Abstract:
A micro-spray cooling system for a plurality of heat sources includes an evaporator contacting the heat sources and comprising a plurality of actuators corresponding to the heat sources, a condenser connected to the evaporator, and at least one driving circuit connected to the actuators to drive some or all of the actuators sequentially according to a predetermined timing to cool the heat sources. The refrigerant in the evaporator is sprayed by the actuators to thermally contact the heat sources, evaporated by heat from the heat sources, condensed in the condenser and re-enters the evaporator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to micro-spray cooling, and in particular to a micro-spray cooling system with piezoelectric actuators to vibrate and spray refrigerant. 
         [0003]    2. Description of the Related Art 
         [0004]    The speed of a computer depends on processing speed of a central processing unit, which generates heat, which must in turn be dissipated by various methods. 
         [0005]    A conventional method for heat dissipation employs fins for heat conduction and fans for heat convection. Fans and fins cannot, however, satisfy the requirements for heat dissipation of many current high speed desktop computers. Nor are they able to satisfy the requirement of heat dissipation over 100 W for a compact laptop. As heat can be absorbed by a refrigerant as latent heat during phase change, the phase change method is preferred. 
         [0006]    As heat dissipation modules for a laptop must be as flat as possible to conserve height and space, a heat pipe is applicable therein. The heat pipe, however, is a passive cooling device which depends on heat convection by phase change and is not capable of actively controlling heat dissipation. 
       BRIEF SUMMARY OF INVENTION 
       [0007]    An embodiment of a micro-spray cooling system for a plurality of heat sources comprises an evaporator contacting the heat sources and comprising a plurality of actuators corresponding to the heat sources, a condenser connected to the evaporator, and at least one driving circuit connected to the actuators to drive some or all of the actuators sequentially according to a predetermined timing to cool the heat sources. The refrigerant in the evaporator, sprayed by the actuators to thermally contact the heat sources, is evaporated by heat from the heat sources, condensed in the condenser and re-enters the evaporator. 
         [0008]    The evaporator comprises at least one chamber storing the refrigerant and at least one evaporation chamber thermally contacting the heat sources, and the refrigerant is sprayed by the actuators disposed above the storage chamber to the evaporation chamber to thermally contact the heat sources. 
         [0009]    The evaporator further comprises a main body and a plurality of spray sheets disposed within the main body. Each spray sheet has at least one hole and divides the main body into the storage chamber and the evaporation chamber. The actuators are disposed on the spray sheets and vibrate the spray sheets to spray the refrigerant to the evaporation chamber via the holes. The actuators are piezoelectric elements. The actuators are annular and encircle the hole. 
         [0010]    The driving circuit controls the vibration amplitude and frequency of the actuators. A negative pressure generated in the storage chamber by the vibration of the actuators enables the refrigerant to flow from the condenser into the storage chamber. 
         [0011]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a schematic view of an embodiment of a micro-spray cooling system of the invention; 
           [0014]      FIG. 2  is a schematic view of detailed structure of a micro-spray cooling system of the invention; 
           [0015]      FIG. 3  is a schematic view showing an actuator assembled to a spray sheet; 
           [0016]      FIG. 4   a  depict the structure of an embodiment of the spray sheet of the invention; 
           [0017]      FIG. 4   b  is a cross section along line A-A of  FIG. 4   a;    
           [0018]      FIG. 4   c  depicts another embodiment of the spray sheet of the invention; 
           [0019]      FIG. 5  is a schematic view of another embodiment of a micro-spray cooling system of the invention; 
           [0020]      FIGS. 6   a - 6   d  depict the micro-spray cooling system of the invention applied to a dual core processor; and 
           [0021]      FIGS. 7   a - 7   d  depict the micro-spray cooling system of the invention applied to a multiple core processor. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0022]    Referring to  FIG. 1 , a micro-spray cooling system  1000  comprises an evaporator  100 , a condenser  200  and ducts  300  and  400  connecting the evaporator  100  and condenser  200 . 
         [0023]    Referring to  FIG. 2 , the evaporator  100  comprises a main body  110 , a spray sheet  120  and an actuator  140 . A chamber is formed in the main body  110 . The spray sheet  120  is disposed in the main body  110  and divides the chamber into a storage chamber  160  and an evaporation chamber  180 . Refrigerant R is stored in the storage chamber  160 . The evaporation chamber  180  contacts a heat source  5 . A plurality of holes  122  is formed on the central portion of the spray sheet  120 . The actuator  140  comprises piezoelectric elements connected to a driving circuit  500 . The driving circuit  500  controls the actuator  140  to vibrate the spray sheet  120 . The vibration pushes the liquid refrigerant R stored in the storage chamber  160 . The pressured liquid refrigerant R passes through the holes  122  and is sprayed into the evaporation chamber  180 . As the evaporation chamber  180  contacts the heat source  5 , heat is absorbed by the liquid refrigerant R as latent heat. The latent heat causes phase change of the liquid refrigerant R to refrigerant vapor. To increase heat dissipation area, a plurality of slots  182  is formed on the walls or the bottom of the evaporation chamber  180 . An exit  165  is formed on the storage chamber  160  to purge unnecessary refrigerant vapor. 
         [0024]    The refrigerant vapor flows through the duct  400  to the condenser  200  with fins  220  on the top thereof. Refrigerant vapor is condensed by conducting latent heat to the fins  220 . The heat conducted to the fins  220  is dissipated by force convection caused by a fan unit  600 . 
         [0025]    When the spray sheet  120  vibrates to push the liquid refrigerant R in the storage chamber  160 , a part of the liquid refrigerant R passes through the holes  122  to spray into the evaporation chamber  180 . As the liquid refrigerant R decreases, the refrigerant pressure in the storage chamber  160  is less than that in the condenser  200 , whereby the liquid refrigerant R flows from the condenser  200  to the storage chamber  160  via the duct  300  due to pressure difference. 
         [0026]    The liquid refrigerant R is sprayed into the evaporation chamber  180  by vibration of the spray sheet  120 , absorbs heat of the heat source  5 , and evaporates. The refrigerant vapor flows through the duct  400  to the condenser  200  and condenses therein. The pressure difference causes the liquid refrigerant to flow into the storage chamber  160 . Completing the cycle of refrigerant for heat dissipation. 
         [0027]      FIG. 3  depicts the spray sheet  120  assembled to the actuator  140 . In this embodiment, the actuator  140  is annular and bonded to the spray sheet  120  by thermal pressing. 
         [0028]    In the embodiment, only one spray sheet  120  and one actuator  140  are used. The size of the actuator  140  is limited by power supply, for example, when the power supply is under 3 W, the size of the annular actuator  140  is limited to an outer diameter of 14 mm and inner diameter of 8 mm. In such a structure, the spray area is limited to a diameter of 8 mm. A heat sink of the Intel CPU is 31 min×31 mm, exceeding the spray area. The small spray area causes poor heat dissipation efficiency, non-uniform temperature in heat sink, and accumulation of liquid refrigerant due to local fast cooling. If the liquid refrigerant is accumulated near the hole  122 , the liquid refrigerant may jam. The structure of the spray sheet  120  is described as follows. 
         [0029]    The spray sheet  120 , shown in  FIG. 4   a,  comprises a nozzle layer  121 , a hole  122  formed on the nozzle layer  121 , and a trench  124  formed on the nozzle layer  121 . The trench is around the hole  122  and separated from the hole  122  by an appropriate distance shown in  FIG. 4   b.  The trench  144  is be ring-shaped and continuous. In another embodiment, the trench  124  is ring-shaped, but discontinuous as shown in  FIG. 4   c.  A filler  126  is filled in the trench  124 . The wetting angle of the surface of the filler is different from the wetting angle of the surface of the nozzle layer. The difference of the wetting angle causes the accumulation of the liquid refrigerant around the hole  122  and prevents the liquid refrigerant from flowing randomly to other regions of the nozzle layer  121 . 
         [0030]    Accordingly, the micro-spray cooling system comprises a plurality of actuators arranged in an array for a larger heat source. The storage chamber  160  and the evaporation chamber  180  can be shared by several actuators, or each actuator can correspond to individual storage chamber and evaporation chamber. 
         [0031]      FIG. 5  depicts another embodiment of the micro-spray cooling system. The evaporator  200  further comprises a fixture  800  having four positioning strictures  820  which are arranged in an array of 2×2. Each positioning structure  820  receives a spray sheet  120  and an actuator  140 . The driving circuit  500  drives a part or all of the actuators  140  sequentially according to a predetermined timing.  FIGS. 6   a - 6   d  depict a cooling method for a CPU with dual cores. In  FIGS. 6   a  and  6   b,  the CPU with dual cores is arranged diagonally.  FIG. 6   a  shows the spray sheet  120  and the actuator  140  driven sequentially. The number in the spray sheet  120  represents the actuating order.  FIG. 6   b  shows the actuators  140  and the spray sheets  120  are driven simultaneously. In  FIGS. 6   c  and  6   d,  the CPU with dual cores is arranged on the same side.  FIG. 6   c  shows the spray sheet  120  and the actuator  140  driven sequentially. The number in the spray sheet  120  represents the actuating order.  FIG. 6   d  shows the actuators  140  and the spray sheets  120  driven simultaneously. 
         [0032]      FIGS. 7   a - 7   d  depict a cooling method for a CPU with multiple cores. For the CPU with multiple cores, a clockwise sequence of driving the spray sheet  120  and the actuator  140  is used as shown in  FIG. 7   a.  The number in the spray sheet  120  represents the actuating order. A counterclockwise sequence of driving the spray sheet  120  and the actuator  140  is used as shown in  FIG. 7   b.  A diagonal sequence ( FIG. 7   c ) or side-by-side sequence ( FIG. 7   d ) can also be applicable. 
         [0033]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.