Patent Application
20110179806
1. Field of the Invention
The present invention relates to a cooling apparatus for cooling heating elements.
2. Description of the Related Art
A cooling system, such as natural air cooling, forced air cooling, water cooling, and ebullient cooling, is well known. In recent years, heating elements that require temperature regulation, such as light emitting devices, are widely used. For example, the following Patent Document 1 proposes a semiconductor laser apparatus which is provided with a cooling mechanism by combining a Peltier device with a heat pipe.
In such a cooling mechanism as described in Patent Document 1, power consumption tends to increase because the Peltier device has a relatively small thermoelectric conversion efficiency. Further, if an endothermic amount of the Peltier device is increased, it may fall into a supercooled state, thereby resulting in dew condensation.
The related prior arts are listed as follows: Japanese Patent Unexamined Publications (kokai) JP-5-167143A (1993), JP-2001-332806A, JP-11-121816A (1999), JP-5-312455A (1993), and International Patent Publication WO2004/029532, and Japanese Utility Model Unexamined Publication JP-61-194170U (1986).
An object of the present invention is to provide a cooling apparatus capable of, when using a plurality of Peltier devices, reducing power consumption thereof by equalizing each operation of the respective Peltier devices.
In order to achieve the above object, the cooling apparatus according to an embodiment of the present invention includes:
a heat receiving plate to which a plurality of heating elements are attached;
a radiator plate to which a plurality of Peltier devices are attached;
a thermal transport heat pipe that couples the heat receiving plate with the radiator plate; and
a heat dissipating device being provided on an exothermic side of the Peltier devices;
wherein the plurality of heating elements are arranged along a longitudinal direction of the thermal transport heat pipe, and
the plurality of Peltier devices are arranged along the longitudinal direction of the thermal transport heat pipe.
It is preferable that the heat dissipating device includes: a second heat receiving plate in contact with the exothermic sides of the Peltier devices; a radiating heat pipe coupled to the second heat receiving plate; and a radiating fin coupled to the radiating heat pipe.
It is preferable that a plurality of radiating heat pipes are arranged at the same interval along a direction perpendicular to the longitudinal direction of the thermal transport heat pipe.
It is preferable that the cooling apparatus further comprising: a temperature sensor located near a coupling portion between the heat dissipating device and the thermal transport heat pipe; a plurality of drive circuits for individually driving the respective Peltier devices; and a control circuit for individually controlling the respective drive circuit based on an output from the temperature sensor.
It is preferable that a tip end of the thermal transport heat pipe is protruded from the end face of the heat dissipating device.
It is preferable that the heat receiving plate and the radiator plate are coupled by a plurality of thermal transport heat pipes, and a smaller amount of liquid is sealed in the heat pipe which is located at a larger distance from the heating element attachment portion.
It is preferable that a wick that generates a capillary force is fixed to an inner surface of the thermal transport heat pipe.
It is preferable that the thermal transport heat pipe is bent in a U-shape, and both ends of the thermal transport heat pipe are thermally coupled by another heat pipe.
It is preferable that the thermal transport heat pipe is bent in a U-shape, and the heat receiving plate and the radiator plate are integrated into a single piece and disposed perpendicularly to each other.
It is preferable that the heating element which is located at a portion closer to the end of the thermal transport heat pipe generates a smaller amount of heat.
It is preferable that an electronic or optical device is located at a position other than under a endothermic surface of the Peltier device in a vertical direction.
It is preferable that the heat receiving plate is provided with a heater.
According to an embodiment of the present invention, heat generated by the plurality of heating elements is dissipated through the heat receiving plate and the thermal transport heat pipes by the plurality of Peltier devices. Therefore, operations of the Peltier devices can be equalized to collectively control the temperature. Further, a difference in temperature between an endothermic side and an exothermic side of each Peltier device can be decreased, thereby reducing power consumption of the Peltier devices.
This application is based on an application No. 2010-16409 filed on Jan. 28, 2010 in Japan, the disclosure of which is incorporated herein by reference.
Hereinafter, preferred embodiments will be described with reference to drawings.
The heat receiving plate 2 is made of a material having favorable thermal conductivity, like a metallic material such as copper or aluminum. An upper surface of the heat receiving plate 2 has a flat shape, on which a plurality of heating elements 1 such as semiconductor lasers are mounted.
The thermal transport heat pipes 5 are constituted such that working fluid is sealed within a metallic pipe, and provide a function of effectively transporting heat by means of evaporation of the working fluid, traveling of vapor, condensation of the vapor, and reflux of liquid due to a capillary force within the heat pipe. One end of each of the thermal transport heat pipes 5 is joined with the heat receiving plate 2, and the other end is coupled with the radiator plate 4, thus the heat receiving plate 2 is thermally coupled with the radiator plate 4, thereby efficiently transporting heat from the heat receiving plate 2 to the radiator plate 4.
The radiator plate 4 is made of a material having favorable thermal conductivity, like a metallic material such as copper or aluminum. A lower surface of the radiator plate 4 has a shape substantially conforming to a shape of each of the thermal transport heat pipes 5, thereby ensuring favorable thermal coupling. An upper surface of the radiator plate 4 has a flat shape, on which a plurality of Peltier devices 3 are mounted.
The Peltier devices 3 utilize the Peltier effect in which an endothermic or exothermic phenomenon can occur at a junction between a p-type and an n-type semiconductors according to the direction of a current flowing through the junction. The endothermic surfaces of the Peltier devices 3 are in contact with the upper surface of the radiator plate 4. The exothermic surface of the Peltier devices 3 are attached with the heat sink 6.
The heat sink 6 is made of a material having favorable thermal conductivity, like a metallic material such as copper or aluminum, and has such a configuration that a number of radiating fins are provided upright on a base plate.
As to a temperature control circuit, the cooling apparatus further includes a temperature sensor 7, a plurality of drive circuits 52 for individually driving the respective Peltier devices 3, and a control circuit 51 for individually controlling the respective drive circuits 52 based on an output from the temperature sensor 7.
Next, an operation of this cooling apparatus is described by way of example based on a laser television, i.e., a television that generates video images using light from R/G/B (Red/Green/Blue) light emitting elements, as one application of the present invention. The three heating elements 1 including an R element, a G element and a B element generate heat during emission of desired light as each element is energized. The heat generated by each of the heating elements 1 is transferred to the heat receiving plate 2, and then transferred to one end of the thermal transport heat pipes 5. The thermal transport heat pipes 5 can efficiently transport heat by circulation of working fluid sealed therein. At this time, when the working fluid receives heat from the plurality of heating elements 1, there is the same pressure within the heat pipe at portions at which each of the heating elements 1 is attached, and the working fluid can receive heat and evaporate at the same temperature and the vapor thus generated can move in a collective manner. Accordingly, each of attachment surfaces of the R element, the G element and the B element has a substantially even temperature.
On the other hand, since at a portion where each of the Peltier devices 3 is attached the vapor is uniformly dispersed and condensed such that each of inner wall surfaces within the heat pipes has the same temperature through the intermediary of the radiator plate 4, each of the endothermic surfaces of the plurality of Peltier devices 3 can receive a uniform amount of heat at an even temperature through the intermediary of the radiator plate 4. In this manner, each of the Peltier devices 3 can receive an averaged heat quantity, and can transfer the thermal energy received from the endothermic surface to the heat sink 6 using the Peltier effect. At this time, the Peltier device 3 has a lower temperature on the side of the radiator plate and a higher temperature on the side of heat sink. Therefore, the heat sink 6 has a temperature higher than that of the thermal transport heat pipes 5, resulting in more efficient heat dissipation due to larger difference of temperature with respect to the ambient temperature. Further, the temperature of each of the thermal transport heat pipes, thus the temperature at the portion where the heating element is attached can be controlled by varying power supply to the Peltier devices 3.
Further, the Peltier device 3 may have a higher temperature on the side of the radiator plate and a lower temperature on the side of heat sink by inverting the flowing direction of a current supplied to the Peltier devices 3. In other words, when heating the radiator plate 4, the heat is transferred through the radiator plate 4 and the thermal transport heat pipes 5 to the attachment surfaces, temperature of each is thus increased. Accordingly, each of the attachment surfaces of the R/G/B elements can be maintained at any constant temperature regardless of the ambient temperature. For example, even when the ambient temperature rises from −5° C. up to 45° C., each of the endothermic surfaces of the Peltier devices 3 can be maintained at a constant temperature of 30° C. In the case of laser televisions, in view of the longer life of the R/G/B elements and the reduction of Peltier power consumption, it is preferable to maintain the temperature at each of the endothermic surfaces of the Peltier devices 3 in a range of 20 to 35° C., more preferably in a range of 25° C. to 30° C.
Thus, the heating elements 1 can be cooled by temperature regulation, and it is possible to obtain desired properties (e.g., optical output) of the heating elements 1 by controlling the heating elements 1 at a desired temperature. The temperature used for temperature regulation can be measured using the temperature sensor 7 such as thermocouple, thermistor, or diode. A measuring position of the temperature sensor 7 may be at any point from the heat receiving plate 2 to the heat sink 6, but preferably at the radiator plate 4, in particular, as shown in
In the cooling apparatus according to this embodiment, the thermal transport heat pipes 5 are used for heat uniformizing elements, and the plurality of heating elements 1 are arranged linearly along the longitudinal direction of the thermal transport heat pipes 5, and the plurality of Peltier devices 3 are arranged linearly along the longitudinal direction of the thermal transport heat pipes 5. Accordingly, the heat transferred from the plurality of heating elements 1 is transported in a collective manner, and uniformly exhausted to the plurality of Peltier devices 3. As a result, the heat receiving plate 2 and the radiator plate 4 can be maintained at a uniform temperature within the respective planes.
Further, even when the heat generated by each of the heating elements 1 is not uniform, the heat can be uniformly transferred to each of the Peltier devices 3. Accordingly, the thermal transport efficiency of each of the Peltier devices 3 can be maintained at a maximal state, in other words, the difference in temperature between the endothermic surface and the exothermic surface of each Peltier device 3 can be maintained at a uniform condition. As a result, it is possible to reduce the power consumption of the Peltier devices 3. Moreover, since the heat is uniformly transferred to each of the Peltier devices 3, local supercooling can be prevented, thereby improving dew condensation resistance.
Further, in a case where each of the plurality of heating elements 1 generates heat in a different mode (for example, one condition in which R element: large, G element: small, B element: medium changes rapidly to another condition in which R element: medium, G element: medium, B element: small), compared to the case in which the Peltier device 3 is provided for every heating element 1, each Peltier device can receive heat of an average heat quantity out of the plurality of heating elements 1. Accordingly, the variation of the generated heat quantity becomes moderate, thereby facilitating the control of the temperature. In particular, when forming a video image of ocean (blue), for example, even when the R element: 0 (no load), the G element: 0 (no load), and the B element: large, the R/G/B elements are provided for the same heat pipe, thereby preventing abnormally low temperature (0° C. when the ambient temperature is 0° C.). Further, even when a particular heating element generates a larger mount of heat among the plurality of heating elements 1, as long as the other heating elements generate a smaller mount of heat, a total amount of heat exhausted is kept relatively small, thereby maintaining the particular heating element 1 at a lower temperature.
Each of the R/G/B elements may change its coloring (wavelength) and light intensity depending on the temperature of a luminescent body (LD) inside the element, and therefore it is preferable that the temperature of the LD does not change too much in order to obtain desired light. However, each of the R/G/B elements has its unique thermal resistance, and the temperature of the LD element (junction temperature) may change by the temperature difference obtained by integration of the generated heat quantity that corresponds to the ever-changing light output for forming various video images (motion pictures). According to the present invention, since the attachment surface can be maintained at a constant temperature as described above, the temperature of each of the LD elements can be more easily predicted and/or controlled only based on each thermal resistance value that is a fixed value and generated heat quantity (supplied power) that represents transient change, without being affected by environment changes such as ambient temperature and surrounding wind speed, which means high robustness. Further, abnormally lower temperature can be avoided even when any of the elements is under no load, and the temperature of the LD element varies only in a smaller range, which defines a minimum temperature. Therefore it is possible to resume the temperature with favorable light emitting efficiency in the next light output.
Incidentally, in the case of performing temperature regulation individually for each of the R/G/B elements using the Peltier devices, 1.5 or more Peltier devices are required in order to cool the R element with the adequately efficient number of the Peltier devices. In other words, in the individual cooling, the number of the Peltier devices required for the R element is 1.5, the number of the Peltier devices required for the G element is 2.3, and the number of the Peltier devices required for the B element is 1.2. Consequently, the total number of the required Peltier devices is seven, which is a physically possible total number of 2, 3, and 2. However, by collectively cooling according to the present invention, all the elements can be satisfactory cooled with five Peltier devices at a maximum output, and practically with four Peltier devices due to interference of heat generation modes of individual elements, thereby decreasing the number of the Peltier devices and reducing the size, power consumption, and cost.
The thermal transport heat pipe 5 according to this embodiment can be a common heat pipe including a circular pipe, a grooved pipe, a wire-lined pipe, or a particle sintered pipe. However, when bending the heat pipe more than one time, a problem may occur that a wick (such as thin wire or particle) that generates an inner capillary force is peeled off from an inner surface of the pipe. Further, when operating at a ultralow temperature (40° C. or lower in the case of water), another problem may occur that a maximum amount of heat transport is reduced as viscosity coefficient of liquid increases. In such cases, it is preferable to use a heat pipe manufactured by lining a number of thin wires along an inner wall of a grooved pipe, followed by providing a ribbon for holding the thin wires from the inner side thereof, and then sintering it to fix the thin wires. By using a heat pipe of this type, the inner wick is hardly peeled off even in deformation due to post processing such as bending more than once, and the maximum amount of heat transport can be improved by ensuring a large flow path configured of grooves that facilitate reflux of high viscosity liquid.
Further, in the case of using the plurality of thermal transport heat pipes 5, a problem may occur that a difference in temperature between a wall of the heat pipe and a liquid becomes smaller as a distance between a heat pipe and the heating element attachment portion increases, resulting in an operational failure (for example, vapor does not easily travel) and deterioration in the thermal transport property. In such a case, it is preferable to seal a smaller amount of liquid in the heat pipe which is located at a larger distance from the heating element attachment portion. Thus, thickness of a liquid film formed on the inner wall of the heat pipe can be made smaller, and evaporation phenomenon can easily occur even with a smaller difference in temperature. As a result, it is possible to ensure thermal transport under normal vapor, thereby improving the maximum amount of heat transport and realizing thermal transport even with a smaller difference in temperature.
Moreover, a portion closer to the end of the thermal transport heat pipe 5 that is in contact with the heat receiving plate 2 has a longer liquid reflux distance, with reflux properties of the liquid being lowered. Therefore, providing the heating element 1 that generates a larger amount of heat at the end of the heat pipe may cause occurrence of “dryout”, that is, no liquid is resupplied and the temperature at the attachment portion may rise up. In order to address this problem, among the plurality of heating elements 1 attached to the heat receiving plate 2, a heating element that generates a smaller amount of heat is preferably located at a portion closer to the end of the thermal transport heat pipe. Consequently, an allowable limit value of a total amount of exhaust heat quantity to be dissipated from the plurality of heating elements 1, that is, the maximum amount of heat transport of the heat pipe is further increased.
In the case of the laser television, the G element is likely to generate the largest amount of heat, therefore, the G element is preferably located at a position closest to the heat sink along the heat pipe.
The heat dissipating unit 20 includes a second heat receiving plate 9 in contact with the exothermic side of each Peltier device 3, the plurality of radiating heat pipes 10 coupled to the second heat receiving plate 9, and radiating fins 11 coupled to the respective radiating heat pipes 10.
The second heat receiving plate 9 is made of a material having favorable thermal conductivity, like a metallic material such as copper or aluminum. A lower surface of the second heat receiving plate 9 has a flat shape which is in contact with the exothermic side of the plurality of Peltier devices 3. An upper surface of the second heat receiving plate 9 has a shape substantially conforming to a shape of each of the radiating heat pipes 10, thereby ensuring favorable thermal coupling.
The radiating heat pipe 10 is constituted similarly to the thermal transport heat pipe 5, such that working fluid is sealed within a metallic pipe, and provides a function of effectively transporting heat by means of evaporation of the working fluid, traveling of vapor, condensation of the vapor, and reflux of liquid due to a capillary force within the heat pipe. One end of each radiating heat pipe 10 is joined with the second heat receiving plate 9, and the other end is joined with the radiating fins 11, thereby efficiently transporting heat from the second heat receiving plate 9 to the radiating fins 11.
The radiating fin 11 is configured of a plurality of plates made of a material having favorable thermal conductivity, like a metallic material such as copper or aluminum. The plates are arranged at substantially the same interval along the longitudinal direction of the radiating heat pipe 10.
According to this embodiment, a heat dissipating capability is dramatically improved by using the heat dissipating unit 20 as described above. Further, it is preferable that the plurality of radiating heat pipes 10 are arranged at the same interval along a direction perpendicular to the longitudinal direction of the thermal transport heat pipe 5. Thus, in the case where the plurality of Peltier devices 3 are provided, a larger number of heat dissipating heat pipes 5 can be located as compared to the case where the thermal transport heat pipes 5 and the radiating heat pipes 10 are parallelly located, thereby further improving heat dissipating properties. Moreover, in the case of using the above-mentioned U-shaped heat pipe, it is preferable to place the heat pipe in a horizontal plane because the operation may be deteriorated if the liquid sealed within the heat pipe accumulates around a U-shaped portion or both ends by gravity. In this case, the entire apparatus can be downsized by providing the heat dissipating unit including the perpendicular heat pipes.
The heat dissipating 20 is required to exhaust the total amount of heat including the heat quantity generated from the heating elements 1 and the driving power of the Peltier devices 3, thus desired to exhaust a greater amount of heat and to have a larger value of maximum heat transport capability. Moreover, the further the heat dissipating properties of the heat dissipating unit 20 improves, the lower the temperature of the exothermic surface of the Peltier device 3 becomes, and the smaller the difference in temperature between the endothermic surface and the exothermic surface of the Peltier device 3 becomes. Accordingly, the power consumption of the Peltier devices 3 can be reduced to save energy.
In this embodiment, a tip end 12 of the thermal transport heat pipes 5 is protruded from the end face of the radiator plate 4. If there is an initial residual non-condensable gas (e.g., nitrogen) or a non-condensable gas generated from residual metals (e.g., hydrogen) present within the heat pipe, the gas can be moved to remain at a condensation side end portion of the heat pipe during operation. Further, an excess of the liquid sealed within the heat pipe can be also moved to remain at the condensation side end portion. Accordingly, the vapor cannot enter the condensation side end portion of the heat pipe, at which the heat cannot be exchanged. If the Peltier devices are attached to this portion, which is then forcibly cooled, this condensation side end portion may have an abnormally lower temperature with respect to other condensation portions. Once dew condensation occurs at the abnormally lower temperature portion, the condensed water droplets are possibly attached to electronic and optical components.
In contrast, when a tip end 12 of the thermal transport heat pipes 5 is protruded from the end face of the radiator plate 4, a non-cooling portion can be formed at the tip end 12 of the thermal transport heat pipes 5, thereby ensuring a space that can accommodate the non-condensable gas and the excessive liquid. As a result, the above-mentioned problems, such as abnormally lower temperature and dew condensation, can be solved.
Further, according to this embodiment, a bypass heat pipe 13 is provided in addition to the thermal transport heat pipes 5. One end of the heat pipe 13 is coupled to the vicinity of a coupling portion between the heat receiving plate 2 and one end of the thermal transport heat pipe 5. The other end of the heat pipe 13 is coupled to the vicinity of another coupling portion between the radiator plate 4 and the other end of the thermal transport heat pipe 5.
As described above, the condensation side end portion of the thermal transport heat pipe 5 is likely to be supercooled by the Peltier devices 3, causing dew condensation. As a countermeasure to this problem, providing the additional heat pipe 13 can make direct supply of heat to a portion to which heat is not easily transferred through vapor movement in the thermal transport heat pipe 5. As a result, dew condensation caused by supercooling can be prevented.
Further, since an end portion on the heat receiving side of the thermal transport heat pipe 5 has the longest distance for reflux of the condensation liquid, and thus lower reflux capability of the liquid. If too large a mount of heat is supplied to this end portion, the liquid inside the pipe is dried, thus causing “dryout”. Also in this case, providing the additional heat pipe 13 allows a part of the heat quantity supplied from the heating elements 1 to be transferred in a bypass manner via the heat pipe 13 to the radiator plate 4, thereby preventing the dryout.
Moreover, according to this embodiment, in the case where the heating elements 1, the heat receiving plate 2, and a control board 14 are to be located from the above under gravity environment, as shown in
In the case of the laser television, at too low a temperature the R/G/B elements cannot generate adequate optical outputs due to their properties, but the R/G/B elements can generate adequate optical outputs according to this embodiment. Further, when turning on the television which has been kept at a lower temperature in a turning-off condition, the R/G/B elements having a lower temperature cannot generate optical outputs, thereby extending a latency time to wait for image formation. According to this embodiment, when the television is turned off, energizing the heater 30 can keep the R/G/B elements at a desired temperature, thereby reducing the latency time.
Further, when the heater 30 is provided, a power source for the Peltier devices 3 or a power source for the heater 30 can alternately operate, hence, the power source can be shared to downsize the apparatus.
Although the present invention has been fully described in connection with the preferred embodiments thereof and the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-016409 | Jan 2010 | JP | national |
