Abstract:
The disclosure relates to an evaporator and a loop heat pipe employing it. The evaporator includes a shell having an evaporation chamber and a compensation chamber defined therein, a partition being received in the shell and partitioning the evaporation chamber and the compensation chamber, and a wick structure being adhered to an inner wall of the shell corresponding to the evaporation chamber and extending through the partition and into the compensation chamber. The loop heat pipe includes the evaporator mentioned above, a pipe connecting two opposite ends of the evaporator to form a closed loop and a working medium contained in the closed loop.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure relates to a heat dissipation device and, more particularly, to an evaporator and a loop heat pipe employing it. 
         [0003]    2. Description of Related Art 
         [0004]    Loop heat pipes have excellent heat transfer performance due to their low thermal resistance, and are therefore an effective means for transfer or dissipation of heat from heat-generating components such as central processing units (CPUs) of computers. 
         [0005]    A conventional loop heat pipe includes an evaporator having a wick structure adhered to an inner wall thereof. The evaporator includes an evaporation chamber and a compensation chamber. A predetermined quantity of bi-phase working medium is contained in the evaporator. 
         [0006]    During operation of the loop heat pipe, the wick structure disposed in the evaporation chamber absorbs heat from the CPU. A part of the heat absorbed by the wick structure in the evaporation chamber evaporates the working medium in the evaporation chamber into vapor; another part of the heat is transferred to the wick structure in the compensation chamber and evaporates the working medium in the compensation chamber into vapor. The compensation chamber gets a reverse vapor pressure to make thus an effective vapor pressure of the loop heat pipe increasingly decreased. On the other hand, the wick structure in the compensation chamber has a large amount of air bubbles accreted thereon to reduce a permeation rate of the working medium in the compensation chamber resulting in that the working medium is evaporated out. 
         [0007]    What is needed, therefore, is a loop heat pipe which can overcome the above problems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0009]      FIG. 1  is an isometric, assembled view of a loop heat pipe in accordance with an embodiment of the disclosure. 
           [0010]      FIG. 2  is a sectional, partially exploded view of an evaporator of the loop heat pipe of  FIG. 1 , together with a part of a pipe connecting two opposite ends of the evaporator. 
           [0011]      FIG. 3  is a partially schematic view of an operation principle of the loop heat pipe of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIG. 1 , a loop heat pipe in accordance with an embodiment of the disclosure is illustrated. The loop heat pipe comprises an evaporator  10 , a pipe  20 , and a heat dissipating component  30  thermally engaging with the pipe  20 . The pipe  20  interconnects two opposite ends of the evaporator  10  to form a closed loop. A predetermined quantity of bi-phase working medium (see  FIG. 3 ) is contained in the closed loop. In this illustrated embodiment, the heat dissipating component  30  consists of a plurality of parallel spaced fins  32  coiled around the pipe  20 . 
         [0013]    Referring to  FIGS. 2-3 , the evaporator  10  is columnar in this embodiment. The evaporator  10  comprises a first tube  11  having an evaporation chamber  14  defined therein and a second tube  13  having a compensation chamber  16  defined therein and engaging with the first tube  11 . The first tube  11  has a partition  12  extending from a right end thereof and separating the evaporation chamber  14  from the compensation chamber  16 . In an alternative embodiment, the first tube  11  and the second tube  13  can be an integrative hollow shell having a space defined therein and disposing the partition  12  therein which divides the space into the evaporation chamber  14  and the compensation chamber  16 . In this embodiment, a wick structure  18  is adhered to an inner surface of the first tube  11  and extends through the partition  12  and into the compensation chamber  16 . A length of the evaporation chamber  14  in an axial direction thereof is larger than that of the compensation chamber  16 . An outer surface of the first tube  11  is thermally connected with a heat generating electronic component such as a CPU (not shown). 
         [0014]    The first tube  11  comprises a first circumferential wall  110 , a first sidewall  111  and the partition  12  extending inwards perpendicularly from two opposite ends of the first circumferential wall  110 , respectively. The first circumferential wall  110 , the first sidewall  111  and the partition  12  cooperatively define the evaporation chamber  14 . The first sidewall  111  and the partition  12  define a through hole (not labeled) in a center thereof, respectively. The right end of the first circumferential wall  110  has an annular outer groove  112  defined in an outer surface thereof corresponding to an edge of the partition  12 . 
         [0015]    The second tube  13  comprises a second circumferential wall  130  and a second sidewall  131  extending inwards perpendicularly from a right end of the second circumferential wall  130 . A left end of the second circumferential wall  130  has an annular inner groove  132  defined in an inner surface thereof to form an insert  133 . The insert  133  is inserted into the outer groove  112  of the first circumferential wall  110  to make the first tube  11  and the second tube  13  engaging together, whereby the second tube  13  and the partition  12  cooperatively define the compensation chamber  16 . The second sidewall  131  defines a through hole (not labeled) in a center thereof. The pipe  20  has an end extending through the through hole of the first sidewall  111  and into the evaporation chamber  14 , and another end extending through the through hole of the second sidewall  131  and into the compensation chamber  16 . 
         [0016]    The wick structure  18  comprises a disc-like main body  180 , a pipe-shaped evaporation portion  182  extending perpendicularly from a left side face of the main body  180  and a cylinder protrusion  184  extending perpendicularly from a right side face of the main body  180 . The main body  180  and the evaporation portion  182  are located in the evaporation chamber  14 , and the protrusion  184  is located in the compensation chamber  16 . 
         [0017]    The main body  180  has the right side face adhered to a left side face of the partition  12 , and has an outer circumferential face adhered to an inner surface of the first circumferential wall  110 . The main body  180  is isolated from the working medium in the compensation chamber  16  by the partition  12  for preventing the working medium from permeating the main body  180  directly. The evaporation portion  182  is adhered to the inner surface of the first circumferential wall  110 . A columnar vapor channel  140  is defined in a middle portion of the evaporation portion  182  of the wick structure  18  and communicates with the pipe  20 . The cross-sectional area of the vapor channel  140  is larger than that of the pipe  20 , whereby a vapor in the vapor channel  140  can flow into the pipe  20  quickly. The protrusion  184  extends through the through hole of the partition  12  and into the compensation chamber  16 , and absorbs the working medium into the main body  180  and the evaporation portion  182 . The protrusion  184  has an outer surface spaced from an inner surface of the second circumferential wall  130 . 
         [0018]    The wick structure  18  can, for example, consist of porous structures, such as fine grooves integrally formed at the inner surface of the first circumferential wall  110  and at the left side face of the partition  12  and extending into the compensation chamber  16 , screen mesh or fiber inserted into the evaporation chamber  14  and the compensation chamber  16 , and held against the first circumferential wall  110 , or sintered powders combined to the inner surface of the first circumferential wall  110  and the left side face of the partition  12  using a sintering process and extending into the compensation chamber  16 . 
         [0019]    The working medium is selected from a liquid which has a low boiling point such as water, methanol, or alcohol. The pipe  20  is made of deformable materials compatible with the working medium, such as aluminum, stainless steel, or copper. 
         [0020]    In operation of the loop heat pipe, the working medium in the evaporation chamber  14  absorbs heat from the heat generating electronic component and evaporates into vapor. A positive vapor pressure is generated due to the vaporization of the working medium and propels the vaporized working medium into the pipe  20  and toward the heat dissipating component  30 . The vaporized working medium dissipates its heat to the heat dissipating component  30  and condenses to liquid in the pipe  20 . The positive vapor pressure still exists since the evaporation chamber  14  supplies the vapor continuously. The positive vapor pressure, therefore, propels the condensed working medium in the pipe  20  into the compensation chamber  16 . The condensed working medium is accumulated in the compensation chamber  16  and submerges the protrusion  184  of the wick structure  18 . The condensed working medium is absorbed by the wick structure  18  from the protrusion  184  to the main body  180  and the evaporation portion  182 , and into the evaporation chamber  14  via a capillary force of the wick structure  18 . The condensed working medium then evaporates to vapor thus starting another cycle in the loop heat pipe and continuously absorbing heat from the heat generating electronic component and dissipating the heat to the heat dissipating component  30 . 
         [0021]    The partition  12  prevents the main body  180  of the wick structure  18  from directly contacting with the working medium in the compensation chamber  16 , decreasing a contact area of the wick structure  18  with the working medium in the compensation chamber  16 , thereby decreasing a reverse evaporation area of the wick structure  18 . A reverse vapor pressure of the compensation chamber  16  is reduced, keeping the positive vapor pressure in a normal range. On the other hand, the protrusion  184  of the wick structure  18  extends into the working medium in the compensation chamber  16 . Heat that is transferred to the protrusion  184  is condensed quickly, and air bubbles on the protrusion  184  are decreased to keep a permeation rate of the working medium in the compensation chamber  16  for preventing the working medium in the evaporation chamber  14  from being evaporated out. 
         [0022]    It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.