Patent Publication Number: US-2012043059-A1

Title: Loop heat pipe

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201010258764.2, filed on Aug. 20, 2010, in the China Intellectual Property Office, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to heat transfer apparatuses, and particularly to a loop heat pipe with a high heat transfer efficiency. 
     2. Description of Related Art 
     Loop heat pipes are widely used for heat dissipation purposes because of their excellent heat transfer efficiency. A commonly used loop heat pipe includes an evaporator thermally attached to a heat-generating electronic component, a condenser, and a vapor line and a liquid line respectively interconnected between the evaporator and the condenser. A predetermined quantity of bi-phase working medium is contained in the closed loop. The working medium conveys heat from the evaporator to the condenser. A wick structure, lining an inner surface of the evaporator, draws the working medium back to the evaporator after it condenses at the condenser. 
     However, in the operation of the loop heat pipe, the vapor cannot be condensed fully to a liquid state working medium at the condenser. Instead, the condensate adjacent to the condenser is a mixture of a vapor state working medium and a liquid state working medium. The vapor state working medium entering the liquid line will obstruct the liquid state working medium flowing back to the evaporator. Thus, the liquid state working medium may not move towards the evaporator in a timely manner, and the evaporator may be prone to dry out. 
     What is needed, therefore, is a means which can overcome the described limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a loop heat pipe according to a first embodiment of the present disclosure. 
         FIG. 2  is a bottom view of the loop heat pipe of  FIG. 1 . 
         FIG. 3  is an isometric view of a loop heat pipe according to a second embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to the figures to describe the present loop heat pipe in detail. 
     Referring to  FIGS. 1 and 2 , a loop heat pipe  10  according to a first embodiment of the present disclosure includes an evaporator  11 , a condenser  12 , a separator  15 , and a vapor line  13  and a liquid line  14  connecting the evaporator  11 , the condenser  12 , and the separator  15  to form a closed loop. The separator  15  is part of the liquid line  14 . A predetermined quantity of bi-phase working medium (not shown) is filled in the closed loop. The working medium is a liquid, which has a low boiling point such as water, methanol, or alcohol. Thus, the working medium can easily evaporate to vapor when it absorbs the heat transferred to the evaporator  11  and condenses to liquid when heat is transferred to the atmosphere at the condenser  12 . 
     The evaporator  11  can be rectangular and have a flat shape, and include a liquid inlet  110  connected to the liquid line  14  and a vapor outlet  112  connected to the vapor line  13 . A wick structure (not shown) consists of a porous structure, such as a screen mesh, fiber inserted into the evaporator  11  and held against an inner surface of the evaporator  11 , or sintered powder combined to the inner surface of the evaporator  11  using a sintering process. The evaporator  11  thermally connects a heat-generating electronic component to absorb heat generated therefrom. 
     Each of the condenser  12 , the vapor line  13 , and the liquid line  14  is an elongated hollow tube. The condenser  12  can be parallel to the evaporator  11 , and includes a vapor inlet  121  connected to the vapor line  13 , and a liquid outlet  123  connected to the liquid line  14 . A heat dissipation component (not shown) thermally contacts an outer surface of the condenser  12  to dissipate heat to the atmosphere. The heat dissipation component can be a fin-type heat sink. Although not shown, the heat dissipation component can include fins for increasing the heat dissipation efficiency thereof. 
     The vapor line  13  and the liquid line  14  can be parallel to each other. The diameter of the vapor line  13  is substantially equal to that of the liquid line  14 . Alternatively, the diameter of the vapor line  13  and the diameter of the liquid line  14  can vary, only to ensure that the diameter of the liquid inlet  110  is no larger than the diameter of the liquid outlet  123 . 
     The separator  15  is located at a middle portion of the liquid line  14 . The separator  15  includes an elongated hollow cylindrical main body  150 , and a tapered entrance  151  and a reverse tapered exit  153  respectively located at two opposite ends of the main body  150 . The entrance  151  is located adjacent to the liquid outlet  123  of the condenser  12 . The exit  153  is located adjacent to the liquid inlet  110  of the evaporator  11 . The separator  15  separates the liquid line  14  into a first portion  141  connected between the liquid outlet  123  and the entrance  151 , and a second portion  142  connected between the exit  153  and the liquid inlet  110 . The entrance  151  can have a trapezoid cross-section, with a diameter gradually increasing from the first portion  141  of the liquid line  14  towards the main body  150 . A diameter of the main body  150  of the separator  15  is larger than that of the liquid line  14 . Thus, a capacitance of the separator  15  is larger than that of a portion of the liquid line  14 , which has substantially the same length as the separator  15 . In this embodiment, the diameter of the main body  150  is about twice as large as the liquid line  14 . The exit  153  has a similar cross-section as the entrance  151  but only differs in orientation, with the diameter gradually decreasing from the main body  153  towards the second portion  142  of the liquid line  14 . 
     During operation of the loop heat pipe  10 , the working medium in the evaporator  11  absorbs heat from the heat-generating electronic component and vaporizes to a vapor state working medium. The vapor pressure of the vapor state working medium expels the vapor state working medium, carrying heat with it, to flow through the vapor line  13  by the vapor outlet  112  of the evaporator  11 . Then, the vapor state working medium enters into the condenser  12  by the vapor inlet  121 . At the condenser  12 , the vapor state working medium dissipates the heat to ambient environment and condenses to a condensed working medium. The condensed working medium flowing out of the liquid outlet  123  of the condenser  12  is then propelled through the first portion  141  of the liquid line  14 , the separator  15 , and the second portion  142  of the liquid line  14  in that order, and moves into the evaporator  11  by the liquid inlet  110  thereof. The condensed working medium at the evaporator  10  then evaporates into vapor again to start another heat transfer cycle. 
     In each heat transfer cycle described above, the vapor state working medium may not be thoroughly condensed to a liquid state working medium at the condenser  12 . That is, during each heat transfer cycle, some of the vapor state working medium is not condensed to a liquid state working medium at the condenser  12 , resulting in the condensed working medium flowing out of the liquid outlet  123  of the condenser  12  and forming a mixture of a liquid state working medium and a vapor state working medium. Due to the presence of the separator  15 , when the condensed working medium flows from the condenser  12  towards the evaporator  11  by the liquid line  14 , the separator  15  separates the liquid state working medium from the vapor state working medium flowing therethrough and then supplies the liquid state working medium to the evaporator  11  continuously. 
     More specifically, when the condensed working medium flows through the separator  15 , the liquid state working medium contained in the condensed working medium directly drips down from a centre of the entrance  151  towards the exit  153 , while the vapor state working medium circumfuses to accumulate in the interior of the main body  150 . Further, the vapor state working medium contained in the interior of the separator  15  dissipates the heat to the ambient environment at the separator  15  and condenses to a liquid state working medium to flow to the evaporator  11  by the exit  153 . Thus, the separator  15  can separate the liquid state working medium from the vapor state working medium when the working medium flows therethrough, to allow the liquid state working medium to flow smoothly to the evaporator  11  without obstruction of the vapor state working medium. The diameter of the exit  153  gradually decreases from the main body  150  towards the second portion  142  of the liquid inlet  14 . This connects the liquid inlet  110  of the evaporator  11 , such that the speed of the liquid state working medium flowing out of the separator  15  towards the liquid inlet  110  of the evaporator  11 , is properly controlled. 
       FIG. 3  shows a loop heat pipe  20  according to a second embodiment. The loop heat pipe  20  differs from the loop heat pipe  10  of the first embodiment only in the shape of the separator  25  thereof. The separator  25  includes a tapered main body  251  connected to the first portion  141  of the liquid line  14  and a reverse tapered exit  252  connected to the second portion  142  of the liquid line  14 . The diameter of the main body  251  gradually increases from the first portion  141  of the liquid line  14  towards the exit  252 . The largest diameter of the main body  251  is much larger than the diameter of the liquid line  14 , which makes a capacitance of the separator  25  larger than that of a portion of the liquid line  14 , which has the same length as the separator  25 . In this embodiment, the largest diameter of the main body  251  is about three times as large as the liquid line  14 . The exit  252  has a diameter gradually decreasing from the entrance towards the second portion  142  of the liquid line  14 . In this embodiment, the separator  25  can separate the liquid state working medium from the vapor state working medium in the same manner of the loop heat pipe  10 . 
     It is to be understood, however, that even though numerous characteristics and advantages of the 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.