Abstract:
A by-pass conduit for a stacked plate heat exchanger. The by-pass conduit comprises first and second plate members that each comprise a substantially planar central portion surrounded by an offset peripheral flange, the peripheral flanges of the first and second plates being sealably joined together and the planar central portions of the first and second plates being in spaced opposition to define a bypass channel. A flow restricting structure provides a fluid restricting barrier in the bypass channel, the flow restricting structure defining a calibrated by-pass passage that regulates the flow of fluid through the bypass channel.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of U.S. patent application Ser. No. 61/043,888 filed Apr. 10, 2008, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Example embodiments described herein relate to heat exchangers, and in particular, to heat exchangers with built-in bypass channels to provide some flow through the heat exchanger under a variety of operating conditions. 
         [0003]    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. 
         [0004]    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. 
         [0005]    Accordingly, an improved bypass structure for a heat exchanger is desired. 
       SUMMARY 
       [0006]    According to one example embodiment, there is provided a heat exchanger comprising a plurality of stacked tubular members defining flow passages therethrough, the tubular members each having 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. 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 flow channel. The opposite end portions of the bypass conduit defining respectively a first fluid opening and a second fluid opening respectively communicating with the inlet manifold and the outlet manifold, the flow channel having a first flow passage portion in direct communication with the fluid inlet and a second flow passage portion in direct communication with the fluid outlet. The first flow passage and second flow passage communicate with each other through a flow restricting calibrated bypass flow passage for a continuous flow of fluid bypassing the stacked tubular members. 
         [0007]    According to another example embodiment is a by-pass conduit for a stacked plate heat exchanger, comprising: first and second plate members that each comprise a substantially planar central portion surrounded by an offset peripheral flange, the peripheral flanges of the first and second plates being sealably joined together and the planar central portions of the first and second plates being in spaced opposition to define a bypass channel, and a flow restricting structure providing a fluid restricting barrier in the bypass channel, the flow restricting structure defining a calibrated by-pass passage that regulates the flow of fluid through the by-pass channel. 
         [0008]    According to another example embodiment is a method of assembling a stacked plate heat exchanger comprising: (a) providing a bypass conduit by forming first and second plate members by roll forming or stamping, the first and second plate members each comprising a substantially planar central portion surrounded by an offset peripheral flange, the first and second plates being roll formed or stamped such that when the peripheral flanges of the first and second plates are sealably joined together the planar central portions are in spaced opposition to form a flow channel and collectively with the peripheral flanges define a flow restricting calibrated bypass flow passage along a portion of the flow channel; providing a plurality of tubular plate pair members each defining flow passages therethrough, the tubular plate pair members each having raised peripheral end portions defining respective inlet and outlet openings; and arranging the bypass conduit and the tubular plate pair members such that the tubular plate pair members are stacked with the respective inlet and outlet openings communicating to define inlet and outlet manifolds, and the bypass conduit is attached to the stacked tubular plate pair members with opposite end portions defining respectively a first fluid opening and a second fluid opening respectively communicating with the inlet manifold and the outlet manifold with the flow channel of the bypass conduit having a first flow passage portion in direct communication with the fluid inlet and a second flow passage portion in direct communication with the fluid outlet, and the first flow passage and second flow passage communicate with each other through the flow restricting calibrated bypass flow passage to permit a continuous flow of fluid bypassing the stacked plate pair tubular members. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Example embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which the same reference numbers are used throughout the drawings to show similar features and components: 
           [0010]      FIG. 1  is an elevational view of an example embodiment of a heat exchanger; 
           [0011]      FIG. 2  is an enlarged, exploded, perspective view of the left side of the heat exchanger shown in  FIG. 1 ; 
           [0012]      FIG. 3  is an enlarged vertical sectional view of the portion of  FIG. 1  indicated by the chain-dotted circle  3 ; 
           [0013]      FIG. 4  is a plan view of the bypass channel of the heat exchanger of  FIG. 1 ; 
           [0014]      FIG. 5  is a partial vertical sectional view taken along lines V-V of  FIG. 4 ; 
           [0015]      FIG. 6  is a vertical sectional view taken along lines VI-VI of  FIG. 4 ; 
           [0016]      FIG. 7  is a vertical sectional view taken along lines VII-VII of  FIG. 4 ; 
           [0017]      FIG. 8  is end view of a tubular member used to provide a calibrated bypass passage through the bypass channel of  FIG. 4 ; 
           [0018]      FIG. 9  is a plan view of the tubular member of  FIG. 8 ; 
           [0019]      FIG. 10  is a plan view of a further embodiment of a bypass channel for a heat exchanger; 
           [0020]      FIG. 11  is a vertical sectional view taken along lines XI-XI of  FIG. 10 ; 
           [0021]      FIG. 12  is a plan view of a further embodiment of a bypass channel for a heat exchanger; 
           [0022]      FIG. 13  is a vertical sectional view taken along lines XIII-XIII of  FIG. 12 ; 
           [0023]      FIG. 14  is a plan view of a further embodiment of a bypass channel for a heat exchanger; 
           [0024]      FIG. 15  is a vertical sectional view taken along lines XV-XV of  FIG. 14 ; 
           [0025]      FIG. 16  is a plan view of a further embodiment of a bypass channel for a heat exchanger; 
           [0026]      FIG. 17  is a vertical sectional view taken along lines XVII-XVII of  FIG. 16 ; 
           [0027]      FIG. 18  is a plan view of a further embodiment of a bypass channel for a heat exchanger; 
           [0028]      FIG. 19  is a partial vertical sectional view taken along lines XIX-XIX of  FIG. 18 ; 
           [0029]      FIG. 20  is a vertical sectional view taken along lines XX-XX of  FIG. 18 ; 
           [0030]      FIG. 21  is a plan view of a separator used to provide a calibrated bypass passage through the bypass channel of  FIG. 18 ; 
           [0031]      FIG. 22  is a diagrammatic view of another example embodiment of a heat exchanger incorporating a bypass channel; 
           [0032]      FIG. 23  is a diagrammatic view of another example embodiment of a heat exchanger incorporating a bypass channel; 
           [0033]      FIG. 24  is a diagrammatic view of another example embodiment of a heat exchanger incorporating a bypass channel; and 
           [0034]      FIG. 25  is a diagrammatic view of another example embodiment of a heat exchanger incorporating a bypass channel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Referring firstly to  FIGS. 1 and 2 , a heat exchanger according to example embodiments of 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. In the illustrated embodiment, 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 . 
         [0036]    The central portions  30  of tubular members  12  may 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 . 
         [0037]    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. 
         [0038]    Heat exchanger  10  also includes an elongate tubular bypass conduit  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 . 
         [0039]    As seen best in  FIGS. 2 and 3 , in an example embodiment a half-height cooling fin  50  is located between bypass conduit  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 . Half-height fins  50 ,  52  may be 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. 
         [0040]    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  200 . The core  200  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. 
         [0041]    Referring next to  FIGS. 4 to 9 , an example embodiment of bypass conduit  38  will now be described in detail. In the embodiment of  FIGS. 4 to 9 , bypass conduit  38  is formed of two face-to-face, identical plates  54 ,  56 , each having a central planar portion  58  and raised or offset 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 an internal bypass channel  65  extending between the respective inlet/outlet openings  64 . 
         [0042]    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 . 
         [0043]    Referring again to  FIGS. 4-7 , the central planar portions  58  of intermediate wall  66  are interrupted at a location between the inlet and outlet openings  64  to provide a flow restricting region  100  that defines a calibrated bypass passage  102  in the bypass channel  65 . In particular, in the illustrated embodiment the intermediate wall  66  tapers inwardly at flow restricting region  100  to provide a smaller cross-sectional flow area than the remainder of the bypass channel  65 . Thus, the bypass channel  65  has first and second flow passages  104  and  106  that communicate with each other solely through intermediate calibrated bypass passage  102 . In an example embodiment, the cross-sectional flow areas of the first and second flow passages  104  and  106  are substantially equal, with the flow resistance of the calibrated bypass passage  102  being substantially greater than the rest of the bypass channel  65 . Thus the bypass passage  102  defines the minimum cross sectional area of the bypass flow that flows along the length of bypass channel  65 . 
         [0044]    In an example embodiment, the plates that make up the bypass conduit  58  and tubular members  12  are formed of brazing clad aluminum. In order to provide a bypass passage  102  that is relatively tolerant to manufacturing and brazing variations that can occur when the plates  54 ,  56  are formed and then subsequently brazed together, a calibrated tubular structure  108 , as shown in  FIGS. 5 ,  6 ,  8  and  9  is secured between the plates  54 ,  58  in the flow restricting region  100  to define the calibrated bypass passage. In one example embodiment the calibrated tubular structure  108  is cylindrical with a length L, an inside diameter DI and an outside diameter DO. In at least some embodiments, the calibrated tubular structure  108  is secured in place in the flow restricting region  100  through brazing to the braze clad plates  54 ,  56 , but is formed from non-braze clad steel or aluminum such that the inside diameter DI is substantially unaffected by the assembly and brazing process used to construct the flow conduit  58 . 
         [0045]    The intermediate wall  66  provided by plates  54 ,  56  is shaped in the flow restricting region  100  to provide a seat  116  for the calibrated tubular structure  108 . As shown in  FIG. 5 , the central planar plate portions  58  of plates  54 ,  56 , each have portions  112  that taper inward both height-wise and width-wise in region  100  to reduce the size of the flow channel defined between plates  54 ,  56  to the outer diameter DO of the tubular structure  108 , and thereby define the seat  116 . Inward bumps or ridges  114  may be formed on the plates  54 ,  56  at opposite ends of the seat  116  to provide shoulders for positioning and retaining the tubular structure  108  in place during and subsequent to assembly of the fluid conduit  38 . In at least one example embodiment, the inner ridges  114  are dimensioned to ensure that although they act against longitudinal movement of the tubular structure  108 , they do not block any flow through the tubular structure  108 . 
         [0046]    As seen in  FIG. 6 , it will be appreciated that the walls of seat  116  defined by plates  54  and  56  may include areas  110  that are spaced apart from outer surface of the tubular structure  108 . In at least some example embodiments, such areas  110  are filled with a fillet of braze material during the brazing process such that a fluid-tight seal is provided substantially around the entire outer surface of the tubular structure  108  and the only flow path between the first and second flow passages  104 ,  106  is through the interior of the calibrated tubular structure  108 . 
         [0047]    By using a tubular insert structure  108  to define the calibrated bypass passage  102  the length L and diameter DI of the bypass passage  102  can be tightly controlled, providing relative immunity against manufacturing variations in plates  54 ,  56  and the brazing process that might otherwise affect the predictability of the flow rate through the calibrated bypass passage  102 . The tubular insert structure  108  and calibrated bypass passage  102  could have a non-circular cross-sectional shape—for example elliptical, rectangular or square shapes, among other things could be used. Furthermore, in at least some applications the tubular insert structure  108  may be omitted from the bypass flow conduit  38  such that the calibrated bypass passage  102  is defined soley by the inner surfaces of the plates  54 ,  56  at the flow restricting region  100 ; in such an embodiment, the bypass flow conduit  38  could for example be similar to what is shown  FIG. 4-7 , but without the tubular insert  108 . In some example embodiments the plates  54 ,  56  are stamped or roll-formed to provide the configurations described herein. 
         [0048]    In example embodiments, the relative dimensions of the calibrated bypass passage  102  to the remainder of the flow channel  65  through the bypass conduit  38  is such that the total amount of fluid flow through the entire bypass flow channel  65  is substantially determined by the dimensions of the calibrated bypass passage  102  rather than the dimensions of the remainder of the bypass flow channel  65 . The length L and diameter DI of the calibrated passage bypass passage  102  are selected to allow a desired amount of fluid to bypass the main heat exchanger core area  200  during cold flow conditions without substantially reducing heat exchanger performance during normal operating or hot flow conditions. By way of non-limiting example, in some configurations the length L of the calibrated passage bypass passage  102  is substantially in the range of 5-8 mm and the diameter DI substantially in the range of 2-5 mm. 
         [0049]    Some example considerations that go into determining the size of the length L and diameter DI of the calibrated bypass flow passage  102  in at least some example embodiments are as follows. It will be appreciated that the flow through the calibrated bypass flow passage  102  may reduce the heat transfer efficiency in the heat exchanger, because less fluid is going through the heat exchange passages. The calibrated bypass flow passage  102  is dimensioned so that this reduction in heat transfer does not exceed a predetermined limit under normal operating conditions. By way of non-limiting examples, in some applications of an engine oil cooler this predetermined limit is as low as 5% of the heat transfer rate of the heat exchanger without an orifice; in some applications of a transmission oil cooler, the predetermined limit is as low as 10% of the heat transfer rate of the heat exchanger without a bypass channel. In some applications, the predetermined limit could for example be as high as 25% of the heat transfer rate of the heat exchanger without a bypass channel. Alternatively, it may be possible to increase the efficiency of the heat exchanger or increase the size or number of the heat exchanger plates or tubes and fins used to make the heat exchange passages in order to make up for the reduction in heat transfer caused by the bypass flow. 
         [0050]    The calibrated bypass flow passage  102  can also be dimensioned so as to reduce the fluid pressure drop in the heat exchanger by a predetermined minimum amount compared to the same heat exchanger with no bypass channel. This predetermined minimum amount may by way of example be between 10 and 30% under normal steady state heat exchanger operating conditions. In at least some engine oil applications, this predetermined minimum amount is could be about 10%, but it could be as high as 20% when the oil is hot. In the case of transmission oil or fluid applications, the predetermined minimum amount could for example be about 15%, but it could be as high as 30% under hot operating temperature conditions. 
         [0051]    The calibrated bypass flow passage  102  can also be dimensioned so that if engine or transmission oil is the fluid passing through the heat exchanger, the flow rate of the oil through the heat exchanger is maintained above a predetermined lower limit at all operating temperatures, including cold start up conditions. By way of example, for some engine oil applications this predetermined lower limit could be about 8 liters (2 U.S. gallons) per minute. For some transmission fluid applications, the predetermined lower limit could be about 2 liters (0.5 U.S. gallons) per minute. By way of example, the calibrated bypass flow passage  102  can also be dimensioned so that the heat exchanger outlet pressure is at least 20 psi (3 kPa) approximately 30 seconds after the engine starts in the case of engine oil. By way of example, in the case of some transmission oil or fluid applications, the flow rate through the heat exchanger should be at least 2 liters per minute (0.5 U.S. gallons) per minute approximately 10 minutes from cold engine start. 
         [0052]    In at least some example embodiments, inwardly directed ribs or dimples are formed on the central planar portions  58  of the plates  54 ,  56  of the bypass flow conduit to provide strength to the conduit. In this regard,  FIGS. 10 and 11  show a further embodiment of a bypass conduit  38 ′ which can be used in heat exchanger  10  is place of bypass conduit  38 . The bypass conduit  38 ′ is similar in construction and operation to conduit  38  except for the differences that will be apparent from the Figures and the following description. In conduit  38 ′ each of the plates  54 ,  56  has elongate inwardly extending ribs  130  formed longitudinally along the central planar portion  58  thereof. Each of the ribs  130  extends from a location spaced apart from a respective inlet or outlet opening  64  to a location that is spaced apart from the restricted flow region  100 . As shown in  FIG. 11 , the ribs  130  from the opposed plates  54 ,  56  mate, thereby dividing the bypass flow channel  65  longitudinally into two portions in the first flow passage  104  and the second flow passage  106 . 
         [0053]    Dimples can be used in bypass fluid conduit  38 ′ instead of or in addition to ribs  130 , as illustrated in  FIGS. 12 to 17 .  FIGS. 12 and 13  show a bypass plate  77  having hemispherical dimples  78 . Dimples  78  thus are circular in plan view.  FIGS. 14 and 15  show a bypass plate  79  having pyramidal dimples  80  that are triangular in plan view.  FIGS. 16 and 17  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. 12 to 17 , it will be noted that the flow restricting region  100  of the conduits  38 ′ can be located at an area other than the middle point between the inlet and outlet openings  64 . 
         [0054]    In at least some example embodiments, the calibrated bypass flow passage  102  can be defined by a structure other than a tubular insert  108  or a narrowing of the plates  54 ,  56  at the flow restricting regions  100 . In this regard,  FIGS. 19-20  illustrate a further embodiment of a bypass conduit  38 ″ which can be used in heat exchanger  10  is place of bypass conduit  38  or  38 ′. The bypass conduit  38 ″ is similar in construction and operation to conduits  38 ,  38 ″ except for the differences that will be apparent from the Figures and the following description. In the bypass conduit  38 ″, the planar central portions  58  do no taper inwards in the area of flow restricting region  100 , but rather a U-shaped flow restricting plate insert  160  is located in the flow channel  65  at flow restricting region  100 . The plate insert  160  includes central planar plate portion  162  from which spaced apart, opposed legs  164 ,  166  extend. Central plate portion  162  has a central opening  168  formed through it that functions as the calibrated bypass passage  102  for the bypass channel  65 . In an example embodiment, the U-shaped flow restricting plate insert  160  is formed from non-braze clad aluminum or steel and is secured in place between the braze-clad plates  54 ,  56  through brazing of the legs  166 ,  164  to the plates  54 ,  56 . As shown in  FIGS. 20 and 21 , the central planar plate portion can include side flanges  170  to conform to the interior walls of plates  54 ,  56 . As the calibrated bypass passage  102  formed though the central plate  162  will have a shorter length than the length L of a tubular insert  108 , the diameter of the calibrated bypass passage  102  would have to be smaller than that of a tubular insert  108  to achieve the same degree of flow restriction. Plate insert  160  could take many configurations other than what is shown. Additionally, the ribs or dimples shown in any of  FIGS. 10-17  could also be used in the bypass conduit  38 ″. 
         [0055]    It will be appreciated that various modifications may be made to the structures described above. For example, in heat exchanger  10 , the bypass conduit is shown at the top adjacent to top mounting plate  40 . However, the bypass conduit could be located anywhere in the core or stack of plate pairs. Bypass conduit  38 ,  38 ′,  38 ″ has been described as being generally rectangular in cross section. However, it could have other configurations such as circular. 
         [0056]      FIGS. 22-25  illustrate diagrammatically examples of different possible configurations for heat exchanger  10 . The heat exchangers in  FIGS. 22-25  are similar in construction and operation to the heat exchanger of  FIG. 1 , except that the locations of one or more of the bypass fluid conduit  38  (or fluid conduit  38 ′ or  38 ″ and the fluid inlet and outlet  44 ,  46  change from the structure that shown in  FIG. 1 . 
         [0057]    In the embodiment of  FIG. 22 , the bypass fluid conduit  38  is located at the bottom end of the heat exchanger core  200  that is remote from the inlet and outlet fittings  44 ,  46 , rather than at the same end with the inlet and outlet fittings  44 ,  46 . The inlet and outlet openings  64  (see  FIG. 4 ) in the top plate  54  of the bypass fluid conduit  38  respectively communicate with the inlet and out manifolds  26  and  28  of the heat exchanger core  12 . The inlet and outlet openings  64  in the bottom plate  56  of the bypass fluid conduit  38  are sealed shut by bottom plate  42 . In the embodiment of  FIG. 22 , fluid entering the inlet manifold  26  can bypass the heat exchanger core  200  and enter the outlet manifold  28  by passing through the by-pass conduit  38  in quantities regulated by the bypass flow restricting region  100 . 
         [0058]    In the embodiment of  FIG. 23 , the bypass fluid conduit  38  is located at the top end of the heat exchanger core  200 , but the inlet and outlet fittings  44 ,  46  are located at opposite end corners. The inlet and outlet openings  64  in the bottom plate  56  of the bypass fluid conduit  38  respectively communicate with the inlet and out manifolds  26  and  28  of the heat exchanger core  12 . The outlet opening  64  in the top plate  54  of the bypass fluid conduit  38  is absent or sealed shut. In the embodiment of  FIG. 23 , fluid entering the inlet fitting  44  can bypass the heat exchanger core  200  and enter the outlet manifold  28  by passing through the by-pass conduit  38  in quantities regulated by the bypass flow restricting region  100 . The configuration of  FIG. 23  could also be modified so the bypass conduit  38  is on the opposite end of the core  200  (i.e. the same end as the outlet fitting  46 ). 
         [0059]    In the embodiment of  FIG. 24 , the bypass fluid conduit  38  is located at the top end of the heat exchanger core  200 , but the inlet and outlet fittings  44 ,  46  are located closer to the center of the heat exchanger such that the by-pass conduit  38  functions not only as a by-pass conduit but also as a cross over conduit. The inlet and outlet openings  64  in the bottom plate  56  of the bypass fluid conduit  38  respectively communicate with the inlet and out manifolds  26  and  28  of the heat exchanger core  12 . The inlet and outlet openings  64  in the top plate  54  of the bypass fluid conduit  38  communicate respectively with the inlet and outlet fittings  44 ,  46 , but are located closer together than the openings on the bottom plate  56 . In the embodiment of  FIG. 24 , the primary hot flow path for fluid entering the inlet fitting  44  is through the first passage  104  of conduit  38  and into the inlet manifold  26 , and then through heat exchanger core  200  and into the outlet manifold  28 . From outlet manifold  28 , the fluid flows into the second passage  106  defined by conduit  38  and then out through outlet fitting  46 . This, the low flow resistance first and second passages  104  of the bypass conduit  38  in  FIG. 24  function as primary hot-flow paths and in particular as a inlet crossover path and an outlet crossover path, respectively. A calibrated by-pass passage between the inlet (first) passage  104  and the outlet (second) passage  106  is provided through the bypass flow restricting region  100  that is located between the conduit  38  connections to inlet and outlet fittings  44 ,  46 . In the embodiment of  FIG. 24 , fluid entering the inlet fitting  44  can bypass the heat exchanger core  200  (and conduit passages  105 ,  106 ) and enter the outlet fitting  46  by passing through the bypass flow restricting region  100 . 
         [0060]    In the embodiment of  FIG. 25 , the inlet and outlet fittings  44  and  46  are each located at the same side of the heat exchanger core  200 . A crossover conduit  202  provides a flow path between the inlet fitting  44  and inlet manifold  26 . The by-pass conduit  38  provides a calibrated by-pass path through restricting region  100  between inlet manifold  26  and outlet manifold  28 . The crossover conduit  202  can alternatively be located at the opposite end of the core  200 . 
         [0061]    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. 
         [0062]    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.