Patent Publication Number: US-9903249-B2

Title: Heat exchanger arrangement, especially for a vehicle heater

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. § 119 of German Patent Application DE 10 2014 214 768.9 filed Jul. 28, 2014, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention pertains to a heat exchanger arrangement, especially for a vehicle heater, comprising a pot-like (pot-shaped) inner heat exchanger housing with a first bottom wall in a first axial end area of the heat exchanger arrangement and with a first circumferential wall adjoining the first bottom wall and enclosing a longitudinal axis, a pot-like outer heat exchanger housing with a second bottom wall in the first axial end area of the heat exchanger arrangement and with a second circumferential wall adjoining the second bottom wall and enclosing the longitudinal axis, wherein the inner heat exchanger housing and the outer heat exchanger housing are connected to one another in a second axial end area, as well as a fluid flow space formed between the inner heat exchanger housing and the outer heat exchanger housing. 
     BACKGROUND OF THE INVENTION 
     A heat exchanger arrangement for a fuel-operated vehicle heater, in which the inner one of the two heat exchanger housings has a double-walled design in an axial end area of the heat exchanger arrangement, which end area is located at a distance from the bottom walls of the two pot-like (pot-shaped) heat exchanger housings inserted one into the other, is known from DE 198 00 241 C1. The inner heat exchanger housing defines in this area the fluid flow space formed between the two heat exchanger housings with a front wall, which is formed thereon [the heat exchanger housing] and extends circumferentially in a ring-shaped manner about a longitudinal axis of the housing, and is connected with its outer circumferential wall, which likewise extends circumferentially in a ring-shaped manner, to the circumferential wall of the outer heat exchanger housing. A waste gas outlet opening, formed in a waste gas outlet connecting piece, is provided in the axial end area of the heat exchanger arrangement, which said end area is located at a distance from the bottom walls. This connecting piece breaks through the fluid flow space with the waste gas outlet opening formed therein and is open, on the one hand, to a waste gas flow space enclosed by the inner heat exchanger housing. The fluid inlet opening leading to the fluid flow space and likewise the fluid outlet opening leading away from the fluid flow space are formed in the axial end area of the heat exchanger arrangement, which end area is located close to the bottom walls, in the outer one of the two heat exchanger housings in respective connection branches. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a heat exchanger arrangement, especially for a vehicle heater, in which heat losses are reduced. 
     This object is accomplished according to the present invention by a heat exchanger arrangement, especially for a vehicle heater, comprising a pot-like (pot-shaped) inner heat exchanger housing with a first bottom wall in a first axial end area of the heat exchanger arrangement and with a first circumferential wall adjoining the first bottom wall and enclosing a longitudinal axis; a pot-like outer heat exchanger housing with a second bottom wall in the first axial end area of the heat exchanger arrangement and with a second circumferential wall adjoining the second bottom wall and enclosing the longitudinal axis, wherein the inner heat exchanger housing and the outer heat exchanger housing are connected to one another in a second axial end area of the heat exchanger arrangement; as well as a fluid flow space formed between the inner heat exchanger housing and the outer heat exchanger housing. Further, provisions are made for providing at least one outwardly open recess in the material of which the inner heat exchanger housing is made or/and in the material of which the outer heat exchanger housing is made at least in the second axial end area of the heat exchanger arrangement. 
     Further, provisions are made for providing at least one an outwardly open recess in the material of which the inner heat exchanger housing is made or/and in the material of which the outer heat exchanger material is made at least in the second axial end area of the heat exchanger arrangement. 
     By providing at least one recess in the material of which the inner heat exchanger housing is made or/and in the material of which the outer heat exchanger material is made, a cavity is created, which is filled, in general, with air, but is basically closed towards the fluid flow space. Since the two heat exchanger housings, but at least the inner heat exchanger housing, which is exposed more heavily to the hot combustion waste gases, is made, in general, of a metallic material, for example, die-cast aluminum, the preparation of recesses in this material, of which the heat exchanger housing is made, leads to an interruption in the metallic material. Since the material of which the heat exchanger arrangement or the heat exchanger housing thereof is made has, in general, a markedly higher thermal conductivity and therefore a lower thermal resistance than for example, the air present in such a recess, the discharge of heat from the heat exchanger arrangement is reduced by the fact that a greater thermal resistance is thus provided, in general, in the area of the recesses. 
     In order to avoid a mutual compromise with the fluid flow space, it is proposed that at least one recess be essentially open outwardly in the axial direction on an end face facing away from the bottom walls. 
     An equally stable design, which can be embodied in a simple manner, can be obtained by providing a plurality of recesses following each other in the circumferential direction about the longitudinal axis, or/and by at least one and preferably each recess to be curved about the longitudinal axis or/and elongated in the circumferential direction. 
     To make it possible for a fluid to be heated to flow through the fluid flow space or to also guarantee the removal of combustion waste gases generated, for example, in a combustion area of a vehicle heater, it is, further, proposed that a fluid inlet opening to the fluid flow space or/and a fluid outlet opening from the fluid flow space or/and a waste gas outlet opening from a waste gas flow space enclosed by the inner heat exchanger housing be provided in the second axial end area. 
     To provide sufficient space for such inlet or outlet openings, it is proposed that at least one recess provided in the circumferential area of the fluid inlet opening or/and at least one recess provided in the circumferential area of the fluid outlet opening or/and at least one recess provided in the circumferential area of the waste gas outlet opening have, at least in some areas, a lower depth than a recess provided in a circumferential area that does not essentially intersect the fluid inlet opening or/and the fluid outlet opening or/and the waste gas outlet opening. The consequence of this design is that where there is no mutual compromise with a fluid inlet opening or fluid outlet opening or a waste gas outlet opening, recesses or a recess with a correspondingly greater depth can be provided, which leads to a further increase in the thermal resistance. 
     A compact embodiment of the heat exchanger arrangement can be obtained by the inner heat exchanger housing having a front wall axially defining the fluid flow space or/and a third circumferential wall that extends over the second circumferential wall on its outer side and is connected to this in the second axial end area. 
     The front wall may be designed as a wall extending circumferentially in a ring-shaped manner in the circumferential direction. However, to make it possible to guarantee the flow of fluid to the fluid inlet opening or to the fluid outlet opening, it is proposed that the fluid flow space extend in the axial direction beyond the front wall in the area of the fluid inlet opening or/and in the area of the fluid outlet opening. This means that the front wall, which is otherwise designed as a wall extending circumferentially in a ring-shaped manner, may be interrupted in the area of these openings or may have bulges enclosing these openings. 
     To avoid the deposit of contaminants in the area of the heat exchanger arrangement, it is, further, proposed that at least one recess be closed by a closing element. 
     The heat-insulating effect introduced by the provision of at least one recess in the material of which a heat exchanger housing is made can be utilized especially efficiently if at least one recess and preferably each recess contains an insulating material with a thermal conductivity lower than that of the material of which the heat exchanger housing having the recess or recesses in question is made. 
     The insulating material preferably fills the at least one recess essentially completely. 
     In one embodiment, which can be embodied in an especially simple manner and provides a highly efficient heat insulation, the insulating material may comprise air. It should be pointed out that a combination of different heat-insulating insulating materials may be provided in another embodiment variant. For example, porous or cellular foam-like material, in the inner volume area of which air is contained, may be contained in at least one recess. For example, PU foam or foamed silicone material may be used. 
     The material of which at least one heat exchanger housing having a recess is made preferably comprises a metallic material, preferably aluminum. Metallic material, i.e., for example, aluminum, advantageously forms the principal component of the material, especially if this material is provided as an alloy. 
     The present invention will be described in detail below with reference to the attached figures. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a perspective view of a heat exchanger arrangement; 
         FIG. 2  is a longitudinal sectional view of the heat exchanger arrangement according to  FIG. 1 , cut along a line II-II in  FIG. 3 ; 
         FIG. 3  is an axial view of the heat exchanger arrangement according to  FIG. 1 ; and 
         FIG. 4  is a longitudinal sectional view of the heat exchanger arrangement, which sectional view corresponds to  FIG. 2 , in conjunction with a combustion chamber assembly unit of a vehicle heater. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, a heat exchanger arrangement, which can be used, for example, in conjunction with a fuel-operated vehicle heater, is generally designated by  10  in the figures. The heat exchanger arrangement  10  comprises two heat exchanger housings  12 ,  14  inserted into one another. The inner heat exchanger housing  12  comprises in a first axial end area  16  of the heat exchanger arrangement  10  a first bottom wall  18  and, adjoining this radially on the outside and extending in the direction of a longitudinal axis L and enclosing the longitudinal axis L, a first circumferential wall  20 . The outer heat exchanger housing  14  also comprises in a first axial end area  16  of the heat exchanger arrangement  10  a second bottom wall  22  as well as, adjoining same radially on the outside, a second circumferential wall  24  extending in the direction of the longitudinal axis L and enclosing same. It should be noted here that the two heat exchanger housings  12 ,  14  with their bottom walls  18 ,  22  and their circumferential walls  20 ,  24  in the exemplary embodiment being shown are each integrally formed components, which are manufactured, for example, as diecast aluminum parts. The circumferential walls or bottom walls could, in principle, also be designed as separately built components connected to one another in one or both of the heat exchanger housings  12 ,  14 . 
     In a second axial end area  26  of the heat exchanger arrangement  10  located at a distance from the bottom walls  18 ,  22 , the inner heat exchanger housing  12  forms, with a ring-shaped end section  28 , a connection to the outer heat exchanger housing  14 . In this ring-shaped end section  28 , the inner heat exchanger housing  12  extends radially on the outside beyond the second circumferential wall  20  of said heat exchanger housing and has a third circumferential wall  30  extending in the direction of the first axial end area. This third circumferential wall  30  extends over the second circumferential wall  24  radially on the outside and is rigidly connected to same via the intermediary of an O-ring-like sealing element  32 , for example, by pressing, welding, bonding or the like. A fluid flow space generally designated by  34 , which is closed or defined in the axial direction at the second axial end area  26  by a front wall  36  extending between the first circumferential wall  20  and the third circumferential wall  30  of the inner heat exchanger housing  12 , is formed in this manner between the inner heat exchanger housing  12  and the outer heat exchanger housing  14 . This front wall  36  is designed such that it extends circumferentially in a ring-shaped manner about the longitudinal axis L, it is advantageously located essentially in an axial area in relation to the longitudinal axis L, i.e., essentially at right angles thereto, and has a plane design, as this is shown in  FIG. 2 , but it could also be provided with a conical or truncated cone-like structure. 
     In a connection area  28  extending axially beyond the outer heat exchanger housing  14 , the inner heat exchanger housing  12  has a fluid inlet opening  40  formed in a fluid inlet connecting piece  38  as well as a fluid outlet opening  44  provided in a fluid outlet connecting piece  42 . The fluid inlet opening  40  and the fluid outlet opening  44  are open towards the fluid flow space  34 . As this is shown in  FIG. 2 , the connecting pieces  40 ,  42  are arranged essentially on the axial side facing away from the fluid flow space  34  in relation to the front wall  36 . To nevertheless establish a fluid exchange connection, the front wall  36 , which otherwise extends circumferentially in a ring-shaped manner, may be interrupted where the fluid inlet opening  40  or the fluid outlet opening  44  is provided, so that a bulge that is in connection with the fluid flow space  34  and is also in connection with the respective opening  40  and  44  is formed in the end section  28 . 
     Further, a waste gas outlet opening  48  is provided in a waste gas outlet connecting piece  46  in the second axial end area  26  of the heat exchanger arrangement  10 . This outlet opening is open towards the inner side of the first circumferential wall  20  and hence towards a waste gas flow space  50  enclosed by the inner heat exchanger housing  12 . As this is shown in  FIG. 4 , the combustion waste gases generated in a combustion chamber assembly unit  52  or in a combustion  54  thereof are sent through a flame tube  56  positioned such that it extends into the inner heat exchanger housing  12  in the direction of the first bottom wall  18 . After reaching the first bottom wall  18 , the combustion waste gases are deflected radially to the outside and then flow back in the waste gas flow space  50  from the first axial end area  16  to the second axial end area  26  and the waste gas outlet opening  48  provided there. The combustion waste gases now flow along heat transfer ribs  58 , which are provided on an inner side of the inner heat exchanger housing  12  to enlarge the heat transfer surface. 
     A plurality of recesses  60 , which are prepared, for example, during the casting operation in which the inner heat exchanger housing  12  is manufactured or/and recesses  60  prepared by machining are provided in the material of which the inner heat exchanger housing  12  is made in the exemplary embodiment being shown in the second axial end area  26  of the heat exchanger arrangement  10  in the inner heat exchanger housing  12 , especially in the end section  28  thereof axially adjoining the fluid flow space  34 . The recesses  60  are arranged such that they follow each other in the circumferential direction about the longitudinal axis L and have, for example, each equal circumferential extensions or/and radial extensions. The recesses  60 , adapted to the ring-shaped form of the heat exchanger housing, are preferably curved or/and elongated in the circumferential direction. Walls  62  separating the individual recesses  60  are located between the individual recesses  60 . The axial depth of the recesses  60  is selected to be such that, as this is clearly shown in  FIG. 2 , a wall area  66  separating the recesses  60  from the fluid flow space  34  is formed between the front wall  36  and a respective bottom area  64  of the recesses  60 . As can be seen in area  68  in  FIGS. 1 and 3 , the recesses  60  may be made with a lower recess depth where there is a circumferential intersection of recesses  60  with the fluid inlet opening  40 , the fluid outlet opening  44  or the waste gas outlet opening  48  or the connecting pieces  38 ,  42 ,  46  providing these openings. In the circumferential areas not overlapping with these openings or connecting pieces, the recesses  60  preferably have each equal depths that maximally utilize the existing axial installation space in the end section  28 . By providing the recesses  60 , which are open towards the outside, in the axial direction in the example being shown, cavities are created in the material of which the heat exchanger arrangement, especially the inner heat exchanger housing  12  exposed comparatively intensely to heat due to the hot combustion waste gases, is made. The dissipation of heat towards the outside to the surrounding area is reduced by these cavities or interruptions in the material of which the heat exchanger arrangement or the inner heat exchanger housing  12  is made, because there is a higher thermal resistance in the area of the recesses  60  than in the area in which the material of which the inert heat exchanger housing  12  is made, for example, in the area of the wall  66 . Heat losses can thus be reduced especially in the second axial end area  26 . 
     As this is shown in  FIG. 4 , a support  72 , which establishes a connection between the combustion chamber assembly unit  52  and the heat exchanger arrangement  10  and is connected, for example, to the flame tube  56  or to a combustion chamber wall  70 , may cover the recesses  60  or at least a part thereof on the end face  74  on which the recesses  60  are axially open in the material of which the inner heat exchanger housing  12  is made. For example, a flexible sealing element  75  of a ring-shaped design may be interposed here. The rigid connection of the support  72  to the inner heat exchanger housing  12  may be brought about, for example, by bolts, which pass through the support  72  in the area thereof that extends radially to the outside and also extends over the recesses  60  and are inserted into the connection area  28  of the inner heat exchanger housing  12 . 
     To make it possible to utilize the insulation effect introduced by the provision of the recesses  60  efficiently, some and preferably all recesses  60  are filled with a heat-insulating material. Heat-insulating means here that the material with which the recesses  60  are filled has a lower thermal conductivity than the material of which the heat exchanger housing having these recesses  60  is made. For example, these recesses  60  may be filled essentially completely with air, which has a lower thermal conductivity than, for example, the aluminum material used to make such a heat exchanger housing by several orders of magnitude. It should be noted in this connection that the thermal conductivity may be considered for the purposes of the present invention in the temperature range relevant for the operation of a heat exchanger arrangement having such a design, for example, in the range of −50° C. to +250° C. in the area in which the recesses  60  are provided in the heat exchanger housing. 
     At least part of the heat-insulating material in at least one recess may be provided as a solid material. This may be provided, for example, as a porous or cellular material, for example, as a foam material, e.g., PU foam or silicone foam, which contains air in its inner volume area. It is also possible that the sealing element  75  providing a closing element covering the recesses  60  or at least some of the recesses  60  is formed with material sections meshing with at least one of the recesses  60  and preferably with each recess  60  covered by it to provide the insulating material. 
     It is obvious that as an alternative or in addition to the recesses in the material of which a heat exchanger housing is made, which recesses are shown in the figures, it is also possible to provide recesses on other areas or recesses that are open in another direction, for example, radially outwardly, and advantageously also recesses that are closed by a closing element. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.