Abstract:
A tubular heat exchanger is provided for a motor vehicle air conditioner with an inner tube through which a fluid or gas can flow and an outer tube radially enclosing the inner tube subject to the formation of an intermediate space through which a flow can flow. The inner tube in this case includes, but is not limited to a quantity of stampings arranged spaced from one another and with their longitudinal extension at least partially extending in axial direction of the inner tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 102009057232.5, filed Dec. 5, 2009, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field relates to a tubular heat exchanger for a motor vehicle air conditioner and in particular a double-walled heat exchanger tube with an inner tube through which a fluid or a gas can flow and an outer tube, which radially encloses the inner tube subject to the forming of an intermediate space through which a flow can flow. 
       BACKGROUND 
       [0003]    Double-walled heat exchanger tubes for motor vehicle air conditioners are thoroughly known. Thus, DE 10 2005 052 972 A1 for example describes a double-walled tube with an outer tube and an inner tube inserted in the outer tube. The inner tube is provided with several rectilinear or helically twisted grooves continuously running in longitudinal direction. Such grooves enlarge the cross-sectional area of a channel running between inner and outer tube so that the flow resistance of the refrigerant flowing in that outer channel and typically subjected to high pressure can be reduced. By reducing the flow resistance the flow rate of the high-pressure refrigerant flowing through the channel can be increased, so that a heat transfer from the high-temperature refrigerant, that is the refrigerant subjected to high pressure to the low-temperature refrigerant flowing in the inner tube, that is the low-pressure refrigerant, can be improved. 
         [0004]    The known continuous grooves running rectilinearly or helically however are accompanied by a comparatively high pressure loss, which is disadvantageous to the overall performance of the air conditioning system. In the case of applications in the field of a motor vehicle air conditioner it is a disadvantage that the tube diameter as well as the tube length is limited within predetermined ranges because of prevailing installation space requirements. Consequently it proves particularly difficult, especially with an already existing vehicle package, to realize a demanded degree of heat exchange with predetermined tube diameter and predetermined tube length. 
         [0005]    It is therefore at least one object to make available a tubular, particularly a double-walled heat exchanger for a motor vehicle air conditioner, which with a predetermined tube outer geometry or with predetermined tube length and predetermined tube diameters makes possible an individually adaptable heat exchange between its flow channels. Preferably, the tubular heat exchanger would be producible without additional expenditure worth mentioning and adaptable to existing geometrical requirements, and preferably the heat exchanger should also be characterized by a lower pressure loss. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0006]    The tubular heat exchanger according to an embodiment is designed for a motor vehicle air conditioner and comprises an inner tube through which a fluid or a gas and/or a fluid-gas mixture can flow. In addition, the coaxial heat exchanger comprises an outer tube, which radially encloses the inner tube subject to the formation of an intermediate space through which a flow can flow. In the final assembly state of the heat exchanger in the refrigerant circuit of a vehicle air conditioner it is thereby more preferably provided that the inner tube fluidically interconnects an evaporator and a compressor of the air conditioner, while the channel formed between inner tube and outer tube makes available a fluidic connection between a condenser and an expansion device of the air conditioner. 
         [0007]    By means of the coaxial heat exchanger a heat transfer of the high-pressure or high-temperature refrigerant flowing on the outside to the low-pressure or low-temperature refrigerant flowing in the inner tube in the opposite direction can take place. Because of this, cooling down of the high-temperature, high-pressure refrigerant can take place even before flowing through the expansion device connected downstream, with the help of which the refrigerant flowing to the evaporator is cooled down because of an isentropic or adiabatic expansion. 
         [0008]    To specifically change, improve and/or manipulate the heat transfer between the refrigerant flowing in the outer channel and in the inner tube that can be achieved with the heat exchanger it is provided that the inner tube comprises a quantity of stampings arranged spaced from one another and with their longitudinal extension, at least partially, extending in axial direction of the inner tube. With the help of these stampings specific swirling of the respective refrigerant in both channels through which flow can flow of the coaxial heat exchanger tube can take place. In this connection, a degree of swirling of the respective refrigerant flow that compared with the prior art can be specifically adjusted can be achieved through an arrangement of local stampings in the inner tube which are spaced from one another. Depending on the orientation of the longitudinal extension of the stampings relative to the longitudinal axis of the inner or outer tube the degree of swirling of the respective refrigerant can be specifically changed and thus ultimately a demanded degree of heat transfer be achieved even without changing the tube diameter and the tube length. 
         [0009]    According to an embodiment the stampings of the inner tube are formed radially to the inside. The production of such stampings turns out to be comparatively simple and can be produced in mass production by inserting a tube substantially running rectilinearly in a stamping tool provided for this purpose. In this connection it is more preferably provided that the stampings protruding to the inside from the inner surface of the tube correspond to corresponding depressions provided on the outer surface of the tube. In this manner, both refrigerants flowing in the inner channel formed by the inner tube and in the outer channel formed by the inner and outer tube can be approximately swirled to the same degree. 
         [0010]    According to another embodiment it is additionally provided that the quantity, the size, the geometrical shape and the orientation of the stampings is matched for achieving a predetermined heat exchange between the preferentially gaseous refrigerant flowing in the inner tube and the liquid refrigerant preferentially flowing in opposite direction between inner and outer tube. In this connection, the heat capacity and additional physical state quantities such as for example a respective pressure and temperature of the refrigerant can be taken into account. Here, the embodiments are not restricted to the described constellation of the refrigerant flows. Thus it can also be provided that the gaseous refrigerant flows in the flow channel between inner and outer tube and the liquid refrigerant in the inner tube. 
         [0011]    Through specific changing of the quantity, the size, the geometrical shape and also the orientation of the stampings with respect to the main flow direction of the refrigerant the degree of the heat transfer between the two opposite refrigerant flows can also be variably adapted to the requirements of the respective refrigerant circuit and consequently optimized even with fixed predetermined tube length and fixed predetermined tube diameter. 
         [0012]    According to a further embodiment it is additionally provided that the quantity of the stampings which are arranged on an imaginary line running perpendicularly to the longitudinal axis of the inner tube or intersect such an imaginary circumferential line, amounts to between approximately 4 to approximately 12, preferentially between approximately 6 to approximately 10. The extension of the stampings in tube circumferential direction in this case is to be more preferably selected smaller than the spacing of stampings in circumferential direction of the tube arranged adjacently. The spacing of adjacent stampings seen in circumferential direction amounts to at least approximately 1.5 to approximately 3 times the extension of the respective stampings in circumferential direction. 
         [0013]    According to a further embodiment it is additionally provided that stampings arranged adjacently to one another in axial direction have a spacing of at least approximately 15 mm to approximately 30 mm. In that the stampings are not formed continuously but interrupted in axial direction, i.e., in tube longitudinal direction, altogether better swirling of the refrigerant than with a continuous groove can be achieved. Here, tests have shown that a higher degree of heat transfer can be achieved within an axial spacing range of approximately 15 mm to approximately 30 mm. According to a further embodiment the depth of the stampings is between approximately 1 mm and approximately 3 mm, preferentially between approximately 1.5 mm and approximately 2.5 mm. 
         [0014]    In this connection it is particularly provided that the depth of the stampings is a maximum of approximately 15% of the diameter of the inner tube. Such a limitation of the stamping depth on the one hand proves to be favorable in terms of manufacturing. On the other hand, this affects the stability of the tube only to a minor extent, at least only to a tolerable degree. 
         [0015]    According to a further embodiment the sum of the areas of all stampings of the inner tube amounts to between approximately 10% and approximately 60%, preferentially between approximately 20% and approximately 50% of the outer surface area of the inner tube. Thus, tests have shown that the degree of the heat transfer is particularly influenced by the overall area of the stampings, whereas in the stated interval of approximately 10% to approximately 60% or approximately 20% to approximately 50% the degree of the heat exchange that is optimal for the present application can be achieved. 
         [0016]    According to a further embodiment the stampings have a substantially rectangular geometry and extend with their longitudinal axis at an angle of approximately 0° to approximately +/−45°, preferentially of approximately +/−10° to approximately +/−35° relative to the longitudinal axis of the inner tube. With increasing inclination relative to the tube longitudinal axis of the stampings of rectangular or oblong design a higher degree of swirling and thus an increased degree of heat exchange can typically be achieved between the flow channels. An inclination of approximately 0° to approximately +/−45° or of approximately +/−10° to approximately +/−35° proves to be advantageous for the intended operating purpose in the refrigerant circuit of a motor vehicle air conditioner. 
         [0017]    With a further embodiment of the heat exchanger the stampings widen in circumferential direction seen in flow direction of the refrigerant. Thus the stampings can be designed for example divergently, triangularly or conically widening in axial direction of the tube. It is likewise conceivable that the stampings seen in circumferential direction of the tube widen contrary to the flow direction in the manner described before. It is additionally conceivable that the stampings seen in flow direction follow a curved course. They can for example be characterized by a substantially crescent-like geometry with a cross-sectional geometry that remains substantially the same but can also be variable, particularly with a divergent or convergent cross-sectional geometry. It is also conceivable that the stampings are substantially designed triangular, diamond, trapezium or substantially circular-shaped. 
         [0018]    According to a further embodiment additionally relates to a motor vehicle air conditioner with a closed refrigerant circuit. The refrigerant circuit fluidically interconnects at least one compressor, one condenser, one expansion device, such as an expansion valve, and an evaporator of the air conditioner. In addition, the refrigerant circuit comprises a previously described heat exchanger. The inner tube of the coaxial heat exchanger fluidically interconnects the evaporator of the air conditioner with the compressor of the air conditioner and the outer tube of the coaxial heat exchanger the condenser and the expansion device of the air conditioner. Depending on the design of the air conditioner and the coolant circuit, inverse coupling of inner tube and outer flow channel to the components evaporator and compressor and condenser and expansion device respectively is also possible in principle. 
         [0019]    In addition, a motor vehicle is provided that comprises the previously described air conditioner or a coaxial tube heat exchanger according to the embodiments. Further objectives, features and advantageous application possibilities of the invention are represented in the following description of the various exemplary embodiments making reference to the drawings. There, all features described in the text in isolation and also graphically depicted in the figures form the subject of the embodiments of the present invention both standing alone as well as in any conceivable practical combination thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0021]      FIG. 1  a schematic cross-sectional representation through a coaxial tube heat exchanger according to the invention according to a first embodiment; 
           [0022]      FIG. 2  a representation of a second embodiment of the heat exchanger corresponding to  FIG. 1 ; 
           [0023]      FIG. 3  an exemplary cross section of a heat exchanger in the sectional plane perpendicularly to the tube longitudinal axis; 
           [0024]      FIG. 4  a schematic lateral view of an inner tube with stampings arranged offset in circumferential direction and spaced from one another in axial direction; 
           [0025]      FIG. 5  a further schematic lateral view of an inner tube with stampings running obliquely relative to the tube longitudinal axis; 
           [0026]      FIG. 6  a configuration comparable to  FIG. 4  however with an increased quantity of stampings; 
           [0027]      FIG. 7  a further inner tube with stampings widening in flow direction; 
           [0028]      FIG. 8  an exemplary embodiment with stampings following a curved course in flow direction; and 
           [0029]      FIG. 9  an exemplary embodiment with stampings of diamond-shaped design and oriented variously relative to one another. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
         [0031]      FIG. 1  to  FIG. 3  shows a coaxial tube heat exchanger  10  with an inner tube  12  and with an outer tube  14 . While the outer tube  14  has a substantially continuous cylindrical shape, individual stampings  16  protruding to the inside are provided on the inner tube  12 . The stampings  16  formed as depression in the outer surface of the inner tube  12  correspondingly thereto protrude from the inner surface of the inner tube  12 . The inner tube predominantly serves for a fluidic connection between an evaporator and a compressor of a motor vehicle air conditioner and thus connects the outlet of the evaporator with the suction side of the compressor. The outer tube  14  or the outer channel formed by the outer tube  14  and inner tube  12  is preferentially subjected to a through flow of a refrigerant subjected to high pressure flowing in a direction opposite to that of the vapor flowing in the inner tube  12 . 
         [0032]    Here, the high-temperature high-pressure refrigerant passes a defined heat quantity on to the vapor flowing in opposite direction in the inner tube  12 . In that the individual stampings  16 ,  18  are formed spaced from one another in axial direction, i.e., in tube longitudinal direction, on the inner tube  12 , an improved heat transfer can be made available compared with continuous grooves of continuous design in axial direction. 
         [0033]    The stampings  16  schematically indicated in  FIG. 1  are substantially rectangular in shape and with their longitudinal axis substantially extend parallel to the axial direction. In contrast with this, the stampings  18  shown in  FIG. 2  are inclined relative to the axial direction of the tube  20 , but arranged parallel relative to one another. The angle assumed between the longitudinal direction of these stampings  18  and the tube axial direction preferentially amounts to approximately 0° to approximately +/−45°, preferably approximately +/−10° to approximately +/−35°. 
         [0034]    As is noticeable by means of the cross-sectional representation according to  FIG. 3 , a total of four stampings  16  for example seen in circumferential direction of an inner tube  20  are arranged along an imaginary circumferential line distributed over the circumference of the inner tube  12  at same, i.e., equidistant spacings. 
         [0035]    In the configuration according to  FIG. 4 , substantially rectangular stampings  26 ,  28  but compared with the tube diameter each having a greater longitudinal extension compared with the configuration according to  FIG. 1  and  FIG. 2  are again provided. Here, too, the stampings  26  as well as the stampings  28  arranged spaced axially thereof are oriented parallel to one another and parallel to the tube longitudinal axis. The stampings  26  as well as the stampings  28  in this case are additionally arranged distributed over the circumference of the inner tube  22  at regular, equidistant spacings. With respect to the  FIG. 4  to  FIG. 9  it is additionally noted that the broken lines running in circumferential direction merely represent a cut off or interrupted tube. 
         [0036]    The arrangement of the stampings  26  by groups and the arrangement of the stampings  28  in this case are turned in circumferential direction so that an imaginary axial extension of a stamping  26  comes to lie in the intermediate space free of stampings between two stampings  28 . Since the stamping density as well as the geometry of the individual stampings  26 ,  28  is substantially identical, this also applies the other way round. This means, an imaginary extension of a stamping  28  preferentially comes to lie in the middle between stampings  26  in circumferential direction arranged adjacent to one another. 
         [0037]    The inner tube  32  according to  FIG. 5  likewise comprises arrangements of stampings  36 ,  38  preferentially distributed equidistantly over the circumference of the tube  32  likewise spaced from one another in axial direction. However, compared with the configuration according to  FIG. 4 , these are oriented slightly inclined relative to the longitudinal axis of the tube  32 . 
         [0038]    In the configuration according to  FIG. 6 , the inner tube  42  comprises stampings  36 ,  38  which in terms of geometry and orientation correspond to the stampings  36 ,  38  shown in  FIG. 5 . However, the individual stampings  36 ,  38  seen in circumferential direction are arranged at a clearly shorter distance from one another. As a whole, the inner tube  42  compared with the inner tube  32  has an increased quantity of stampings  36 ,  38 . In addition, the axial spacing of the stampings  36 ,  38  shown in  FIG. 6  is shorter than the axial spacing of the inner tube stampings  36 ,  38  shown in  FIG. 5 . 
         [0039]      FIG. 7  schematically shows additional conceivable stamping geometries. The stampings  56  are for instance designed as isosceles triangles, which seen in a tube longitudinal direction, have approximately 2 to approximately 4 times a greater extension than in circumferential direction. The inner tube  52  additionally comprises stampings  58  which widen funnel-like or conically in certain regions, which likewise seen in tube longitudinal direction have a greater extension than in circumferential direction of the tube  52 . 
         [0040]    The stampings  66 ,  68  additionally represented in  FIG. 8  by means of an inner tube  62  are designed curved relative to the tube longitudinal direction at least in certain regions, wherein the stampings  68  seen in stamping longitudinal direction have a substantially constant cross-sectional profile, while the stampings  66 , seen in tube longitudinal direction, from the left to the right, have a cross-sectional profile which seen in circumferential direction of the tube  62 , is growing larger. In addition, the stampings  66 ,  68  differ in terms of their mutual orientation. While stampings  68  lying adjacently to one another are curved in the same direction, stampings  66  arranged adjacent to one another in circumferential direction have curves facing away from one another. 
         [0041]      FIG. 9  finally shows a further inner tube  72  with diamond-shaped stampings  76 ,  78  wherein the stampings  76  are each oriented parallel to one another, while the stampings  78  arranged adjacent to one another in circumferential direction are arranged turned relative to one another or mirror-symmetrically to the axial direction of the tube. The quantity, the geometrical configuration, the mutual arrangement, the spacings and dimensioning of the individual stampings shown in  FIG. 1  to  FIG. 9  serve for the optimization and an adaptation of the degree of heat transfer between the fluids flowing in the outer and in the inner channel preferentially in opposite directions to suit the requirement, which fluids can be gaseous and/or liquid. Here, a required degree of heat exchange can also be achieved largely independently of the predetermined tube length and a predetermined overall tube diameter. 
         [0042]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.