Abstract:
Provided are a heat exchanger having a novel structure and efficiently cooling a heat generating body, and a method of manufacturing the heat exchanger. A heat exchanger has flow paths formed by being closed by an upper plate and a lower plate which have rectilinearly formed upstanding fins parallelly arranged at specific intervals, and gaps extend between adjacent fins in the top-bottom direction along the direction in which the fins extend. Either of or both the upper plate and the lower plate are provided with projections arranged in the longitudinal direction of the flow path and projecting inward of the flow path.

Description:
[0001]    This is a national phase application filed under 35 U.S.C. 371 of PCT/JP2009/062701 filed on Jul. 14, 2009, which claims the benefit of priority from the prior Japanese Patent Application No. 2008-190946 filed on Jul. 24, 2008, the entire contents of all of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a heat exchanger provided with passages defined by a plurality of straight fins arranged in parallel, the heat exchanger being configured to allow a refrigerant or cooling medium to pass through the passages to thereby dissipate heat from a heating element. Particularly, the invention relates to a heat exchanger in which passages for allowing a refrigerant to pass are formed to enhance heat dissipation effect and a method of manufacturing the heat exchanger. 
       BACKGROUND OF THE INVENTION 
       [0003]    Hybrid electric vehicles or the like incorporate a semiconductor device in an inverter to drive a motor, and a water-cooling heat exchanger is adopted for cooling the semiconductor device. With respect to the inverter mounting the semiconductor device, higher output power has been desired while a reduction in size and weight also has been demanded increasingly. Accordingly, a demand for a heat exchanger excellent in a heat dissipation effect has been increased. Patent Literature I described below discloses a conventional heat exchanger having improved cooling performance.  FIG. 16  is a sectional view of a heat exchanger of Patent Literature 1 in a plan view. 
         [0004]    A heat exchanger  100  includes a case  101  provided with a supply port  102  and a discharge port  103 . In the case  101 , passages (flow paths) are formed to allow a refrigerant to pass from the supply port  102  to the discharge port  103 . In this heat exchanger  100 , the passages are defined by a plurality of fins  111  and the passages are divided into three in the linear direction; first, second, and third fin groups  201 ,  202 , and  203 . Each of the fin groups  201  to  203  includes a plurality of the fins  111  arranged in parallel with the lateral direction. The fins  111  of each fin group  201  to  203  are arranged in alignment with those of the adjacent fin groups to form a plurality of straight passages. The straight flow passages are however interrupted in between the fin groups  201 ,  202 , and  203  and merging sections  105  and  106  are formed there. 
         [0005]    Further, the heat exchanger  100  is provided with separating fins  112  placed between the laterally extending fins  111  to form a wide passage  107  wider than the passages defined between the fins  111 . In the third fin group  203 , two adjacent separating fins  112  are connected to close one end of the passage  107 . Then, in this heat exchanger  100 , semiconductor devices serving as heating elements are placed respectively in nine sections partitioned by the merging sections  105  and  106  and the separated passage  107  defined by the separating fins  112 . To be specific, in the heat exchanger  100 , the refrigerant taken into the exchanger  100  from the supply port  102  passes through the linear passages formed between the fins  111 . Multiple refrigerant flows join together at the merging sections  105  and  106  to equalize flow distribution and then diverge into downstream passages. 
       Patent Literature 
       [0006]    Patent Literature 1: JP2007-335588A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    When the passages defined by the fins are straight as in the heat exchanger  100 , the refrigerant is apt to flow in laminar flow. Therefore, while the refrigerant flows fast in the central portion of each passage, the flow is slow in boundary layers or areas where the refrigerant contacts with the fins  111 . As a result, the heat of each heating element transferred to the fins is hard to be dissipated, interfering enhancement of the cooling performance. With regard to this point, an effective way to efficiently dissipate the heat from the fins by the refrigerant is to break the boundary layers by disturbing the flow of the refrigerant. However, traversing passages like the merging sections  105  and  106  in the heat exchanger  100  are not enough to achieve the above effect. 
         [0008]    In recent years, a semiconductor device tends to have larger heat generating density because of its reduced size. This leads to a demand for improvement of the cooling performance of the heat exchanger to be used in an inverter or the like. In response to that, the heat exchanger in which the fins are arranged in an offset pattern has been proposed. However, the heat exchanger having such offset fin arrangement requires complicated working, leading to an increase in manufacturing cost. Especially, when the conventional fin member is formed by casting or other methods, a high processing cost is needed, which results in a high cost of the heat exchanger itself. Further, such fin member is hard to finely machine and thus the improvement of cooling performance could not be achieved. 
         [0009]    The present invention has been made to solve the above problems and has a purpose to provide a heat exchanger having a novel structure capable of efficiently cooling a heating element and a manufacturing method of the heat exchanger. 
       Solution to Problem 
       [0010]    According to one aspect of the present invention, there is provided a heat exchanger having a plurality of upstanding fins formed linearly and arranged in parallel with each other at predetermined intervals, and an upper plate and a lower plate placed top and bottom in an upstanding direction of the fins to enclose spaces between the adjacent fins to provide a plurality of passages defined by the enclosed spaces, wherein at least one of the upper and lower plates includes a plurality of protrusions arranged in a longitudinal direction of each passage to protrude therein, and the protrusions formed in the adjacent passages are arranged in a staggered pattern in a direction perpendicular to a flat surface of the passages. 
         [0011]    Further, in the above heat exchanger, it is preferable that the heat exchanger has: a fin member including the fins integrally formed on a base constituting either one of the upper and lower plates; and a cover plate constituting the other one of the upper and lower plates which is connected to the fins in an opposite side from the base, wherein the protrusions are formed on either the base or the cover plate. 
         [0012]    In the above heat exchanger, preferably, the fin member is formed by extrusion-molding. 
         [0013]    In the above heat exchanger, preferably, the protrusions are formed by press working. 
         [0014]    In the above heat exchanger, preferably, ones of the protrusions adjacently arranged in a longitudinal direction of each passage are placed at such intervals as to prevent cooling performance to be generated between the protrusions from falling below a predetermined reference value. 
         [0015]    According to another aspect of the invention, there is provided a heat exchanger including a plurality of upstanding fins formed linearly and arranged in parallel with each other at predetermined intervals and an upper plate and a lower plate placed top and bottom in an upstanding direction of the fins to enclose spaces between the adjacent fins to provide a plurality of passages defined by the enclosed spaces, wherein one of the upper and lower plates includes a plurality of protrusions protruding into the passages in a longitudinal direction thereof; the heat exchanger includes: a fin member including the fins integrally formed on a base constituting either one of the upper and lower plates; and a cover plate constituting the other one of the upper and lower plates which is connected to the fins in an opposite side from the base, the protrusions being formed on either the base or the cover plate; the fin member is formed by extrusion-molding; the protrusions are formed by press-fitting a punch in the base or the cover plate on an opposite side from a passage surface to extrude a material toward the passage surface side; and when the protrusions are to be formed, a plate-shaped holding member is inserted in the spaces between the adjacent fins to hold the fins. 
         [0016]    According to another aspect of the invention, there is provided a method for manufacturing a heat exchanger including a plurality of upstanding fins formed linearly in parallel with having predetermined spaces and an upper plate and a lower plate placed top and bottom in an upstanding direction of the fins to enclose spaces between the adjacent fins, wherein one of the upper and lower plates includes a plurality of protrusions protruding into the passages in a longitudinal direction thereof; the heat exchanger includes: a fin member including the fins integrally formed on a base constituting either one of the upper and lower plates; and a cover plate constituting the other one of the upper and lower plates which is connected to the fins in an opposite side from the base, the protrusions being formed on either the base or the cover plate; the fin member is formed by extrusion-molding; the fin member is formed as an intermediate fin member having raised portions each continuous in the extruding direction in each space between the adjacent fins; and the protrusions are formed by inserting pressing plates separately formed in the extruding direction into the spaces to squash the raised portions except separating portions to form the protrusions. 
       Advantageous Effects of Invention 
       [0017]    According to a heat exchanger of the invention, a refrigerant flowing through passages is disturbed its flow by protrusions so that boundary layers contacting with fins are broken, and thereby the refrigerant deriving heat from the fins smoothly flows downstream without causing stagnation. Accordingly, the cooling performance is enhanced. Therefore, even when the heat generating density has been increased due to a small-sized heating element, the heating element can be cooled compared to the conventional one because the cooling performance has been improved. Further, the heat exchanger of the invention is simply configured in a manner that passages defined by straight fins are provided with protrusions, simplifying its structure and working and leading to cost reduction in manufacturing operation. In particular, the heat exchanger in the invention is manufactured by applying a fin member formed by extrusion-molding and a base and a cover plate formed with protrusions by pressing, so that mass production of the heat exchanger is achieved, capable of supplying the heat exchanger at low cost. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is a perspective view of a heat exchanger according to an embodiment; 
           [0019]      FIG. 2  is a perspective view of the heat exchanger from which a holding frame is removed; 
           [0020]      FIG. 3  is a perspective view of a fin member of the heat exchanger; 
           [0021]      FIG. 4  is a diagram showing a flow of a refrigerant flowing inside a passage of the heat exchanger; 
           [0022]      FIG. 5  is a graph showing a result of a cooling performance test conducted by flowing the refrigerant inside the passage of the heat exchanger; 
           [0023]      FIG. 6 . is a perspective view of the heat exchanger in use state; 
           [0024]      FIG. 7  is a conceptual view showing one step of a working process to form the fin member for the heat exchanger; 
           [0025]      FIG. 8  is a sectional view of a press device for forming protrusions; 
           [0026]      FIG. 9  is a perspective view of a heat exchanger from which a holding frame is removed in another embodiment; 
           [0027]      FIG. 10  is a simplified diagram showing a working process of forming protrusions in the fin member shown in  FIG. 9 ; 
           [0028]      FIG. 11  is a plan view showing one example of arrangement of the protrusions in the passages; 
           [0029]      FIG. 12  is a sectional view of a press device for forming protrusions; 
           [0030]      FIG. 13  is a perspective view showing a method of forming the protrusions by pressing; 
           [0031]      FIG. 14  is a sectional view of the fin member immediately after the extrusion-molding before the protrusions are to be formed as shown in  FIG. 13 ; 
           [0032]      FIG. 15  is a perspective view of the fin member formed with the protrusions formed by the method shown in  FIG. 13 ; and 
           [0033]      FIG. 16  is a planar sectional view of a conventional heat exchanger. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0034]    A detailed description of a preferred embodiment of a heat exchanger and a method of manufacturing the same embodying the present invention will now be given referring to the accompanying drawings.  FIG. 1  is a perspective view showing a heat exchanger of the present embodiment. 
         [0035]    A heat exchanger  1  includes a plurality of fins  11  arranged in a main body  2  formed in a rectangular tubular shape. The main body  2  has an inlet-side opening  21  and an outlet-side opening which open at both ends to form a plurality of passages  3 . In the main body  2  of the heat exchanger  1 , a refrigerant is allowed to flow in a direction indicated by an arrow Q in the figure, thus the passages  3  extend through from the inlet-side opening  21  to the outlet-side opening. 
         [0036]    In the heat exchanger  1  shown in  FIG. 1 , the inlet-side opening  21  and the outlet-side opening largely open on either side of the main body  2 . During use, on the other hand, the inlet-side opening  21  and the outlet-side opening are closed and connected respectively to a refrigerant supply pipe or a refrigerant discharge pipe, both of which are not shown. The refrigerant supply pipe is connected to a supply pump for pumping a refrigerant at a constant pressure to the heat exchanger  1  and the refrigerant discharge pipe is connected to a tank for collecting the refrigerant discharged from the heat exchanger  1 . 
         [0037]    The heat exchanger  1  includes a holding frame  13  having a U-shaped cross section and an upper opening and a cover plate  14  fitted on that opening, forming the tubular-shaped main body  2 . A fin member  10  is incorporated in the main body  2  to form the plurality of passages  3 . Herein,  FIG. 2  is a perspective view of the heat exchanger  1  of  FIG. 1  from which the holding frame  13  is removed and  FIG. 3  is a perspective view of the fin member  10  from which the cover plate  14  is removed. 
         [0038]    The fin member  10  is integrally formed with the plurality of fins  11  protruding from a base  12 . The base  12  is a rectangular flat plate and formed with the fins  11  upstanding therefrom in a perpendicular direction to the base  12 . The fins  11  have the same height with each other and the same length with the base  12  in a longitudinal direction. The adjacent fins  11  are arranged in parallel with one another. The thus configured fin member  10  is inserted in the holding frame  13  without backlash and the cover plate  14  is placed on the holding frame  13  so that the plate  14  abuts on tips of the fins  11 . The heat exchanger  1  is integrally configured by welding the fin member  10  mounted in the holding frame  13 , the holding frame  13 , and the cover plate  14 . 
         [0039]    In the heat exchanger  1 , spaces between the adjacent fins  11  are enclosed by the base  12  as a lower plate and the cover plate  14  as an upper plate to define the passages  3  arranged in parallel. The fins  11  at both end sides of the fin member  10  form spaces from the upstanding wall plates of the flame  13 , the spaces being enclosed by the base  12  and the cover plate  14  to form the passages  3 . 
         [0040]    When the refrigerant flows through the inlet-side opening  21  to the main body  2  in the direction Q in  FIG. 1 , the refrigerant branches off to the passages  3  partitioned by the fins  11 . In the heat exchanger  1  of the present embodiment, the passages  3  defined by the fins  11  are straight paths and therefore the refrigerant tends to flow in laminar flow as same as the conventional technique, resulting in poor cooling performance. Accordingly, the heat exchanger  1  of the embodiment is provided with a configuration to disturb the refrigerant flow. Specifically, the cover plate  14  defining the passages  3  is formed with protrusions  23  serving as obstacles to the refrigerant flowing through the passages  3 . 
         [0041]    The protrusions  23  are provided on an opposite side of recesses  25  formed on one side of the cover plate  14  in the thickness direction as shown in  FIG. 2 , each protrusion  23  being spaced at a predetermined interval from each other in the vertical and lateral directions. To be more concrete, the protrusions  23  are provided to be insertable in the spaces between the adjacent fins  11  so that the protrusions are present at fixed intervals in each passage  3  when the cover plate  14  is set to assemble the heat exchanger  1  as shown in  FIG. 1 . 
         [0042]      FIG. 4  is a diagram showing the flow of the refrigerant inside the passage  3 . Since the passage  3  defined by the fins  11  is linearly formed, the flow of the refrigerant could be a laminar flow, leading to the same problem with the conventional technique if the passage  3  is left as it is. In the present embodiment, therefore, the flow of the refrigerant is disturbed by the existence of the protrusions  23  to break a boundary layer contacting with the fins  11  generated in the laminar flow, thereby efficiently dissipating heat of the fins  11 . 
         [0043]    Further, especially in the heat exchanger  1  of the present embodiment, the protrusions  23  are placed at the specific intervals inside each passage  3  to maintain the cooling performance.  FIG. 5  is a graph showing a result of a cooling performance test conducted by flowing the refrigerant in the passage  3 . The horizontal axis of the graph indicates specific positions taken out from an arbitrary part of the passage  3  and the vertical axis indicates the cooling performance (heat transfer coefficient). Passage points p 1 , p 2 , and p 3  in the horizontal axis represent the positions in which the protrusions  23  are formed, and the refrigerant flows in the direction from the point p 1  to the point p 3 . 
         [0044]    The graph of  FIG. 5  shows that the cooling performance of the refrigerant flowing through the passage  3  is not constant but changes like a waveform. In other words, the heat transfer coefficient differs from position to position in the passage. Especially, in the graph k, the cooling performance goes up toward each of the points p 1 , p 2 , and p 3  representing the existence of the protrusions  23  and reaches at peak immediately after each of the points p 1 , p 2 , and p 3  and then the graph gradually goes down. This is because the flow of the refrigerant is disturbed by the protrusions  23  and the refrigerant flows to efficiently remove the heat from the fins  11 . On the other hand, the graph goes down thereafter. This is conceivably because the flow of the refrigerant returns to the laminar flow as it comes away from the protrusions  23 , so that the flow of the boundary layer contacting with the fins  11  tends to be stagnant. 
         [0045]    In response to this, in the present embodiment, the cooling performance required to dissipate heat of the heating element is set to be a reference value “s” and the position of each protrusion  23  is determined in a manner that the heat transfer coefficient would not fall below the reference value “s”. Specifically, the distance between the protrusions  23  arranged in the longitudinal direction of the passage  3  is determined so that the heat transfer coefficient indicated with the graph k goes up just before the graph falls below the reference value “s”. The distance between the protrusions  23  differs depending on a size of the passage  3 , a flow rate of the refrigerant to be supplied, the height of the protrusions  23 , a heat generating amount of the heating elements, and others. Further, since the protrusions  23  also serve to interfere with the flow of the refrigerant to cause pressure increase, the height of each protrusion  23  in the present embodiment is determined to be one third of the passage  3 , taking into account of the capability of the supply pump and others. 
         [0046]    In the heat exchanger  1  in use, as shown in  FIG. 6  for example, a heat spreader  6  for thermal diffusion is placed on the cover plate  14  and semiconductor devices  7  serving as heating elements are orderly arranged on the heat spreader  6 . When the semiconductor devices  7  used for an inverter or the like generate heat, the heat is transferred to the heat spreader  6  and diffused to be further transferred through the main body  2  to the fins  11 . In the main body  2 , the refrigerant is supplied from the inlet-side opening  21  and flows toward the outlet-side opening in the opposite side of the main body  2 . As a result, the heat transferred to the fins  11  is taken away by the refrigerant flowing in contact with the fins  11 , so that heat dissipation is carried out. 
         [0047]    The refrigerant flowing in each passage  3  is disturbed in flow by the protrusions  23  to break the boundary layers contacting with the fins  11 . Since the protrusions  23  are arranged with predetermined intervals, the refrigerant is caused to flow in each passage  3  while being constantly agitated. Thus, the refrigerant having removed the heat efficiently flows downstream. Especially, the cooling performance is maintained equal to or higher than the reference value “s” in  FIG. 5 . 
         [0048]    Even when the semiconductor devices are downsized, having a larger heat generating density, the heat exchanger  1  with extremely enhanced cooling performance compared to the conventional ones can cool such semiconductor devices. Further, the heat exchanger  1  has such a simple configuration of only providing the protrusions  23  in each passage  3  defined by the fins  11  that less number of components are required, thereby enabling cost reduction. 
         [0049]    The present embodiment realizes reducing the working cost for manufacturing the heat exchanger  1  having the excellent cooling performance, and thereby providing the heat exchanger  1  at low cost. The manufacturing method of such heat exchanger  1  is now explained. 
         [0050]    First, the fin member  10  for the heat exchanger  1  is formed by extrusion-molding. A material used herein for the fin member  10  is aluminum having a good heat transfer coefficient. The molten material is extruded from a molding die for integrally forming the plurality of fins  11  and the base  12 , and a long-fin member having a several meters length is formed, for example.  FIG. 7  is a conceptual view of a part of a working process to form the fin member  10 . 
         [0051]    An extruded long-fin member  10 L is directly transferred to and cut by a press device shown in the figure after the extrusion-molding. The long-fin member  10 L is integrally formed with a long base  12 L and long fins  11 L vertically upstanding from the long base  12 L. Thereafter, the long-fin member  10 L is transferred in the extruding direction F as shown in the figure. The long-fin member  10 L just extruded remains soft because a material forming the long-fin member  10 L is heated to some extent. Such long-fin member  10 L is further forwarded to and cut by a press device  50  for cutting. 
         [0052]    The cutting press device  50  includes a not-shown lower die for supporting a bottom part of the long base  12 L and a plate-shaped upper die  51  placed perpendicularly to the extrusion direction F to be movable vertically downward with respect to the lower die. The upper die  51  is a flat plate having a uniform thickness and a flat bottom end surface. Further, a pair of fin holding jigs  53  is provided on both sides of the upper die  51  to prevent the fins  11  from buckling and falling down due to the pressing force of the upper die  51 . Each of the fin holding jigs  53  is formed with a plurality of flat plate-shaped supporting teeth  55  to be inserted individually in the spaces between the adjacent fins  11 . 
         [0053]    The conveyance of the extruded long-fin member  10 L is once. Then, the supporting teeth  55  of the fin holding jigs  53  are individually inserted in the spaces between the adjacent long fins  11 L of the long-fin member  10 L to support every single long fin  11 L from both sides. Subsequently, the upper die  51  comes down to a space between the pair of fin holding jigs  53  to cut off the long fins  11 L at one time. At the same time, the long base  12 L is also cut off on the same cutting line with the long fins  11 . In this cutting process, the long fin member  10 L of long length is cut off at predetermined pitches, so that the plurality of fin members  10  is successively produced. In addition, the holding frame  13  is also formed by extrusion-molding and cutting as similar to the above method. 
         [0054]    A working or machining method for forming the cover plate  14  is now explained. The cover plate  14  is produced in such a way that a flat plate of a predetermined size is cut off from an aluminum plate having a uniform thickness and formed with the protrusions  23  in predetermined positions. The protrusions  23  are formed in the flat plate by press working.  FIG. 8  is a sectional view of a press device for forming protrusions. 
         [0055]    Each protrusion  23  of the heat exchanger  1  is of a triangular shape, but the shape of the protrusion is not limited thereto as long as the protrusion can perform the same function as the protrusion  23 . Though  FIG. 8  shows a press device for forming protrusions of cylindrical shape, the explanation of the pressing method is given regarding the protrusions as same as the protrusions  23  in  FIG. 2 . 
         [0056]    In a press device  60  for forming protrusions, a lower receiving base for holding a flat plate  14 X is formed with a die  62 . This die  62  is formed with a die hole  61  of circular shape in cross section. On the other side, an upper pressing base is provided with a stopper  63  for holding down the flat plate  14 X by use of a not-shown spring and the stopper  63  is formed with a guiding through hole  64  in which a tubular-shaped punch  65  is inserted. A diameter of the punch  65  is designed to be wider than that of the die hole  61 .  FIG. 8  shows a partial configuration for forming one protrusion  23 , but the press device  60  as a whole includes a plurality of identical configurations to that shown in  FIG. 8  to form a predetermined number of protrusions  23  in the flat plate  14 X at one time. 
         [0057]    In a protrusion forming process, the flat plate  14 X is held in place between the die  62  and the stopper  63  and thereafter the punch  65  in the guiding through hole  64  is press-fitted in the flat plate  14 X. At that time, the punch  65  is press-fitted to the halfway of the flat plate  14 X without penetrating through the flat plate  14 X. In the vicinity of the press-fitted region of the flat plate  14 X, a material of the surface of the flat plate  14 X is drawn by the punch  65 , but displacement of the flat plate  14 X can be prevented by the stopper  63  to maintain the planar surface to some extent. In the opposite side of the flat plate  14 X from the punch  65 , on the other hand, the material of the flat plate  14 X is extruded into the die hole  61  to form a columnar shaped protrusion  23 . With respect to the flat plate  14 X, a predetermined number of the protrusions  23  are formed by pressing. Thus the cover plate  14  is formed in one working operation. 
         [0058]    According to the manufacturing method of the heat exchanger in the present embodiment, the fin member  10  is formed by cutting the long-fin member  10 L by use of the press device  50  immediately after the long-fin member  10 L is extrusion-molded. Therefore, a large number of the fin members  10  can be produced in a short time compared to other methods such as casting. In particular, the material is cut immediately after the extrusion-molding while the material is still soft, so that the re-heating process can be omitted, thus shortening the working time. Further, as for the cover plate  14 , the protrusions  23  are formed by press working of the flat plate  14 X by use of the press device  60 , so that the working operation is simplified and working time is shortened, enabling mass production of the cover plate  14 . This can reduce costs for components of the heat exchanger  1  and hence provide the heat exchanger  1  itself at low cost. 
         [0059]    An explanation is given for modifications of the above embodiment of the heat exchanger and the manufacturing method thereof. 
         [0060]    In the heat exchanger  1  of the above embodiment, the protrusions  23  are formed in the cover plate  14 . Alternately, protrusions  33  may be formed in a fin member  30  as shown in  FIG. 9 .  FIG. 9  is a perspective view of a heat exchanger having the same configuration with the heat exchanger in  FIG. 1  from which the holding frame  13  is removed. In this modification, a heat exchanger is configured such that the fin member  30  and a cover plate  34  are attached to the holding frame  13  shown in  FIG. 1 . 
         [0061]    The fin member  30  is integrally formed with a plurality of fins  31  perpendicularly formed on a base  32 . The protrusions  33  are arranged in spaces between fins  31  arranged in parallel with each other at predetermined intervals. The protrusions  33  shown in the figure are placed in a passage formed in the space between one fin  31  and the holding frame  13 . A plurality of the protrusions  33  are formed in each passage  3  in the longitudinal direction thereof at predetermined intervals to maintain the cooling performance at the reference value “s” as shown in  FIG. 5 . On the other hand, the cover plate  34  in this modification is a flat plate. However, the cover plate  34  may also be formed with protrusions to provide a heat exchanger having protrusions on both upper and lower sides of each passage  3 . Further excellent cooling performance can be expected if the protrusions in each passage  3  are displaced alternately, or staggered, between an upper side and a lower side. 
         [0062]    A method of manufacturing a heat exchanger, especially a step of working or machining the fin member  30  having the protrusions  33  is now explained.  FIG. 10  is a diagram showing a working step of forming the protrusions  33  of the fin member  30  shown in a simplified manner. The fin member  30  is formed as with the fin member  10  which is cut out from the long-fin member  10 L as shown in  FIG. 7 . Thereafter, the fin member  30  is further subjected to a pressing step for forming protrusions, in which the protrusions  33  are formed in the base  32 . 
         [0063]    A press device for forming a protrusion includes a pressing die  72  and a receiving die  74 . The pressing die  72  includes a plurality of punches  71  to be placed under the base  32  and the receiving die  74  is to receive pressing load. The receiving die  74  is formed with a plurality of supporting projections  73  arranged corresponding to the spaces between the fins  31  so as to prevent the fins  31  from buckling and falling down due to the load applied by the pressing die  72 . Each fin  31  of the fin member  30  is inserted in each space between the supporting projections  73  so that a tip of the fin  31  abuts on the receiving die  74  and is thereby supported. With respect to the supported fin member  30 , the punches  71  of the pressing die  72  are held against the base  32  and the material deformed by press-fitting of the punches  71  is extruded into the spaces between the fins  31  to form the protrusions  33  in the base  32 . 
         [0064]    In the heat exchanger  1  in  FIG. 1 , the protrusions  23  are arranged along each of the passages  3  (see  FIG. 2 ) and further the protrusions  23  are arranged in rows in the direction perpendicular to the passages  3 . In this case, if a distance between the adjacent fins  11  is set shorter in order to enhance the cooling performance, a distance between the adjacent protrusions  23  could also be shorter. As a result, the adjacent punches could interfere with each other because the punches for forming the protrusions  23  are larger than the protrusions  23  in size. Further, the shorter distance between the adjacent protrusions  23  causes deterioration of flatness of the cover plate  14 . For instance, when the protrusions  23  are to be formed in the cover plate  14  as shown in  FIG. 2 , the material around each recess  25  is drawn by press-fitting of the punches, generating some dents. Consequently, the dents around the recess  25  could be overlapped to enlarge deformation of the material if the distance between the adjacent recesses  25  is short. 
         [0065]    In the case where the distance between the fins  11  is made shorter, the protrusions  23  are arranged in a staggered pattern in the direction perpendicular to the fins  11 , as shown in  FIG. 11 . Thereby, the distance between the adjacent protrusions  23  is increased and the interference of the punches can be avoided. It is thus possible to provide a heat exchanger with the fins  11  arranged at narrow distances from each other to enhance the cooling performance. Furthermore, as well as the protrusions  23 , the distance between the adjacent recesses  25  is wider, so that deterioration of the flatness can be prevented. Incidentally, an insulating sheet is bonded to a surface on which the recesses  25  are to be formed, and the flatness therefor is assured. 
         [0066]    Working for forming the protrusions provided in each passage is now explained. The press device for protrusions is disclosed in  FIG. 8  for processing the protrusions, but alternately, an extrusion-molding type of a press device shown in  FIG. 12  may be adopted. A press device  80  for forming a protrusion includes a die  82  in a receiving base to be placed under the flat plate  14 X and the die  82  is formed with a recess  81  conforming to the shape of the protrusion to be formed. In a pressing base on the upper side, a stopper  83  for holding down the flat plate  14 X by use of a not-shown spring is provided. The stopper  83  is formed with a guiding through hole  84  penetrating through the stopper  83 , and a columnar-shaped punch  85  having an acute-angled tip is inserted in the hole  84 . 
         [0067]    The device of the present embodiment including the punch  85  smaller in diameter than the recess  81  is used to form the relatively large protrusions  23 . On the contrary, the press device  60  in  FIG. 8  is suitable for forming relatively small-sized protrusions.  FIG. 12  shows only a partial configuration of the press device  80  to from one protrusion  23 , but the press device  80  is provided with a plurality of identical configurations to that shown in  FIG. 12  to form a predetermined number of the protrusions  23  in the flat plate  14 X at one time. Even though the protrusion formed by the press device  80  in  FIG. 12  is of trapezoidal shape, which is different from the shape of the protrusion in  FIG. 2 , it is also herein referred to as a protrusion  23 . 
         [0068]    In the press device  80 , the flat plate  14 X is held between and positioned by the die  82  and the stopper  83 . Thereafter, the punch  85  in the guiding through hole  84  is press-fitted in the flat plate  14 X. The punch  85  is pressed into the flat plate  14 X until the tip of the punch  85  reaches the recess  81 . At this time, in the vicinity of the pressing region, the surface material of the flat plate  14 X is drawn by the punch  85 , but the stopper  83  restricts displacement of the plate and the flatness is maintained to some extent. On the opposite side of the flat plate  14 X, the material is extruded into the recess  81 , thereby forming the trapezoidal-shaped protrusion  23 . With respect to the flat plate  14 X, a predetermined number of the protrusions  23  are formed by the press working, so that manufacturing of the cover plate  14  is completed in a single working. 
         [0069]    The explanation is now given for a working method of forming extrusions by pressing referring to  FIG. 13 . In the present modification, a long-fin member is formed by extrusion-molding and then a fin member of a predetermined length is cut off from the long-fin member. Further, the protrusions are formed in the fin member by pressing as shown in  FIG. 13 . A fin member  40  extrusion-molded in the present modification has a sectional shape in the longitudinal direction as shown in  FIG. 14 . Specifically, fin members  41  are arranged perpendicularly protruding from a base  42  at predetermined pitches and raised portion 43  of trapezoidal shape in section are formed between the fins  41  which define passages. Each raised portion  43  is formed in continuous shape in the longitudinal direction as same as the fins  41 . 
         [0070]    A press device  90  for forming protrusions includes a lower die  91  for supporting the fin member  40  from the bottom side and an upper die  92  for shaping protrusions. The upper die  92  includes pressing plates  95 ,  96 , and  97  each inserted in a clearance  45  between the fins  41 . One set of the pressing plates  95 ,  96 , and  97  are placed linearly along the clearance  45  and formed with separating portions  98  in between the plates. A plurality of sets of the pressing plates  95 ,  96 , and  97  are placed to hold each fin  41  from both sides, the sets of plates being arranged in parallel to one another as shown in the figure. In the figure, each pressing plate  95 ,  96 , and  97  is shown in an independent (separated) state, but the plates are configured to integrally transmit a pressing load applied by a single pressurizing device. 
         [0071]    The press device  90  is configured to move the upper die  92  downward to the fin member  40  having the sectional view in  FIG. 14  so that the pressing plates  95 ,  69 , and  97  are inserted in the clearances  45  to hold the fins  41 . The upper die  92  continues to move down to squeeze or squash the raised portion  43  pressurized by the plates  95 ,  96 , and  97 . At this time, the portions of the fins  41  located in the separating portions  98  between the plates  95 ,  96 , and  97  are not squashed, so that protrusions  46  are formed as shown in  FIG. 15 . 
         [0072]    Therefore, according to the manufacturing method of the present embodiment, the protrusions  46  can be formed by use of a simple die without requiring a processing device having a complicated die for forming protrusions. Accordingly, a cost for a processing device can be reduced, leading to cost reduction in processing a heat exchanger. 
         [0073]    While the presently preferred embodiment of the heat exchanger and the manufacturing method thereof according to the present invention has been shown and described, the invention is not limited to the above embodiments and may be embodied in other specific forms without departing from the essential characteristics thereof. 
       REFERENCE SIGNS LIST 
       [0074]      1  Heat exchanger 
         [0075]      2  Main body 
         [0076]      3  Passage 
         [0077]      6  Heat spreader 
         [0078]      7  Semiconductor device 
         [0079]      10  Fin member 
         [0080]      11  Fin 
         [0081]      12  Base 
         [0082]      13  Holding frame 
         [0083]      14  Cover plate 
         [0084]      23  Protrusion 
         [0085]      50  Press device for cutting 
         [0086]      60  Press device for forming protrusions 
         [0087]      62  Die 
         [0088]      63  Stopper 
         [0089]      65  Punch