Electronic apparatus having pump unit

An electronic apparatus includes a housing having a heat generating component, a heat radiating portion which radiates heat generated by the heat generating component, a pump unit having an impeller and a heat receiving portion thermally connected to the heat generating component, wherein the pump unit supplies liquid to the heat radiating portion by rotating the impeller, and a circulation path which circulates the liquid between the heat receiving portion and the heat radiating portion and transfers the heat generated by the heat generating component to the heat radiating portion through the liquid. The pump unit is arranged such that the center of the impeller is deviated from the center of the heat generating component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-339984, filed Sep. 30, 2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic apparatus having a pump unit.

2. Description of the Related Art

A CPU (Central Processing Unit) for use in an electronic apparatus tends to generate increased heat during operation, as the processing speed is increased or the functions thereof are expanded. As a countermeasure against heat, an electronic apparatus employing a so-called liquid cooling system is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-99356. In this electronic apparatus, the CPU is cooled by a coolant, whose specific heat is much higher than that of air.

However, in the field of electronic apparatuses, there is a demand for a cooling system that can more efficiently cool a heat-generating component, such as a CPU.

BRIEF SUMMARY OF THE INVENTION

According to an embodiment of the present invention, there is provided an electronic apparatus comprising: a housing having a heat generating component; a heat radiating portion which radiates heat generated by the heat generating component; a pump unit having an impeller and a heat receiving portion thermally connected to the heat generating component, wherein a center of the impeller is deviated from a center of the heat generating component and the pump unit supplies liquid to the heat radiating portion by rotating the impeller; and a circulation path which circulates the liquid between the heat receiving portion and the heat radiating portion and transfers the heat generated by the heat generating component to the heat radiating portion through the liquid.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1discloses a portable computer1as an electronic apparatus. The portable computer1comprises an apparatus main body2and a display unit3.

As shown inFIGS. 1 and 2, the apparatus main body2comprises a flat box-shaped housing10. The housing10comprises a bottom wall11a, an upper wall11b, a front wall11c, left and right side walls11dand11eand a rear wall11f. The upper wall11bhas a palm rest12and a keyboard attachment portion13. The keyboard attachment portion13is located at the back of the palm rest12. A keyboard14is attached to the keyboard attachment portion13.

The upper wall11bhas a display support portion15at the back of the keyboard14. The display support portion15protrudes upward from the rear end portion of the upper wall11b, and extends in the width direction of the housing10. The display support portion15has a pair of coupling recess portions16aand16b. The coupling recess portions16aand16bare separated from each other in the width direction of the housing10.

As shown inFIGS. 1 and 2, the display unit3comprises a liquid crystal display panel20and a flat box-shaped display housing21which houses the liquid crystal display panel20.

The liquid crystal display panel20has, on its front surface, a screen20athat displays an image. The display housing21comprises a mask22and a cover23. The mask22forms a front wall24of the display housing21. The front wall24has an opening24a. The cover23forms a rear wall25and four side walls26ato26dof the display housing21. The mask22and the cover23are arranged such that the front wall24and the rear wall25face each other, thus surrounding the liquid crystal display panel20.

The liquid crystal display panel20is housed in the display housing21, with the periphery thereof being held by a rubber frame (not shown). The screen20aof the liquid crystal display panel20is exposed to the outside of the display housing21through the opening24aof the front wall24.

The display housing21has a pair of leg portions27aand27bprotruding from an end thereof. The leg portions27aand27bare hollow and separated from each other in the width direction of the display housing21. The leg portions27aand27bare inserted in the coupling recess portions16aand16bof the housing10, and coupled to the housing10via hinge devices (not shown).

Thus, the display unit3is rotatable between a closed position, at which it flattens to cover the keyboard14from above, and an open position, at which the keyboard14and the screen20ais exposed.

As shown inFIG. 2, the housing10houses a printed wiring board30, a hard disk driver31, a battery pack32, etc. The printed wiring board30, the hard disk driver31and the battery pack32are arranged side by side on the bottom wall11aof the housing10.

A CPU33as a heat generating component is mounted on the upper surface of the printed wiring board30. The CPU33forms a microprocessor, which is the nucleus of the portable computer1, and is positioned in the back half of the printed wiring board30. The CPU33has a base board34, and an IC chip35having a square shape in a plan view and arranged in a central portion of the upper surface of the base board34. As the IC chip35is operated at a high processing speed and has many functions, it generates a great amount of heat during operation. Therefore, the IC chip35needs cooling to maintain stable operations.

The portable computer1incorporates a cooling system of liquid cooling type for cooling the CPU33. As shown inFIG. 2, the cooling system comprises a heat radiating portion40, a circulation path50and a pump unit60, which serves also as a heat receiving portion and a heat exchanger.

As shown inFIG. 2, the heat radiating portion40is housed inside the display housing21, that is, between the rear wall25of the display housing21and the liquid crystal display panel20. The heat radiating portion40has a rectangular plate shape, which is substantially the same in size as the liquid crystal display panel20.

More specifically, the heat radiating portion40comprises a first heat radiating plate41and a second heat radiating plate42as shown inFIG. 3. The first and second heat radiating plates41and42, made of metal having high thermal conductivity, are put together one on another. The first heat radiating plate41has an expanded portion43expanded in the opposite direction from the second heat radiating plate42. As shown inFIG. 2, the expanded portion43meanders on substantially the overall surface of the first heat radiating plate41. The opening end of the expanded portion43is closed by the second heat radiating plate42. Thus, a coolant flow path44is formed between the expanded portion43of the first heat radiating plate43and the second heat radiating plate42.

As shown inFIG. 2, the heat radiating portion40to radiate the heat generated from the CPU33has a coolant inlet port45and a coolant outlet port46. The coolant inlet port45is located at a left end portion (on the left side inFIG. 2) of the heat radiating portion40, communicates with an upstream end44aof the coolant flow path44, and is close to the left leg portion27aof the display housing21. The coolant outlet port46is located at a right end portion (on the right side inFIG. 2) of the heat radiating portion40, communicates with a downstream end44bof the coolant flow path44, and is close to the right leg portion27bof the display housing21. Thus, the coolant inlet port45and the coolant outlet port46are separated from each other in the width direction of the display housing21.

The circulation path50causes a liquid coolant (hereinafter referred to as the coolant L) to circulate between the pump unit60(to be described later) and the coolant flow path44of the heat radiating portion40, and transfer the heat of the CPU33to the heat radiation portion40via the coolant L. As shown inFIG. 2, the circulation path50has a first coupling pipe51and a second coupling pipe52.

The first coupling pipe51extends across the apparatus main body2and the display unit3and connects between a coolant outlet port95bof the pump housing70(to be described later) and the coolant inlet port45of the heat radiating portion40. The first coupling pipe51is led from the inside of the housing10to the inside of the display housing21through the inside of the display support portion15and the inside of the left leg portion27a.

The second coupling pipe52extends across the apparatus main body2and the display unit3and connects between a coolant inlet port93aof the pump housing70(to be described later) and the coolant outlet port46of the heat radiating portion40. The second coupling pipe52is led from the inside of the housing10to the inside of the display housing21through the inside of the display support portion15and the inside of the right leg portion27b.

As shown inFIGS. 4 to 7, the pump unit60comprises the pump housing70, serving also as a heat receiving portion, a reserve tank90having a tank main body91and a gas-liquid separating mechanism92, a rotor100having an impeller101a, an O ring110, a first cover111, a stator120and a PC board121serving as a control section.

The pump housing70has a flat rectangular shape and is made of material having a thermal conductivity of 30 W/mK of higher, for example, iron or aluminum. The pump housing70has a housing recess portion71, which opens upward. The housing recess portion71is defined by the inner surface of a bottom wall72, the inner surfaces of four side walls73ato73d, and the inner surfaces of four corner portions74ato74dshaped as substantially right-triangular columns; that is, the housing recess portion71has an octagonal shape in the plan view.

An outer surface of the bottom wall72serves as a heat receiving surface72a, which receives the heat from the CPU33. The heat receiving surface72aof the pump housing70is larger than a second region T2, which is thermally connected to the CPU33. In this embodiment, the heat receiving surface72ais greater than the area of the upper surface of the IC chip35. A groove75is formed in an upper end surface of the pump housing70, that is, the upper end surfaces of the side walls73ato73dand the corner portions74ato74dalong the periphery of a top opening71aof the housing recess portion71. The O ring110is provided along the groove75.

A recess portion78is formed in each of the four corner portions74ato74d. The recess portions78form an attachment mechanism to fix the pump unit60to the printed wiring board30. A through hole79, which allows passage of a cylindrical insert80as a part of the attachment mechanism, is formed in a bottom wall78adefining the recess portion78. The attachment mechanism will be described later. Screw receiving portions86are formed on both sides of the recess portion78(seeFIG. 6).

A partition member76rises from the inner surface of the bottom wall72defining the housing recess portion71. It serves as a partition that isolates a space having a circular shape in a plan view from the housing recess portion71. The circular space is formed in proximity to one of the four corner portions74ato74d, for example, the corner portion74d. The housing recess portion71is divided by the partition member76into a pump chamber77having a circular shape in a plan view and a remainder space surrounding the pump chamber77from the side of the three corner portions74ato74c. In other words, the pump chamber77, which houses the impeller101a, is defined by a part of the bottom wall72of the pump housing70and the partition member76. The remainder space corresponds to the tank main body91to be described later. As shown inFIG. 7, first and second communicating holes82and83, which connect the inside and the outside of the pump chamber (the inside of the pump chamber77and the inside of the tank main body91), are formed in the partition member76. Further, third and fourth communicating holes84and85, which connect the inside of the tank main body91and the outside of the pump housing70, are formed in the side walls73ato73dof the pump housing defining the tank main body, for example, the side wall73a. The portions where the third and fourth communicating holes84and85are formed are not limited to the side wall73a. The third and fourth communicating holes84and85may be formed in a region which defines the tank main body91. The third and fourth communicating holes84and85may be formed in different side walls.

The reserve tank90comprises the tank main body91as a reservoir which stores liquid, a first pipe93, a second pipe94, a third pipe95, etc. The first pipe93and the second pipe94form the gas-liquid separating mechanism92.

One end portion of the first pipe93has a coolant inlet port93ato supply the coolant L into the pump unit60. The other end portion thereof has a discharge port93bto discharge the coolant L into the tank main body91. The first pipe93is inserted into the tank main body91through the third communicating hole84from the outside of the pump housing70. The coolant inlet port93aof the first pipe93, protruding from the side wall73ato the outside of the pump housing70(toward the rear of the housing10), is connected to the second coupling pipe52of the circulation path50(seeFIG. 2). The discharge port93bis located inside the tank main body91and open to the inside of the tank main body91. In the reserve tank90, the discharge port93bis located at or near the barycenter of the tank main body91(hereinafter referred to as a barycenter portion G).

One end of the second pipe94has an inflow port94athrough which the coolant L stored in the tank main body91flows in. The inflow port94bis located inside the tank main body91and open to the inside of the tank main body91. The inflow port94aas well as the discharge port93bis located at the barycenter portion G in the tank main body91. Thus, the inflow port94aand the discharge port93bface each other at the barycenter portion G in the tank main body91. The inflow port94aand the discharge port93bare located under an initial liquid surface F0of the coolant L in the state where the coolant L is stored in the tank main body91, so that they are always kept submerged under the coolant L (seeFIGS. 8 and 9).

The other end of the second pipe94communicates with the first communicating hole82. In other words, the inside of the pump chamber77and the inside of the tank main body91are connected through the second pipe94. As a result, the coolant L transferred from the tank main body91flows into the pump chamber77through the communicating hole82.

One end of the third pipe95communicates with the second communicating hole83. The other end of the third pipe95has the coolant outlet port95b, through which the coolant L flows out of the pump unit60. The third pipe95connects the inside of the pump chamber77and the outside of the pump housing70through the second communicating hole83and the fourth communicating hole85. The coolant outlet port95bof the third pipe95, protruding from the side wall73ato the outside of the pump housing70(toward the rear of the housing10), is connected to the first coupling pipe51of the circulation path50.

With the above structure, the reserve tank90storing the coolant L can be incorporated in the pump unit60. In addition, the reserve tank90can be interposed in the circulation path50by connecting the first pipe93to the second coupling pipe52and connecting the third pipe95to the first coupling pipe51.

It is preferable that the gas-liquid separating mechanism92be arranged in a region corresponding to the second region T2where the pump housing (heat receiving portion)70is thermally connected to the CPU33, as shown inFIG. 7. In this embodiment, the second region T2corresponds to a region where the IC chip35is thermally connected to the heat receiving surface72a. With the gas-liquid separating mechanism92arranged as described above, the first pipe93can be heated by the heat generated from the CPU33. Therefore, if gas is trapped in the first pipe93, the gas is expanded and satisfactorily discharged in the tank main body91through the gas-liquid separating mechanism92(between the discharge port93band the inflow port94a).

The rotor100is housed in the pump chamber77. The rotor100comprises a rotor assembly101and a shaft102. The rotor assembly101comprises the impeller101a, a magnet (not shown), and a rotor yoke, the ends of which form a pair of protrusion poles (not shown). The shaft102, made of metal, is passed through a center O1of each of the rotor yoke, the magnet and the impeller101a, and fixes the rotor yoke, the magnet and the impeller101a. The shaft102is rotatably supported by the pump housing70.

The impeller101ahas a plurality of vanes101b. The vanes101bextend radially from the center O1of the impeller101a.

As shown inFIGS. 4 to 6, the first cover111, made of resin, is shaped as a square plate. Each of the corner portions of the first cover111has a hole portion112of the diameter substantially the same as that of the recess portion78. Screw through holes113are formed on both sides of the hole portion112. The first cover111is provided above the pump housing70so as to cover the top opening71aof the housing recess portion71. Since the O ring110is provided at the upper edge of the pump housing70, the housing recess portion71and the tank main body91are liquid-tight by closing the top opening71aof the pump housing70with the first cover111. When the first cover111is stacked on the pump housing70to cover the top opening71a, the inner periphery of the hole portion112is continuos to the inner surface of the recess portion78of the pump housing70.

A first recess portion114, which houses the stator120, and a second recess portion115, which house the PC board121, are provided on the upper surface of the first cover111. The stator120is housed in the first recess portion114so that the center thereof coincides with the center of the rotor100(the axial line of the shaft102). The second recess portion115is formed at a position other than the position of the first recess portion114.

Even when the first cover111covers the pump housing70, the coolant L may be seeped out of the pump housing70or evaporated. If the first cover111is made of resin, in particular, the coolant L is easily seeped out of the pump housing70or evaporated. Therefore, in the portable computer1, a second cover130made of metal further covers the first cover111over the pump housing70.

More specifically, the second cover130is substantially shaped as a rectangle, the corner portions of which are cut off (seeFIG. 6). Screw through holes131are provided on both sides of the cut-off portion of each corner portion. The second cover130is fixed to the pump housing70by screwing screws133in the screw receiving portions86of the pump housing70through the screw through holes131of the second cover and the screw through holes113of the first cover.

In the pump unit60of the structure described above, the rotor100is rotated to transfer the coolant L by applying power to the stator120. Since power is applied to the stator120with the magnetization phase successively changed, a rotary magnetic field is generated in the circumferential direction of the stator120accordingly. The magnetic field magnetically couples with the magnet of the rotor100, so that torque is generated between the stator120and the magnet. As a result, the rotor100with the impeller101arotates in the direction of an arrow Y shown inFIG. 7. The rotor100is rotated, for example when the portable computer1is powered on or the temperature of the CPU33rises to a predetermined value. The application of power to the stator120is controlled by the PC board121.

The pump unit60is housed in the housing10and mounted on the upper surface of the printed wiring board30. Four boss portions30aare formed in the printed wiring board30at positions corresponding to the corner portions74ato74dof the pump housing70(inFIG. 5, only one boss portion30ais shown).

The attachment mechanism comprises a cylindrical insert80, a screw81, a coil spring87and a C ring88. The insert80has a flange portion80aprotruding outward horizontally from the outer periphery of its upper end portion along the circumferential direction. Further, a groove80bis formed in the outer periphery of the insert80along the circumferential direction.

The pump unit60is pressed against the CPU33by the attachment mechanism as described below (seeFIG. 5). First, the insert80is inserted through the coil spring87. The insert80is inserted in the opening of the hole portion112of the first cover111, and passed through the through hole79. The groove portion80bis positioned below the heat receiving surface72aof the pump unit60, and the C ring88is fitted into the groove portion80b. As a result, the insert80is attached to the pump unit60in the state where the flange portion80ais forced away from the bottom wall78aby means of the coil spring87.

Conductive grease (not shown) is applied to the upper surface of the IC chip35, and the heat receiving surface72aof the pump housing70is caused to face the IC chip35. The screw81passed through the insert80is screwed in the boss portion30aof the printed wiring board30. Thus, the insert80is fixed to the boss portion30a. As a result, the pump unit60is pressed against the IC chip35by the elasticity of the coil spring87. Consequently, the IC chip35of the CPU33is thermally connected to the heat receiving surface72aof the pump housing70via the conductive grease.

In the portable computer1, the pump unit60is fixed to the printed wiring board30so that the center of the pump unit60(the center of the heat receiving surface) coincides with the center O2of the IC chip35(which coincides with the center of the CPU33in this embodiment). On the other hand, in the pump unit60, the center O1of the impeller101ais deviated from the center of the pump unit60. Therefore, the center O2of the IC chip35is deviated from the center O1of the impeller101a, which faces the IC chip35via the pump housing70(seeFIG. 7). Further, the impeller101ahas a radius longer than the distance between the center O1of the impeller101aand the center O2of the IC chip35. In other words, the length of each of the vanes101bis longer than the distance between the center O1of the impeller101aand the center O2of the IC chip35. Thus, the pump unit60is arranged such that the peripheral portion of the impeller101aoverlaps the center O2of the IC chip35.

Further, the pump unit60has a projecting portion140in a first region T1of the inner surface of the bottom wall72. The first region T1is formed by connecting the first communicating hole82, the second communicating hole83and the center O1of the impeller101a(seeFIG. 6). The projecting portion140is a so-called side channel employed in a side-channel pump. It is preferable that the first region T1of the pump unit60overlap the position of the center O1of the CPU33. Particularly preferably, the projecting portion140of the pump unit60covers the position of the center O1of the CPU33(seeFIG. 7).

With the arrangement described above, the CPU33as a heat generating component can be cooled more efficiently.

The pump chamber77of the pump unit60, the tank main body91of the reserve tank90, the coolant flow path44of the heat radiating portion40and the circulation path50are filled with the coolant L as a liquid cooling agent. For example, an antifreezing solution containing an aqueous solution of ethylene glycol, to which a corrosion inhibitor is added if necessary, can be used as the coolant L.

In the structure as described above, the IC chip35of the CPU33generates heat while the portable computer1is used. Since the IC chip35is thermally connected to the heat receiving surface72aof the pump housing70, the heat of the IC chip35is transferred to the pump housing70. The pump chamber77of the pump housing70is filled with the coolant L, which absorbs a large-amount of heat generated from the IC chip35transferred to the pump housing70.

When the IC chip35is heated to a predetermined temperature, power is applied to the stator120with the magnetization phase successively changed. As a result, torque is generated between the stator120and the magnet of the rotor100, so that the rotor100with the impeller101arotates. When the rotor100is rotated, the coolant L circularly flows in the pump chamber77and sent out to the heat radiating portion40through the second communicating hole83and the third pipe95. Thus, the coolant L is forced to circulate between the pump unit60and the heat radiating portion40.

More specifically, the coolant L heated by the heat exchange in the pump chamber77is supplied to the first coupling pipe51of the circulation path50through the third pipe95. The coolant L supplied to the first coupling pipe51is transferred to the heat radiating portion40, and the heat is radiated from the heat radiating portion40to the outside of the portable computer1. The coolant L cooled by the heat exchange in the heat radiating portion40is returned to the pump unit60through the second coupling pipe52of the circulation path50. The coolant L returned to the pump unit60flows through the first pipe93and discharged through the discharge port93binto the tank main body91.

The reserve tank90includes the gas-liquid separating mechanism92described above. If bubbles X are trapped in the coolant L flowing through the first pipe93(seeFIG. 9), they move upward in the coolant L inside the tank main body91and collected in an air layer A in an upper portion of the tank main body91. Therefore, even if the bubbles X are trapped in the coolant L, they can be discharged out of the discharge port93bof the first pipe93. As a result, the bubbles X can be separated from the coolant L.

Further, since the inflow port94ais submerged under the coolant L stored in the tank main body91, the coolant L in the tank main body91is caused to flow into the pump chamber77through the second pipe94. Thus, the gas-liquid separating mechanism92(the first and second pipes93and94) not only separates bubbles from the coolant L but also forms a part of the path for circulating the coolant L between the pump housing70and the heat radiating portion40.

The coolant L guided to the pump chamber77again absorbs the heat from the IC chip35and is sent out to the heat radiating portion40through the third pipe95and the first coupling pipe51. As a result, the heat generated in the IC chip35is successively transferred to the heat radiating portion40via the circulating the coolant L, and discharged out of the portable computer1through the heat radiating portion40.

When the portable computer1is carried or transported, the posture of the housing10incorporating the reserve tank90is changed. Therefore, the posture of the reserve tank90is changed in various directions as shown inFIGS. 8 and 9. Accordingly, the liquid surface F of the coolant L changes.

Even in such a case, according to this embodiment, the inflow port94aof the second pipe94is always located under an initial liquid surface F0of the coolant L, because the discharge port93bof the first pipe93and the inflow port94aof the second pipe94face at the barycenter portion G of the tank main body91. Therefore, the inflow port94aof the second pipe94is kept submerged under the coolant L.

Further, since the inflow port94aof the second pipe94is located at the barycenter portion G, even if the coolant L stored in the tank main body91reduces and the liquid surface F lowers, the inflow port94awill not open to the air layer A in the tank main body91before the coolant L is reduced to substantially half of the tank main body91or less. Therefore, air is prevented from entering into the pump chamber77or the circulation path50from the inflow port94a. Consequently, the heat of the CPU33can be efficiently absorbed by the coolant L.

Furthermore, since the center O1of the impeller101ais deviated from the center O2of the IC chip35as described above, a greater amount of heat of the IC chip35can be absorbed by the coolant L. The IC chip35preferably faces a position where the coolant L flows at a higher speed with the pump housing70(a heat receiving portion) interposed therebetween so that the coolant L can absorb a greater amount of heat from the IC chip35. As well known, the flow rate of the coolant L caused by the rotation of the rotor100increases with the distance from the center O1of the impeller101a. Therefore, with the arrangement of the pump unit60such that the center O1of the impeller101ais deviated from the center O2of the CPU33or the outer periphery thereof overlaps the center O2of the CPU33, a greater amount of heat from the IC chip35can be absorbed by the coolant L. The arrangement of the pump unit60such that the projecting portion (side channel)140overlaps the center O2of the CPU33is also advantageous in that a greater amount of heat from the IC chip35can be absorbed by the coolant L.

As described above, with the gas-liquid separating mechanism92of this embodiment, the discharge port93band the inflow port94aface each other in the coolant L stored in the tank main body91. Further, in this embodiment, the gas-liquid separating mechanism92is provided in the reserve tank90. Therefore, the bubbles X in the coolant L in the heat radiating portion40or the circulation path50can be separated from the coolant L and collected in the air layer A in the upper portion of the tank main body91with the simple structure. Consequently, the CPU33can be efficiently cooled by applying the gas-liquid separating mechanism92and the reserve tank90to the portable computer.

In addition, air is prevented from entering into the pump chamber77or the circulation path50from the inflow port94awith the simple structure of the discharge port93band the inflow port94afacing each other at the barycenter portion G of the tank main body91. Thus, the structure of the cooling system is simplified and the manufacturing cost is reduced without adding a complicated gas-liquid separating mechanism to the reserve tank90.

Further, in the portable computer1of this embodiment, the pump unit60is arranged such that the center of the impeller101ais deviated from the center of the CPU33, and that the outer periphery of the impeller101aoverlaps the center O2of the CPU33. Thus, since the CPU33faces a portion where the coolant L flows at a high rate with the pump housing70interposed therebetween, a greater amount of heat from the CPU33is absorbed by the coolant L. Furthermore, the pump unit60is arranged such that the projecting portion (side channel)140overlaps the center O2of the CPU33. Therefore, a greater amount of heat from the IC chip35can be absorbed by the coolant L. Consequently, the CPU33can be efficiently cooled.

Moreover, in the portable computer1of this embodiment, the second cover130made of metal covers the pump unit60over the first cover111. Therefore, seeping out of the coolant L from the pump unit60is suppressed by the second cover130. Consequently, the CPU33can be efficiently cooled by the coolant L. In addition, since the coolant L stays long in the cooling system, the cooling effect of the CPU33is maintained for a long time and there is no need of replenishing the coolant L.

Furthermore, in the portable computer1of this embodiment, the pump unit60has the reserve tank90, which is interposed in the circulation path50and stores the coolant L. Therefore, the heat generating component, such as the CPU33, can be efficiently cooled by applying the pump unit60as described above with a simple structure. Moreover, since the assembly of the cooling system is simplified, the manufacturing cost is reduced.

A second embodiment of the present invention will be described below with reference toFIG. 10.

The portable computer1comprises a reserve tank90as shown inFIG. 10. The reserve tank90comprises a pipe96in place of the first pipe93and the second pipe94of the first embodiment. One end of the pipe96is connected to the first communicating hole82. The other end of the pipe96has the coolant outlet port95bthrough which the coolant L flows out of the pump unit60. The pipe96connects the inside of the pump chamber77and the outside of the pump housing70through the third communicating hole84. The coolant outlet port95bof the pipe96, protruding from the side wall73ato the outside of the pump housing70(toward the rear of the casing10), is connected to the second coupling pipe52of the circulation path50.

The pipe96has distribution ports96a, which allow passage of the liquid, in an intermediate portion thereof. The distribution ports96aare realized by forming a plurality of slits in the wall that forms the pipe96. The pipe96is arranged such that the distribution ports96aare located inside the tank main body91. In this embodiment, the distribution ports96aare located at the barycenter portion G of the tank main body91. In the state where the coolant L is stored in the tank main body91, the distribution ports96aare submerged in the coolant L in the tank main body91. The other structures, including the portions not shown in the drawings, are the same as those of the first embodiment described above. Therefore, the same parts are identified by the same reference symbols and redundant description will be omitted.

In this embodiment, the pipe96forms the gas-liquid separating mechanism92. If bubbles X are trapped in the coolant L flowing through the pipe96, they are discharged through the distribution ports96ainto the tank main body91, move up in the coolant L in the tank main body91, and are collected in the air layer A in the upper portion of the tank main body91. Thus, even if bubbles X are trapped in the coolant L, they can be discharged through the distribution ports96aof the pipe96and separated from the coolant L by the gas-liquid separating mechanism92.

As described above, according to the gas-liquid separating mechanism92of the second embodiment, the pipe96is arranged such that the distribution ports96aformed therein are located inside the tank main body91. Therefore, the bubbles X trapped in the coolant L in the heat radiating portion40or the circulation path50can be separated from the coolant L and collected in the air layer A in the upper portion of the tank main body91. Consequently, the CPU33can be efficiently cooled by applying the gas-liquid separating mechanism92and the reserve tank90as described above to the portable computer1.

In addition, air is prevented from entering into the pump chamber77or the circulation path50through the inflow port94awith the simple structure of the distribution ports96aprovided at the barycenter portion G. Thus, because it is unnecessary to add a complicated gas-liquid separating mechanism to the reserve tank90, the structure of the cooling system is simplified and the manufacturing cost is reduced.

In the second embodiment, a plurality of slits are provided as the distribution ports96a. However, the shape and the number of the distribution ports96aare not limited to those in this embodiment.

A third embodiment of the present invention will be described below with reference toFIG. 11.

The portable computer1of this embodiment comprises the reserve tank90as shown inFIG. 11. The open end of the inflow port94aof the second pipe94is widened toward the first pipe93. The other structures, including the portions not shown, are the same as those of the first embodiment described above. Therefore, the same parts are identified by the same reference symbols and redundant description will be omitted.

According to this embodiment, since the open end of the inflow port94aof the second pipe94is widened toward the first pipe93, the coolant L in the tank main body91can be efficiently taken through the second pipe94and supplied to the pump chamber77.

The portable computer1of the fourth embodiment comprises the reserve tank90as shown inFIG. 12. The open end of the discharge port93bof the first pipe93is widened toward the second pipe94. The other structures, including the portions not shown, are the same as those of the first embodiment described above. Therefore, the same parts are identified by the same reference symbols and redundant description will be omitted.

According to the fourth embodiment, since the open end of the discharge port93bis widened toward the second pipe94, the coolant L flowing through the first pipe93can be efficiently discharged into the tank main body91. Moreover, the bubbles in the first pipe93can be efficiently discharged into the tank main body91. Therefore, the gas-liquid separating capacity of the gas-liquid separating mechanism92can be improved.

A fifth embodiment of the present invention will be described below with reference toFIG. 13.

The portable computer1of the fifth embodiment comprises the reserve tank90as shown inFIG. 13. The open end of the discharge port93bof the first pipe93is widened toward the second pipe94. The open end of the inflow port94aof the second pipe94is widened toward the first pipe93. The other structures, including the portions not shown, are the same as those of the first embodiment described above. Therefore, the same parts are identified by the same reference symbols and redundant description will be omitted.

According to the fifth embodiment, since the open end of the discharge port93bis widened toward the second pipe94, the coolant L flowing through the first pipe93can be efficiently discharged into the tank main body91and the gas-liquid separating capacity of the gas-liquid separating mechanism can be improved. In addition, since the open end of the inflow port94ais widened toward the first pipe93, the coolant L in the tank main body91can be efficiently taken through the second pipe94and supplied to the pump chamber77.

The gas-liquid separating mechanism of the present invention is widely applicable to not only the reserve tank but also anything that has a reservoir portion for storing liquid. The reserve tank having the gas-liquid separating mechanism may be independent of the pump unit.

The electronic apparatus of the present invention is not limited to the portable computer. The present invention is applicable to various types of electronic apparatus, which incorporates a heat generating body, such as a circuit part that generates a large amount of heat.