Abstract:
A heat exchanger for use with exhaust pipes. A shroud inlet communicates with a rear chamber, which communicates with a front chamber via a center plate vent. The front chamber communicates with a shroud outlet. Ambient air entering the rear chamber is routed around at least one J-pipe in the rear chamber, and around a collector in the front chamber, thus being twice heated prior to exiting the heat exchanger through the shroud outlet. The double heating provided by this design increases the efficiency of the heat exchanger. The collector is attached to the center plate by means of a full-penetration fillet weld, and the J-pipes are attached to the center plate, a front plate, and a pipe assembly baffle by stitch welding external to the J-pipes, thus strengthening the integrity of the hermetic seal between exhaust gasses and ambient air passing through the heat exchanger.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to aircraft heating systems, and in particular to a heat exchanger for aircraft exhaust. 
     2. Background of the Invention 
     Heating systems for aircraft frequently take exhaust heat from the exhaust pipes of an aircraft by means of a heat exchanger, and transfer the heat into the cabin of the aircraft via ambient air through ducts. Aircraft heating may be necessitated by the colder temperatures of higher altitudes, and also winter flight frequently mandates the use of aircraft cabin heat. 
     A typical aircraft heating system which uses exhaust gas heat from the aircraft engine generally involves a heat exchanger having a heat shroud around one or more exhaust pipes, whose heat shroud inlet takes in ambient air from the atmosphere. This ambient air is heated while it circulates through the heat exchanger, and then the heated air departs the heat shroud through a heat shroud exit, and from there flows into the aircraft cabin to heat the cabin. A valve is generally provided which regulates how much heated air is allowed to flow into the cabin, and thus controls the cabin temperature. 
     Exhaust heater shrouds must be sturdily built to withstand the vibrations of an aircraft exhaust, and also be reasonably air-tight, to prevent loss of heated air. It is also important to preserve the air-tightness of the exhaust pipes passing through the heater exhaust shroud. If an exhaust pipe were to leak carbon monoxide, carbon dioxide, and other exhaust oxygen-poor gasses into the exhaust shroud, these gasses could wind up in the cabin, and could cause asphyxiation of the occupant(s). One way to help preserve the integrity of exhaust pipes within the shroud is to keep welds to a minimum within the heat exchanger, and only use full-penetration fillet welds and stitch welds external to the exhaust pipes within the heat exchanger itself. 
     Another design objective in exhaust heater shrouds for aircraft is the maximization of contact between ambient air flowing through the shroud to be heated, and the hot exhaust pipes and collector. The more contact between fresh air flowing through the shroud to be heated and the hot exhaust pipes, the more efficient the exhaust heater shroud. One existing design provides J-pipes and straight pipes feeding into a collector, all encased in a shroud through which ambient air flows, but this design does not provide a serpentine path to maximize heating. 
     Thus, it would be desirable to provide a heat exchanger for aircraft exhaust which maximizes the contact between fresh air flowing through the shroud and the hot exhaust pipes. It would also be desirable to provide a heat exchanger for aircraft exhaust which keeps welds to a minimum within the shroud, and only uses full-penetration fillet welds and stitch welds external to the exhaust pipes within the shroud. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a heat exchanger for aircraft exhaust which provides for the maximization of contact between fresh air to be heated flowing through the shroud, and the hot exhaust pipes. Design features allowing this object to be accomplished include a shroud encasing a pipe assembly, a center plate having a center plate vent, and the resulting serpentine air pathway. Advantages associated with the accomplishment of this object include more efficient heating, and the ability to maintain a comfortable cabin temperature at higher altitudes. 
     It is another object of the present invention to provide a heat exchanger for aircraft exhaust which keep welds to a minimum within the heat exchange section, and only uses full-penetration fillet welds and stitch welds external to the exhaust pipes within the heat exchange section itself. Design features allowing this object to be accomplished include a full-penetration weld between a center plate and a collector, and stitch weld attachments between J-pipes and a front plate, center plate, and pipe assembly baffle. A benefit associated with the accomplishment of this object is increased strength in the heat exchanger, and consequent greater longevity. 
     It is yet another object of this invention to provide a heat exchanger for aircraft exhaust which is economical to build. Design features allowing this object to be achieved include the use of components made of readily available materials. Benefits associated with reaching this objective include reduced cost, and hence increased availability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with the other objects, features, aspects and advantages thereof will be more clearly understood from the following in conjunction with the accompanying drawings. 
       Three sheets of drawings are provided. Sheet one contains  FIGS. 1 and 2 . Sheet two contains  FIGS. 3 and 4 . Sheet three contains  FIGS. 5 and 6 . 
         FIG. 1  is a front elevated isometric view of a pipe assembly. 
         FIG. 2  is a front elevated isometric view of a shroud. 
         FIG. 3  is a top cross-sectional view of a shroud taken at section III-III of  FIG. 2 . 
         FIG. 4  is a front elevated isometric view of a pipe assembly about to be installed in a shroud. 
         FIG. 5  is a front elevated isometric view of an assembled heat exchanger. 
         FIG. 6  is a top cross-sectional view of a heat exchanger taken at section VI-VI of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a front elevated isometric view of pipe assembly  2 . The figures depict a four-cylinder engine heat exchanger for illustrative purposes; the instant heat exchanger may be used in engines of different configurations (e.g. two-cylinder, six-cylinder, eight-cylinder, etc.) merely by adding or subtracting J-pipes  12  and/or straight pipes  15 . Such differing numbers of J-pipes  12  and/or straight pipes  15  are intended to fall within the scope of this disclosure. 
     For illustrative purposes, the following discussion will describe the four-cylinder embodiment depicted in the drawings. The instant disclosure follows the conventions that the front of heat exchanger  50  is at front plate  4 ; the rear of heat exchanger  50  is at shroud back plate  38 ; the left side of heat exchanger  50  is at shroud left wall  34 ; the right side of heat exchanger  50  is at shroud right wall  35 . 
     Heat exchanger  50  comprises pipe assembly  2  installed in shroud  30  as depicted in  FIGS. 4-6 . Pipe assembly  2  comprises at least one J-pipe  12  and at least one straight pipe  15 , which collectively are attached to, and feed into, collector  20 . Collector  20  comprises a collector leg  21  corresponding to each pipe feeding into it, and collector outlet  23  communicating with collector legs  21 . 
     Pipe assembly  2  further comprises front plate  4  and center plate  6 . In the preferred embodiment, front plate  4  was substantially parallel to center plate  6 . Front plate  4  comprises a front plate J-pipe aperture  8  corresponding to each J-pipe  12 , and a front plate collector aperture  10  sized to admit collector outlet  23 . Center plate  6  comprises a center plate J-pipe aperture  14  corresponding to each J-pipe  12 , and a center plate collector aperture  22  sized to admit collector  20  where collector legs  21  join collector outlet  23 . Center plate  6  also comprises center plate vent  28 , which serves to direct ambient air in a serpentine path past J-pipe(s)  12  and collector  20  en route to shroud outlet  42 , thus maximizing the efficiency of heat exchanger  50 . 
     Collector  20  extends through, and is attached to, center plate collector aperture  22  in the area where collector legs  21  join collector outlet  23 . Collector outlet  23  extends through, and is attached to, collector aperture  10 , which is sized to slidably admit collector outlet  23 . J-pipe  12  comprises J-pipe leg  9  communicating with J-pipe hook  11 . The end of J-pipe hook  11  opposite J-pipe leg  9  is attached to and communicates with a corresponding collector leg  21 . The end of J-pipe leg  9  opposite J-pipe hook  11  is attached to, and extends through, front plate J-pipe aperture  8 . 
     Pipe assembly  2  further comprises pipe assembly baffle  16  attached to, and extending backwards from, center plate  6 . Pipe assembly baffle  16  comprises a pipe assembly baffle J-plate aperture  18  corresponding to each J-pipe  12 . Pipe assembly baffle aperture  18  is sized to slidably admit J-pipe hook  11 . Each J-pipe hook  11  passes through a corresponding pipe assembly baffle J-plate aperture  18  during its travel from J-pipe leg  9  to collector  20 . In the preferred embodiment, pipe assembly baffle  16  was attached to center plate  6  at substantially a 50 degree angle±15 degrees, leaning towards straight pipe(s)  15 . The heights of front plate  4 , center plate  6 , and pipe assembly baffle  16  all substantially equal the height of shroud  30 . 
       FIG. 2  is a front elevated isometric view of shroud  30 . The height of shroud  30  is substantially equal to the heights of front plate  4 , center plate  6 , and pipe assembly baffle  16 ; shroud  30  is sized to slidably admit pipe assembly  2  as illustrated in  FIG. 4 . 
     Shroud  30  comprises shroud floor  32 , shroud left wall  34 , shroud right wall  35 , and shroud roof  36 , which together define shroud void  37 . Shroud void  37  is sized to slidably admit pipe assembly  2 . 
     As may be observed in  FIG. 3 , a top cross-sectional view of a shroud taken at section of  FIG. 2 , shroud void  37  communicates with the exterior of shroud  30  through shroud inlet  40  in shroud left wall  34 , and shroud outlet  42  in shroud right wall  35 . Shroud  30  further comprises shroud back plate  38  attached along the rear edges of shroud floor  32 , shroud left wall  34 , and shroud roof  36 . Shroud baffle  39  is attached to an edge of shroud back plate  38  opposite shroud left wall  34 . The heights of shroud back plate  38  and shroud baffle  39  are substantially equal to the height of shroud  30  as defined by shroud left wall  34  and shroud right wall  35 . 
     Shroud  30  is sized to slidably admit pipe assembly  2  as illustrated in  FIG. 4 .  FIG. 4  is a front elevated isometric view of pipe assembly  2  about to be installed in shroud void  37 , as indicated by arrow  52 . During installation, pipe assembly  2  is slid into shroud  30 . Then the front edges of shroud floor  32 , shroud left wall  34 , shroud right wall  35 , and shroud roof  36  are attached to the bottom, left, right, and top edges of front plate  4  respectively. The result is heat exchanger  50 , depicted in  FIGS. 5 and 6 . 
       FIG. 5  is a front elevated isometric view of heat exchanger  50 .  FIG. 6  is a top cross-sectional view of heat exchanger  50  taken at section VI-VI of  FIG. 5 . 
     As may be observed in  FIG. 6 , the structure of heat exchanger  50  defines front chamber  54  and rear chamber  56 . Ambient air is generally routed into heat exchanger  50  through shroud inlet  40  in shroud left wall  34 , through rear chamber  56  past J-pipe hook(s)  11 , through center plate vent  28  en route to front chamber  54 , past heat exchanger  20  in front chamber  54 , and finally out of heat exchanger  50  through shroud outlet  42  in shroud right wall  35 , as indicated by arrows  58 - 64 . 
     Front chamber  54  is defined by front plate  4 , center plate  6 , shroud roof  36 , shroud floor  32 , shroud left wall  34  and shroud right wall  35 . Rear chamber  56  is defined by center plate  6 , shroud back plate  38 , shroud baffle  39 , pipe assembly baffle  16 , shroud roof  36 , shroud floor  32 , and shroud left wall  34 . Front chamber  54  communicates with rear chamber  56  through center plate vent  28 , and with the exterior via shroud inlet  40  and shroud outlet  42 . Rear chamber  56  communicates with an exterior of heat exchanger  50  via shroud inlet  40 . 
     It is intended to fall within the scope of this disclosure that the edge of pipe assembly baffle  16  opposite center plate  6  may be attached directly to shroud back plate  38 , thus eliminating shroud baffle  39 . This attachment could be facilitated by changing the angle at which pipe assembly baffle  16  is attached to center plate  6 , curving pipe assembly baffle  16 , etc. In this embodiment, rear chamber  56  is defined by center plate  6 , shroud back plate  38 , pipe assembly baffle  16 , shroud roof  36 , shroud floor  32 , and shroud left wall  34 . 
     In operation, ram air impinging on an aircraft or other vehicle to which the instant heat exchanger  50  is mounted forces ambient air into heat exchanger  50  through shroud inlet  40  as indicated by arrow  58  in  FIG. 6 . Ambient air initially enters rear chamber  56  through shroud inlet  40  as indicated by arrow  58 . In rear chamber  56 , the ambient air passes over J-pipe hook(s)  11  as indicated by arrow  60 , thereby heating the ambient air. 
     From rear chamber  56 , ambient air enters front chamber  54  through center plate vent  28 , as indicated by arrow  62 . In front chamber  54 , the ambient air passes over collector  20  as indicated by arrow  64 , thus further heating the ambient air, after which the heated ambient air exits heat exchanger  50  through shroud outlet  42 , as indicated by arrow  64 . The serpentine pathway the instant heat exchanger  50  forces ambient air to take brings the ambient air first into contact with J-pipe(s)  12 , and then with collector  20 , thus doubly heating the ambient air and increasing the efficiency of the instant heat exchanger  50 . 
     Some ambient air passes over J-pipe leg(s)  9  en route to front chamber  54  as depicted by arrow  66  in  FIG. 6 . This air is first heated by J-pipe leg(s)  9 , and then further heated by collector  20  enroute to shroud outlet  42 , as described above. 
     An important design objective in the instant invention is to keep welds to a minimum within heat exchanger  50 , and only use full-penetration fillet welds and stitch welds external to the exhaust pipes within the heat exchanger itself. As may be observed in  FIG. 4 , design features allowing this object to be accomplished include full-penetration fillet weld  24  between center plate  6  and collector  20 , and stitch weld  26  attachments between J-pipes  12  and front plate  4 , center plate  6 , and pipe assembly baffle  16 . A benefit associated with the accomplishment of this object is increased strength in the heat exchanger, and consequent greater longevity. 
     Another important benefit is safety. It is important to avoid any leakage of exhaust gasses out of J-pipes  12  and collector  20  into the ambient air being heated within front chamber  54  and rear chamber  56 , because these exhaust gasses contain poisons such as carbon monoxide, and the air being heated may be used for cabin heating and be breathed in by the vehicle occupants. Within front chamber  54  and rear chamber  56 , the instant heat exchanger  50  design provides only stitch welds  26  external to J-pipe(s)  12 , and full-penetration fillet weld  24  at the junction of collector  20  and center plate  6 . In this manner, the strength of the hermetic seal between exhaust gasses and ambient air is enhanced by the instant invention. 
     In the preferred embodiment the instant heat exchanger was manufactured of a metal such as stainless steel, or other appropriate materials. Attachments between J-pipe(s)  12  and front plate  4 , center plate  6 , and pipe assembly baffle  16  were made by stitch welds external to J-pipe(s)  12 , or other appropriate means of attachment. The attachment between collector  20  and center plate  6  was made by full-penetration fillet weld, or other appropriate means of attachment. 
     The rest of the attachments between the components of the instant heat exchanger  50  were made by means of welds, fasteners such as screws, nut plates, and nuts, or other appropriate means of attachment. Attachment flanges and lips through which fasteners may be fastened are old and well-known in the art, are irrelevant to the instant invention, and thus are not depicted in the figures. 
     J-pipes  12  and straight pipes  15  were each integral, single-piece fabrications. J-pipe  12  was fabricated by bending a straight pipe into a hook shape using conventional pipe-bending methods, or by any other appropriate means. 
     While a preferred embodiment of the invention has been illustrated herein, it is to be understood that changes and variations may be made by those skilled in the art without departing from the spirit of the appending claims. 
     DRAWING ITEM INDEX 
     
         
           2  pipe assembly 
           4  front plate 
           6  center plate 
           8  front plate J-pipe aperture 
           9  J-pipe leg 
           10  front plate collector aperture 
           11  J-pipe hook 
           12  J-pipe 
           14  center plate J-pipe aperture 
           15  straight pipe 
           16  pipe assembly baffle 
           18  pipe assembly baffle J-plate aperture 
           20  collector 
           21  collector leg 
           22  center plate collector aperture 
           23  collector outlet 
           24  full-penetration weld 
           26  stitch weld 
           28  center plate vent 
           30  shroud 
           32  shroud floor 
           34  shroud left wall 
           35  shroud right wall 
           36  shroud roof 
           37  shroud void 
           38  shroud back plate 
           39  shroud baffle 
           40  shroud inlet 
           42  shroud outlet 
           50  heat exchanger 
           52  arrow 
           54  front chamber 
           56  rear chamber 
           58  arrow 
           60  arrow 
           62  arrow 
           64  arrow 
           66  arrow