Liquid cooling system and electronic device including the same   

Abstract: Disclosed is a liquid cooling system mounted on an electronic device. The liquid cooling system includes flow path (20) through which a refrigerant circulates, and pump (21) and reserve tank (22) arranged on flow path (20). A part of the side face of reserve tank (22) is set back to the vicinity of the center of reserve tank (22) to form concave portion (40). on the front center of concave portion (40), outlet (42) through which the refrigerant flows out is formed.

TECHNICAL FIELD

The present invention relates to a liquid cooling system mounted on an electronic device.

BACKGROUND ART

An electronic device such as a personal computer or a projector includes an element or a light source for generating heat during an operation. The electronic device also includes a component or an element heated by the heat generated from the element or the light source. For example, a CPU (Central Processing Unit) included in the personal computer, or a discharge lamp or a LED (Light-Emitting Diode) included in the projector generates heat during its operation. Further, a memory or a hard disk included in the personal computer is heated by the heat generated from the CPU. An image forming element (liquid crystal panel or DMD (Digital Micro-mirror Device) included in the projector, or a mirror, a lens or a polarizing plate disposed on an optical path is heated by the heat generated from the light source (heat of light output from the light source). This necessitates cooling of the element, the light source or the component. Hereinafter, the element, the light source, or the component is generically referred to as a “cooling target”.

Systems that cool the cooling targets are largely classified into an air cooling type and a liquid cooling type. The liquid cooling system cools the cooling target by heat exchanging between the cooling target and a liquid (refrigerant). Therefore, a general liquid cooling system includes a flow path to circulate the refrigerant, on which a pump for circulating the refrigerant and a tank for storing a predetermined amount of refrigerant are arranged.

In the tank, there is formed a gas layer for absorbing volume expansion of the refrigerant caused by the temperature change. A gas may be mixed in the flow path against the aim. The entry of the gas from the tank or the flow path into the pump may cause a pump operation failure.

Thus, there is proposed a technology for preventing the entry of the gas from the tank or the flow path into the pump. For example, Patent Literature 1 describes a liquid cooling system (water cooling system) that includes a reserve tank. An inlet is formed on the right side face of the reserve tank disclosed in Patent Literature 1, and a hollow tube having an outlet is formed on the left side face. One end (outlet) of the hollow tube extends to the center of the reserve tank. In other words, the outlet is located in the center of the reserve tank. Locating the outlet in the center of the reserve tank enables the outlet to be always held below the water surface of the refrigerant. As a result, even when the posture change of the reserve tank is accompanied by the change of the water surface of the refrigerant, the gas does not flow out from the reserve tank through the outlet.

Patent Literature 1: JP2003-78271A

SUMMARY

However, the technology disclosed in Patent Literature 1 has the following problem. In Patent Literature 1, there is no description as to whether the hollow tube is formed integrally with a tank body. Supposing that the hollow tube is formed integrally with the tank body, the following problem occurs. Generally, the reserve tank is formed by using a mold. However, it is extremely difficult to manufacture a molded article where a slender tubular portion and a body portion are integrally formed by using a mold.

On the other hand, when the hollow tube and the tank body are separately formed, the following problem occurs. When the hollow tube and the tank body are separately formed, the hollow tube must be inserted into a hole formed in the side face of the tank body to be fixed. This increases the number of manufacturing steps. Specifically, the step of fixing the hollow tube inserted into the hole formed in the side face of the tank body by fixing means such as adhesion or welding is necessary.

Generally, in the case of the reserve tank disclosed in Patent Literature 1, manufacturing the reserve tank is difficult, or manufacturing takes time and labor, and costs are high.

A liquid cooling system according to the present invention is mounted on an electronic device. The liquid cooling system of the present invention includes a flow path through which a refrigerant circulates, and a pump and a reserve tank arranged on the flow path. A part of the side face of the reserve tank is set hack to the vicinity of the center of the reserve tank to form a concave portion. On the front center of the concave portion. an outlet through which the refrigerant flows out is formed.

In the liquid cooling system according to the present invention, the outlet is located near the center of the tank by setting hack the outlet of the reserve tank to the tank center. As a result, without using any slender tubular member such as a hollow tank, the outlet can be disposed near the center of the tank.

FIG. 1 is a perspective view showing the built-in structure of a projector in which the liquid cooling system of the present invention is mounted.

FIG. 2 is an exploded perspective view showing a light source unit shown in FIG. 1.

FIG. 3 is a perspective view showing the main flow of a refrigerant in the liquid cooling system shown in FIG. 1.

FIG. 4 is an appearance perspective view showing a reserve tank shown in FIG. 1.

FIG. 5 is a plan view showing each surface of the reserve tank shown in FIG. 1.

FIG. 6 is a sectional view showing the reserve tank shown in FIG. 1.

FIG. 7 is an exploded perspective view showing the reserve tank shown in FIG. 1.

FIG. 8A is a perspective view showing the first posture of the projector.

FIG. 8B shows the posture of the reserve tank when the projector is in the first posture.

FIG. 9A is a perspective view showing the second posture of the projector.

FIG. 9B shows the posture of the reserve tank when the projector is in the second posture.

FIG. 10A is a perspective view showing the third posture of the projector.

FIG. 10B shows the posture of the reserve tank when the projector is in the third posture.

FIG. 11A is a perspective view showing the fourth posture of the projector.

FIG. 11B shows the posture of the reserve tank when the projector is in the fourth posture.

FIG. 12A is a perspective view showing the fifth posture of the projector.

FIG. 12B shows the posture of the reserve tank when the projector is in the fifth posture.

FIG. 13A is a perspective view showing the sixth posture of the projector.

FIG. 13B shows the posture of the reserve tank when the projector is in the sixth posture.

A liquid cooling system according to the first embodiment of the present invention is described. FIG. 1 is a perspective view showing a part of the internal structure of a projector in which the liquid cooling system of the present invention is mounted. In FIG. 1, a case is omitted to show the internal structure.

The projector according to this embodiment includes image forming unit 1, three LED (Light Emitting Diode) light source units 2 arranged around image forming unit 1, projection lens 3 for projecting an image formed by image forming unit 1, and liquid cooling system 4.

Three LED light source units 2 respectively include red light source unit 2R that generates red light, green light source unit 2G that generates green light, and blue light source unit 2B that generates blue light. As shown in FIG. 2, each light source unit 2 includes at least a pair of holders 11 in each of which LED 10 is mounted, cooling mechanism 12 for maintaining the temperature of LED 10 equal to or lower than a predetermined temperature, and condenser lens 13. The components of each light source unit 2 that includes holder 11, cooling mechanism 12, and condenser lens 13 are received in box 14 to be integrated. The pair of holders 11 in each light source unit 2 are arranged to face each other, and light generated from LED 10 mounted in holder 11 is condensed by condenser lens 13 to enter image forming unit 1 (shown in FIG. 1).

Referring again to FIG. 1, image forming unit 1 includes at least a cross dichroic prism, and three liquid crystal panels arranged around the prism. The three liquid crystal panels are prepared for the respective light source units. On each liquid crystal panel, light output from each light source unit 2 is modulated based on a video signal. Specifically, the light (red light) output from red light source unit 2R enters a liquid crystal panel for a red color that is to be modulated. The light (green light) output from green light source unit 2G enters a liquid crystal panel for a green color that is to be modulated. The light (blue light) output from blue light source unit 2B enters a liquid crystal panel for a blue color that is to be modulated. The lights modulated on the respective liquid crystal panels are synthesized by the cross dichroic prism to be projected to a screen or the like via projection lens 3.

Next, liquid cooling system 4 according to this embodiment is described. Liquid cooling system 4 includes flow path 20 laid via light source units 2R, 2G, and 2B, On flow path 20, there are arranged at least pump 21, reserve tank 22, radiator 23, and fan 24 for supplying cooling air to radiator 23. Further, liquid cooling system 4 according to this embodiment includes two radiators (first radiator 23a and second radiator 23b), and two fans (first fan 24a and second fan 24b) for supplying cooling air to radiators 23a and 23b. Flow path 20 includes a flexible tube.

FIG. 3 schematically shows the flow of a refrigerant in liquid cooling system 4. Each arrow shown in FIG. 3 indicates the flow of the refrigerant in liquid cooling system 4. However, the arrow shown in FIG. 3, which indicates the main flow of the refrigerant, does not completely match that of an actual flow path design.

Before the refrigerant that flows out of pump 21 reaches radiator 23, it is divided into two flow paths so that it flows into first radiator 23a and second radiator 23b. The refrigerants that flowed into radiators 23a and 23b are cooled by heat exchanging. The refrigerants that flow out of first radiator 23a and second radiator 23b are merged to flow into reserve tank 22. The refrigerant that flow out of reserve tank 22 flows into red light source unit 2R to cool the LED therein. Then, the refrigerant returns to pump 21 via green light source unit 2G and blue light source unit 2B. The refrigerant that flowed into green light source unit 2G and blue light source unit 2B cools the LEDs therein. In other words, when pump 21 is set as a starting point, the refrigerant circulates in the order of pump 21→radiator 23→reserve tank 22→red light source unit 2R→green light source unit 2G→blue light source unit 2B→pump 21. Because of this circulation route, the temperature of the refrigerant is lowest immediately after its flows of radiator 23, and gradually increases during the passage through light source units 2R, 2G, and 2B.

The amount of heat generated by the red LED included in red light source unit 2R is smaller than that of the green LED and the blue LED respectively included in other light source units 2G and 28. However, the change in luminance of the red LED that is caused by a change in the temperature is greater than the luminance of the green LED and the blue LED. In other words, by the temperature change, the luminance of the red LED changes greater than those of the green LED and the blue LED. However, the red LED is more sensitive to the temperature change than the green LED and the blue LED. In other words, the change in temperature characteristics of the red LED is greater than that of the green LED and the blue LED. Accordingly, temperature management of the red LED is most important. This is why the abovementioned flow path design is employed. Specifically, the flow path design where the refrigerant cooled at radiator 23 is first supplied to red light source unit 2R is employed.

Further, as described above, each light source unit 2 includes a pair of LEDs 10. Accordingly, it is preferred that the temperature difference between the pair of LEDs 10 be small. It is particularly preferred that the temperature difference between the pair of red LEDs 10 included in red light source unit 2R be maintained at zero as much as possible. Different flow path designs are therefore employed for red light source unit 2R and other light source units 2G and 2B. Specifically, red light source unit 2R has a parallel flow path, while green light source unit 2G and blue light source unit 2B have serial flow paths.

As shown in FIG. 2, in box 14 of each light source unit 2, a pair of holders 11 having LEDs 10 mounted on the surfaces are arranged to face each other. Each heat discharge elements (Pertier element 15 in this embodiment) is disposed in close contact with the rear surface of each holder 11 of red light source unit 2R. On the back surface of Pertier element 15, cold plate 16 is disposed in close contact. In box 14, two assemblies including holders 11, Peltier elements 15, and cold plates 16 are arranged. However, FIG. 2 shows only the structure of one assembly. The two assemblies have identical structures.

The refrigerant flows into cold plate 16 via an inlet, and flows out of cold plate 16 via an outlet. In other words, heat exchanging is carried out between Peltier element 15 and the refrigerant via cold plate 16. Further, in other words, heat exchanging is carried out between the refrigerant and LED 10 via cold plate 16 and Pertier element 15.

Referring back to the description of the difference in flow path design between the light source units, the refrigerant that flowed into red light source unit 2R that has the abovementioned structure is divided to be supplied to two cold plates 16. On the other hand, the refrigerant that flowed into green light source unit 2G and blue light source unit 2B is sequentially supplied to two cold plates 16 without being divided. Accordingly, two red LEDs 10 included in red light source unit 2R are cooled by the refrigerants that have equal temperatures. As described above, the refrigerant that has the lowest temperature is supplied to red light source unit 2R. In other words, two red LEDs 10 included in red light source unit 2R are uniformly cooled by the refrigerants that have the lowest and equal temperatures. As a result, the temperatures of two red LEDs 10 are maintained equal to or lower than a predetermined temperature. while the temperature difference between two red LEDs 10 is maintained at zero as much as possible.

Needless to say, two LEDs 10 included in each of green light source unit 2G and blue light source unit 2B that include the serial flow paths are cooled by the refrigerants that have different temperatures. Specifically, rear LED 10 of is cooled by a refrigerant whose temperature increased due to heat exchanging with front LED 10. More specifically, the refrigerant that has flown into green light source unit 2G flows into front cold plate 16 to cool front green LED 10, and then flows into rear cold plate 16 to cool rear green LED 10. Similarly, the refrigerant that has flown into the blue light source unit flows into front cold plate 16 to cool front blue LED 10, and then flows into rear cold plate 16 to cool rear blue LED 10. 100261 However, luminance changes caused by the temperature changes of green LED 10 and blue LED 10 are smaller than that of red LED 10. This permits a slight temperature difference between two green LEDs 10 in green light source unit 2G. Similarly, a slight temperature difference between two blue LEDs 10 in blue light source unit 2B is permitted.

Next, reserve tank 22 included in liquid cooling system 4 is described. FIG. 4 is an appearance perspective view showing reserve tank 22. FIG. 5 is a plan view showing each surface of reserve tank 22. FIG. 6 is a sectional view showing reserve tank 22. FIG. 7 is an exploded perspective view showing the reserve tank.

Reserve tank 22 includes, as a whole, roughly cylindrical body 30, lower lid 31 disposed at one end of body 30 in a longitudinal direction, and upper lid 32 disposed at the other end in the longitudinal direction. Body 30, lower lid 31, and upper lid 32 are made of metal such as aluminum or aluminum alloys. Body 30, lower lid 31, and upper lid 32 are individually formed by molds, and assembled as shown in FIG. 7. Specifically, the four corners of lower lid 31 are fixed to the lower end surface of body 30 by screws 34. The four corners of upper lid 32 are fixed to the upper end surface of body 30 by screws 35. Watertight gaskets (O rings 36) are arranged between body 30 and upper and lower lids 31 and 32. Further, upper lid 32 includes refrigerant replenishment holes 37.

Mainly as shown in FIG. 6, concave portion 40 is formed in the body side face of reserve tank 22, and inlet 43 and outlet 42 are formed in front face 41 of concave portion 40. To describe the structure of reserve tank 22, three axes orthogonal to one another at the center of tank 22 are defined. One of the two axes present within a plane parallel to the opening surface of body 30 and orthogonal to each other at the tank center is defined as an X axis, and the other is defined as a Y axis. The axis orthogonal to both X and Y axes at the tank center is defined as the Z axis. Each axis thus defined is shown in FIG. 5 or FIG. 6. It can be understood that FIG.

6 shows the section of reserve tank 22 (body 30) cut along the X-Y plane. It can also be understood that the Y-axis direction is parallel to the flow-in direction and the flow-out direction of the refrigerant. However, the definition is only for convenience of description.

Concave portion 40 is located in the center of body 30 in the Z-axis direction (center axis direction). Concave portion 40 is concaved in the Y-axis direction toward the center of body 30. In other words, concave portion 40 is set back in the Y-axis direction. Front face 41 of concave portion 40 is set back deeper than the X-Z plane. In other words, front face 41 of concave portion 40 is set back deeper than the center of body 30.

Outlet 42 is formed in the front center of concave portion 40 set back as described above. In other words, outlet 42 is located roughly in the center of reserve tank 22. Inlet 43 is formed adjacently to outlet 42 in front face 41 of concave portion 40 set back as described above. More precisely, outlet 42 is located in the center of reserve tank 22 in the X-axis direction and the Z-axis direction, and located deeper than the center of reserve tank 22 in the Y-axis direction.

In other words, the center of outlet 42 is shifted from the center (intersection point of the three axes) of reserve tank 22 along the Y axis. Concerning the flow path resistance and device size, the inner diameters of outlet 42 and inlet 43 should preferably be set within the range of 3 millimeters to 10 millimeters, more preferably within the range of 4 millimeters to 6 millimeters. According to this embodiment, the inner diameters of outlet 42 and inlet 43 are 4 millimeters.

In front face 41 of concave portion 40, joint 51 that communicates with outlet 42 and joint 52 that communicates with inlet 43 are integrally formed. Joints 51 and 52 project from the edges of outlet 42 and inlet 43 in a direction opposite to the set-back direction of concave portion 40. The projection lengths (heights) of joints 51 and 52 with respect to front face 41 of concave portion 40 are shorter than the set-back amount of concave portion 40. Tubes that constitute parts of flow path 20 are connected to two joints 51 and 52. Specifically, the tube for connecting reserve tank 22 and radiator 23 is connected to joint 52 that communicates with inlet 43. The tube for connecting reserve tank 22 and red light source unit 2R is connected to joint 51 that communicates with outlet 42.

The location of outlet 42 enables preventing gas from flowing out of reserve tank 22 through outlet 42 even when the posture change of the projector is accompanied by the change in the water surface of the refrigerant in reserve tank 22. In other words, outlet 42 is never set above the water surface of the refrigerant.

Each of FIGS. 8A to 13B shows the relationship between the posture of projector 60 and the posture of reserve tank 22. In each of FIGS. 8B to 13B, the refrigerant in reserve tank 22 is indicated by a hatched line.

FIG. 8A shows the first posture of projector 60. In the first posture, projector 60 is horizontally disposed with its bottom surface 61 set down. FIG. 8B shows the posture of reserve tank 22 when projector 60 is in the first posture.

FIG. 9A shows the second posture of projector 60. In the second posture, projector 60 is horizontally disposed with its top surface 62 set down. FIG. 9B shows the posture of reserve tank 20 when projector 60 is in the second posture.

FIG. 10A shows the third posture of projector 60. In the third posture, projector 60 is vertically erected with its right side face 63 set down. FIG. 10B shows the posture of reserve tank 22 when projector 60 is in the third posture.

FIG. 11A shows the fourth posture of projector 60. In the fourth posture, projector 60 is vertically erected with its left side face 64 set down. FIG. 11B shows the posture of reserve tank 22 when projector 60 is in the fourth posture.

FIG. 12A shows the fifth posture of projector 60. In the fifth posture, projector 60 is vertically erected with its back surface 65 set down. FIG. 12B shows the posture of reserve tank 22 when projector 60 is in the fifth posture.

FIG. 13A shows the sixth posture of projector 60. In the sixth posture, projector 60 is vertically erected with its front face 66 set down. FIG. 13B shows the posture of reserve tank 22 when projector 60 is in the sixth posture.

The first posture is a posture in the most common use state of projector 60. When projector 60 is suspended from the ceiling, projector 60 may be set in the second posture. During transportation or the like of projector 60, projector 60 may he set in one of the third to sixth postures. Further, when an image is projected to the ceiling, projector 60 may be set in the fifth posture. In any case, the posture of projector 60 varies depending on use, transportation, and storage. However, as shown in FIGS. 8A to 13B, in any of the first to sixth states of projector 60, outlet 42 of reserve tank 22 is located lower than the water surface of the refrigerant. In other words, outlet 42 never communicates with the gas in reserve tank 22. As a result, the gas in reserve tank 22 does not flow out through outlet 42.

The liquid cooling system according to the present invention can be applied to an electronic device such as a personal computer other than the projector. Even when the liquid cooling system is mounted on an electronic device other than the projector, the same effects can be provided.

20 Flow path 21 Pump 22 Reserve tank 40 Concave portion 41 Front face of concave portion 42 Outlet 43 Inlet