Patent Publication Number: US-6220340-B1

Title: Heat exchanger with dimpled bypass channel

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to heat exchangers, and in particular, to heat exchangers with built-in bypass channels to provide some flow through the heat exchanger under all operating conditions. 
     FIELD OF THE INVENTION 
     Where heat exchangers are used to cool oils, such as engine or transmission oils in automotive applications, the heat exchangers usually have to be connected into the flow circuit at all times, even where the ambient temperature is such that no oil cooling is required. Usually, the engine or transmission includes some type of pump to produce oil pressure for lubrication, and the pump or oil pressure produced thereby causes the oil to be circulated through the heat exchanger to be returned to a sump and the inlet of the pump. Under cold ambient conditions, the oil becomes very viscous, sometimes even like a gel, and under these conditions, the flow resistance through the heat exchanger is so great that little or no oil flows through the heat exchanger until the oil warms up. The result is that return flow to the transmission or engine is substantially reduced in cold conditions to the point where the transmission or engine can become starved of lubricating oil causing damage, or the oil inside the engine or transmission can become overheated before the heat exchanger becomes operational, in which case damage to the engine or transmission often ensues. 
     One way of overcoming these difficulties is to provide a pipe or tube that allows the flow to bypass the heat exchanger in cold flow conditions. Sometimes a bypass channel or conduit is incorporated right into the heat exchanger between the inlet and outlet of the heat exchanger. The bypass conduit has low flow resistance, even under cold ambient conditions, so that some bypass or short circuit flow can be established before any damage is done, as mentioned above. Usually these bypass channels are straight or plain tubes to minimize cold flow resistance therethrough, and while such bypass channels provide the necessary cold flow, they have a deleterious effect in that when the oil heats up and the viscosity drops, excessive flow passes through the bypass channels and the ability of the heat exchanger to dissipate heat is reduced. In order to compensate for this, the heat exchanger must be made much larger than would otherwise be the case. This is undesirable, because it increases costs, and often there is insufficient room available to fit a larger heat exchanger into an engine compartment or the like. 
     The present invention attempts to overcome these difficulties by providing a dimpled bypass channel in the heat exchanger, the dimples having a height, width and spacing to produce a desired cold flow resistance to permit cold flow, but also an increasing hot flow resistance as the temperature of the fluid in the bypass channel increases. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a heat exchanger comprising a plurality of stacked tubular members defining flow passages therethrough. The tubular members have raised peripheral end portions defining respective inlet and outlet openings, so that in the stacked tubular members, the respective inlet and outlet openings communicate to define inlet and outlet manifolds. The tubular members have a predetermined internal cold flow resistance. A bypass conduit is attached to the stacked tubular members. The bypass conduit has opposite end portions and a tubular intermediate wall extending therebetween defining a bypass channel. The opposite end portions of the bypass conduit define, respectively, a fluid inlet and a fluid outlet, the inlet and outlet communicating with the respective inlet and outlet manifolds for the flow of fluid through the bypass channel. The intermediate wall has a plurality of longitudinally spaced-apart, inwardly disposed, mating dimples formed therein. The mating dimples define flow restrictions between the mating dimples and adjacent areas of the intermediate wall. The mating dimples have a predetermined height and transverse width such that the cold flow resistance past the flow restrictions is less than the predetermined internal cold flow resistance of the tubular members. Also, the mating dimples are spaced apart such that the hot flow resistance pass the dimples increases as the temperature of the fluid in the bypass channel increases. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is an elevational view of a preferred embodiment of a heat exchanger according to the present invention; 
     FIG. 2 is an enlarged, exploded, perspective view of the left side of the heat exchanger shown in FIG. 1; 
     FIG. 3 is an enlarged vertical sectional view of the portion of FIG. 1 indicated by the chain-dotted circle  3 ; 
     FIG. 4 is a plan view of one of the plates used to make the bypass channel of the heat exchanger of FIG. 1; 
     FIG. 5 is a vertical sectional view taken along lines  5 — 5  of FIG. 4; 
     FIG. 6 is a vertical sectional view taken along lines  6 — 6  of FIG. 4; 
     FIG. 7 is a vertical sectional view showing FIG. 5 superimposed on top of FIG. 6; 
     FIG. 8 is an enlarged view of the portion of FIG. 4 indicated by chain-dotted circle  8 ; 
     FIG. 9 is a plan view of another embodiment of a plate used to make a bypass channel for a heat exchanger according to the present invention; 
     FIG. 10 is a vertical sectional view taken along lines  10 — 10  of FIG. 9; 
     FIG. 11 is a plan view of another embodiment of a plate used to make a bypass channel for a heat exchanger according to the present invention; 
     FIG. 12 is a vertical sectional view taken along lines  12 — 12  of FIG. 11; 
     FIG. 13 is a plan view of yet another embodiment of a plate used to make a bypass channel for a heat exchanger according to the present invention; and 
     FIG. 14 is a vertical sectional view taken along lines  14 — 14  of FIG.  13 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring firstly to FIGS. 1 and 2, a preferred embodiment of a heat exchanger according to the present invention is generally indicated by reference numeral  10 . Heat exchanger  10  is formed of a plurality of stacked tubular members  12  defining flow passages therethrough. Tubular members  12  are formed of upper and lower plates  14 ,  16  and thus may be referred to as plate pairs. Plates  14 ,  16  have raised peripheral end portions  18 ,  20 . End portions  18 ,  20  have respective inlet or outlet openings  22  (see FIG.  3 ), so that in the stacked tubular members  12 , inlet/outlet openings  22  communicate to define inlet and outlet manifolds  26 ,  28 . Tubular members  12  also have central tubular portions  30  extending between and in communication with inlet and outlet manifolds  26 ,  28 . Inlet and outlet manifolds  26 ,  28  are interchangeable, so that either one could be the inlet, the other being the outlet. In any case, fluid flows from one of the manifolds  26  or  28  through the central portions  30  of tubular members  12  to the other of the manifolds  26 ,  28 . 
     The central portions  30  of tubular members  12  preferably have turbulators or turbulizers  32  located therein. Turbulizers  32  are formed of expanded metal or other material to produce undulating flow passages to increase the heat transfer ability of tubular members  12 . Turbulizers  32  and the internal dimensions of the plate central portions  30  cause tubular members  12  to have a predetermined internal cold flow resistance, which is the resistance to fluid flow through tubular members  12  when the fluid is cold. Heat exchanger  10  is typically used to cool engine or transmission oil, which is very viscous when it is cold. As the oil heats up, its viscosity drops and normal flow occurs through tubular members  12 . 
     As seen best in FIGS. 2 and 3, the raised end portions  18 ,  20  of plates  14 ,  16  cause the central portions  30  of tubular members  12  to be spaced apart to define transverse external flow passages  34  between the tubular members. Corrugated cooling fins  36  are located in external flow passages  34 . Normally air passes through cooling fins  36 , so heat exchanger  10  may be referred to as an oil to air type heat exchanger. 
     Heat exchanger  10  also includes a dimpled bypass channel  38 , and top and bottom end plates or mounting plates  40 ,  42 . Top mounting plate  40  includes inlet and outlet fittings or nipples  44 ,  46  for the flow of fluid into and out of inlet and outlet manifolds  26 ,  28 . Bottom mounting plate  42  has a flat central planar portion  48  that closes off the inlet/outlet openings  22  in the bottom plate  16  of bottom tubular member  12 . 
     As seen best in FIGS. 2 and 3, a half-height cooling fin  50  is located between bypass channel  38  and the top tubular member  12 . Another half-height cooling fin  52  is located between the bottom tubular member  12  and bottom mounting plate  42 . Preferably, half-height fins  50 ,  52  are formed of the same material used to make turbulizers  32  to reduce the number of different components used to make heat exchanger  10 . However, cooling fins  50 , 52  can be made in other configurations as well, such as the same configuration as cooling fins  36 , but of reduced height. 
     As mentioned above, tubular members  12  are formed of face-to-face plates  14 ,  16  and may thus be referred to as plate pairs. Plates  14 ,  16  are identical. Instead of using turbulizers  32  between the central portions  30  of these plate pairs  12 , the central portions  30  could have inwardly disposed mating dimples to create the necessary flow turbulence inside the tubular members. Further, tubular members  12  do not need to be made from plate pairs. They could be made from tubes with appropriately expanded end portions to define manifolds  26 ,  28 . Also, cooling fins  36 ,  50  and  52  could be eliminated if desired. In this case, outwardly disposed dimples could be formed in the tubular member central portions  30  to provide any necessary strengthening or turbulence for the transverse flow of air or other fluid between tubular members  12 . It will be apparent also that other types of mounting plates  40 ,  42  can be used in heat exchanger  10 . The stacked tubular members  12  may be referred to as a core. The core can be any width or height desired, but usually, it is preferable to have the core size as small as possible to achieve a required heat transfer capability. 
     Referring next to FIGS. 4 to  8 , bypass channel or conduit  38  will now be described in detail. Bypass conduit  38  is formed of two face-to-face, identical plates  54 ,  56 , each having a central planar portion  58  and raised peripheral flanges  60 . Peripheral side walls  61  join central planar portion  58  to flanges  60 . Bypass conduit  38 , or at least plates  54 ,  56 , have opposite end portions  62  that define inlet/outlet openings  64 . Central portions  58  and peripheral side walls  61  form a tubular intermediate wall extending between opposite end portions  62  to define a bypass channel  65  extending between the respective inlet/outlet openings  64 . 
     As seen best in FIG. 3, the inlet/outlet openings  64  of bypass conduit  38  communicate with the respective inlet and outlet manifolds  26 ,  28  and the inlet and outlet fittings  44 ,  46 . So, for example, flow entering fitting  44  will pass into manifold  26  to pass through tubular members  12 , but part of the flow will pass through the bypass channel  65  defined by the tubular intermediate wall  66 . 
     The central planar portions  58  of intermediate wall  66  are formed with a plurality of longitudinally spaced-apart, inwardly disposed, mating dimples  68 . Dimples  68  define flow restrictions between dimples  68  and the adjacent peripheral side wall areas  61  of intermediate wall  66 . Dimples  68  extend inwardly and are located in a longitudinal central plane  70  to define longitudinal flow passages  72 ,  74  (see FIG. 8) on either side of the mating dimples  68 . 
     Intermediate wall  66  also includes a plurality of peripheral, inwardly disposed dimples  76  located longitudinally between mating dimples  68  and extending part way into bypass channel  65 , or at least longitudinal flow passages  72 ,  74 , as seen best in FIGS. 7 and 8. 
     Referring in particular to FIG. 7, it will be noted that the cross-sectional shape of longitudinal flow passages  72 ,  74 , as represented by the crosshatched areas, is sort of diamond shaped at the location of peripheral dimples  76 . This crosshatched area represents the minimum cross sectional area of the bypass flow that flows along the length of bypass channel  65 . This is the shape of the bypass flow in cold flow conditions. The height of longitudinal flow passages  72 ,  74  is predetermined. It is equal to twice the height of dimples  68  and is greater than the height of the flow passages inside tubular members  12  that contain turbulizers  32 . The width of longitudinal flow passages  72 ,  74  must be considered from the point of view of an average or effective width in view of its irregular shape. This average or effective width is also predetermined and is preferably less than the height of longitudinal flow passages  72 ,  74 . In fact, the average width of longitudinal flow passages  72 ,  74  is preferably one half or less of the height of these flow passages. 
     In a preferred embodiment of heat exchanger  10 , where the plates that make up bypass conduit  38  and tubular members  12  are formed of brazing clad aluminum having a width of 19 mm (0.75 inches) and a material thickness of 0.71 mm (0.028 inches), the predetermined height of longitudinal flow passages  72 ,  74  is 5.6 mm (0.22 inches) and the predetermined average width of these flow passages is generally about 2.3 mm (0.09 inches). The longitudinal spacing or pitch of dimples  68  is about 3.2 centimeters (0.820 inches). Dimples  68  are as nearly square as possible within given metal deformation limits. The base of these dimples in the example under discussion would be about 7 mm (0.27 inches) square and the crests would be about 4 mm (0.16 inches) square. 
     The height of longitudinal flow passages  72 ,  74  is equal to the height of the combined mating dimples  68 , and the effective width of these flow passages is equal to or less than the average transverse distance between mating dimples  68  and peripheral dimples  76 . While it is preferred to have the height of longitudinal flow passages  72 ,  74  at least twice the effective width of these longitudinal flow passages, there are limits as to how high the aspect ratio of these longitudinal flow passages can be because of the metal formation limits that exist when forming plates  54 ,  56 . 
     Under cold flow conditions, the bypass flow through bypass channel  65  would be as indicated in FIG. 7 and 8. The predetermined height and transverse width of longitudinal flow passages  72 ,  74  are such that the cold flow resistance past the flow restrictions imposed by dimples  68  and  76  is less than the cold flow resistance inside tubular members  12 . As the fluid inside bypass conduit  38  heats up, however, the dimples  68  and  76  cause turbulent flow or changes in flow velocity and direction inside conduit  38  and actually higher flow resistance than what would occur if bypass channel  65  were just a straight through passage. 
     It will be appreciated that by changing the dimensions of longitudinal flow passages  72 , 74 , such as by changing the dimensions of dimples  68  and  76 , the pressure drop of the whole heat exchanger  10  can be adjusted or tuned to suit a desired application. 
     As mentioned above, tubular members  12  can be formed of dimpled plates instead of using turbulizers  32 . In this case, the height of the dimples in tubular members  12  preferably would be less than the height of the dimples in bypass conduit  38 , so that the cold flow resistance in bypass conduit  38  is less than the cold flow resistance in tubular members  12 . Alternatively, the number and the spacing of the dimples in tubular members  12  could be chosen to give higher cold flow resistance in tubular members  12  than is bypass conduit  38 . 
     Although dimples  68  shown in FIGS. 1 to  8  preferably are as square as possible to maximize the hot flow turbulence inside bypass conduit  38 , the dimples can be other shapes, as illustrated in FIGS. 9 to  14 . FIGS. 9 and 10 show a bypass plate  77  having hemispherical dimples  78 . Dimples  78  thus are circular in plan view. FIGS. 11 and 12 show a bypass plate  79  having pyramidal dimples  80  that are triangular in plan view. FIGS. 13 and 14 show a bypass plate  81  having rectangular dimples  82  having the long side of the rectangles in the transverse direction and the short side of the rectangles in the longitudinal direction, but dimples  82  could be orientated differently, such as on an angle, if desired. In fact, such elongate dimples  82  could be considered to be more like ribs than dimples. In the embodiment of FIGS. 13 and 14, the width of bypass plate  81  is about 32 mm (1.26 inches). However, the dimensions of longitudinal flow passages  72 , 74  preferably are about the same as in the embodiment shown in FIGS. 1 to  8 , all other dimensions (except the width of ribs or dimples  82 ) being about the same as the embodiment shown in FIGS. 1 to  8  as well. 
     Having described preferred embodiments of the invention, it will be appreciated that various modifications may be made to the structures described above. For example, in heat exchanger  10 , bypass conduit  38  is shown at the top adjacent to top mounting plate  40 . However, bypass conduit  38  could be located anywhere in the core or stack of plate pairs. Bypass conduit  38  has been described as being generally rectangular in cross section. However, it could have other configurations such as circular. Mating dimples  68 ,  78 ,  80  and  82  could also be located in a horizontal plane rather than a vertical plane. The peripheral dimples would then be located in a plane that is 90 degrees to the plane containing the central mating dimples. 
     It will also be appreciated that the heat exchanger of the present invention can be used in applications other than automotive oil cooling. The heat exchanger of the present invention can be used in any application where some cold flow bypass flow is desired. 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.