Abstract:
A heat exchanger includes a plurality of tubes positioned substantially transverse to a direction of airflow through the heat exchanger and arranged in a plurality of tube rows extending substantially along the direction of airflow. The heat exchanger further includes a plurality of webs substantially integral to two or more tubes of the plurality of tubes, each web extending between and connected to adjacent tubes of the plurality of tubes. At least one tube of the plurality of tubes has a cross section with an aspect ratio greater than 1:1, relative to a substantially horizontal web.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to heat exchangers. More specifically, the subject disclosure relates to tube and fin configuration for heat exchangers. 
         [0002]    Micro-channel heat exchangers have represented the typical construction of heat exchangers for, for example, automotive and heating, ventilation and air conditioning (HVAC) applications, for several years. These heat exchangers are finding wider application in residential and even aerospace HVAC products due to their compactness, relatively low cost, and reduced refrigerant charge when compared to other heat exchanger configurations. 
         [0003]    In micro-channel heat exchangers, liquid or two-phase refrigerant flows through small ports internal to extruded tubes. Air flows through folded fins arranged between the tubes. Due to the high surface density of this construction, and a flat shape of the typical tube, these heat exchangers are prone to moisture and condensate retention and subsequent frost accumulation issues. This is especially problematic when the tubes are arranged horizontally. Water collects on the horizontal surfaces of the tubes, resulting in higher flow and thermal resistance as well as corrosion and pitting of the tube surfaces. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, a heat exchanger includes a plurality of tubes positioned substantially transverse to a direction of airflow through the heat exchanger and arranged in a plurality of tube rows extending substantially along the direction of airflow. The heat exchanger further includes a plurality of webs substantially integral to two or more tubes of the plurality of tubes, each web extending between and connected to adjacent tubes of the plurality of tubes. At least one web has an enhanced surface such as a louver, tab, or vortex generator. (the main claim should be the combination of the tube, web, and surface enhancements. We may have a configuration with round tubes with some form of web surface enhancement. I don&#39;t believe this is covered in the claims) 
         [0005]    According to another aspect of the invention, a heat exchanger includes a plurality of tubes positioned substantially transverse to a direction of airflow through the heat exchanger and arranged in a plurality of tube rows extending substantially along the direction of airflow. At least one tube of the plurality of tubes includes two or more fluid-conveying pathways. A plurality of webs are substantially integral to two or more tubes of the plurality of tubes. Each web extends between and is connected to adjacent tubes of the plurality of tubes. 
         [0006]    According to yet another aspect of the invention, a heat exchanger includes a plurality of tubes positioned substantially transverse to a direction of airflow through the heat exchanger and arranged in a plurality of tube rows extending substantially along the direction of airflow. A plurality of webs are substantially integral to at least two tubes of the plurality of tubes. Each web extends between and is connected to adjacent tubes of the plurality of tubes. A plurality of tabs are located at the plurality of webs substantially transverse to the airflow to generate vortices in the airflow. 
         [0007]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  is a perspective view of an embodiment of an integral tube and fin heat exchanger; 
           [0010]      FIG. 2  is an embodiment of an integral tube and fin heat exchanger having elliptical tubes; 
           [0011]      FIG. 3  is an embodiment of an integral tube and fin heat exchanger having airfoil-shaped tubes; 
           [0012]      FIG. 4  is an embodiment of an integral tube and fin heat exchanger having web louvers; 
           [0013]      FIG. 5  is an embodiment of an integral tube and fin heat exchanger having multiple web louvers; 
           [0014]      FIG. 6  is an embodiment of an integral tube and fin heat exchanger having multiple fluid pathways per tube; 
           [0015]      FIG. 7  is another embodiment of an integral tube and fin heat exchanger having multiple fluid pathways per tube; 
           [0016]      FIG. 8  is yet another embodiment of an integral tube and fin heat exchanger having multiple fluid pathways per tube; 
           [0017]      FIG. 9  is still another embodiment of an integral tube and fin heat exchanger having multiple fluid pathways per tube; 
           [0018]      FIG. 10  is an embodiment of an integral tube and fin heat exchanger including web tabs; 
           [0019]      FIG. 11  is a schematic of vortex flow through an embodiment of an integral tube and fin heat exchanger; 
           [0020]      FIG. 12  is another embodiment of an integral tube and fin heat exchanger including web tabs; 
           [0021]      FIG. 13  is another schematic of vortex flow through an embodiment of an integral tube and fin heat exchanger; and 
           [0022]      FIG. 14  is another embodiment of a heat exchanger  10 . 
       
    
    
       [0023]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Shown in the  FIG. 1  is a heat exchanger  10  structure. In some embodiments, the heat exchanger  10  is a micro-channel heat exchanger (MCHX). The heat exchanger  10  has an integrated tube-fin structure where a plurality of tubes  12  are arranged with a plurality of webs  14  extending between adjacent tubes  12  of the plurality of tubes  12 , and acting as fins in this structure. The webs  14  in some embodiments are substantially integral to the tubes  12 . A refrigerant flow  16 , for example, a liquid or two phase refrigerant, is flowed through the plurality of tubes  12 . While the term “refrigerant flow” is utilized throughout the present application, it is to be appreciated that any selected liquid, gas, or two-phase fluid may be flowed through the plurality of tubes  12  for the purposes of heat transfer. In some embodiments, the plurality of tubes  12  are arranged in rows  18 . An airflow  20  flows across the plurality of tubes  12  and the plurality of webs  14  such that thermal energy is transferred between the airflow  20  and the refrigerant flow  16  via the tube  12  and web  14  structure. In some embodiments, a direction of the airflow  20  is substantially perpendicular to the refrigerant flow  16 . 
         [0025]    Referring now to  FIG. 2 , the tubes  12  have a cross-section that improves air flow  20  and thus heat transfer between the airflow  20  and the heat exchanger  10 . In some embodiments, as shown in  FIG. 2 , the cross-section of the tubes  12  are elliptical or may be airfoil shaped as shown in  FIG. 3 . Elliptic or airfoil shapes reduce the wake size behind the tubes  12 , which decreases pressure drop and improves heat transfer. Referring to  FIG. 4 , the webs  14  include a plurality of louvers  22  formed in the webs  14  which extend into the airflow  20 . The louvers  22  may be formed by, for example, a punching operation which cuts the web  14  on three sides of the louver  22  and folds the louver  22  into position, resulting in a web opening  24  in the web  14 . In some embodiments, the louvers  22  each have a louver face  42  which is aligned substantially parallel to the airflow  20 . In some embodiments, as shown in  FIG. 5 , the webs  14  may be configured with multiple rows of multiple louvers  22  between adjacent tubes  12 . Utilizing louvers  22  and web openings  24  allows for reduction in material and refrigerant volume compared to a conventional micro-channel heat exchanger and allows for drainage of condensate through the web openings  24  to reduce condensate/ice buildup and/or corrosion. 
         [0026]    In some embodiments, the webs  14  between adjacent tubes  12  are substantially equal in web length  26 . It is to be appreciated, however, that the web length  26  may vary as desired. In some embodiments, as also shown in  FIG. 2 , the tubes  12  in a first row  18   a  of tubes  12  can be offset or staggered relative to an adjacent second row  18   b  of tubes  12  along a length  30  of the heat exchanger  10  to allow for a more compact structure and to increase heat transfer between the airflow  20  and the refrigerant flow  16 . 
         [0027]    Referring now to  FIG. 6 , some embodiments it is desired to increase a distance between the tubes  12  or reduce the number of tubes  12  because heat transfer via the webs  14  is highly effective. Further, reducing a number of tubes  12  reduces necessary connections of tubes  12  to a header (not shown) which distributes refrigerant flow  16  to the tubes  12 . A reduction of the number of tubes  12  alone, however, increases a refrigerant flow pressure drop for the same capacity and flow rates. Further, a reduction of the number of tubes  12  combined with an increase in the cross-sectional area of the tubes  12  to increase flow capacity, results in a reduction in heat transfer due to an increase in a hydraulic diameter of the tubes  12  and a reduction in a total refrigerant side heat transfer area. 
         [0028]    The embodiments of  FIGS. 6-8  address this problem by providing multiple smaller refrigerant pathways  32  in each tube  12  of the plurality of tubes  12 . As shown in  FIGS. 6 ,  7 , and  8 , respectively, two, three, or four pathways  32  may be arranged in each tube  12  to decrease the pressure drop compared to a similar-sized tube  12  with a single pathway while increasing the heat transfer capability of the tube  12  and reducing connections to the header. While it is possible to include more than four pathways  32  in the tube  12 , the heat transfer effectiveness of the additional pathways will be decreased since heat conduction from innermost pathways will be limited compared to the outermost pathways. As shown in  FIG. 9 , louvers  22  may be utilized with these multi-pathway  32  configurations to increase heat transfer and to provide condensate drainage through the web openings  24 . 
         [0029]    Referring now to  FIG. 10 , the heat exchanger  10  may include vortex generators, for example, tabs  34  disposed along the web  14 . The tabs  34  are oriented across the airflow  20 , as shown schematically in  FIG. 11 , in order to generate streamwise votices  36  in the airflow  20  as the airflow passes along the web  14 . The presence of vortices  36  can increase heat transfer between the web  14  and the airflow  20 . Referring again to  FIG. 10 , the tabs  34  are triangular in shape, or may be other shapes, for example, trapezoidal, or asymmetrically polygonal, or the like, to generate the desired vortices  36 . The tabs  34  may be disposed in rows  40  extending along a tube length  38 , with multiple rows, for example, two or three rows of tabs  34  between adjacent tubes  12 . The positions of tabs  34  in a first row  40   a  may be staggered relative to the positions of tabs  34  in a second row  40   b,  or may be aligned, depending on the vortex  36  desired. 
         [0030]    Comparing  FIGS. 10 and 12 , it can be seen that in some embodiments the tabs  34  are aligned such that a tab tip  42  of the tabs  34  faces the same direction, while in other embodiments, as shown in  FIG. 12 , tab tips  42  of tabs  34  or rows of tabs  34  may face opposing directions. Further, as shown in  FIG. 13 , tabs  34  may be located and oriented to boost a strength of the vortices  36  along the web  14 . 
         [0031]    Referring to  FIG. 14 , in some embodiments, the webs  14  may not be substantially planar, but may be a wave or ruffle shape to further have a desired effect on the airflow  20 , such as increased vortex generation. The wavy web  14  may be utilized in conjunction with the louvers  22 , and/or tabs  34 . 
         [0032]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.