1. Field of the Invention
The present invention relates generally to a heat exchanger. More specifically, the present invention relates to a heat transfer tube for a heat exchanger.
2. Related Technology
Heat exchanger assemblies, such as radiators, heater cores, and condensers, for automotive vehicle powertrain cooling and air conditioning systems typically include a pair of headers and a core having a plurality of tubes disposed horizontally between the two headers. Within the headers, partitions divide the interior space of the headers into multiple, fluidly separate spaces. As a result, refrigerant passing through the heat exchanger is caused to flow generally horizontally along the length of the tubes, in a serpentine fashion, making more than one pass between the headers. A plurality of thin heat exchange fins extend generally vertically from the top and bottom surfaces of the tubes to increase the surface area of heat exchanging components.
During operation of the heat exchanger, air flows across the exterior. of the tubes and between the fins in a direction generally perpendicular to the length of the tubes. In order to maximize the heat exchange between the fins and the air flowing therethrough, the fins and the tubes have an increased width in the direction parallel to the airflow. Additionally, to decrease the wind resistance on the airflow, the tubes have a decreased thickness in the direction perpendicular to the airflow. Thus, the tubes preferably have a generally oblong shape with relatively small end faces and relatively large top and bottom faces.
The non-circular cross-section of the tubes, however, may cause non-constant stress along the perimeter of the tubes. More specifically, the oblong configuration causes increased stress in the curved areas between the end faces and the top and bottom faces. Therefore, the tubes may be subject to premature part failure along these increased stress areas.
Furthermore, the walls of the tubes have a minimum thickness to maximize heat exchange between the refrigerant and the airflow. Thus, it may be undesirable to increase the thickness of the tube walls to compensate for potential increased stress areas.
Therefore, it is desirable to provide heat exchange tubes having enhanced strength and a method of manufacturing such tubes.
In over coming the drawbacks and limitations of the known technology, a heat transfer tube is provided having opposing top and bottom walls connected by end walls to each other. The top and bottom walls each define a substantially planar surface and the end walls each define a generally arcuate surface. Furthermore, the end walls each include a plurality of deformations to strengthen the heat transfer tube. More specifically, the deformations include a recess or concave depression on the exterior surface of the tube.
In another aspect, the deformations extend in a generally linear direction along the end walls. More specifically, the deformations extend along the end walls at an angle between 15 and 165 degrees with respect to a longitudinal axis of the tube. Even more specifically, the angle is between 15 and 75 degrees or between 105 and 165 degrees with respect to the longitudinal axis.
In yet another aspect of the present invention, the concave depressions have a deformation height that is substantially equal to the tube thickness, generally between 0.05 and 1.5 millimeters.
In still another aspect of the present invention, the tube is formed of a metal sheet having a pair of end portions. The sheet is folded back upon itself to define a passageway therein and the end portions meet at and extend across the passageway so as to contact an inner surface of the sheet opposite thereof. This construction strengthens the heat transfer tube. Alternatively, only one of the two end portions may extend across the passageway to contact the inner surface opposite thereof. This end portion may exhibit a generally arcuate cross-section so as to provide a spring-like characteristic to the tube.
In another aspect, the present invention is provided as a heat exchanger for a vehicle HVAC system. The heat exchanger includes a core utilizing a series of tubes to extend between a pair of headers and to facilitate heat exchange from a fluid flowing through the heat exchanger.
A method of manufacturing the tube and heat exchanger is also provided. The method includes the steps of: forming a plurality of deformations in a sheet material, forming opposing top and bottom walls such that each of the top and bottom walls defines a substantially planar surface, and forming end walls connecting the top and bottom walls to each other. The end walls having a generally arcuate surface and the plurality of deformations being defined therein.
Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification.
Referring now to the drawings,
The heat exchanger assembly 10 includes a core 12 with first and second headers 14, 16 located on opposing ends. The first header 14 is provided with an inlet 15 at its upper end and an outlet 17 at its lower end. Within the header 14 are one or more baffles 30 that divide the header 14 into fluidly separate spaces. The second header 16 is an integrated header having a manifold and a receiver/dryer tube 18 with features that remove unwanted water from the refrigerant, as is generally known in the art. The heat exchanger 10 may further include a pair of brackets 20 to mount the heat exchanger 10 to the vehicle (not shown) during use in an air conditioning system (not shown).
The core 12 itself is a tube stack comprised of a series of tubes 22 extending between the headers 14, 16. More specifically, a first end 24 of the tubes 22 extend into openings in the first header 14 and a second end 26 of the tubes 22 extend into openings in the second header 16. The tubes 22 are generally parallel and vertically stacked with respect to each other. The tubes 22 are also generally evenly-spaced apart from one another such that a space 28 is defined therebetween.
Provided as described above, the first and second ends 24, 26 of the tubes 22 are in fluid communication with the first and second headers 14, 16. Therefore, refrigerant received into the first header 24 flows through the passageway 31 defined by the tubes 22 and into the second header 26. As mentioned above, the baffles 30 divide the headers 14, 16 into respective chambers 32, 34, 36, and 38 and as a result, the refrigerant is caused to flow back and forth across various tubes 22 and between the headers 14, 16 in a generally serpentine fashion.
During operation of the heat exchange assembly 10, air flows across the core 12 in an airflow direction into the drawing as generally indicated by arrow 40. The airflow removes heat from the refrigerant that is flowing through the tubes 22 causing it to cool and condense.
Referring to
The tubes 22 are formed from a sheet 37 of material, such as sheet metal, having first and second edges 39, 41. The sheet 37 is bent back upon itself such that the edges 39, 41 extend towards and engage each other to form a seam 43 generally at the middle or longitudinal axis 78 of the tube 22. The edges 39, 41 are connected to each other along the seam 43 by any appropriate technique such as welding.
In order to maximize the space 28 between adjacent tubes 22, and minimize the portion of the core 12 that obstructs the airflow through the core, the tube height 44 is substantially less than the tube width 50. Additionally, to provide effective mating surfaces for heat transfer promoting components, such as those described below, and to simplify manufacturing steps, the top and bottom walls 46, 48 are both preferably planar and parallel with each other. Furthermore, to maintain a generally smooth flow through the core 12 and to simplify manufacturing steps, the front and back end walls 52, 54 are arcuate with substantially constant radii of curvature. Also to simplify manufacturing steps, the tubes 22 have a substantially constant wall thickness 58 at all four walls 46, 48, 52, and 54.
Located within the space 28 between each adjacent tube 22 is a fin 60 that increases heat transfer between the tubes 22 and the airflow intersecting the heat exchanger assembly 10. The fins 60 exhibit a generally corrugated shape or a series of convolutes, as is commonly known in the industry, that extend substantially completely across the space 28 between adjacent tubes 22. A series of louvers may be provided on each corrugation of the fins 60 in order to further aid in heat transfer to the air passing therethrough. Preferably, the fins 60 also extend substantially completely across the tube width 50.
Referring now to
The deformations 64 extend in a direction 75 that forms an angle 76 with regard to a longitudinal axis 78 of the tubes 22. The direction 75 is preferably not parallel to the longitudinal axis 78 so that the deformations 64 will not undesirably contact each other in the area adjacent to the end walls 52, 54. If provided perpendicular to the tube axis 78, the convex ridges formed by the deformations 64 may contact each other within the tube 22 and restrict refrigerant flow. Therefore, the angle 76 is preferably greater than 15 degrees and less than 165 degrees.
Furthermore, the direction 75 is preferably not perpendicular with the longitudinal axis 78 because the deformations 64 may cause turbulent refrigerant flow through the tubes 22 in the area adjacent to the front and back surfaces 52, 54. More specifically, ridges perpendicular to the flow may cause the refrigerant to have a turbulent, sinusoidal flow, rather than a smooth, vortex flow caused by deformations 64 having another angle. Therefore, the angle is more preferably between 15 and 75 degrees or between 105 and 165 degrees with respect to the longitudinal axis.
Referring now to
The bowed surfaces 146, 148 cause a spring-like force between the respective surfaces 146, 148 and the fins 60 between adjacent tubes 22, thus improving the connection therebetween. More specifically, the fins 60 engage and force inwardly the bowed surfaces 146, 148, causing a secure engagement therebetween. Once the bowed surfaces 146, 148 are forced inwardly towards each other in this fashion, they become substantially parallel with each other.
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Next, as shown in
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The top and bottom rollers 115, 116 may alternatively have generally arcuate surfaces to form the tube 122 shown in
Furthermore, the tube 22 may also be formed by any other appropriate method, such as extrusion. In this alternative process, a blank of material is preferably extruded into the oblong shaped tube shown in the Figures. Next, the outer surface of the tube is deformed by an appropriate method, such as stamping, to form the deformations.
It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.