Abstract:
A loop type heat dissipating apparatus with a sprayer for transferring heat between a heat source and a heat sink includes an evaporator, a condenser, and a working fluid. The evaporator contacts the heat source and includes a first chamber, a second chamber, and a sprayer disposed between therebetween. The condenser contacts the heat sink and includes a third chamber communicating with the second chamber and a wick structure disposed on one side of the third chamber. The working fluid fills the loop type heat dissipating apparatus and is turned into microdroplets via a sprayer. The sprayer impinges the microdroplets into the second chamber where the microdroplets are then evaporated by the heat source before proceeding to the third chamber for condensation, liquefaction and adhering to the wick structure. Eventually, the working fluid flows back to the first chamber under a pumping force actuated by the sprayer and completes the cycle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to heat dissipation techniques, and more particularly, to a loop type heat dissipating apparatus for use with an active cooling technique. 
     2. Description of the Prior Art 
     As the electronic and information industries continue to develop, people nowadays have visions of owning electronic products which are multi-function, fast at computation and miniaturized. Manufacturers make efforts to enhance the performance of electronic products, thus producing electronic products which are more and more power-consuming. What the manufacturers are also multiplying is the heat flux of a heat source inside the electronic products produced, such as a CPU, laser diode, LED array, and multi-chip module (MCM). Hence, great importance is attached to rapid heat transfer across tiny space inside an electronic product. 
     Taking a CPU as an example, existing designs of heat dissipations are, namely a heat spreader, a heat pipe disposed between cooling fins, a loop heat pipe, a droplet-cooling heat dissipating apparatus, and etc. 
     There are patents related to a heat dissipating apparatus with a heat spreader, namely Taiwanese utility model Nos. M270407 and M260724. The purpose of a heat spreader is to take in heat evenly and thereby prevent uneven heat dissipation. Nevertheless, the performance of a conventional cooler equipped with a heat spreader is subject to the thermal conductivity of a constituent material and thereby achieves only passive cooling, thus being unfit to meet the increasingly strict requirements for heat dissipation. 
     There are patents related to a heat pipe, namely Taiwanese Patent Nos. I241156, I236337, I225584, and etc. A heat pipe removes a huge amount of heat by phase change. Referring to  FIG. 1 , a conventional heat pipe  10  is filled with a working fluid, and the direction in which the liquid phase of the working fluid flows  101  is opposite to the direction in which the gaseous phase of the working fluid flows  103 . 
     However, in so doing, thermal resistance increases and thereby limits the maximum quantity of heat transferred. In addition, the heat pipe  10  using a wick structure  109  is disadvantaged due to great flow resistance and thereby unfit to deal with great heat flux. Last but not least, a conventional heat pipe has drawbacks, such as short heat transfer distance and small contact surface area. 
     There are patents related to a loop type heat dissipating apparatus, namely Taiwanese Patent Nos. 508487 and 502101. A conventional loop type heat dissipating apparatus, such as a micro loop heat pipe, is shown in  FIG. 2  which depicts a loop type heat dissipating apparatus  20  comprising an evaporator  201  and a condenser  203  working in conjunction with a liquid phase working fluid channel  205  and a gaseous phase working fluid channel  207  spaced apart therefrom, thus the loop type heat dissipating apparatus  20  is spatially flexible and capable of long-distance heat transfer. 
     Although the liquid phase of the working fluid returns to the condenser  203  after being evaporated by the evaporator  201 , the liquid phase of the working fluid forms a liquid film (not shown) at the bottom of the evaporator  201  and thereby increases the thermal resistance of the heat dissipating apparatus. 
     Taiwanese Patent No. I251656 discloses a pool boiling heat dissipating apparatus which comprises a buffer space whereby a boiling fluid steadily comes into contact with a heat dissipating surface. However, as stated in J. Yang, “Spray Cooling with an Air Atomizing Nozzle,” Ph. D. Thesis, University of Kentucky, Lexington, Ky., 1993, taking water as an example, the heat transfer coefficient of a pool boiling heat dissipating apparatus is 5×10 4  W/m 2 K approximately, whereas that of spray cooling exceeds 5×10 5  W/m 2 K, and thus the performance of a heat dissipating system can be enhanced by spray cooling. 
     A droplet cooling device disclosed in Embedded Droplet Impingement for Integrated Cooling of Electronics (EDIFICE) presented by the America-based Carnegie Mellon University involves spraying microdroplets to an area where a hot spot is created on a heat source, removing heat from the hot spot by phase change of the microdroplets, conveying vapor to a condenser having a heat sink, such as a cooling fin, a cooler, and a fan, by a vapor conveying path, condensing the vapor to liquid, and sending the liquid to micro-orifices under a pressure gradient provided by a driving pump, so as to keep the heat dissipation cycle going and provide the cooling function. 
     Nonetheless, a droplet cooling device based on spray cooling requires an external pump to expel droplets out of micro-orifices, which increases the overall volume inevitably and therefore fails to meet the requirements for product miniaturization. 
     Accordingly, an issue that needs an urgent solution is related to endeavors to overcome the aforesaid drawbacks of the prior art. 
     SUMMARY OF THE INVENTION 
     In light of the aforesaid drawbacks of the prior art, it is a primary objective of the present invention to provide a loop type heat dissipating apparatus with a sprayer so as to enhance efficiency of heat dissipation. 
     Another objective of the present invention is to provide a loop type heat dissipating apparatus with a sprayer so as to reduce thermal resistance. 
     Yet another objective of the present invention is to provide a loop type heat dissipating apparatus with a sprayer so as to minimize accumulation of a working fluid at the bottom of the evaporator. 
     A further objective of the present invention is to provide a miniaturized loop type heat dissipating apparatus with a sprayer. 
     In order to achieve the above and other objectives, the present invention provides a loop type heat dissipating apparatus with a sprayer, for use in heat transfer between a heat source and a heat sink, comprising an evaporator, a condenser, and a working fluid. In contact with the heat source, the evaporator comprises a first chamber, a second chamber disposed underneath the first chamber, and a sprayer disposed therebetween. The condenser comprises a third chamber and a wick structure, the third chamber communicating with the second chamber, the wick structure being disposed on a side of the third chamber and communicating with the first chamber. The working fluid fills the loop type heat dissipating apparatus. 
     Preferably, the working fluid fills the wick structure all the way to the first chamber so as to be atomized and sprayed to the second chamber by the sprayer, evaporated by the heat source, conveyed to the third chamber, condensed, liquefied, and adheres to the wick structure. The sprayer is of two types, namely piezoelectric and capacitive. The liquid phase of the working fluid flows back to the first chamber under a pumping force actuated by the sprayer and completes the cycle of heat transfer. 
     As regards the loop type heat dissipating apparatus with a sprayer, the evaporator is panel-shaped. The sprayer comprises a diaphragm and a piezoelectric driving unit. The diaphragm includes a plurality of orifices. The piezoelectric driving unit, which abuts on the diaphragm, is a circular piezoceramic device. In a preferred embodiment, the loop type heat dissipating apparatus with a sprayer further comprises a first channel and a second channel. The first channel connects the first chamber and the wick structure. The second channel connects the second chamber and the third chamber. The first channel is a liquid-oriented pipe while the second channel is a gas-oriented pipe. Preferably, the second channel has a larger diameter than the first channel. The first channel is one of a capillary and a smooth pipe while the second channel is a smooth pipe. Another wick structure is disposed at a point of connection between the first channel and the condenser. The first channel and the second channel are parallel, or, alternatively, are crossed. 
     As regards the loop type heat dissipating apparatus with a sprayer, the evaporator and the condenser have a quantitative relationship which is one selected from the group consisting of a one-to-one relationship, a one-to-many relationship, a many-to-one relationship, and a many-to-many relationship. The wick structure comprises one selected from the group consisting of a plurality of grooves, a porous structure formed by sintered metal powder, a metal mesh, and a rough surface structure inside the condenser. The working fluid is a liquid which evaporates readily and has a high latent heat of evaporation, for example, pure water. The inside of the loop type heat dissipating apparatus is a low-pressure region so as to facilitate evaporation of the working fluid. 
     Compared to the prior art, the present invention discloses a loop type heat dissipating apparatus with a sprayer. The sprayer turns the liquid phase of the working fluid into microdroplets and ejects microdroplets to the heat source, such that no liquid film is formed at the bottom of the evaporator. Hence, a loop type heat dissipating apparatus with a sprayer disclosed by the present invention has less thermal resistance but is more efficient than a conventional loop heat pipe. The evaporator of the present invention is panel-shaped and thereby comes into contact with the heat source via a relatively large contact surface. The layout of both the first channel and the second channel of the present invention may be designed in light of the space available, so as to overcome the drawbacks of the prior art, namely short distance of heat transfer, and small contact surface area. In the present invention, the sprayer integrated into the evaporator has a pumping function embodying two merits. First, heat is dissipated more efficiently by spray cooling. Second, products are miniaturized, as the present invention functions well without a pump while the prior art uses a pump. 
     Accordingly, the loop type heat dissipating apparatus of the present invention increases heat dissipation efficiency, reduces thermal resistance, prevents accumulation of a working fluid at the bottom of the evaporator, achieves miniaturization, and enhances industrial applicability, thus solving the problems posed by the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  (PRIOR ART) is a schematic view illustrating the principle of the operation of a conventional heat pipe; 
         FIG. 2  (PRIOR ART) is a schematic view illustrating the principle of the operation of a conventional loop heat pipe; 
         FIG. 3  is a schematic view showing a loop type heat dissipating apparatus with a sprayer of the first embodiment in accordance with the present invention; 
         FIG. 4  is a lateral view showing a loop type heat dissipating apparatus with a sprayer depicted in  FIG. 3 ; 
         FIG. 5  is an exploded view showing an evaporator depicted in  FIG. 3 ; 
         FIGS. 6A and 6B  are schematic views showing a variation of a loop type heat dissipating apparatus with a sprayer of the first embodiment in accordance with the present invention; 
         FIG. 7  is a schematic view showing a loop type heat dissipating apparatus with a sprayer of the second embodiment in accordance with the present invention; and 
         FIG. 8  is a lateral view showing a loop type heat dissipating apparatus with a sprayer depicted in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention is herein illustrated with specific embodiments so that one skilled in the pertinent art can easily understand other advantages and effects of the present invention from the disclosure of the invention. It should be noted that, in the following embodiments, a loop type heat dissipating apparatus with a sprayer is applicable to heat transfer between a heat source (for example, a CPU, laser diode, LED array, and multi-chip module (MCM)) and a heat sink (for example, a cooling fin, a cooler, and a fan). The aforesaid kinds of heat sources and heat sinks are not herein described in detail, as they are known devices and known skills. Considering the way of driving, the sprayer is a capacitive device or alternatively a piezoelectric device; the choice is known and thereby is not herein described in detail. 
     First Embodiment 
       FIGS. 3 to 6B  are drawings drawn according to the first embodiment of a loop type heat dissipating apparatus with a sprayer of the present invention. 
     Referring to  FIG. 3  which is a schematic view showing a loop type heat dissipating apparatus  1  with a sprayer of the present invention. As shown in the drawing, the loop type heat dissipating apparatus  1  is applicable to heat transfer between a heat source and a heat sink (neither is shown). The loop type heat dissipating apparatus  1  comprises an evaporator  11 , a condenser  13  communicating with the evaporator  11 , and a working fluid  15  flowing between the evaporator  11  and the condenser  13 . Connected between the evaporator  11  and the condenser  13  are a first channel  17  and a second channel  19 . Although in this embodiment the evaporator  11  and the condenser  13  are connected by both the first channel  17  and the second channel  19 , a means to connection is not limited to this embodiment and what are disclosed in the accompanying drawings. For instance, an opening for connecting the evaporator  11  and the condenser  13  may be disposed therebetween, or, alternatively, any other equivalent component may be disposed for connecting the evaporator  11  and the condenser  13 . 
     Referring to  FIGS. 3 and 4 , in contact with the heat source, the evaporator  11  comprises a first chamber  111 , a second chamber  113  disposed underneath the first chamber  111 , and a sprayer  115  disposed therebetween. The loop type heat dissipating apparatus  1  of this embodiment further comprises a working fluid  15 . As shown in  FIG. 5 , in this embodiment, the evaporator  11  which is panel-shaped comprises a first through-hole  117  and a second through-hole  119 . The first through-hole  117  communicates with both the first chamber  111  and the first channel  17 . The second through-hole  119  communicates with both the second chamber  113  and the second channel  19 . 
     The sprayer  115  comprises a diaphragm  1151  and a driving unit  1153 . The driving unit  1153  which abuts on the diaphragm  1151  comprises a plurality of orifices  1157 . The diaphragm  1151  is a metal film while the orifices  1157  are tiny round holes having an average diameter of 30 micron. The driving unit  1153  is a piezoelectric device for piezo-actuation, for example, a circular piezoceramic device. 
     In contact with the heat sink, the condenser  13  comprises a third chamber  131  and a wick structure  133 . The third chamber  131  communicates with the second chamber  113 . The wick structure  133  is disposed on one side of the third chamber  131  and communicates with the first chamber  111 . In this embodiment, the wick structure  133  is disposed at the bottom of the third chamber  131  while a wick structure  135  is disposed at the point of connection between the first channel  17  and the wick structure  133 . Owing to the wick structure  135 , the working fluid  15  is confined to the first chamber  111 , the first channel  17 , the wick structure  135  and the wick structure  133 . The working fluid  15  flows back to the first chamber  111  under a capillary action of the wick structure  135  and completes the cycle of heat transfer. 
     In this embodiment, the wick structure  133  includes, but is not limited to, a porous structure formed by sintered metal powder. Alternatively, the wick structure  133  can be a plurality of grooves, a metal mesh, or a rough surface structure inside the condenser  13 . In other words, the wick structure  133  can be whatever is capable of confining the working fluid  15  to a surface of the condenser  13  and conveying liquid by a capillary action. 
     The condenser  13  comprises a surface which is mostly smooth except one disposed with the wick structure  133  and the wick structure  135 . As shown in  FIG. 6A , the condenser  13  may be in contact with a heat spreader  30 , or, alternatively, the heat spreader  30  may be affixed to the condenser  13 . As shown in  FIG. 6B , a cooling structure  40  is disposed on an external surface of the condenser  13  so as to increase the heat dissipation efficiency. The shape and layout of the heat spreader  30  and the cooling structure  40  are not limited to what are described in this embodiment, as they may be supplemented or changed by persons ordinarily skilled in the art if necessary. 
     The working fluid  15  fills the wick structure  133  all the way to the first chamber  111  so as to be atomized and sprayed to the second chamber  113  by the sprayer  115 , evaporated by the heat source, conveyed to the third chamber  131 , condensed, liquefied, and adheres to the wick structure  133 . The liquid phase of the working fluid  15  flows back to the first chamber  111  under a pumping force actuated by the sprayer  115  and completes the cycle of heat transfer. In this embodiment, the working fluid  15  is, for example, pure water, methanol, acetone, ammonia, or any appropriate fluid which evaporates readily and has a high latent heat of evaporation. 
     The first channel  17  connects the first chamber  111  and the wick structure  135 . The second channel  19  connects the second chamber  113  and the third chamber  131 . The first channel  17  and the second channel  19  are parallel. In this embodiment, the first channel  17  is a liquid line while the second channel  19  is a vapor line. The second channel  19  has a larger diameter than the first channel  17 . The wick structure  135  is disposed at a point of connection between the first channel  17  and the condenser  13  and is configured to guide the working fluid  15 . The first channel  17  is one of a capillary and a smooth pipe. The second channel  19  is a smooth pipe. 
     It should be noted that, in this embodiment, the first channel  17  and the second channel  19  are disposed between the evaporator  11  and the condenser  13  such that their layouts are spatially flexible but are not limited to those of this embodiment. For instance, the first channel  17  and the second channel  19  can be disposed as a whole between the evaporator  11  and the condenser  13 . In other words, persons ordinarily skilled in the art may modify the layout of a connection between the evaporator  11  and the condenser  13  when necessary, so as to provide the cycle of heat dissipation for the working fluid  15 . 
     It should also be noted that, as shown in the drawings, the evaporator  11  and the condenser  13  has a one-to-one quantitative relationship which merely illustrates the structure of the loop type heat dissipating apparatus of the present invention in a schematic manner. In fact, the structures shown in the drawings are not drawn according to a practical case in terms of quantity, shape and size. In practice, the quantitative relationship between the evaporator  11  and the condenser  13  is one selected from the group consisting of a one-to-one relationship, a one-to-many relationship, a many-to-one relationship, and a many-to-many relationship. 
     When the sprayer  115  is idle and still, the capillary action generated toward the working fluid  15  by the plurality of orifices  1157  is exactly offset by the weight of the working fluid  15  above the diaphragm  1151 . As soon as the diaphragm  1151  starts to vibrate under a voltage, the sprayer  115  disposed right above the heat source turns the liquid phase of the working fluid  15  into microdroplets and conveys microdroplets to the heat source. In so doing, the heat generated by the heat source causes the droplets sprayed over the heat source to undergo phase change, and thus the heat is removed from the heat source because of the latent heat of evaporation, and the goal of spray cooling is achieved. 
     Afterward, the working fluid  15  is evaporated to gas, and then the gas phase of the working fluid  15  flows toward the condenser  13  via the second channel  19 . Then, inside the condenser  13 , the gas phase of the working fluid  15  condenses to liquid and adheres to the wick structure  133 . Inasmuch as the wick structure  133  is disposed at the bottom of the condenser  13  and the wick structure  135  at a point of connection between the condenser  13  and the first channel  17 , the liquid phase of the working fluid  15  in the condenser  13  flows back to the evaporator  11  and completes the cycle of heat transfer under the capillary action of the wick structure  133  and the wick structure  135  as well as the pumping force actuated by vibration of the sprayer  115 . 
     Accordingly, in this embodiment, performance of a heat dissipating apparatus is enhanced by spray cooling, and flow resistance is reduced by a structure for the separation of liquid and gas flow, thus increasing heat transfer and enhancing heat dissipation efficiency. 
     Second Embodiment 
       FIGS. 7 and 8  are schematic views showing a loop type heat dissipating apparatus with a sprayer of the second embodiment in accordance with the present invention. The drawings use the same or similar denotations for any second embodiment components the same as or similar to the corresponding first embodiment components, and the description is concise, 
     This embodiment markedly differs from the first embodiment in that the first channel and the second channel are parallel in the first embodiment but crossed in the second embodiment. 
     As shown in  FIGS. 7 and 8 , not only are the first channel  17  and the second channel  19  crossed, but the first channel  17  is directly connected to the wick structure  133 , and thus the wick structure  135  of the first embodiment is spared. 
     Unlike the prior art, this embodiment involves using a sprayer to dissipate the heat of a heat source by spray cooling, so as to increase the efficiency of heat dissipation and prevent the liquid phase of a working fluid from accumulating at the bottom of an evaporator. And further, thermal resistance decreases greatly, not only because there is no wick structure at the bottom of the evaporator, but also because the evaporator is panel-shaped and thereby comes into contact with the heat source through a large contact surface. Last but not least, the panel-shaped evaporator absorbs a huge amount of heat through phase change and thereby eliminates a heat spot of the heat source. 
     With a sprayer being driven by piezoelectric or capacitive means, the diaphragm vibrates and actuates a pumping force. The pumping force, coupled with the wick structures, allows the working fluid to complete the cycle of heat transfer without an external pump and brings advantages like compactness and low power consumption. Installing the sprayer inside the evaporator decreases the size of the loop type heat dissipating apparatus greatly and thereby is conducive to product miniaturization. 
     The foregoing specific embodiments are only illustrative of the features and functions of the present invention but are not intended to restrict the scope of the present invention. It is apparent to those skilled in the art that all equivalent modifications and variations made in the foregoing embodiments according to the spirit and principle in the disclosure of the present invention should fall within the scope of the appended claims.