Liquid cooling unit and heat exchanger therefor

BACKGROUND OF THE INVENTION

Field of the Invention:

0001The present invention relates to a liquid cooling unit incorporated in an electronic apparatus such as a notebook personal computer, for example.

Description of the Prior Art:

0002A liquid cooling unit is incorporated in a notebook personal computer as disclosed in <patcit id="pcit0001" dnum="JP2004293833A"><text>Japanese Patent Application Publication No. 2004-293833</text></patcit>, for example. The liquid cooling unit includes a heat exchanger. The heat exchanger includes tubes each defining a flow passage for coolant. Airflow runs between the tubes. The airflow absorbs heat from the coolant flowing, through the tubes. The coolant gets cooled in this manner.

0003The tubes are designed to extend on parallel lines in the heat exchanger. The tubes are formed as a cylindrical duct. Since the tubes each have a relatively small cross-section, the coolant flows through the tubes at a high speed. The coolant is only allowed to contact the tubes in a considerably limited duration. Heat cannot sufficiently be transferred from the coolant to the tubes. The heat of the coolant cannot be radiated into the air in an efficient manner.

SUMMARY OF THE INVENTION

0004It is accordingly desirable to provide a heat exchanger for a liquid cooling unit, a liquid cooling unit and an electronic apparatus, capable of enhancing the efficiency of heat transfer.

0005According to an embodiment of the present invention, there is provided a heat exchanger for a liquid cooling unit, comprising: a first plate extending along a reference plane; a second plate opposed to the surface of the first plate so as to define a first flat space along the first plate between the first plate and the second plate; a third plate extending along the reference plane, the first and third plates extending along parallel lines established within the reference plane; and a fourth plate opposed to the surface of the third plate so as to define a second flat space along the third plate between the third plate and the fourth plate, the first and second flat spaces extending along parallel lines.

0006The heat exchanger allows establishment of the first flat space between the first and second plates. The heat exchanger also allows establishment of the second flat space between the third and fourth plates. The first and second flat spaces have a cross-section larger than that of a cylindrical duct of a closed circulating loop for coolant. These flat spaces serve as a flow passage for coolant. An increased cross-section enables a reduction in the flow speed of the coolant. The coolant is allowed to slowly flow through the first and second flat spaces. The coolant thus contacts with the first and second plates and the third and fourth plates for a longer time. The heat of the coolant is sufficiently transferred to the first and second plates and the third and fourth plates. The efficiency of heat radiation is enhanced.

0007The heat exchanger is incorporated in a liquid cooling unit. The liquid cooling unit may comprise: a closed circulating loop; a heat receiver inserted in the closed circulating loop, the heat receiver having a thermal conductive plate received on an electronic component; and a heat exchanger inserted in the closed circulating loop so as to absorb heat from coolant. In this case, the heat exchanger may comprise: a first plate extending along a reference plane; a second plate opposed to the surface of the first plate so as to define a first flat space along the first plate between the first plate and the second plate; a third plate extending along the reference plane, the first and third plates extending along parallel lines established within the reference plane; and a fourth plate opposed to the surface of the third plate so as to define a second flat space along the third plate between the third plate and the fourth plate, the first and second flat spaces extending along parallel lines.

0008The liquid cooling unit may be incorporated in an electronic apparatus. The electronic apparatus may comprise: an electronic component; a closed circulating loop; a heat receiver inserted in the closed circulating loop, the heat receiver having a thermal conductive plate received on the electronic component; and a heat exchanger inserted in the closed circulating loop so as to absorb heat from coolant. In this case, the heat exchanger may comprise: a first plate extending along a reference plane; a second plate opposed to the surface of the first plate so as to define a first flat space along the first plate between the first plate and the second plate; a third plate extending along the reference plane, the first and third plates extending along parallel lines established within the reference plane; and a fourth plate opposed to the surface of the third plate so as to define a second flat space along the third plate between the third plate and the fourth plate, the first and second flat spaces extending along parallel lines.

0009The electronic apparatus achieves the aforementioned advantages. In addition, the heat exchanger defines parallel flat spaces along the reference plane. The heat exchanger of this type allows a single directional flow of the coolant through the first flat space from a first end to a second end, opposite to the first end, of the heat exchanger, for example. The heat exchanger also allows a single directional flow of the coolant through the second flat space from the second end to the first end of the heat exchange, for example. The inflow and outflow of the coolant can be realized on the first end of the heat exchanger, for example. The position of the inflow and outflow of the coolant can optionally be determined in response to the positions of electronic components and the heat receiver in the electronic apparatus. The electronic components and the heat receiver are allowed to enjoy a wide variety of positions in the electronic apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

0010The above and other features and advantages of the present invention will become apparent from the following description of the preferred embodiments in conjunction with the accompanying drawings, wherein: <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a perspective view schematically illustrating a notebook personal computer as a specific example of an electronic apparatus according to a first embodiment of the present invention;</li><li>Fig. 2 is a perspective view schematically illustrating the inner structure of the notebook personal computer;</li><li>Fig. 3 is a plan view schematically illustrating a liquid cooling unit according to a specific embodiment of the present invention;</li><li>Fig. 4 is a sectional view schematically illustrating a heat receiver according to a specific example of the present invention;</li><li>Fig. 5 is a sectional view taken along the line 5-5 in Fig. 4;</li><li>Fig. 6 is a partial sectional view schematically illustrating a fan unit;</li><li>Fig. 7 is a sectional view taken along the line 7-7 in Fig. 6, for schematically illustrating a heat exchanger according to a specific example of the present invention;</li><li>Fig. 8 is a sectional view taken along the line 8-8 in Fig. 7;</li><li>Fig. 9 is a front schematic view of an inflow nozzle;</li><li>Fig 10 is a sectional view, corresponding to Fig. 7, schematically illustrating a heat exchanger according to another specific example of the present invention;</li><li>Fig. 11 is a sectional view, corresponding to Fig. 7, schematically illustrating a heat exchanger according to still another specific example of the present invention;</li><li>Fig. 12 is a sectional view, corresponding to Fig. 8, schematically illustrating a heat exchanger according to still another specific example of the present invention;</li><li>Fig. 13 is a sectional view, corresponding to Fig. 8, schematically illustrating a heat exchanger according to still another specific example of the present invention;</li><li>Fig. 14 is a perspective view schematically illustrating the inner structure of a notebook personal computer according to a second embodiment of the present invention;</li><li>Fig. 15 is a perspective view schematically illustrating a main body enclosure;</li><li>Fig. 16 is a sectional view, corresponding to Fig. 4, schematically illustrating a heat receiver according to a specific example of the present invention;</li><li>Fig. 17 is a sectional view taken along the line 17-17 in Fig. 16;</li><li>Fig. 18 is a sectional view, corresponding to Fig. 8, schematically illustrating a heat exchanger according to still another specific example of the present invention; and</li><li>Fig. 19 is a sectional view, corresponding to Fig. 8, schematically illustrating a heat exchanger according to still another specific example of the present invention.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0011Fig. 1 schematically illustrates a notebook personal computer 11 as a specific example of an electronic apparatus according to a first embodiment of the present invention. The notebook personal computer 11 includes a thin first enclosure, namely a main body enclosure 12, and a second enclosure, namely a display enclosure 13. The display enclosure 13 is coupled to the main body enclosure 12 for relative swinging movement. The main body enclosure 12 includes a base 12a and a cover 12b removably coupled to the base 12a. Input devices such as a keyboard 14 and a pointing device 15 are embedded in the surface of the cover 12b, for example. Users manipulate the keyboard 14 and/or the pointing device 15 to input commands and/or data.

0012A liquid crystal display (LCD) panel module 16 is enclosed in the display enclosure 13, for example. The screen of the LCD panel module 16 exposes within a window opening 17 defined in the display enclosure 13. Texts and graphics appear on the screen. Users can see the ongoing operation of the notebook personal computer 11 basedon the texts and graphics on the screen. The display enclosure 13 can be superposed on the main body enclosure 12 through the swinging movement relative to the main body enclosure 12.

0013As shown in Fig. 2, a printed circuit board unit 18 is placed in the inner space defined in the main body enclosure 12. The printed circuit board unit 18 includes a printed wiring board 19 and electronic components, namely first and second large-scale integrated circuit (LSI) packages 21, 22, mounted on the surface of the printed wiring board. The first LSI package 21 includes a central processing unit (CPU) chip, not shown, mounted on a small-sized substrate, for example. The second LSI package includes a video chip, not shown, mounted on a small-sized substrate, for example. The CPU chip is designed to execute various kinds of processing based on an operating system (OS) and/or application software, for example. The video chip is designed to execute image processing based on the processing of the CPU chip, for example.

0014Storage medium drives or storage devices, such as digital versatile disk (DVD) drive 23 and a hard disk drive, HDD, 24, are placed in the inner space of the main body enclosure 12 at a position outside the printed wiring board 19. The aforementioned operating system and application software may be stored in the hard disk drive 24. A card unit 25 is placed in the inner space of the main body enclosure 12. PC cards, such as a memory card, a small computer system interface (SCSI) card and a local area network (LAN) card, are inserted into the card unit 25 through the card slot. The card unit 25 may be mounted on the printed wiring board 19, for example.

0015A liquid cooling unit 27 is placed on the printed wiring board 19 in the inner space of the main body enclosure 12. The liquid cooling unit 27 includes a first heat receiver 28 received on the first LSI package 21. The first heat receiver 28 is designed to absorb heat generated in the CPU chip. Screws may be utilized to fix the first heat receiver 28 onto the printed wiring board 19, for example. The liquid cooling unit 27 allows establishment of a closed circulating loop for coolant. The first heat receiver 28 is inserted in the closed circulating loop. Here, antifreeze of propylene glycol series may be utilized as coolant, for example. The first heat receiver 28 will be described later in detail.

0016A second heat receiver 29 is inserted in the closed circulating loop. The second heat receiver 29 is received on the second LSI package 22. The second heat receiver 29 is located at a position downstream of the first heat receiver 28. The second heat receiver 29 includes a thermal conductive plate received on the video chip. The second heat receiver 29 absorbs heat from the video chip in this manner. The thermal conductive plate is coupled to a metallic tube, which will be described later. Screws may be utilized to fix the thermal conductive plate onto the printed wiring board 19, for example. The thermal conductive plate may be made of a metallic material having thermal conductivity, such as aluminum, for example.

0017A heat exchanger 31 is inserted in the closed circulating loop so as to absorb heat from coolant. The heat exchanger 31 is located at a position downstream of the second heat receiver 29. The heat exchanger 31 is opposed to a ventilation opening defined in a fan unit 32. Screws may be utilized to fix the heat exchanger 31 and the fan unit 32 onto the printed wiring board 19, for example. The heat exchanger 31 is placed between the fan unit 32 and an air outlet 33 defined in the main body enclosure 12. The fan unit 32 generates airflow sequentially running through the heat exchanger 31 and the air outlet 33. The heat exchanger 31 and the fan unit 32 will be described later in detail. The fan unit 32 may be placed within a recess formed in the printed wiring board 19.

0018The fan unit 32 includes a fan housing 34. The fan housing 34 defines a predetermined inner space. The air inlet 35 is formed in each of the top and bottom plates of the fan housing 34. The air inlets 35 spatially connect the inner space of the fan housing 34 to a space outside the fan housing 34. A fan 36 is placed in the inner space of the fan housing 34.

0019A tank 37 is inserted in the closed circulating loop. The tank 37 is located at a position downstream of the heat exchanger 31. The tank 37 may be made of a metallic material having thermal conductivity such as aluminum, for example. Screws may be utilized to fix the tank 37 onto the printed wiring board 19, for example. The tank 37 serves to store the coolant and air in the closed circulating loop. The coolant and air are kept in a storage space defined in the tank 37. A coolant outlet is defined in the storage space. The coolant outlet is set at a position closest to the bottom of the storage space. Even if the coolant is leaked out of the circulating loop because of evaporation, for example, the gravity makes the coolant kept on the bottom of the storage space. Only the coolant is allowed to flow into the coolant outlet, so that air is prevented from reaching an outlet nozzle, which will be described later in detail.

0020A pump 38 is inserted in the closed circulating loop. The pump 38 is located at a position downstream of the tank 37. The first heat receiver 28 is located at a position downstream of the pump 38. Screws may be utilized to fix the pump 38 onto the printed wiring board 19. A piezoelectric pump may be utilized as the pump 38, for example. A piezoelectric element is incorporated in the piezoelectric pump. When the piezoelectric element vibrates in response to supply of electric power, the coolant is discharged from the pump 38 to the first heat receiver 28. The pump 38 allows the circulation of the coolant through the closed circulating loop in this manner. The pump 38 may be made of a resin material having a relatively low liquid permeability, such as polyphenylene sulfide (PPS), for example. Alternatively, a cascade pump, a piston pump, or the like, may be utilized as the pump 38, for example.

0021As shown in Fig. 3, a tube 41 is utilized for each connection between the first heat receiver 28 and the second heat receiver 29, between the second heat receiver 29 and the heat exchanger 31, between the heat exchanger 31 and the tank 37, between the tank 37 and the pump 38, and between the pump 38 and the first heat receiver 28. The ends of the tubes 41 are coupled to metallic tubes 42 attached to the first heat receiver 28, the second heat receiver 29, the heat exchanger 31, the tank 37 and the pump 38, respectively. Fixing members, not shown, such as bands, may be utilized to fix the tubes 41 onto the corresponding metallic tubes 42.

0022The tubes 41 may be made of an elastic resin material having flexibility, such as rubber, for example. The metallic tubes 42 may be made of a metallic material having thermal conductivity, such as aluminum, for example. The elasticity of the tubes 41 serves to absorb relative positional shifts between the first heat receiver 28, the second heat receiver 29, the heat exchanger 31, the tank 37 and the pump 38, The length of the respective tubes 41 may be set minimum enough to accept the relative positional shifts. Decoupling of the tubes 41 from the corresponding metallic tubes 42 allows independent replacement of the first heat receiver 28, the second heat receiver 29, the heat exchanger 31, the tank 37 and the pump 38 in a relatively facilitated manner.

0023As shown in Fig. 4, the first heat receiver 28 includes a box-shaped casing 44, for example. The casing 44 defines a closed inner space. The casing 44 may be made of a metallic material having thermal conductivity, such as aluminum, for example. The casing 44 includes a bottom plate defining a flat thermal conductive plate 45. A flow passage 46 is defined on the thermal conductive plate 45.

0024At least two inflow nozzles 47, 47 are coupled to the casing 44 at positions outside the periphery of the thermal conductive plate 45 so as to extend into the casing 44 from the outside. The inflow nozzles 47, 47 have discharge openings opposed to the upstream end of the flow passage 46. The inflow nozzles 47 may be formed in a cylindrical shape, for example. The inflow nozzles 47 may bifurcate from the metallic tube 42. The inflow nozzles 47, 47 are placed to extend along parallel lines. In this case, the inflow nozzles 47, 47 may be set in parallel with each other. The flow passage 46 is designed to extend on the extensions of the inflow nozzles 47.

0025An outflow nozzle 48 is coupled to the casing 44 at a position outside the periphery of the thermal conductive plate 45. The outflow nozzle 48 has an inflow opening opposed to the downstream end of the flow passage 46. The outflow nozzle 48 may be formed in a cylindrical shape, for example. The inflow nozzles 47 and the outflow nozzle 48 are oriented in the same direction. When the coolant flows into the flow passage 46 from the inflow nozzles 47, the coolant flows along the inner surface of the casing 44. The inner surface of the casing 44 allows the coolant to turn around. The coolant thus flows to the outflow nozzle 48 along the inner surface of the casing 44. The coolant is discharged from the outflow nozzle 48. The coolant absorbs heat from the thermal conductive plate 45. The flow passage 46 takes a U-shape in the casing 44 in this manner.

0026Heat radiating fins 49 are arranged on the thermal conductive plate 45 in a zigzag pattern. The heat radiating fins 49 stand upright from the surface of the thermal conductive plate 45. The heat radiating fins 49 are designed to extend in the direction of the coolant flow. The heat radiating fins 49 may be made of a metallic material having thermal conductivity, such as aluminum, for example. The heat radiating fins 49 may be formed integral with the thermal conductive plate 45, for example. Since the heat radiating fins 49 are arranged in a zigzag pattern, the aforementioned flow passage 46 is kept between the heat radiating fins 49 in the direction of the coolant flow. The coolant can flow through the flow passage 46 without stagnating. Heat is transmitted to the heat radiating fins 49 from the thermal conductive plate 45. The coolant absorbs the heat from the heat radiating fins 49.

0027As shown in Fig. 5, the thermal conductive plate 45 is received on a CPU chip 51 in the first LSI package 21. The first LSI package 21 may be formed as a pin grid array (PGA) package. The first LSI package 21 may be received on a socket mounted on the printed wiring board 19, for example. A heat spreader 52 in the shape of a plate is interposed between the CPU chip 51 and the thermal conductive plate 45. The heat spreader 52 may be made of a metallic material having a high thermal conductivity, such as copper, for example. The heat spreader 52 serves to transfer heat of the CPU chip 51 to the thermal conductive plate 45 in an efficient manner.

0028The casing 44 includes a depression 53 sinking from the thermal conductive plate 45 between the downstream end of the flow passage 46 and the outflow nozzle 48. The depression 53 provides a space 54 having the level lower than the flow passage 46 in the casing 44. The outflow nozzle 48 is designed to extend into the space 54. The inflow opening of the outflow nozzle 48 is thus opposed to the peripheral edge of the thermal conductive plate 45. The casing 44 likewise defines a depression 53a sinking from the thermal conductive plate 45 between the upstream end of the flow passage 46 and the inflow nozzles 47, 47. The depression 53a provides a space 54a having the level lower than the flow passage 46 in the casing 44. The inflow nozzles 47, 47 are designed to extend into the space 54a. The openings of the inflow nozzles 47 are in this manner opposed to the peripheral edge of the thermal conductive plate 45. The casing 44 also defines a top plate 55. The top plate 55 is opposed to the thermal conductive plate 45 and the depressions 53, 53a.

0029The first heat receiver 28 allows establishment of the depressions 53, 53a between the downstream end of the flow passage 46 and the outflow nozzle 48 as well as between the upstream end of the flowpassage 46 and the inflow nozzles 47, respectively. Specifically, the spaces 54, 54a are positioned outside the periphery of the thermal conductive plate 45, namely the first LSI package 21. The outflow and inflow nozzles 48, 47 are designed to extend into the spaces 54, 54a, respectively. The casing 44 is thus prevented from an increase in the thickness of the casing 44 as compared with the case where the inflow and outflow nozzles 47, 48 extends in the flow passage 46 inside the periphery of the first LSI package 21. This results in reduction in the height of the first heat receiver 28 from the front surface of the printed wiring board 19. The first heat receiver 28 having a reduced height significantly contributes to reduction in the thickness of the main body enclosure 12.

0030The thermal conductive plate 45 extends in the horizontal direction in the casing 44. Since the space 54 sinks from the flow passage 46, the gravity forces the coolant to flow into the space 54 from the flow passage 46. Even if the coolant is leaked out of the closed circulating loop because of evaporation from the tubes 41, the pump 38, and the like, for example, the coolant can constantly be maintained in the space 54. Even if air gets into the flow passage 46, the air goes up toward the top plate 55 in the space 54. The outflow nozzle 48 is thus prevented from sucking air as much as possible. This results in prevention of circulation of the air through the closed circulating loop.

0031As shown in Fig. 6, the fan 36 has the structure of a so-called centrifugal fan. The fan 36 includes a rotating body 56 and blades 57 extending outward in the radial directions from the rotating body 56. When the fan 36 is driven for rotation around a rotation axis 58, fresh air is introduced along the rotation axis 58 through the air inlets 35, 35 of the bottom and top plates of the fan housing 34. The rotation of the fan 36 serves to generate airflow running in the centrifugal direction.

0032A ventilation opening 59 is defined in the fan housing 34 at a position outside the orbit of the blades 57. The heat exchanger 31 is placed between the ventilation opening 59 and the air outlet 33. The centrifugal airflow is guided to the ventilation opening 59 along the inner surface of the fan housing 34. The air is discharged from the ventilation opening 59 in this manner. The discharged air sequentially runs through the heat exchanger 31 and the air outlet 33. The heat exchanger 31 is designed to extend in the direction perpendicular to the direction of the airflow.

0033As shown in Fig. 7, the heat exchanger 31 includes a first flat plate 61 extending in parallel with the bottom surface of the base 12a. A second flat plate 62 is opposed to the front surface of the first flat plate 61. The second flat plate 62 extends in parallel with the first flat plate 61. The peripheral edges of the first and second flat plates 61, 62 are coupled to each other. A flat space 63 is in this manner defined between the first and second flat plates 61, 62 along the front surface of the first flat plate 61. The flat space 62 serves as a flow passage. The flat space 63 is designed to extend along an imaginary plane including the longitudinal axis of the metallic tube 42. The first and second flat plates 61, 62 are made of a metallic material having thermal conductivity, such as aluminum, for example.

0034First heat radiating fins 64 are formed to stand upright from the outer surface of the first flat plate 61. Second heat radiating fins 65 are likewise formed to stand upright from the outer surface of the second flat plate 62. The first and second heat radiating fins 64, 65 are designed to extend from the ventilation opening 59 of the fan unit 32 to the air outlet 33. Airflow passages are defined between the adjacent first heat radiating fins 64, 64 and between the adjacent second heat radiating fins 65, 65. The airflow runs through the airflow passages along the outer surfaces of the first and second flat plates 61, 62. The first and second heat radiating fins 64, 65 are made of a metallic material having thermal conductivity, such as aluminum, for example.

0035As shown in Fig. 8, the flat space 63 extends wide in the horizontal direction. The flat space 63 thus provides a flow passage having a sufficiently large cross-section as compared with the cross-section of the metallic tube 42. The flow speed of the coolant is suppressed at the flat space 63. The coolant is allowed to flow through the flat space 63 at a relatively low speed in this manner. The coolant thus contacts the first and second flat plates 61, 62 for a relatively longer time. The heat of the coolant can sufficiently be transferred to the first and second flat plates 61, 62. The airflow can absorb the heat of the coolant in an efficient manner.

0036Now, assume that the coolant circulates along the closed circulating loop. Antifreeze of propylene glycol series, for example, is utilized as the coolant as described above. When the notebook personal computer 11 is switched on, the CPU chip 51 starts the operation of the fan unit 32. The fan 36 is driven for rotation. Fresh air is introduced through an air inlet, not shown, formed in the main body enclosure 12. The air is introduced along the rotation axis 58 through the air inlets 35. The airflow thus runs along the front and back surfaces of the printed wiring board 19. Simultaneously, the CPU chip 51 directs the operation of the pump 38. The circulation of the coolant is thus generated in the closed circulating loop.

0037The CPU chip 51 generates heat of a first calorific power or a higher thermal energy during the operation of the CPU chip 51. The heat of the CPU chip 51 is transferred to the thermal conductive plate 45 and the heat radiating fins 49 of the first heat receiver 28. The coolant in the flow passage 46 absorbs the heat of the thermal conductive plate 45 and the heat radiating fins 49. The coolant flows into the flow passage 46 through the inflow nozzles 47, 47. Two streams of the coolant are generated in the flow passage 46 in this manner. The streams expand in the horizontal direction in the flow passage 46. The coolant flows through the flow passage 46 without stagnating. The coolant can absorb the heat of the thermal conductive plate 45 in an efficient manner. The CPU chip 51 gets cooled in this manner.

0038The coolant flows from the first heat receiver 28 to the second heat receiver 29. The video chip generates heat of a second calorific power smaller than the first calorific power, namely a lower thermal energy, during the operation of the video chip. The heat of the video chip is transferred to the thermal conductive plate of the second heat receiver 29. The coolant in the metallic tube 42 absorbs the heat of the thermal conductive plate. The video chip gets cooled in this manner. The coolant flows into the heat exchanger 31 from the second heat receiver 29. In this case, the video chip generates heat of the second calorific power smaller than the first calorific power of heat generated at the CPU chip 51. The coolant is first subjected to cooling action of the CPU chip 51 having a larger thermal energy. The CPU chip 51 and the video chip can thus be cooled in an efficient manner.

0039The coolant flows into the flat space 63 in the heat exchanger 31. The heat of the coolant is transferred to the first and second flat plates 61, 62 as well as the first and second heat radiating fins 64, 65. The fan unit 32 generates airflow from the ventilation opening 59 to the air outlet 33. The heat of the coolant is radiated into the air from the outer surfaces of the first and second flat plates 61, 62 and the surfaces of the first and second heat radiating fins 64, 65. The coolant thus gets cooled. The air is discharged out of the main body enclosure 12 through the air outlet 33. The coolant flows into the tank 37. The coolant then flows into the pump 38 from the tank 37.

0040The liquid cooling unit 27 of the notebook personal computer 11 is placed within the inner space of the main body enclosure 12. No component of the liquid cooling unit 27 is incorporated in the display enclosure 13. Accordingly, no tube 41 and no metallic tube 42 extend between the main body enclosure 12 and the display enclosure 13. The liquid cooling unit 27 can be assembled into the main body enclosure 12 in a relatively facilitated manner in the process of making the notebook personal computer 11. This results in reduction in the cost of making the notebook personal computer 11. The liquid cooling unit 27 is also removed from the main body enclosure 12 in a relatively facilitated manner.

0041In addition, when the notebook personal computer 11 is placed on the desk, the main body enclosure 12 is set on the desk, for example. As is apparent from Fig. 1, the main body enclosure 12 takes the horizontal attitude. The display enclosure 13 takes an inclined attitude around the edge of the main body enclosure 12. Since the liquid cooling unit 27 is incorporated in the main body enclosure 12, the weight of the liquid cooling unit 27 serves to locate the centroid of the notebook personal computer 11 at a lower position. The notebook personal computer 11 is thus allowed to enjoy a stabilized attitude.

0042In addition, the first heat receiver 28, the second heat receiver 29, the heat exchanger 31, the tank 37 and the metallic tubes 42 are all made of aluminum in the liquid cooling unit 27. The coolant is thus prevented from contacting with any metallic material other than aluminum in the closed circulating loop. The coolant is prevented from suffering from elution of metallic ions. This results in prevention of corrosion of the first heat receiver 28, the second heat receiver 29, the heat exchanger 31, the tank 37 and the metallic tubes 42. The coolant is in this manner prevented from leakage from the closed circulating loop.

0043In addition, the first and second flat plates 61, 62 of the heat exchanger 31 are allowed to contact with the first and second heat radiating fins 64, 65 at larger areas as compared with the case where a cylindrical tube is utilized to define the flow passage. This results in an enhanced efficiency of heat radiation. Moreover, the flat space 63 is designed to expand along an imaginary plane including the longitudinal axis of the metallic tube 42. Even when the coolant flows in a reduced amount, the coolant is allowed to contact the first and second flat plates 61, 62 over a larger area. This results in a further enhanced efficiency of heat radiation.

0044As shown in Fig. 9, the tip ends of the inflow nozzles 47 may expand in the horizontal or lateral direction in the first heat receiver 28, for example. In this case, the tip ends of the inflow nozzles 47 may expand in a direction parallel to the thermal conductive plate 45 and the top plate 55. The inflow nozzles 47 allow the coolant to expand in the horizontal direction in the flow passage 46 through the tip ends of the inflow nozzles 47. The stream of the coolant is allowed to further expand in the horizontal direction in the flow passage 46. The coolant absorbs heat from the thermal conductive plate 45 and the heat radiating fins 49 in a highly efficient manner.

0045As shown in Fig. 10, the liquid cooling unit 27 may include a heat exchanger 31a in place of the aforementioned heat exchanger 31. The heat exchanger 31a includes third and fourth flat plates 66, 67 in addition to the aforementioned first and second flat plates 61, 62. The third flat plate 66 is opposed to the front surface of the second flat plate 62. The fourth flat plate 67 is opposed to the front surface of the third flat plate 66. The peripheral edges of the third and fourth flat plates 66, 67 are coupled to each other. A flat space 68 is defined between the third and fourth flat plates 66, 67 along the front surface of the third flat plate 66 in this manner. The flat space 68 serves as a flow passage. The third and fourth flat plates 66, 67 are made of a metallic material having thermal conductivity, such as aluminum, for example.

0046The first heat radiating fins 64 are formed to stand upright from the outer surface of the first flat plate 61 in the same manner as the aforementioned heat exchanger 31. The second heat radiating fins 65 are likewise formed to stand upright from the outer surface of the fourth flat plate 67. A gap is defined between the front surface of the second flat plate 62 and the back surface of the third flat plate 66 in this manner. This gap serves as an airflow passage extending from the ventilation opening 59 of the fan unit 32 to the air outlet 33.

0047Support columns 69, 69 are placed in the gap between the front surface of the second flat plate 62 and the back surface of the third flat plate 66. The support columns 69 are interposed between the second and third flat plates 62, 66. The support columns 69 serve to maintain the gap between the second and third flat plates 62, 66. Even when an urging force is applied to the first and second flat plates 61, 62 toward the third and fourth flat plates 66, 67, or even when an urging force is applied to the third and fourth flat plates 66, 67 toward the first and second flat plates 61, 62, during the process of making the heat exchanger 31a, the first to fourth flat plates 61, 62, 66, 67 is reliably prevented from deformation. This results in prevention of reduction in the cross-section of the gap between the second flat plate 62 and the third flat plate 66.

0048The heat exchanger 31a allows establishment of the parallel flat spaces 63, 68. The coolant flows through the flat spaces 63, 68. The cross-section of the flow passage can be increased as compared with the aforementioned heat exchanger 31. This results in a reduction in the flow speed of the coolant. The coolant is allowed to flow through the flat spaces 63, 68 at a lower speed. The coolant contacts with the first and second flat plates 61, 62 and the third and fourth flat plates 66, 67 for a longer time. The heat of the coolant can thus sufficiently be transferred to the first and second flat plates 61, 62 and the third and fourth flat plates 66, 67. The airflow absorbs the heat from the coolant in an efficient manner.

0049Moreover, the airflow runs through the gap defined between the second and third flat plates 62, 66. The airflow runs along the front surface of the second flat plate 62 and the back surface of the third flat plate 66. The heat is radiated into the air from the front surface of the second flat plate 62 and the back surface of the third flat plate 66. This results in an enhanced efficiency of heat radiation as compared with the aforementioned heat exchanger 31.

0050As shown in Fig. 11, the liquid cooling unit 27 may include a heat exchanger 31b in place of the aforementioned heat exchangers 31, 31a. The heat exchanger 31b includes fifth and sixth flat plates 71, 72 in addition to the first and second flat plates 61, 62 and the third and fourth flat plates 66, 67 of the heat exchanger 31a. The fifth flat plate 71 is opposed to the front surface of the second flat plate 62. The sixth flat plate 72 is opposed to the front surface of the fifth flat plate 71. The sixth flat plate 72 is also opposed to the back surface of the third flat plate 66. The peripheral edges of the fifth and sixth flat plates 71, 72 are coupled to each other. A flat space 73 is defined between the fifth and sixth flat plates 71. 72 along the front surface of the fifth flat plate 71. The flat space 73 serves as a flow passage. The fifth and sixth flat plates 71, 72 are made of a metallic material having thermal conductivity, such as aluminum, for example.

0051The first heat radiating fins 64 are formed to stand upright from the outer surface of the first flat plate 61 in the same manner as the aforementioned heat exchanger 31a. The second heat radiating fins 65 are formed to stand upright from the outer surface of the fourth flat plate 67. A gap is defined between the front surface of the second flat plate 62 and the back surface of the fifth flat plate 71. A gap is also defined between the front surface of the sixth flat plate 72 and the back surface of the third flat plate 66. These gaps serve as airflow passages extending from the ventilation opening 59 of the fan unit 32 to the air outlet 33. The support columns 69, 69 may be placed in each of the gaps in the same manner as described above.

0052Three of the flat spaces 63, 68, 73 are defined along parallel lines in the heat exchanger 31b. The coolant flows through the flat spaces 63, 68, 73. The cross-section of the flow passage is increased as compared with the aforementioned heat exchangers 31, 31a. The coolant is allowed to flow through the flat spaces 63, 68, 73 at a still lower speed. The airflow absorbs the heat from the coolant in an efficient manner in the same manner as described above. The flow speed of the coolant can be adjusted depending on the number of the flat spaces 63, 68, 73 in the heat exchangers 31, 31a, 31b. In addition, the airflow runs across the gaps. This results in a further enhanced efficiency of heat radiation as compared with the aforementioned heat exchangers 31. 31a.

0053As shown in Fig. 12, the liquid cooling unit 27 may include a heat exchanger 31c in place of the aforementioned heat exchangers 31, 31a, 31b. The first and second flat plates 61, 62 of the aforementioned heat exchanger 31 are divided to extend in parallel with each other in the direction of the coolant flow in the heat exchanger 31c. Specifically, the heat exchanger 31c includes a first flat plate 74 extending along a reference plane, and a second flat plate 75 opposed to the front surface of the first flat plate 74. A flat space 76 is defined between the first and second flat plates 74, 75. The flat space 76 serves as a flow passage. The first and second flat plates 74, 75 are made of a metallic material having thermal conductivity, such as aluminum, for example.

0054Likewise, the heat exchanger 31c includes a third flat plate 77 and a fourth flat plate 78 opposed to the front surface of the third flat plate 77. The third flat plate 77 is designed to extend along the aforementioned reference plane. A flat space 79 is defined between the third and fourth flat plates 77, 78. The flat space 79 serves as a flow passage. The flat space 79 is designed to extend in parallel with the flat space 76. In this case, the length <i><u style="single">L1</u></i> of the flat space 76 defined in the direction of the airflow from the ventilation opening 59 to the air outlet 33 may be set equal to the length <i><u style="single">L2</u></i> of the flat space 79 likewise defined. The third and fourth flat plates 77, 78 are made of a metallic material having thermal conductivity, such as aluminum, for example.

0055As shown in Fig. 13, the liquid cooling unit 27 may utilize a heat exchanger 31d in place of the heat exchanger 31c. The lengths <i><u style="single">L1</u>, <u style="single">L2</u></i> of the flat spaces 76, 79 of the aforementioned heat exchanger 31c are changed in the heat exchanger 31d. Here, the length <i><u style="single">L2</u></i> of the flat space 79 may be set larger than the length <i><u style="single">L1</u></i> of the flat space 76. Alternatively, the length <i><u style="single">L2</u></i> of the flat space 79 may be set smaller than the length <i><u style="single">L1</u></i> of the flat space 76.

0056Fig. 14 schematically illustrates the inner structure of a notebook personal computer 11a as a specific example of an electronic component according to a second embodiment of the present invention. The notebook personal computer 11a includes a liquid cooling unit 27a placed in the inner space of the main body enclosure 12. The liquid cooling unit 27a includes a first heat receiver 81, a second heat receiver 82 and a heat exchanger 83 in place of the aforementioned first heat receiver 28, second heat receiver 29 and heat exchanger 31. A closed circulating loop is established in the liquid cooling unit 27a. The first heat receiver 81 is inserted in the closed circulating loop. Like reference numerals are attached to the structure or components equivalent to those of the aforementioned notebook personal computer 11.

0057The fan unit 32 of the liquid cooling unit 27a is placed outside the closed circulating loop. The tank 37 and the pump 38 are placed outside the periphery of the printed wiring board 19. The tank 37 is placed between the printed wiring board 19 and the DVD drive 23. The pump 38 is placed between the printed wiring board 19 and the hard disk drive 24. Screws may be utilized to fix the tank 37 and the pump 38 onto the bottom plate of the base 12a, for example. It should be noted that an opening, not shown, may be formed in the bottom plate of the base 12a, for example. In this case, the tank 37 and the pump 38 can be replaced through the opening of the bottom plate.

0058A partition plate 84 is placed in a space between the printed wiring board 19 and the tank 37 as well as between the printed wiring board 19 and the pump 38. The partition plate 84 may stand upright from the bottom plate of the base 12a. The partition plate 84 serves to isolate a space containing the printed wiring board 19 from a space containing both the tank 37 and the pump 38. Movement of air is thus prevented between the space for the printed wiring board 19 and the space for both the tank 37 and the pump 38. The space for the tank 37 and the pump 38 can be prevented from receiving airflow that has absorbed heat from the first and second LSI packages 21, 22 in the space for the printed wiring board 19. The tank 37 and the pump 38 is thus prevented from a rise in the temperature. The coolant is prevented from evaporation in the pump 38.

0059As shown in Fig. 15, first and second air inlets 85, 86 are defined in the bottom plate of the base 12a. Fresh air is introduced into the inner space of the main body enclosure 12 from the outside through the first and second air inlets 85, 86. Here, the first air inlet 85 is opposed to the tank 37 in the inner space of the main body enclosure 12. The second air inlet 86 is opposed to the pump 38 in the inner space of the main body enclosure 12. The tank 37 and the pump 38 can be exposed to the fresh air outside the main body enclosure 12 in this manner. The first and second air inlets 85, 86 may be combined with each other in the bottom plate of the base 12a.

0060Pads 87 are formed on the four corners of the bottom surface of the main body enclosure 12. The pads 87 protrude from the bottom surface of the main body enclosure 12. The pads 87 may be made of an elastic resin material, such as rubber, for example. When the notebook personal computer 11a is placed on the desk, the main body enclosure 12 is received on the surface of the desk at the pads 87. The pads 87 serve to establish a gap between the bottom surface of the main body enclosure 12 and the surface of the desk. The first and second air inlets 85, 86 are thus prevented from being closed with the surface of the desk.

0061As shown in Fig. 16, the inflow nozzles 47, 47 and the outflow nozzle 48 are opposed to each other in the first heat receiver 81. The flow passage 46 thus extends straight from the inflow nozzles 47, 47 to the outflow nozzle 48 on the thermal conductive plate 45. As shown in Fig. 17, the inflow nozzles 47 are designed to extend into the space 54a. The outflow nozzle 48 is likewise designed to extend into the space 54. The inflow nozzles 47 and the outflow nozzle 48 are connected to the flow passage 46 at positions outside the periphery of the first LSI package 21 in the same manner as described above. This results in prevention of increase in the thickness of the casing 44.

0062As shown in Fig. 18, the heat exchanger 83 defines the flat spaces 76, 79 extending along parallel lines in the same manner as the aforementioned heat exchanger 31c. A pair of parallel metallic tubes 42 is connected to one end of the heat exchanger 83. The coolant thus flows into one end of the flat space 79 through one of the metallic tubes 42. The coolant flows across the flat space 79 to one end of the flat space 76. The coolant flows into the other metallic tube 42 from the other end of the flat space 76. The coolant is allowed to contact with the first and second flat plates 74, 75 and the third and fourth flat plates 76, 77 for a longer time in this manner. Simultaneously, the flow passage is narrowed. The coolant is allowed to flow through the flow passage without stagnating. The airflow can absorb the heat of the coolant in an efficient manner.

0063When the flat spaces 76, 69 are defined to extend along parallel lines in the aforementioned manner, the heat exchanger 83 enables an intensive location of the metallic tubes 42, 42 at one end of the heat exchanger 83. No metallic tube 42 needs to be connected to the other end of the heat exchanger 83. This results in reduction in the size of the heat exchanger 83. In addition, the positions of the metallic tubes 42 can be changed depending on the positions of electronic components on the printed wiring board 19. The heat exchanger 83 contributes to realization of wide possibility for arrangement of electronic components in the inner space of the main body enclosure 12.

0064The pump 38 allows circulation of the coolant through the closed circulating loop in the notebook personal computer 11a in the same manner as the aforementioned notebook personal computer 11. Heat of the CPU chip 51 is transferred to the first heat receiver 81. Heat of the video chip is transferred to the second heat receiver 82. The temperature of the coolant thus rises. The coolant flows into the heat exchanger 83 from the second heat receiver 82. The heat of the coolant is radiated into the air through the heat exchanger 83. The coolant thus gets cooled. The airflow is discharged out of the main body enclosure 12 through the air outlet 33. The cooled coolant flows into the tank 37.

0065The heat of the CPU chip 51 and the video chip is also transferred to the printed wiring board 19. The heat spreads over the printed wiring board 19 through wiring patterns on the printed wiring board 19. Since the tank 37 and the pump 38 are placed outside the periphery of the printed wiring board 19, the tank 37 and the pump 38 are reliably prevented from receiving the heat from the printed wiring board 19. This results in prevention of rise in the temperature of the coolant in the tank 37 and the pump 38. The tank 37 and the pump 38 contribute to radiation of heat from the coolant into the inner space of the main body enclosure 12.

0066In addition, the tank 37 and the pump 38 are opposed to the first air inlet 85 and the second air inlet 86, respectively. Fresh air is introduced into the main body enclosure 12 through the first and second air inlets 85, 86. The tank 37 and the pump 38 are exposed to the fresh air. The heat of the coolant in the tank 37 and the pump 38 can be radiated into the fresh air from the tank 37 and the pump 38. The heat of the coolant can be radiated into the air not only at the heat exchanger 83 but also at the tank 37 and the pump 38. The coolant gets cooled in a highly efficient manner.

0067As shown in Fig. 19, the lengths <i><u style="single">L1</u>, <u style="single">L2</u></i> of the flat spaces 76, 79 may be changed in the heat exchanger 83 in the same manner as in the heat exchanger 31d. In this case, the length <i><u style="single">L2</u></i> of the flat space 79 is set larger than the length <i><u style="single">L1</u></i> of the flat space 76. Alternatively, the length <i><u style="single">L2</u></i> of the flat space 79 may be set smaller than the length <i><u style="single">L1</u></i> of the flat space 76.

0068The liquid cooling units 27, 27a can be incorporated in electronic apparatuses other than the notebook personal computers 11, 11a, such as a personal digital assistant (PDA), a desktop personal computer, a server computer, and the like.