The different fluids are positively separated within the core of the heat exchanger by reason of the tubes 10 being of such one-piece construction as to provide no basis for joint failure by which one fluid may leak from its assigned flow path into the flow path of the other. At the ends of the heat exchanger core'the header means comprising plate elements 18, 19 and 21 are sealed to the tubes and accordingly tends to preclude an exchange of fluids through the headers. The instant invention provides additional safeguards, however, in that the several plates 18, 19 and 21 define sealed chambers 28 and 29. These provide low pressure collection chambers and are suitably drained, as shown in FIG. 2, by connections 31 and 32 which make common communication with inner and outer chambers 28 and 29 at respectively opposite ends of the heat exchanger. Accordingly, should fluid flowing along the fin strips 15, between the tubes 10, find an imperfection in the brazed joint between the plate 18 and a tube 10 or between the plate 18'and a core sheets 16 or 17, such fluid will be admitted to chamber 28 but will be denied by intermediate plate 21, any further escape. The leaked fluid is drained from chamber 28 by the connection 31. Similarly, should the fluid guided to and through the tubes 10 find an imperfection in the brazed joint between header plate 19 and the tubes or between the header plate and the core sheets 16 and 17, such fluid will be permitted access to collection chamber 29 but will be denied by intermediate plate 21 further access to the core interior. Fluids leaked into chambers 29 are drained by connection 32.
The heat exchanger is thus constructed positively to prevent mingling of the fluids within the core thereof, and, at the ends of the heat exchanger leak protection means insures that inadvertently leaked fluids will be denied access to one another. Throughout their passage through the heat exchanger, therefore, and at entrance and exit ends thereof, segregation of the fluids is enforced.
What is claimed is:
second fluids, said means including opposing header means at opposite faces of the heat exchanger through which flow passages open for conducting said first fluid into and out of the heat exchanger by way of said faces, said header means'in part defining other flow. passages for flow of said second fluid intermediately thereof,
, said header means comprising plural superposing parts 1. A leak protected heat exchanger wherein first and second fluids at elevated pressure and of different temperature are brought into heat transfer relation to one another, comprising means defining separated flow passages through the heat exchanger for said first and forming Separated non-communicating chambers adaptedrespectively-to accept leakage of said first and second fluids and which are normally out of communication with either of the both fluids, and means for separately draining said chambers.
2. A heat exchanger according to claim 1, wherein said means defining separated flow passages includes tubes forming said flow passages forconducting said first fluid and contributing to the defining of said other flow passages, said header means being constructed to accommodate to projection of said tubes therethrough and each comprising a plurality of spaced apart plates apertured for projection of said tubes therethrough and joined to said tubes in a normally leak tight manner, said plates being interconnected at their margins in a leak tight manner to define said chambers.
3. A heat exchanger according to claim 2, wherein an inner one of said plates presents a surface to flowing second fluid in said other flow passages and an outer one of said plates presents a surface to inflowing and outflowing first fluid, and wherein an intermediate plate partitions the space between said inner and outer plates and is in mutually facing relation to opposite surfaces of said inner andouter plates.
4. A heat exchanger according to claim 1, wherein said means for draining said chambers comprises tube means in common communication with different respective chambers at the opposite faces of said heat exchanger.
5. A heat exchanger according to claim 3, wherein said intermediate and said outer plates have turned over margins establishing the width of said chambers.