Abstract:
A heat exchanger for an automotive vehicle includes two headers, first tubes for carrying fluid between the headers, and second tubes for carrying engine coolant between the headers, staggered with respect to the first tubes, each tube inclined relative to an air stream entering the heat exchanger.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to a heat exchanger for transferring heat from a heat source contained in tubes to an air stream, and, in particular, to a heater core in the passenger compartment of an automotive vehicle. 
         [0003]    2. Description of the Prior Art 
         [0004]    Conventionally, the tubes, which carry engine coolant through the heater core of an automotive vehicle, are arranged parallel to the stream of air that passes through the heater core. The heater core usually includes one or two rows of tubes, the second row being in-line and parallel to the first row. 
         [0005]    Generally, fins located between the tubes and secured to the outer surface of the tubes enhance heat transfer from the coolant to the air stream. 
         [0006]    It has long been understood that the heat transfer rate is much larger for turbulent flow than for laminar flow. Increasing turbulence of the air stream through the heater core is beneficial to the convection heat transfer rate and improves the overall performance of the heat exchanger. It is also more effective to increase the heat transfer on the air-side to improve the heat exchanger, as this is the more restrictive side compared to the rate of heat transferred from the fluid flowing inside the tube. 
         [0007]    In order to induce turbulence in the air stream, fins on the outer surface of the tubes are usually mutually staggered and offset, but the tubes are aligned parallel to the air stream. 
         [0008]    A need exists in the industry for techniques that further improve heat transfer in a heater core without increasing its package size. 
       SUMMARY OF THE INVENTION 
       [0009]    A heat exchanger for an automotive vehicle includes two headers, first tubes for carrying fluid between the headers, and second tubes for carrying engine coolant between the headers and staggered with respect to the first tubes. Each tube is inclined relative to an air stream entering the heat exchanger. 
         [0010]    The heater core provides improved performance over a current production heater core by up to five percent without increasing fin density or changing tube geometry. The heater core realizes an increase of about five percent in heat transfer surface area without increasing the size of the heater core. 
         [0011]    An increase in turbulence of the air stream flowing through the heater core improves heat transfer performance of the heater core. 
         [0012]    Design enhancements include offsetting the second row of tubes to increase impingement effect on tube surface and redirection of the air through the core face. Additionally, both the first and second tube rows may be inclined or angled relative to the air stream to increase the heat transfer surface area of the tube and to enhance impingement of the air on the tubes and fins. Both the first and second rows of tubes are angled in relation to the incoming flow of air up to 20 degrees. The optimal angle modeled in the simulations is about 15 degrees to maximize both the surface area for heat transfer and turbulence to the air flow through the core. 
         [0013]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0015]      FIG. 1A  is an end view showing a prior art arrangement of a single row of parallel, flat tubes for a heater core arranged parallel to the air flow; 
           [0016]      FIG. 1B  is an end view of a single row of parallel, flat tubes for a heat exchanger inclined relative to the air flow; 
           [0017]      FIG. 2A  is an end view showing a prior art arrangement of two rows of parallel, flat tubes in a heater core arranged in-line and parallel to the air flow; 
           [0018]      FIG. 2B  is an end view showing two rows of parallel, flat tubes of a heat exchanger arranged parallel to the air flow, with the second row offset or staggered with respect to the first row of tubes. 
           [0019]      FIG. 2C  is an end view showing two rows of parallel, flat tubes of a heat exchanger inclined relative to the air flow 
           [0020]      FIG. 3B  is a top view of an alternate heat exchanger; 
           [0021]      FIG. 3B  is a top view of a heat exchanger; 
           [0022]      FIG. 3C  is a top view of an alternate heat exchanger; 
           [0023]      FIG. 4  is a cross section taken at plane  4 - 4  in  FIG. 3A ; 
           [0024]      FIG. 5  is a cross section taken at plane  4 - 4  in  FIG. 3A  showing an alternate arrangement of tubes; 
           [0025]      FIG. 6  is a cross section taken at plane  4 - 4  in  FIG. 3A  showing another arrangement of tubes; 
           [0026]      FIG. 7  is a cross section taken at plane  4 - 4  in  FIG. 3A  showing another arrangement in which the tubes are angled in first and second directions; and 
           [0027]      FIGS. 8A ,  8 B and  8 C show folded tubes whose surfaces are joined and sealed along at least one longitudinal seam. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    Referring now to the drawings, there is illustrated in  FIG. 1A  a single row of parallel, flat, thin-walled tubes  12  for use in a heater core, the tubes being arranged parallel to the air stream  13 . 
         [0029]      FIG. 1B  shows a single row of parallel, flat, thin-walled tubes  14  for a heater core, the tubes being inclined relative to the air stream  13 . In the heater core, tubes  12 ,  14  carry hydraulic engine coolant along the tubes, and air passes over the outer surface of the tubes. Each tube  14  has a height, which extends between flat surfaces  15 ; a depth, which extends laterally between the leading edge  16  and trailing edge  17 ; and a length, which extends along the tube, normal to the plane of the page. 
         [0030]      FIG. 2B  illustrates two rows of flat, thin-walled tubes  18 ,  20  for use in a heater core, wherein the tubes of one row are staggered relative to the tubes of the other row and all the tubes are mutually parallel and parallel to the air stream  14 . 
         [0031]      FIG. 2C  shows two rows of parallel, flat, thin-walled tubes  22 ,  24  for a heater core, wherein the tubes of the second row  24  are staggered relative to the tubes of the first row  22  and all the tubes are mutually parallel and inclined relative to the air stream  14  at an angle A, which may be as large as about 20 degrees. 
         [0032]    The heater core  26  illustrated in  FIG. 3A  includes a housing  28  containing tubes organized in a first bank of tubes  30 , which extends longitudinally between headers  31 ,  32 , and a second bank of tubes  33 , which extend longitudinally between headers  32 ,  34 . Header  31 , which is partitioned from header  34  by a short cross baffle  35 , is formed with an inlet  36 . Header  34  is formed with an outlet  37 . Tubes  30  carry hydraulic engine coolant at relatively high temperature from inlet  36  and header  31  to return to return header  32 . Tubes  33  carry the coolant from header  32  to header  34  and the outlet  37 . Heat is transferred from the engine coolant to the air stream  13 , which flows into the passenger compartment of a vehicle. 
         [0033]    Alternatively the tubes  30 ,  33  may be organized in a first bank comprising the tubes of the first row  22  and a second bank comprising the tubes of the second row  24 . 
         [0034]      FIG. 3B  demonstrates an alternative, in which a second bank of tubes  24  carries relatively high temperature engine coolant from an inlet  48  between a header  42  and a return header  44 . A first bank of tubes  22  returns the engine coolant to header  42  and outlet  40 . Header  42  is partitioned with a long longitudinal baffle  50 . 
         [0035]      FIG. 3C  demonstrates an alternative, in which tubes  22 ,  24  carry coolant from inlet  52 , between headers  54 ,  56  and through the outlet  58 . 
         [0036]      FIG. 4  shows the tubes arranged as shown in  FIG. 2B  with a first row  18  and a second row  20 , each row parallel with respect to the air stream  13 , the second row  20  being offset or staggered such that the leading edge  16  of each tube of the second row  24  is aligned with a space  60  between successive tubes of the first row  18 . 
         [0037]      FIG. 5  shows that the tubes are arranged with a first row  22  and a second row  24 , each row inclined with respect to the air stream  13 , the second row  24  aligned such that the leading edge  16  of each tube of the second row  24  is aligned with a tube of the first row  22 . 
         [0038]      FIG. 6  shows that the tubes are arranged as shown in  FIG. 2C  with a first row  22  and a second row  24 , each row inclined with respect to the air stream  13 , the second row  24  offset or staggered such that the leading edge  16  of each tube of the second row  24  is aligned with a space  60  between successive tubes of the first row  22 . 
         [0039]      FIG. 7  shows that the tubes of the second row  62  may be directed in another direction from the tubes of the first row  22 , each tube  22 ,  62  being inclined at an angle A with respect to the air stream, the second row  24  being offset or staggered such that the leading edge  16  of each tube of the second row  62  being aligned with a space  60  between successive tubes of the first row  22 . 
         [0040]    In another embodiment, the tubes may be arranged in the heater core  26  as shown in  FIG. 1B  with a single row  16  but no second row, each tube  16  being inclined at an angle A with respect to the air stream  14 . 
         [0041]    The tubes may be welded along a longitudinal seam or brazed along the seam. Alternatively, as shown in  FIG. 8A , the tubes may be folded from sheet stock and brazed or welded at overlapping, longitudinal seams  66 ,  68 . 
         [0042]      FIG. 8B  illustrates a tube folded from sheet stock and brazed or welded at overlapping seams  70 ,  71 ,  72 . The flat surfaces  15  are formed with beads  74 ,  75 ,  76 . 
         [0043]      FIG. 8C  illustrates a clenched tube folded from sheet stock and brazed or welded at an overlapping seam  78 . The flat surfaces  15  are formed with beads  80 ,  81 ,  82 ,  83 ,  84 . 
         [0044]    Inclining the tubes with respect to the air stream  14  and staggering the tubes enhances turbulence of the air flow through the heater core  26  and increase the impingement effect on the surfaces of the tubes by redirecting the air at the face of the heater core. Inclining the tubes with respect to the air stream  13  and staggering the tubes improves the rate of heat transfer in the heater core. 
         [0045]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.