Heat exchanger, light source device, projector and electronic apparatus

A heat exchanger, includes a housing including an inlet passage through which a fluid is introduced, an outlet passage from which the fluid is discharged, an inner communication space in which the fluid flows from the inlet passage and the outlet passage, and a plurality of unit plates of thin flat plates that are disposed in parallel to a flowing direction of the fluid, the plurality of unit plates layered in a direction to be substantially orthogonal to the flowing direction, the plurality of unit plates each having a fin in parallel to the flowing direction of the fluid, a frame enclosing the fin and projecting in an out-of-plane direction of the fin, and holes respectively communicating with the inlet passage and the outlet passage. Heat is exchanged between a heating body attached on an outer surface of the housing and the fluid.

The entire disclosure of Japanese Patent Application No. 2005-364078, filed Dec. 16, 2005, is expressly incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a heat exchanger, a light source device, a projector and an electronic apparatus.

2. Related Art

Projectors have been known as an image projecting device.

The projectors each include a light source and an optical modulation panel which modulates light from the light source for each pixel. The projectors project the light modulated by the optical modulation panel on a screen to display an image.

Recently, LEDs (light-emitting diodes) or LDs (laser diodes), which have characteristics such as immediate lighting and long lifetime, have been considered for use as a light source for the projectors.

However, the LEDs and the LDs generate an extremely large amount of heat and an area of a portion of the LEDs and the LDs from which the heat is generated is extremely small compared with light sources in the related art, which requires a heat exchanger capable of absorbing the large amount of heat from the extremely small area.

As such a heat exchanger, a heat exchanger having a below-described arrangement is known (see, for example, JP-A-2005-166855).

This document discloses the heat exchanger that includes fins inside and circulates a cooling medium inside such that heat is exchanged between the fins and the cooling medium. For the heat exchanger, thin plate members for forming the fins and spacers that are held between the fins for spacing the fins are prepared. The fins and the spacers are made of a metal having a high thermal conductivity and formed by punching. The thin plate members and the spacers are alternately layered and then integrated as a whole by brazing. Consequently, small passages are formed between the fins. While the cooling medium flows through the small passages, heat is efficiently exchanged between the fins and the cooling medium. Since the fins can be processed to be thin, the heat exchanger can have high heat exchange efficiency.

However, as disclosed in the document, the arrangement in which the thin plate members and the spacers are layered requires many joint surfaces. Specifically, one small passage needs two joint surfaces. Such joint surfaces have a low thermal conductivity, hindering heat of a heat generating body from diffusing in a direction in which the thin plate members are layered. Accordingly, fins far from the heat generating body may not become hot enough, so that the thermal conductivity to the fluid may be lowered, thereby lowering the heat exchanging capability of the heat exchanger.

Further, the number of the fins and the spacers is very large, which may cause an increase in component costs and a decrease in assembling efficiency.

SUMMARY

An exemplary aspect of the invention is to provide a heat exchanger that can be manufactured at low cost and that has a high performance.

A heat exchanger according to an aspect of the invention includes: a housing including an inlet passage through which a fluid is introduced, an outlet passage from which the fluid is discharged, an inner communication space in which the fluid flows from the inlet passage and the outlet passage, and a plurality of unit plates of thin flat plates that are disposed in parallel to a flowing direction of the fluid. The plurality of unit plates are layered in a direction to be substantially orthogonal to the flowing direction. The plurality of unit plates each have a fin in parallel to the flowing direction of the fluid. The heat exchanger also includes: a frame enclosing the fin and projecting in an out-of-plane direction of the fin, and holes respectively communicating with the inlet passage and the outlet passage. Heat is exchanged between a heating body attached on an outer surface of the housing and the fluid.

In such an arrangement, the housing having the communication space inside is formed by layering the plurality of unit plates.

Specifically, by jointing surfaces of the frames of the unit plates, an outer surface of the housing is formed. Since the unit plates each are provided with the fin that is disposed in parallel to the flowing direction of the fluid, the plurality of fins are disposed (in the communication space) inside the housing formed by layering the plurality of unit plates. Accordingly the small passages are formed between the fins. The heating body is attached on the outer surface of the thus assembled heat exchanger. The heating body may be a heat generating body that generates heat of high temperature or a heat absorber that absorbs heat.

The heat from the heating body is transferred to the outer surface of the heat exchanger and to the fins of the unit plates. In this state, when the fluid is introduced from the inlet passage to the communication space, the fluid flows through the small passages between the fins to the outlet passage. During flowing, the heat is exchanged between the fins and the fluid via the contact between the fins and the fluid.

In the arrangement, since the plurality of fins are disposed in the communication space in which the fluid flows, a contact area between the fins and the fluid can be large, heat exchange efficiency can be enhanced.

Note that since the housing is formed by layering the unit plates, when the number of joint portions is increased, the thermal conductivity in the joint portions may be lowered. Thereby, the heat from the heating body may not transfer enough in the layering direction, which may be a problem For example, when the fins and the spacers are alternately layered like the related art, one small passage between the fins is formed by jointing one fin with another fin with one spacer interposed, so that two jointing portions are required for one small passage. This means that one hundred jointing portions are necessary to form fifty small passages.

In contrast, in the exemplary aspect of the invention where the fin and the frame are integrally formed to the unit plate, two unit plates can be jointed by one jointing surface to form one small passage. Namely only one jointing portion is necessary for one small passage. In other words, only fifty jointing portions are necessary to form fifty small passages. Accordingly, the number of the joint portions becomes a half of the number in the related art. Thus, since the number of the joint portions can be halved, the thermal conductivity of the heat exchanger can be enhanced, so that the heat of the heating body can be efficiently transferred to the fins of the unit plates. As a result, the heat can be transferred from the fins to the fluid, so that the heat exchanger can have high heat exchange efficiency.

According to the exemplary aspect of the invention, since the fin and the frame are integral, the number of components can be halved compared with the related art, halving assembling work.

Hence, the manufacturing cost of the heat exchanger can be low and the heat exchanger can have a high performance.

The unit plates may be made of copper, aluminum or an alloy of copper or aluminum which have a high thermal conductivity.

For example, diffusion jointing may be employed to joint the unit plates.

According to the exemplary aspect of the invention, the frame may be provided so as to project toward one of a front surface side and a rear surface side of the fin, and the unit plates each have a C-shape in cross section.

According to the exemplary aspect of the invention, since the frame of the unit plate projects in one direction relative to the fin, the small passages can be formed by layering the unit plates such that the respective projecting directions of the frames of the unit plates are the same, thereby forming the heat exchanger.

According to the exemplary aspect of the invention, the frame may be provided so as to project toward both of the front surface side and the rear surface side of the fin, and the unit plates each have an I-shape in cross section.

According to the exemplary aspect of the invention, when the unit plates are layered, the small passages are formed between the fins, thereby forming the heat exchanger.

Note that in forming the unit plates having the I-shape in cross section, the frame may be formed so as to project by pressing the thin plate from both of the front and rear surfaces to thin the fin, for example.

When the frame is formed by pressing the thin plate so as to project by an amount in which the fin is thinned, a height of the frame (a projecting height from the fin) can be extremely thin. Accordingly, the small passage can be thin by reducing the distance between the fins when layering the unit plates. As a result, since the contact area between the fins and the fluid can be increased, the thermal conductivity from the fins to the fluid can be enhanced, thereby enhancing the performance of the heat exchanger.

According to the exemplary aspect of the invention, the frame may be provided so as to project toward both of the front surface side and the rear surface side of the fin and such that a projecting direction of the frame is slant relative to the surfaces of the fin, and the unit plates each have a Z-shape in cross section.

In the arrangement, since the frame is slant relative to the fin, the area of the fin can be larger. Accordingly, since the contact area between the fluid and the fin having a larger area can be increased, the thermal conductivity from the fins to the fluid can be enhanced.

According to the aspect of the invention, the heat exchanger may further include a fin plate having a fin in parallel to the flowing direction of the fluid and holes respectively communicating with the inlet passage and the outlet passage, the fin plate provided between the unit plates.

In the arrangement, by providing the fin plates between the unit plates, the distance between the fins can be extremely small. In addition, the small passages can be narrow and the number of the fins can be increased (for example, doubled), thereby enhancing the performance of the heat exchanger.

A light source device according to an exemplary aspect of the invention includes a light source and a heat exchanger attached to the light source.

In the arrangement, although heat is generated when the light source emits light, the heat is absorbed by the fluid of the heat exchanger, so that the heat of the light source can be absorbed.

In the arrangement, since the heat of the light source can be efficiently absorbed by the heat exchanger, a temperature rise of the light source can be suppressed and the light emission of the light source can be stable. In addition, the light source can have a longer life.

Further, since the heat of the light source can be efficiently absorbed by the heat exchanger, LEDs (light-emitting diodes) or LDs (laser diodes) which generate a large amount of heat from an extremely small area can be employed as a light source of light source devices.

A projector according to an exemplary aspect of the invention includes a light source device; an optical modulator that modulates light irradiated from the light source device in accordance with image data, and a projecting device that projects the light modulated by the optical modulator.

In the arrangement, the light from the light source is modulated by the light modulator. The modulated light is projected by the projecting device and an image is projected on, for example, a screen.

In the arrangement, since the heat of the light source can be efficiently absorbed by the heat exchanger, an increase in temperature of the light source can be suppressed and the light emission of the light source can be stable. In addition, the light source can have a longer life. Thereby, the performance of the projector can be enhanced. Further, since the heat of the light source can be efficiently absorbed by the heat exchanger, LEDs (light-emitting diodes) or LDs (laser diodes) which generate a large amount of heat from an extremely small area can be employed as a light source of light source devices. As a result, luminance of the image by the projector can be high.

An electronic apparatus according to an exemplary aspect of the invention includes the aforesaid heat exchanger and an electronic device that is attached to the heat exchanger and generates heat during operation.

In such an arrangement, the heat from the electronic device can be efficiently absorbed by the heat exchanger. As a result, an increase in temperature of the electronic device can be suppressed and the operation of the electronic device can be stable. Further, the electronic device can have a longer life.

DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

Exemplary embodiments of the invention are illustrated in the attached drawings and will be described below with reference to the reference numerals assigned to elements in the drawings.

First Exemplary Embodiment

A first exemplary embodiment will be described.

FIG. 1shows an appearance of a projection system100.

The projection system100includes a personal computer (an information processor)110which outputs an image data signal based on an image of image source, a projector (an image display device)120which generates a present image frame based on the image data signal from the personal computer110and projects the generated present image frame onto a screen180and a USB cable (a signal transmitter)170which connects the projector120and the personal computer110.

FIG. 2shows an inner structure of the projector120.

The projector120includes LEDs (light sources, heating bodies)131to133which respectively emit color light of R (red), G (green) and B (blue), liquid crystal panels (optical modulators)141to143which modulate the light from the LEDs131to133, a prism150which combines the light modulated by the liquid crystal panels141to143, a projection optical system (a projecting device)160which projects the combined light onto the screen180and a heat absorbing mechanism200which absorbs heat generated by the LEDs131to133.

The LEDs131to133are respectively provided for the colors. Specifically, the LEDs131to133are a red color LED131, a green color LED132and a blue color LED133.

The LEDs131to133are heat generating bodies which generate a large amount of heat from a small area. Accordingly, the heat of the LEDs131to133needs to be absorbed in order to stabilize the colors of the light emitted from the LEDs131to133or to prevent damage on the LEDs131to133.

The liquid crystal panels as the optical modulators are a red color liquid crystal panel141, a green color liquid crystal panel142and a blue color liquid crystal panel143which are disposed so as to face the LEDs131to133of respective colors.

The liquid crystal panels141to143are driven by a predetermined drive signal in accordance with image information. The liquid crystal panels141to143modulate the light from the LEDs131to133for each pixel. The light from the liquid crystal panels141to143is combined by the prism150to form an image. The combined image is irradiated from the projection optical system160and projected on the screen180in an enlarged manner.

The heat absorbing mechanism200includes heat exchangers300which are attached on rear surfaces of the LEDs131to133and absorb the heat from the LEDs131to133, a pump210for supplying a cooling medium to the heat exchangers300, a radiator220which releases heat of the cooling medium and a pipe230which connects the heat exchangers300, the pump210and the radiator220.

The heat exchangers300are respectively attached on the rear surfaces of the red color LED131, the green color LED132and the blue color LED133.

FIG. 3shows an appearance of the heat exchangers300on which the LEDs131to133are attached.FIG. 4is a cross section of the heat exchangers300.

The heat exchangers300each include two end plates311,312and a plurality of unit plates320layered on each other between the two end plates311,312.

The heat exchangers300are made of a metal having a high thermal conductivity such as copper, aluminum or an alloy of copper or aluminum.

The two end plates311,312have a rectangular thin flat plate shape.

The end plate311on a front side out of the two end plates is provided with two nozzles311A,311B for connecting with the pipe230. The two nozzles311A,311B are respectively disposed near ends of the end plate311.

The nozzle311A is an inlet nozzle (an inlet passage) into which the cooling medium flows. The nozzle311B is an outlet nozzle (an outlet passage) from which the cooling medium is discharged.

FIG. 5is a perspective view of the unit plates320.

As shown inFIG. 5, the unit plates320each are a thin plate in a substantially same shape as a whole as that of the end plates311,312. The unit plates320each include a frame321, holes322and a fin323. The frame321has a thickness of about 100 μm. The frame321encloses a center portion at an outer periphery of the unit plate320.

The holes322are formed so as to penetrate the unit plate320at ends in a lengthwise direction of the unit plate320, the holes322being on inner sides of the frame321.

The fin323has a smaller thickness than the frame321, the thickness being about a half of that of the frame321. The fin323is not provided on a rear surface side of the unit plate320out of a front surface side and the rear surface side of the unit plate320. Specifically, the frame321projects toward the front surface side from the fin323by about 50 μm.

FIGS. 6 and 7are illustrations for explaining a manufacturing process of the unit plates320.

The manufacturing process of the unit plates320will be described with reference toFIGS. 6 and 7.

Firstly, a thin plate330having a thickness of about 100 μm and a rectangular shape is prepared. Both of front and rear surfaces of a portion to be the frame321of the thin plate330are provided with masks331. Only one surface of a portion to be the fin323of the thin plate330is provided with the mask331. No mask331is provided on portions to be the holes332of the thin plate330. Accordingly, the thin plate330is provided with the masks331as shown inFIG. 6.

In this state, the thin plate330is dipped in a dissolving solution. In the dissolving solution, a portion provided with no mask331begins to be dissolved. The portions for the holes332begin to be dissolved from both surfaces while the portion for the fin323begins to be dissolved from one surface. By picking up the thin plate330from the dissolving solution when the holes332penetrate the thin plate330and the thickness of the fin323is the half of the thin plate330, the formed unit plate320that has the holes332and the fin323having the half thickness of that of the frame321can be obtained as shown inFIG. 7. The unit plate320has a C-shape in cross section.

The thus obtained unit plates320and the separately prepared end plates311,312are layered and integrated by diffusion bonding. Then, the nozzles331A,331B are fixed, thereby completing the heat exchanger300.

As shown inFIG. 4, in the assembled heat exchanger300, a communication space340is defined by the frames321of the unit plates320.

In the communication space340, the fins323of the unit plates320are aligned at a small interval, forming small passages between the fins323.

Since the LEDs131to133are attached on upper surfaces of the heat exchangers300, the upper surfaces of the heat exchangers300are processed to be smooth such that the heat exchangers300can firmly stick to the LEDs131to133. When the cooling medium is flown from the inlet nozzle311A, the cooling medium flows through the small passages between the fins323to the outlet nozzle311B and is discharged from the outlet nozzle311B to the outside of the heat exchanger300.

As shown inFIG. 2, the three heat exchangers300with the LEDs131to133attached thereon and the pump210are parallel connected by the pipe230. The radiator220is provided on the pipe230, so that the heat of the cooling medium is released by the radiator220.

Next described will be an operation of the projection system100that has the above-stated arrangement.

When the projector120is turned ON, a voltage is applied on the LEDs131to133to light the LEDs131to133. Thereby, the LEDs131to133emit the light of the colors and generate heat.

When the projector120is turned ON, the pump210is also operated. Accordingly, the cooling medium is supplied from the pump210through the pipe230to the three heat exchangers300.

The heat generated by the LEDs131to133is transferred to the upper surfaces of the heat exchangers300and to the fins323of the unit plates320. The cooling medium flown from the inlet nozzle311A flows through the small passages between the fins to the outlet nozzle311B. During flowing, the heat of the fins323is transferred to the cooling medium in a contact between the fins323and the cooling medium. The cooling medium which has become hot is discharged from the outlet nozzle311B and flows through the pipe230to be introduced to the radiator220. The radiator220releases the heat of the cooling medium.

In such a cycle, in the state in which the heat of the LEDs131to133is absorbed and a temperature rise of the LEDs is suppressed, the LEDs131to133are maintained so as to light in a good condition.

To project an image on the screen180, image source is firstly input to the personal computer110. The image source is image-processed in a predetermined manner and an image data signal is generated. The image data signal is transferred from the personal computer110to the projector120. Present image data is generated from the image data signal in the projector120, and a drive signal is provided to the liquid crystal panels141to143to display the present image data The light from the LEDs131to133is modulated by the liquid crystal panels141to143for each pixel and the modulated light is combined by the prism150. Thereby, an image is generated. The generated image is projected from the projection optical system160onto the screen180, so that the image is shown on the screen180.

According to the first exemplary embodiment, following effects can be obtained.

As a first effect, since the plurality of fin323are disposed in the communication space in which the cooling medium flows, a contact area between the fins323and the cooling medium can be large and the heat exchange efficiency can be enhanced.

As a second effect, since the fins323and the frames321are integrally formed in the unit plates320, one small passage can be formed by jointing two unit plates320on one joint surface. In other words, one small passage can be formed by only one joint portion, so that the number of the joint portions can be a half of that of the related art. Since the number of the joint portions can be halved, the thermal conductivity of the heat exchangers300can be enhanced, so that the heat of the LEDs131to133can be efficiently transferred to the fins323of the unit plates320. As a result, the heat can be transferred from the fins323to the cooling medium, so that the heat exchangers300can have high heat exchange efficiency.

As a third effect, since the fins323and the frames321are integral, the number of components and assembling work can be half compared with the related art. Hence, the heat exchangers300can be manufactured at low cost while having a high performance. As a fourth effect, the heat of the LEDs131to133can be efficiently absorbed by the heat exchangers300, an increase in temperature of the LEDs131to133can be suppressed and the LEDs131to133can provide stable light emission and have a longer life. In addition, since the heat of a light source can be efficiently absorbed by the heat exchangers300, a light source such as the LEDs (light-emitting diodes)131to133which generate a large amount of heat from a small area can be used. As a result, luminance of the image of the projector120can be high.

Second Exemplary Embodiment

A second exemplary embodiment will be described with reference toFIGS. 8 to 10.

The second exemplary embodiment has a basic structure similar to that of the first exemplary embodiment but has a feature in which unit plates420have an I-shape in cross section.

FIG. 8is a cross section of the second exemplary embodiment.

FIG. 9shows the unit plate420of the second exemplary embodiment.

InFIG. 8, a heat exchanger400includes the two end plates411,412and the plurality of unit plates420layered on each other between the two end plates411,412. The unit plates420each include a frame421, holes422and a fin423, which is the same as the first exemplary embodiment. However, in the second exemplary embodiment, as shown inFIG. 9, the frame421is formed to project toward both of the front surface side and the rear surface side of the fin423. The frame421has a height of about 10 to 50 μm relative to the fin423.

FIG. 10is an illustration for explaining a manufacturing process of the unit plates420.

To manufacture the unit plates420, a thin plate430having a thickness of about 100 μm is prepared. The thin plate430is pressed from both of a front surface and a rear surface thereof by a press die440having a pressing surface corresponding to the fin423. Thereby, the fin423is compressed to be thin, so that the frame421projects from the front and rear surfaces of the fin423by an amount in which the fin423is reduced. Thus, the unit plate420is formed into the I-shape in cross section. Note that the holes422may be punched at the same time of the pressing or may be formed by etching.

According to the second exemplary embodiment, following effects can be obtained in addition to the effects of the first exemplary embodiment.

As a fifth effect, the heat exchanger400can be formed by layering the unit plates420of the I-shape in cross section on each other and forming small passages between the fins423.

As a sixth effect, in forming the unit plates420, since the thin plate430is pressed such that the frame421projects by the amount in which the fin423is reduced to be thin by pressing the thin plate430, a height of the frame421(an projecting height from the fin423) can be extremely thin. Hence, when the unit plates420are layered, the fins423can be disposed with a small distance from each other, thereby narrowing the width of the small passages. As a result, since the contact area between the fins423and the cooling medium can be increased, the thermal conductivity from the fins423to the cooling medium can be enhanced, thereby improving the performance of the beat exchanger400.

Third Exemplary Embodiment

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

The third exemplary embodiment has a basic structure similar to that of the second exemplary embodiment but has a feature in which fin plates450are disposed between the unit plates420.

FIG. 11is a cross section of the third exemplary embodiment.

InFIG. 11, a heat exchanger500is the same as the second exemplary embodiment in that the unit plates420in the I-shape in cross section are layered to form the heat exchanger but has a feature in which the fin plates450are provided between the unit plates420.

The fin plates450each are a thin plate having a similar thickness to that of the fins423of the unit plates420and two holes451,451are formed so as to penetrate through the fin plates450. In other words, the fin plates450is equal to the unit plates420with the frame421removed.

By providing such fin plates450between the unit plates420, the distance between the fins can be a half of that of the second exemplary embodiment and the small passages can be narrow. Further, the number of the fins is doubled.

According to the third exemplary embodiment, following effects can be obtained in addition to the effects of the above-described exemplary embodiments. As a seventh effect, by providing the fin plates450between the unit plates420, the distance between the fins can be extremely narrow.

In addition, since the small passages can be narrow and the number of the fins can be doubled, the heat exchanger500can have a high performance.

Fourth Exemplary Embodiment

A fourth exemplary embodiment will be described with reference toFIGS. 12 to 13.

The fourth exemplary embodiment has a basic structure similar to that of the second exemplary embodiment but has a feature in which a unit plate620has a Z-shape in cross section.

FIG. 12is a perspective view with some unit plates620removed such that how the unit plates620are layered can be understood in the fourth exemplary embodiment.

FIG. 13is a perspective view of the unit plates620of the fourth exemplary embodiment.

InFIG. 12, the heat exchanger600includes two end plates611,612and the plurality of unit plates620layered on each other between the two end plates611,612.

The unit plates620each include a frame621, holes622and fins623, which is the same as the second exemplary embodiment. However, in the fourth exemplary embodiment, as shown inFIG. 13, the frame621is formed to project toward both of the front surface side and the rear surface side of the fin623.

The fin623is slant relative to the projection direction of the frame621.

When seen from a lateral side in the lengthwise direction of the unit plate620, the fin is provided in parallel to a diagonal line of the rectangular unit plate620, so that the unit plate620has the Z-shape in cross section.

Since the fin623is slant relative to the unit plate620, the vertical length of the fin623becomes large and the area of the fin623becomes large.

According to the fourth exemplary embodiment, following effects can be obtained in addition to the effects of the above-described exemplary embodiments. As an eighth effect, since the fin623is slant relative to the frame621, the area of the fin623can be large, so that the contacting area of the fluid and the fin623is increased by an increased amount of the area of the fin623, thereby enhancing the thermal conductivity from the fin623to the fluid.

Fifth Exemplary Embodiment

A fifth exemplary embodiment will be described with reference toFIGS. 14 to 15.

The fifth exemplary embodiment has a basic structure similar to that of the fourth exemplary embodiment but has a feature in which a frame721is a parallelogram and a fin723projects from a position substantially on a diagonal line of the frame721.

FIG. 14is a perspective view with some unit plates720removed such that how the unit plates720are layered can be understood in the fifth exemplary embodiment.

FIG. 15is a perspective view of the unit plates720of the fifth exemplary embodiment.

InFIG. 14, a heat exchanger700includes end plates711,712and unit plates720. The unit plates720each include a frame721and a fin723, and the frame721is formed so as to project toward both of the front surface side and the rear surface side of the fin723.

The projecting direction of the frame721and a surface of the fin723are orthogonal to each other. When seen from a lateral side in the lengthwise direction of the unit plate720, the fin is provided in parallel to a diagonal line of the parallelogram unit plate720.

By layering such unit plates720, the heat exchanger700can be formed, in which a large number of fins are provided in the communication space with a small distance from each other.

First Modification

A first modification of the invention will be described with reference toFIG. 16.

In the above-described exemplary embodiments, the pipe230of the heat absorbing mechanism200connects the three heat exchangers300parallel, but the three heat exchangers300may be connected in parallel as shown in the first modification inFIG. 16.

Second Modification

A second modification of the invention will be described with reference toFIG. 17.

The above-described exemplary embodiments have been described by taking as an example a case for absorbing the heat from the light sources. However, heat from another electronic device of the personal computer110such as a CPU may be absorbed as shown inFIG. 16. In such an arrangement, the heat from the CPU can be efficiently absorbed by the heat exchangers300. As a result, an increase in temperature of the CPU can be suppressed and the operation of the CPU can be stable. Further, the CPU can have a longer life.

The scope of the invention is not limited to the above-stated exemplary embodiments and the invention includes modifications, improvements and the like as long as an object of the invention can be obtained.

In the third exemplary embodiment, a case in which the fin plates are interposed between the unit plates is described. However, when disposing the fin plates between the unit plates, the fin plates may be provided for every other unit plates or every three unit plates.

The unit plates in the C-shape in cross section of the first exemplary embodiment and the unit plates in the I-shape in cross section of the second exemplary embodiment may be alternately layered to form the heat exchanger.

An aspect of the invention may be used in a heat exchanger.