Patent Publication Number: US-2004042171-A1

Title: Electronic apparatus having display unit containing radiator radiating heat of heat generating component

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-128821, filed Apr. 30, 2002, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to a liquid-cooled electronic apparatus which cools a heat generating component, such as a microprocessor, by using a liquid refrigerant, in particular, to a structure for enhancing performance for radiating heat of a heated refrigerant.  
       [0004] 2. Description of the Related Art  
       [0005] With the increase in the processing speed and functions of computers, the amount of heat generated by microprocessors, which are used for notebook portable computers, during operation is rapidly increasing. Therefore, it is feared that conventional air-cooled cooling systems using an electric fan will not be able to deal with an increased heat-radiation amount of microprocessors, and are insufficient in, or reach the limit of, performance of cooling a microprocessor.  
       [0006] As a countermeasure, portable computers mounting a liquid-cooled cooling system which absorbs heat of a microprocessor by using a cooling liquid having a specific heat far greater than that of air have been tried.  
       [0007] U.S. Pat. No. 5,383,340 discloses a portable computer with a liquid-cooled cooling system. The portable computer has a computer main body and a display unit. The computer main body contains a microprocessor which generates heat. The display unit contains a display panel, and is rotatably supported by the computer main body.  
       [0008] The cooling system has an evaporator, a condenser and a conduit for circulating the coolant. The evaporator is contained in the computer main body, and thermally connected to the microprocessor. The condenser is contained in the display unit. The conduit connects the evaporator with the condenser, to transfer the coolant evaporated in the evaporator to the condenser. The coolant transferred to the condenser is liquefied by means of heat exchange therein, and returns to the evaporator through the conduit. Therefore, the coolant repeatedly circulates between the evaporator and the condenser, and thereby heat of the microprocessor is radiated to the outside of the display unit through the condenser.  
       [0009] According to the liquid-cooled cooling system, the heat of the microprocessor can be efficiently transferred to the condenser through the flow of the coolant. This enhances the performance for cooling the microprocessor in comparison with a conventional common air-cooled cooling system.  
       [0010] The condenser contained in the display unit comprises a pipe through which the coolant flows, and a heat radiating plate thermally connected to the pipe. When a heated coolant is introduced into the condenser, the heat of the coolant is conducted from the pipe to the heat radiating plate while the coolant flows through the pipe. The heat conducted to the heat radiating plate is diffused to the heat radiating plate, and thereafter radiated from the surface of the plate.  
       [0011] However, the condenser only radiates the heat of the coolant by means of spontaneous air cooling caused by diffusion of the heat from the pipe to the heat radiating plate. Therefore, supposing that the surface temperature of the display unit containing the condenser should not exceed, for example, 60° C., the heat-radiation amount of the condenser is at best less than 20 W.  
       [0012] Microprocessors of portable computers are expected to be further improved in performance in the near future, thus the amount of heat generated by the microprocessors will rapidly increase in parallel. Therefore, even if a liquid-cooled cooling system is adopted, the radiating power required of a condenser will reach tens of watts, and a problem will rise that a current condenser is insufficient in radiating power.  
       BRIEF SUMMARY OF THE INVENTION  
       [0013] The embodiment of the present invention is to obtain an electronic apparatus which can efficiently radiate heat transferred from a heat generating component to a radiating part, and can enhance the performance for cooling the heat generating component.  
       [0014] An electronic apparatus according to an embodiment of the present invention comprises: a main body having a heat generating component; a heat receiving portion thermally connected to the heat generating component; a display unit supported by the main body and having a display panel; a heat radiating portion contained in the display unit; and a circulation path which circulates a liquid refrigerant between the heat receiving portion and the heat radiating portion. The display unit contains a fan. The fan supplies cooling air to the heat radiating portion to cool the heat radiating portion.  
       [0015] In such a structure, the heat of the heat generating component is absorbed by the refrigerant in the heat receiving portion. The refrigerant heated by heat exchange in the heat receiving portion is transferred to the heat radiating portion through the circulation path. The heat of the heat generating component absorbed by the refrigerant is conducted to the heat radiating portion in the process in which the refrigerant flows through the heat radiating portion, and radiated from the surface of the heat radiating portion. The heat radiating portion is cooled by force by contact with cooling air sent from the fan. This improves radiating performance of the heat radiating portion, and enables efficient radiation of the heat of the heat generating component.  
       [0016] Additional embodiments and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The embodiments and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
     [0017] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.  
     [0018]FIG. 1 is a perspective view of a portable computer in a first embodiment of the present invention, showing a positional relation among a heat receiving head, radiator, refrigerant circulation path, centrifugal pump, and electric fan.  
     [0019]FIG. 2 is a perspective view of the portable computer in the first embodiment of the present invention, showing the state where a display unit has been rotated to an open position.  
     [0020]FIG. 3 is a cross-sectional view of the portable computer in the first embodiment of the present invention, showing a positional relation among the heat receiving head, radiator, refrigerant circulation path, centrifugal pump, and electric fan.  
     [0021]FIG. 4 is a cross-sectional view of the portable computer in the first embodiment of the present invention, showing a positional relation between a semiconductor package and the heat receiving head.  
     [0022]FIG. 5 is a cross-sectional view of the heat receiving head thermally connected with the semiconductor package, in the first embodiment of the present invention.  
     [0023]FIG. 6 is a cross-sectional view of the portable computer in the first embodiment of the present invention, showing a positional relation between the electric fan and a second housing of the display unit.  
     [0024]FIG. 7 is a cross-sectional view taken along line F 7 -F 7  of FIG. 3.  
     [0025]FIG. 8 is a cross-sectional view taken along line F 8 -F 8  of FIG. 3.  
     [0026]FIG. 9 is a perspective view of a portable computer in a second embodiment of the present invention, showing a positional relation among a heat receiving head, radiator, refrigerant circulation path, centrifugal pump, and electric fan.  
     [0027]FIG. 10A is a cross-sectional view taken along line F 10 A-F 10 A of FIG. 9.  
     [0028]FIG. 10B is a cross-sectional view taken along line F 10 B-F 10 B of FIG. 9.  
     [0029]FIG. 11 is a cross-sectional view of a radiator according to a third embodiment of the present invention.  
     [0030]FIG. 12 is a cross-sectional view of a portable computer in a fourth embodiment of the present invention, showing a positional relation among a heat receiving head, radiator, refrigerant circulation path, centrifugal pump, and electric fan.  
     [0031]FIG. 13 is a cross-sectional view of a portable computer in a fifth embodiment of the present invention, showing a positional relation among a heat receiving head, radiator, refrigerant circulation path, and centrifugal pump.  
     [0032]FIG. 14 is a cross-sectional view of a portable computer in a sixth embodiment of the present invention, showing a positional relation among a heat receiving head, radiator, refrigerant circulation path, centrifugal pump, and electric fan. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0033] A first embodiment of the present invention will now be described on the basis of FIGS.  1  to  8 .  
     [0034] FIGS.  1  to  3  disclose a portable computer  1  as an electronic apparatus. The portable computer  1  is formed of a computer main body  2  and a display unit  3 .  
     [0035] The computer main body  2  has a first housing  4  having a flat box shape. The first housing  4  has a bottom wall  4   a , top wall  4   b , front wall  4   c , right and left walls  4   d  and rear wall  4   e . The top wall  4   b  supports a keyboard  5 . Further, the top wall  4   b  has a display support portion  6  in the rear of the keyboard  5 . The display support portion  6  projects upward from the read end portion of the top wall  4   b , and extends in the width direction of the first housing  4 . The display support portion  6  has a pair of recesses  7   a  and  7   b . The recesses  7   a  and  7   b  are spaced from each other in the width direction of the first housing  4 .  
     [0036] As shown in FIGS. 1 and 6, the display unit  3  has a second housing  10  having a flat box shape, and a liquid crystal display panel  11  contained in the second housing  10 . The second housing  10  has a front wall  13 , rear wall  14  and four side walls  15 . The liquid crystal display panel  11  is located between the front wall  13  and the real wall  14 , and surrounded with the side walls  15 . The liquid crystal display panel  11  has a display screen  11   a . The display screen  11   a  is exposed outside the second housing  10  through an opening portion  12  formed at the front wall  13 .  
     [0037] As shown in FIGS. 2 and 3, the second housing  10  has a pair of leg portions  16   a  and  16   b  at one end. The leg portions  16   a  and  16   b  are hollow, and spaced from each other in the width direction of the second housing  10 . The leg portions  16   a  and  16   b  are inserted in the recesses  7   a  and  7   b  of the first housing  4 , respectively, and connected to the first housing  4  via hinge devices (not shown).  
     [0038] Therefore, the display unit  3  is rotatable between a closed position at which the unit lies to cover the keyboard  5  from the above, and an open position at which the unit stands to expose the keyboard  5  and the display screen  11   a.    
     [0039] As shown in FIGS. 1 and 3, the first housing  4  contains a printed wiring board  18 , hard disk drive  19 , and CR-ROM drive  20 . The printed wiring board  18 , the hard disk drive  19  and the CD-ROM drive  20  are arranged side by side on the bottom wall  4   a  of the first housing  4 .  
     [0040] As shown in FIG. 4, a semiconductor package  21  as a heat generating component is mounted on an upper surface of the printed wiring board  18 . The semiconductor package  21  forms a microprocessor serving as a brain of the portable computer  1 , and is located in a rear portion of the printed wiring board  18 . The semiconductor package  21  has a base substrate  22 , and an IC chip  23  soldered on an upper surface of the base substrate  22 . The IC chip  23  generates a very large amount of heat during operation due to the increased processing speed and functions, and requires cooling to maintain a stable operation.  
     [0041] As shown in FIGS. 1 and 3, the portable computer  1  is equipped with a liquid-cooled cooling unit  25  which cools the semiconductor package  21 . The cooling unit  25  has a heat receiving head  26  serving as a heat receiving portion, radiator  27  serving as a heat radiating portion, circulation path  28 , and electric fan  29 .  
     [0042] The heat receiving head  26  is contained in the first housing  4 . As shown best in FIGS. 4 and 5, the heat receiving head  26  has a flat box shape and a size greater than the semiconductor package  21 . The heat receiving head  26  is fixed on an upper surface of the printed wiring board  18  by a plurality of screws. A lower surface of the heat receiving head  26  is a flat heat receiving surface  30 . The heat receiving surface  30  is thermally connected to the IC chip  23  of the semiconductor package  21 .  
     [0043] A refrigerant channel  31  is formed inside the heat receiving head  26 . The refrigerant channel  31  is thermally connected to the IC chip  23  with the heat receiving surface  30  intervened therebetween, and divided into a plurality of sections  33  by a plurality of guide walls  32 . Further, the heat receiving head  26  has a refrigerant inlet  34  and a refrigerant outlet  35 . The refrigerant inlet  34  is located at an upstream end of the refrigerant channel  31 . The refrigerant outlet  35  is located at a downstream end of the refrigerant channel  31 .  
     [0044] As shown in FIGS. 1, 3 and  6 , the radiator  27  is contained in the second housing  31  of the display unit  3 . The radiator  27  is intervened between the rear wall  14  of the second housing  10  and the liquid crystal display panel  11 . The radiator  27  has a rectangular board shape having a size almost equal to that of the rear wall  14 . As shown in FIG. 8, the radiator  27  has a first heat radiating plate  37  and a second heat radiating plate  38 . The first and second heat radiating plates  37  and  38  are formed of a metal material having an excellent thermal conductivity, such as aluminum alloy. The first and second heat radiating plates  37  and  38  superposed on each other.  
     [0045] The first heat radiating plate  37  has a bulge portion  39  bulging away from the second heat radiating plate  38 . The bulge portion  39  is formed to meander over the whole surface of the first heat radiating plate  37 , and has an open end opened to the second heat radiating plate  38 . The open end of the bulge portion  39  is closed by the second heat radiating plate  38 . Therefore, the bulge portion  39  of the first heat radiating plate  37  forms a refrigerant channel  40  between the second heat radiating plate  38 . The refrigerant channel  40  has a plurality of straight tube portions  41  extending in the width direction of the second housing  10 . The straight tube portions  41  are arranged in parallel with each other at regular intervals in the height direction of the second housing  10 .  
     [0046] The radiator  27  has a refrigerant inlet  42  and a refrigerant outlet  43 . The refrigerant inlet  42  communicates with an upstream end of the refrigerant channel  40 , and is located in the vicinity of the leg portion  16   a  on the left side of the second housing  10 . The refrigerant outlet  43  communicates with a downstream end of the refrigerant channel  40 , and is located in the vicinity of the leg portion  16   b  on the right side of the second housing  10 . Therefore, the refrigerant inlet  42  and the refrigerant outlet  43  are spaced from each other in the width direction of the second housing  10 .  
     [0047] The first heat radiating plate  37  of the radiator  27  faces the rear wall  14  of the second housing  10 . The rear wall  14  is located behind the radiator  27 . A slight space is formed between the rear wall  14  and the bulge portion  39  of the first heat radiating plate  37 . The rear wall  14  has a plurality of air holes  44  as shown in FIGS. 2 and 6. The air holes  44  are spread over almost the whole surface of the rear wall  14 .  
     [0048] As shown in FIGS. 6 and 7, the second heat radiating plate  38  of the radiator  27  is opposite to the liquid crystal display panel  11 . A cooling air passage  46  is formed between the second heat radiating plate  38  and the liquid crystal display panel  11 .  
     [0049] A plurality of heat radiating fins  47  are attached to the second heat radiating plate  38 . The heat radiating fins  47  are formed of an aluminum plate separate from that of the second heat radiating plate  38 , and exposed to the cooling air passage  46 . Each of the heat radiating fins  47  has an elongate plate shape, and has at one edge a rising portion  47   a  which is bent at right angle. The heat radiating fins  47  are bonded to the second heat radiating plate  38  to be thermally connected to the second heat radiating plate  38 . The heat radiating fins  47  are arranged in parallel with each other at intervals in the width direction of the display unit  3 .  
     [0050] The cooling air passage  46  and the heat radiating fins  47  stand along the display unit  3  when the display unit  3  has been rotated to the open position. In this state, the upper end of each heat radiating fin  47  is opposite to one side wall  15  located at the upper end of the second housing  10 . The side wall  15  has a plurality of exhaust slots  48 . The exhaust slots  48  are located above a downstream end of the cooling air passage  46 , as long as the display unit  3  is located at the open position.  
     [0051] As shown in FIGS. 1 and 3, the circulation path  28  of the cooling unit  25  has a first conduit  50  and a second conduit  51 . The first and second conduits  50  and  51  extend over the first housing  4  and the second housing  10 .  
     [0052] The first conduit  50  connects the refrigerant outlet  35  of the heat receiving head  26  and the refrigerant inlet  42  of the radiator  27 . The first conduit  50  has an upstream portion  50   a , a downstream portion  50   b  and a pipe joint  50   c . The upstream portion  50   a  is connected to the refrigerant outlet  35  of the heat receiving head  26  and contained in the first housing  4 . The downstream portion  50   b  is connected to the refrigerant inlet  42  of the radiator  27 , and contained in the left edge portion of the second housing  10 . The pipe joint  50   c  rotatably connects the upstream portion  50   a  with the downstream portion  50   b . The pipe joint  50   c  pierces into the recess  7   a  and the leg portion  16   a , and is located on the rotation center line of the display unit  3 .  
     [0053] The second conduit  51  connects the refrigerant outlet  43  of the radiator  27  with the refrigerant inlet  34  of the heat receiving head  26 . The second conduit  51  has an upstream portion  51   a , a downstream portion  51   b , and a pipe joint  51   c . The upstream portion  51   a  is connected to the refrigerant outlet  43  of the radiator  27 , and contained in the right edge portion of the second housing  10 . The downstream portion Sib is connected to the refrigerant inlet  34  of the heat receiving head  26 , and contained in the first housing  4 . The pipe joint Sic rotatably connects the upstream portion  51   a  with the downstream portion  51   b . The pipe joint Sic pierces into the recess  7   b  and the leg portion  16   b , and is located on the rotation center line of the display unit  3 .  
     [0054] A coolant as a liquid refrigerant is filled into the refrigerant channel  31  of the heat receiving head  26 , the refrigerant channel  40  of the radiator  27 , and the circulation path  28 . An antifreeze solution is used as the coolant. The antifreeze solution is made by adding an ethylene glycol solution and, if necessary, a corrosion inhibitor, to water, for example.  
     [0055] As shown in FIGS. 1 and 3, the circulation path  28  includes a centrifugal pump  53 , for example. The centrifugal pump  53  is provided to circulate the coolant between the heat receiving head  26  and the radiator  27  by force. The centrifugal pump  53  is driven, for example, when the power of the portable computer  1  is turned on, or when the temperature of the semiconductor package  21  has reached a predetermined value.  
     [0056] The centrifugal pump  53  is set in the downstream portion  50   b  of the first conduit  50 , and contained in the second housing  10 . The radiator  27  in the second housing  10  has a cut-out portion  54  at an end portion adjacent to the left leg portion  16   a . The centrifugal pump  53  is located in the cut-out portion  54 . Therefore, the centrifugal pump  53  is disposed between the front wall  13  and the rear wall  14  of the second housing  10  without overlapping the radiator  27 .  
     [0057] Further, the centrifugal pump  53  is located at the bottom of the refrigerant channel  40  of the radiator  27 , when the display unit  3  has been rotated to the open portion. Therefore, the centrifugal pump  53  is located below the central portion of the display unit  3 , as long as the display unit  3  is located in the open position.  
     [0058] As shown in FIGS. 1, 3 and  6 , the electric fan  29  of the cooling unit  25  is provided to send cooling air by force to the radiator  27 , and contained in the second housing  10 . The electric fan  29  is located in the cut-out portion  54  of the radiator  27 . Therefore, the electric fan  29  and the centrifugal pump  53  are arranged side by side in the width direction of the second housing, in the cut-out portion  54 .  
     [0059] The electric fan  29  has a centrifugal impeller  57 , and a fan casing  58  for containing the impeller  57 . The impeller  57  is driven by a motor (not shown) when the temperature of the semiconductor package  21  has reached a predetermined value, for example. The fan casing  58  has a flat box shape, and is intervened between the front wall  13  and the rear wall  14  of the second housing  10 .  
     [0060] The fan casing  58  has a first inlet port  60   a , a second inlet port  60   b  and an outlet port  61 . The first and second inlet ports  60   a  and  60   b  are opposite to each other. The impeller  57  is located between the first and second inlet ports  60   a  and  60   b . The first inlet port  60   a  is opposite to a plurality of first air intakes  62  opened at the front wall  13  of the first housing  4 . The second inlet port  60   b  is opposite to a plurality of second air intakes  63  opened at the rear wall  14  of the first housing  4 . The outlet port  61  is opened to the radiator  27 .  
     [0061] The electric fan  29  is located under the radiator  27 , when the display unit  3  has been rotated to the open position. Therefore, the outlet port  61  of the fan casing  58  is located below the lower ends of the heat radiating fins  47 , as long as the display unit  3  is located at the open position.  
     [0062] In such a structure, the IC chip  23  of the semiconductor package  21  generates heat during use of the portable computer  1 . The heat of the IC chip  23  is conducted to the heat receiving surface  30  of the heat receiving head  26 . Since the heat receiving head  26  has the refrigerant channel  31  filled with the coolant, the coolant absorbs most of the heat conducted to the heat receiving surface  30 .  
     [0063] When the temperature of the semiconductor package  21  reaches a predetermined temperature, the centrifugal pump  53  is driven. Thereby, the coolant is transmitted from the heat receiving head  26  to the radiator  27 , and the coolant is circulated by force between the refrigerant channel  31  of the heat receiving head  26  and the refrigerant channel  40  of the radiator  27 .  
     [0064] To describe it in more detail, the coolant heated by heat exchange in the heat receiving head  26  is guided to the centrifugal pump  53  through the first conduit  50 . The coolant pressurized by the centrifugal pump  53  is guided to the radiator  27  through the first conduit  50 , and flows through the refrigerant channel  40  bent meanderingly to the refrigerant outlet  43 . During this flow, the heat of the IC chip  23  absorbed to the coolant is diffused into the first and second heat radiating plates  37  and  38 , and radiated from the surface of the radiator  27  into the second housing  10 .  
     [0065] Further, a part of the heat conducted to the radiator  27  is conducted from the second heat radiating plate  38  to the heat radiating fins  47 , and radiated from the surface of the heat radiating fins  47  to the cooling air passage  46 . Consequently, the heated coolant is cooled by heat exchange in the radiator  27 .  
     [0066] When the temperature of the semiconductor package  21  reaches a predetermined value, the electric fan  29  is driven. When the impeller  57  of the electric fan  29  rotates, air outside the display unit  3  is sucked through the air intakes  62  and  63  of the second housing  10  into the inlet ports  60   a  and  60   b  of the fan casing  58 , as shown by arrows in FIG. 6. The sucked air is exhaled from the external peripheral portions of the impeller  57 , and emitted as cooling air from the outlet port  61  of the fan casing  58  to the radiator  27 .  
     [0067] Thereby, a flow of cooling air is formed inside the second housing  10 . As shown by arrows in FIGS. 3 and 6, the cooling air flows through the cooling air passage  46  upward from the bottom, and cools the radiator  27  by force while it passes between the heat radiating fins  47 . Therefore, the heat of the IC chip  23  conducted to the radiator  27  is taken away by the flow of the cooling air. The cooling air heated by heat exchange with the radiator  27  is discharged to the outside of the display unit  3  from the exhaust slots  48  of the second housing  10 .  
     [0068] The coolant cooled while passing through the radiator  27  returns to the refrigerant channel  31  of the heat receiving head  26  through the second conduit  51 . The coolant absorbs heat of the IC chip  23  again while flowing through the refrigerant channel  31 , and then is guided to the radiator  27 . By repeating this cycle, heat of the IC chip  23  is radiated to the outside of the portable computer  1  through the display unit  3 .  
     [0069] According to such a structure, the radiator  27  contained in the display unit  3  is cooled by force of the cooling air sent from the electric fan  29 . Further, since the radiator  27  has a plurality of heat radiating fins  47  exposed to the cooling air passage  46 , the area of the radiator  27  contacting cooling air increases. This improves the heat radiating performance of the radiator  27 , and enables heat radiation of tens of watts. Therefore, it is possible to efficiently radiate heat of the IC chip  23  transferred to the radiator  27 , and to deal with increased heat generation amount of the IC chip  23  without overwork.  
     [0070] In addition, according to the above structure, plural air holes  44  are opened at the rear wall  14  of the second housing  10  opposite to the radiator  27 . Therefore, the hot air radiated from the surface of the radiator  27  can be discharged from the air holes  44  to the outside of the second housing  10 , and thereby heat hardly remains between the radiator  27  and the rear wall  14 . As a result, it is possible to prevent rise in the temperature of the surface of the rear wall  14 , and to reduce the effective temperature felt by the user when the user touches the second housing  10 .  
     [0071] Further, the electric fan  29  is located under the radiator  27 , as long as the display unit  3  is located at the open position. Therefore, the cooling air discharged from the outlet port  61  of the electric fan  29  is guided to the lower end of the cooling air passage  46 , and flows inside the second housing  10  to uniformly cover the radiator  27 . As a result, the flow of the cooling air in the second housing  10  uniformly runs inside the second housing  10 , and it is possible to efficiently cool the radiator  27 .  
     [0072] In the meantime, the portable computer  1  having the CD-ROM drive  20  sometimes plays back a music CD in the state where the display unit  3  is located at the closed position. When the display unit  3  is closed as in this state, the front wall  13  of the second housing  10  faces the top wall  4   b  of the first housing  4  and the keyboard  5 , and the first air intakes  62  formed at the front wall  13  are covered by the keyboard  5 .  
     [0073] The second housing  10  has the second air intakes  63  formed at the rear wall  14 , and in such a case the second air intakes  63  are opposite to the second inlet port  60   b  of the electric fan  29 . Therefore, even when the electric fan  29  is driven in the state where the display unit  3  is closed, the electric fan  29  can suck air outside the display unit  3  through the second air intakes  63 . Thus, the cooling air supplied to the radiator  27  is not insufficient, and the radiator  27  can utilize its radiating characteristic to the full.  
     [0074] Further, according to the above structure, the centrifugal pump  53  which circulates the coolant is contained in the second housing  10 . Therefore, it is unnecessary to secure a space only for containing the centrifugal pump  53  inside the first housing  4  including, with high density, main components of the portable computer  1 , such as the hard disk drive  19  and the CD-ROM drive  20 . Therefore, it is possible to reduce the thickness of the first housing  4 , and thin the portable computer  1 .  
     [0075] The present invention is not limited to the above first embodiment. FIGS. 9 and 10 disclose a second embodiment of the present invention. The second embodiment is different from the first embodiment in the structure of the radiator  27 . The other parts of the structure of the portable computer  1  in the second embodiment are basically the same as those in the first embodiment. Therefore, in the second embodiment, the same elements as those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and their explanations are omitted.  
     [0076] As shown in FIG. 9, the radiator  27  has a refrigerant channel  71  through which a coolant flows. The refrigerant channel  71  is formed of a plurality of first passage portions  72  and a pair of second passage portions  73   a  and  73   b . The first passage portions  72  extend in the height direction of a display unit  3 , and are arranged in parallel with each other at intervals in the width direction of the display unit  3 . The second passage portions  73   a  and  73   b  extend in the width direction of the display unit  3 , and are arranged in parallel with each other, with a space, in the height direction of the display unit  3 . The first passage portions  72  are located between the second passage portions  73   a  and  73   b . One end of each first passage portion  72  is connected to one second passage portion  73   a . The other end of each first passage portion  72  is connected to the other second passage portion  73   b.    
     [0077] As shown in FIG. 10A, a second heat radiating plate  38  of the radiator  27  has a plurality of first and second bulge portions  74  and  75 . The bulge portions  74  and  75  bulge away from the first heat radiating plate  37 . The first bulge portions  74  are provided to form the first passage portions  72 , and each has an open end opened to a first heat radiating plate  37 . The second bulge portions  75  are provided to form the second passage portions  73   a  and  73   b , and each has an open end opened to the first heat radiating plate  37 . The open ends of the first and second bulge portions  74  and  75  are closed by the first heat radiating plate  37 . Therefore, the first and second passage portions  72 ,  73   a  and  73   b  are formed between the first heat radiating plate  37  and the second heat radiating plate  38 .  
     [0078] As shown in FIGS. 10A and 10B, a bulge height H1 of the first bulge portions  74  is greater than a bulge height H2 of the second bulge portions  75 . The taller first bulge portions  74  also function as heat radiating fins  76  projecting to the cooling air passage  46 . The heat radiating fins  76  extend in the height direction of the display unit  3 , when the display unit  3  has been rotated to the open position.  
     [0079] According to the above structure, the cooling air supplied from an electric fan  29  to the cooling air passage  46  flows between the first bulge portions  74 , and cools the radiator  27  during this flow. Therefore, the first bulge portions  74  can be used as heat radiating fins  76 , and it is possible to omit dedicated fins. Therefore, it is possible to reduce the number of parts of the radiator  27 , and reduce the weight and cost thereof.  
     [0080] Further, since the cooling air flows along the surfaces of the tall first bulge portions  74 , the contact area between the radiator  27  and the cooling air increases. Therefore, the cooling air can efficiently remove the heat of the coolant flowing through the refrigerant channel  71 , and the heat radiating performance of the radiator  27  is further improved.  
     [0081]FIG. 11 discloses a third embodiment of the present invention.  
     [0082] The third embodiment is different from the first embodiment in the structure of the radiator  27 . As shown in FIG. 11, a first heat radiating plate  37  and a second heat radiating plate  38  of a radiator  27  have bulge portions  81  and  82 , respectively. The bulge portions  81  of the first heat radiating plate  37  bulge away from the second heat radiating plate  38 , and have open ends opened to the second heat radiating plate  38 . In the same manner, the bulge portions  82  of the second heat radiating plate  38  bulge away from the first heat radiating plate  37 , and have open ends opened to the first heat radiating plate  37 . The open ends of the bulge portions  81  meet the respective open ends of the bulge portions  82 .  
     [0083] Therefore, the bulge portions  81  and  82  together form refrigerant channels  83  through which the refrigerant flows. The refrigerant channels  83  project to a cooling air passage  46 , and between the radiator  27  and a rear wall  14  of a second housing  10 .  
     [0084] According to the above structure, the surface area of the radiator  27  increases, and the heat radiating area increases. Therefore, the radiator  27  improves in the heat radiating power, and can efficiently radiate the heat of the IC chip  23 .  
     [0085]FIG. 12 discloses a fourth embodiment of the present invention.  
     [0086] In the fourth embodiment, a centrifugal pump  53  is located in a downstream portion  51   b  of a second conduit  51  and contained in a first housing  4 . The centrifugal pump  53  is set to send the coolant cooled by a radiator  27  to a heat receiving head  26 . The other parts of the structure of a portable computer  1  are the same as those in the first embodiment.  
     [0087]FIG. 13 discloses the fifth embodiment of the present invention.  
     [0088] The fifth embodiment has a structure wherein a centrifugal pump  53  contained in a second housing  10  circulates coolant by force, and a radiator  27  in the second housing  10  is cooled by spontaneous air cooling. The centrifugal pump  53  is located in the vicinity of a leg portion  16   a  on the left side of the second housing  10 , below the central portion of the display unit  3 , as seen when the display unit  3  has been rotated to the open position. In the embodiment, the centrifugal pump  53  is located near the bottom portion of a refrigerant channel  40  of the radiator  27 .  
     [0089] According to such a structure, the coolant which absorbed heat of an IC chip  23  in a heat receiving head  26  is sent by force of the centrifugal pump  53  to the radiator  27 , and flows through the refrigerant channel  40  of the radiator  27 . The heat of the IC chip  23  absorbed into the coolant during this flow is diffused into first and second heat radiating plates  37  and  38 , and radiated from the surface of the radiator  27  into the second housing  10 .  
     [0090] If air bubbles exist in the coolant, air bubbles tends to collect and stay in the highest portion of the coolant passage. In the embodiment, the centrifugal pump  53  which pressurizes the coolant is located near the bottom portion of the refrigerant channel  40  of the radiator  27 , when the display unit  3  is located at the open position. Therefore, air bubbles in the coolant hardly remain in the centrifugal pump  53 , and it is possible to prevent the centrifugal pump  53  from being damaged due to cavitation.  
     [0091]FIG. 14 discloses a sixth embodiment of the present invention.  
     [0092] In the sixth embodiment, a radiator  27  and a centrifugal pump  53  form a unitary one-piece structure. The other parts of the structure of a portable computer  1  in the embodiment are basically the same as those in the first embodiment.  
     [0093] As shown in FIG. 14, the radiator  27  has a pump support portion  91 . The pump support portion  91  is located adjacent to an electric fan  29 , and is located below a refrigerant inlet  42  of a refrigerant channel  40  when a display unit  3  has been rotated to the open position. The centrifugal pump  53  is put in the pump support portion  91 . The inlet port of the centrifugal pump  53  is connected to a downstream portion  50   b  of the first conduit  50 . The outlet port of the centrifugal pump  53  is directly connected to the refrigerant inlet  42  of the radiator  27 .  
     [0094] According to such a structure, since the centrifugal pump  53  is put in the radiator  27 , the radiator  27  and the centrifugal pump  53  can be contained together in a second housing  10  of the display unit  3 . This reduces the number of the work steps in comparison with the case of containing the radiator  27  and the centrifugal pump  53  individually in a second housing  10 , and simplifies assembling of the display unit  3 .  
     [0095] Further, since the outlet port of the centrifugal pump  53  is directly connected to the refrigerant inlet  42  of the radiator  27 , it is unnecessary to provide a pipe to connect the outlet port of the centrifugal pump  53  with the refrigerant inlet  42 . This reduces the number of the parts as a matter of course, and reduce the number of work steps for mounting the radiator  27  in the display unit  3 , and thereby the manufacturing cost of the portable computer  1  can be reduced.  
     [0096] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.