Abstract:
The apparatus is a capillary loop evaporator in which the vapor space is the internal volume of a cup shaped evaporator wick with sidewalls in full contact with the outer casing of the evaporator. Liquid is furnished to the wick through thicker wick wall sections, slabs protruding from the liquid-vapor barrier wick, eccentric wick cross sections, or tunnel arteries. The tunnel arteries can also be formed within heat flow reducing ridges protruding into the vapor space. The tunnel arteries can be fed liquid by bayonet tubes or cable arteries, and can be isolated from the heat source with regions of finer wick to impede vapor flow into the liquid. Tunnel arteries also enable separation of the evaporator and the reservoir for thermal isolation and structural flexibility. A wick within the reservoir aids collection of liquid in low gravity applications.

Description:
BACKGROUND OF THE INVENTION 
   This invention deals generally with heat transfer and more particularly with a capillary loop evaporator that has full thermal contact of the wick with the heat input surface. 
   A capillary loop and a loop heat pipe are devices for transferring heat by the use of evaporation at the source of heat and condensation at the cooling location, and they eliminate some of the limitations of a simple heat pipe by separating the vapor and liquid movement into different conduits. Thus, liquid fed to an evaporator is evaporated and moves through a vapor transport line to the condenser, and condensate moves from the condenser to the evaporator through a liquid transport line. Typically, a liquid reservoir is constructed in close vicinity to the evaporator and a barrier wick separates the liquid in the reservoir from the vapor in the evaporator while moving liquid into the evaporator wick by capillary action. 
   Prior art capillary loop and loop heat pipe evaporators typically have vapor channels at the contact boundary between the evaporator wick and the heat input surface, which is the wall of the evaporator enclosure. The vapor channels are formed as grooves in the wick or the evaporator enclosure inner wall at the boundary, and the lands between the grooves are the only direct thermal path from the heat input surface to the liquid within the wick. From the wick the liquid is evaporated and fed into the vapor channels. The vapor channels then open into a vapor space that is available to the vapor transport line. Some such devices, such as that disclosed in U.S. Pat. No. 6,058,711 to Maciaszek et al, even have the vapor generating wick completely surrounded by the thermally insulating vapor space. 
   Basic limitations of the typical capillary loop evaporator are the limited direct contact between the wick and the heated surface, and the tendency of the vapor generated at the heat transfer surface to interfere with heat transfer into and through the wick. Another disadvantage of the conventional loop heat pipe evaporator is its proximity and thermal transfer to the reservoir. This phenomenon is referred to as parasitic heat loss or heat leakage, and it causes some heat to be transferred from the evaporator to the reservoir by means of heat conduction across the wick and two phase heat transfer in the central volume which the wick surrounds. Such heat is therefore not moved to the condenser for disposal. Still other problems arise in the difficulty of manufacturing capillary loop and loop heat pipe evaporators since they usually require cylindrical wicks with longitudinal grooves on the outer surface. 
   It would be very beneficial to have available a capillary loop evaporator that has improved heat transfer from the heat source to the evaporator wick, reduced parasitic heat leakage to the reservoir, and reduced manufacturing complexity. 
   SUMMARY OF THE INVENTION 
   The present invention is a capillary loop evaporator wick that has full contact at its outer boundary with the walls of the heated enclosure within which it is installed. In its simplest form the evaporator has a cup with sidewalls of wick material installed tightly against the inside walls of an enclosure of heat conductive material, and in most embodiments the cup has an integral end wall at one end extending across the entire enclosure and resembling a cup bottom. The end wall acts as a barrier between the vapor space in the center of the cup and the liquid reservoir on the other side of the end wall of the cup, and the barrier can be made of impervious material or porous capillary material. 
   The capillary pumping action of the barrier of wick material and the wick sidewalls of the cup deliver the liquid all along the boundary of the wick and the heated enclosure wall at which location it is vaporized. After the vapor is formed it moves across the wick sidewalls into the vapor space without significant interference from other vapor, and is replaced by other liquid within the wick. The open end of the wick cup is located near an end cap of the enclosure to which is attached the vapor line connecting the evaporator to the condenser. 
   Several structural variations can be added to enhance the performance of the simple cup of wick material. One such modification is selection of the sidewall wick thickness and pore size to accommodate different liquids within the capillary loop and different heat loads. 
   Another structure that can be used advantageously when the heat input is located in a specific area of the enclosure is wick sidewalls of varying thickness. In such a structure the sidewall adjacent to the heated area of the enclosure is formed with a thinner cross section to more easily permit the vapor to escape from the wick and thus maintain a lower evaporative temperature drop. Thicker sidewall sections are used adjacent to the enclosure wall where heat is not directly applied, so that the larger cross section is available for liquid transport, reducing the liquid pressure drop. Using a larger pore size wick in the thicker sidewalls can further enhance the characteristics of such a wick. The evaporative surface and the barrier wall are then made with finer pore sizes, and the finer evaporative pores draw liquid from the coarser wick, while the finer barrier wall wick allows operation against high gravitational or accelerational heads. 
   Another structure that reduces the liquid pressure drop is a web structure built into the interior of the cup. Such a structure extends longitudinally from the barrier wall toward the open end of the cup and across the interior between two or more sides. Such a web decreases the liquid pressure drop by increasing the wick cross section, delivers liquid to large portions of the heated wick, and permits heat input around the entire enclosure. The web&#39;s position in the interior of the cup and away from the heat input improves its liquid transport capability because very little of its volume is occupied by vapor. The web can also be constructed with a tunnel artery to further facilitate liquid distribution. 
   The ridge wick is a variation of the web structure that also provides increased wick cross section and allows more liquid flow into the wick sidewalls. Such a structure is essentially a partial web in that it extends longitudinally along the sidewall from the barrier wall, but it does not extend completely across the interior to another sidewall. Nevertheless, it furnishes liquid to much of the heated sidewall and is relatively vapor free. 
   The tunnel artery wick is an enhancement that immensely increases the liquid transport capability of ridge wicks and web structures. In such a configuration the ridges or webs of wick material include longitudinally extending tunnel arteries located inward, toward the center of the enclosure and away from the heated sidewall. The arteries are therefore somewhat isolated from the heat and the generated vapor. Such arteries extend through the barrier wick and directly into the reservoir of the capillary loop. Thus, liquid enters the arteries and moves directly into proximity with most of the length of the evaporator&#39;s wick. In effect the tunnel artery wick places parts of the liquid supplying reservoir adjacent to the very part of the evaporator wick that uses the liquid. 
   However, tunnel arteries have the risk of boiling and blockage of liquid flow by vapor if a heat source is too close to a tunnel. The present invention therefore includes several design enhancements to counteract this problem, the simplest of which is to simply modify the ridge into a higher ridge protruding farther inward toward the center of the evaporator. Locating the arteries in the part of the ridge nearest to the center of the evaporator reduces the heat flow into the artery and reduces the risk of boiling and vapor blockage. 
   Another approach to preventing boiling in the arteries is the use of isolating wicks of finer pore structure or lower thermal conductivity between the heat source and the artery. Such isolating wicks can be located at the artery as an artery wall structure, at the junction between the artery support ridge and the evaporative wick on the sidewalls of the enclosure, or anywhere between those locations. Such construction encourages vapor flow around rather than through the isolating wick and thus avoids accumulation of vapor in the arteries. 
   The arteries can also be constructed to include cable arteries. A cable artery is essentially a structure that has a multiple strand cable running through its length. The cable then pumps liquid along its length by capillary action between its strands, and has the advantage of allowing vapor to vent back into the reservoir in the annular space around the cable without blocking the liquid flow within the cable. Other high permeability arteries similar to cable arteries can also be constructed from mesh screen and metal felt. The added benefit of operation in a zero gravity environment can be attained by installing a reservoir wick on the interior walls of the reservoir and extending the high permeability arteries into contact with the reservoir wick. The reservoir wick then collects liquid in the reservoir and moves it into the evaporator through the high permeability arteries. This action can be enhanced even further by installing an additional wick structure in the reservoir, such as a web interconnecting opposite sidewalls, thereby capturing more liquid that is directed into the evaporator arteries. 
   Another way to feed liquid to the evaporator wick is the use of tubing extending from the reservoir into tunnels within the evaporator wick. The tubing extends well into each of the tunnels, and all the lengths of tubing are connected to a common liquid manifold within the reservoir. The liquid manifold is fed by the liquid return line from the condenser, and any vapor in the tunnel can escape back into the reservoir through the annular gap between the tubing and the tunnel wall. A reservoir wick then captures and returns liquid condensed from the escaped vapor back into the evaporator wick. 
   Cable and other high permeability arteries and tubing fed tunnels lend themselves to a structure that significantly simplifies the construction of an evaporator for a capillary loop. As previously described, the conventional evaporator has both an evaporator wick on the sidewalls of the enclosure and a barrier wick across the enclosure at one end of the evaporator wick. Not only is the junction of these two wicks a difficult construction problem, but any crack that occurs in the barrier wick will prevent the system from operating. Furthermore, the barrier wick must withstand the difference in pressure between the evaporator and the reservoir. 
   However, the use of either cable arteries or tubing fed tunnels permits the complete elimination of the barrier wick because liquid is fed to the evaporator wick by the cables or the tubing, and it also permits the separation of the evaporator and reservoir enclosures. When the evaporator and reservoir enclosures are separated, all that is needed is that the two enclosures have interconnecting pipes or tubing sealed to both enclosures through which excess vapor and the tunnel arteries, cable arteries, or artery feed tubes can pass. 
   The present invention thereby provides a capillary loop evaporator that has improved heat transfer from the heat source to the evaporator wick, reduced likelihood of vapor blockage of the liquid supply, and particularly with the separated evaporator and reservoir, reduced parasitic heat loss to the reservoir. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of the typical capillary loop showing the location of the evaporator wick of the preferred embodiment. 
       FIG. 2  is a perspective cut away view showing the interior of the basic evaporator of the preferred embodiment of the invention 
       FIG. 3  is a perspective cut away view showing the interior of an alternate embodiment of an evaporator of the invention with an evaporator wick of greater thickness and a strength enhancing barrier plate. 
       FIG. 4  is a perspective cut away view showing the interior of an alternate embodiment of an evaporator of the invention with an evaporator wick with sidewalls of varying thicknesses. 
       FIG. 5  is a perspective cut away view showing the interior of an alternate embodiment of an evaporator of the invention with an evaporator wick which includes a web wick structure across the interior of the evaporator. 
       FIG. 6  is a perspective cut away view showing the interior of an alternate embodiment of an evaporator of the invention with an evaporator wick which includes a longitudinal ridge with a tunnel artery. 
       FIG. 7  is a cross section view across a cylindrical evaporator wick showing an alternate embodiment of the invention in which the evaporator wick includes high longitudinal ridges with tunnel arteries. 
       FIG. 8  is a cross section view across a cylindrical evaporator wick showing an alternate embodiment of the invention in which the evaporator wick includes high longitudinal ridges with tunnel arteries including artery walls with isolating wicks with pore structures that prevents vapor flow into the arteries. 
       FIG. 9  is a cross section view across a cylindrical evaporator wick showing an alternate embodiment of the invention in which the evaporator wick includes high longitudinal ridges with tunnel arteries and isolating wick structures within the ridges that have pore structures that prevent vapor flow into the arteries. 
       FIG. 10  is a perspective cut away view showing the interior of an alternate embodiment of an evaporator of the invention which has an evaporator wick that includes longitudinal ridges with tunnels and cable arteries within the tunnels. 
       FIG. 11  is a perspective cut away view showing the interior of an alternate embodiment of an evaporator of the invention with an evaporator wick which includes longitudinal ridges with tunnels and tubing that feeds liquid from a manifold in the reservoir into the tunnels. 
       FIG. 12  is a perspective cut away view showing the interior of an alternate embodiment of the evaporator of the invention with a detached and separated reservoir rather than an integrated reservoir. 
       FIG. 13  is a perspective cut away view showing the interior of an alternate embodiment of the evaporator of the invention with a barrier formed within an easily sintered combined evaporator wick and reservoir wick. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic diagram of typical capillary loop  10  showing evaporator wick  12  of the preferred embodiment of the invention within evaporator  14 . Evaporator wick  12  of  FIG. 1  is a simple cup and is also shown in  FIG. 2  in a perspective cut away view to better show the interior of evaporator  14 . The important characteristic of evaporator wick  12  is that all the outer surfaces of its sidewalls are in intimate contact with heated walls  16  of the enclosure forming evaporator  14 . This complete contact between evaporator wick  12  and heated enclosure walls  16  makes heat transfer and vaporization of the liquid within evaporator wick  12  much more effective, and the vapor generated moves through evaporator wick  12  into vapor space  13 . 
   When capillary loop  10  is in operation, heat enters evaporator  14  and travels through evaporator enclosure wall  16  into wick  12  which is saturated with liquid. The heat causes the liquid to vaporize, and the vapor pressure moves the vapor out of evaporator wick  12 , into vapor space  13 , to vapor line  18 , and then into condenser  20 . Since condenser  20  is cooled by fins  21 , the vapor within it condenses, and, driven by the vapor pressure generated in evaporator  14 , the condensate liquid moves into liquid line  22  and back to reservoir  24  within evaporator  14 . Barrier wick  26 , which is attached to evaporator wick  12 , separates the liquid in reservoir  24  from vapor space  13  and moves the liquid by capillary action from reservoir  24  into evaporator wick  12 , from where the continuous cycle is repeated. 
   Capillary loop  10  is shown in an orientation that is ideal for gravity aided operation, in which the condensate flows down liquid line  22  under the influence of gravity. However, loop  10  will also operate against gravity if it contains sufficient liquid, including liquid in vapor line  18 , to assure that evaporator wick  12  is wetted when heat is not being applied. In such a circumstance, when heat is applied the generated vapor will displace any liquid from vapor line  18  and the necessary part of condenser  20 , and when the loop is operating, the displaced liquid will be located in the internal volume of reservoir  24 . 
     FIGS. 3 through 6  are perspective cut away views of alternate embodiments of the invention showing the interior of evaporator  14  with evaporators of different construction. In each embodiment evaporator  14  is the same except for the specific structure of the evaporator wick. 
     FIG. 3  shows evaporator  14  with the sidewalls of evaporator wick  30  having greater thicknesses than evaporator wick  12  of  FIG. 2 . This increase in thickness of evaporator wick  30 , and in fact any increase in thickness of the sidewalls of an evaporator wick, adds cross section area to the liquid flow path and thereby reduces the liquid pressure drop within the wick. This enhances the ability of the wick to furnish liquid for evaporation to its regions that are most remote from barrier wick  26 , which is the initial source of the liquid in the wick. Wick thickness, and the pore size within the wick, can also be used to better accommodate an evaporator to different liquids and different heat loads.  FIG. 3  also shows strengthening plate  27  which is a solid plate bonded to or formed within barrier wick  26 . Strengthening plate  27  not only prevents cracks in barrier wick  26  but assures that a crack that occurs in barrier wick  26  will not prevent the system from operating, and plate  27  helps barrier wick  26  withstand the difference in pressure between the evaporator and the reservoir. Holes  29  in plate  27  provide access to barrier wick  26  so that liquid in reservoir  24  can enter barrier wick  26 . 
     FIG. 4  is a perspective cut away view showing the interior of an alternate embodiment of an evaporator of the invention with evaporator wick  32  having varying thicknesses. Thus, portion  34  of wick  32  has a greater thickness than portion  36 . Such a configuration is advantageous when the heat input into evaporator  14  is restricted to a specific area of the evaporator. In such an application thinner portion  36  is located adjacent to the heat input of evaporator  14  so that vapor formed in portion  36  has a shorter travel path to vapor space  13 , and vapor can more easily escape and thereby maintain a lower evaporative temperature drop. Thicker sidewall portion  34 , located where there is little or no heat input, furnishes a larger cross section, thus reducing the liquid pressure drop and furnishing more liquid to heated thinner portion  36 . 
   It should be appreciated that the very gradual transition from thinner to thicker wick portions on opposite sides of the evaporator as shown in  FIG. 4  is not a requirement for the benefit to be derived, and it is also possible to have a relatively steep transition to a thicker portion of wick that occupies much more of the sidewalls of the evaporator. Furthermore, larger pore sizes within the thicker portion of the wick can also improve the action of the wick. 
     FIG. 5  is a perspective cut away view showing the interior of another alternate embodiment of an evaporator of the invention with evaporator wick  38  constructed to include wick web structure  40  across the interior of the evaporator. The benefit of web structure  40  is similar to that of a section of thicker wick sidewall in that it provides an increased cross section and multiple paths for feeding liquid to the heated portions of the wick. Web structure  40  extends longitudinally from barrier wick  26  toward the open end of the cup structure of evaporator wick  38  and across the interior between sidewalls of the cup. Although  FIG. 5  suggests only a single web structure across the evaporator, a true web with multiple extensions across vapor space  13  is also possible.  FIG. 5  also shows tunnel artery  41  located within web  40 . Tunnel arteries are discussed in greater detail in the following text, but it is important to appreciate that tunnel artery  41  passes through barrier wick  26  and opens into reservoir  24 , but is dosed off at the end of web  40  seen in  FIG. 5 . It is also important to appreciate that such a tunnel artery can also include within it cable arteries as shown in  FIG. 10 , other high permeability arteries, and feed tubes as shown in  FIG. 11 . 
     FIG. 6  is a perspective cut away view showing the interior of another alternate embodiment of an evaporator of the invention in which evaporator wick  42  includes limited width longitudinal ridge  44  within which is tunnel artery  46 . Ridge  44  itself, even without a tunnel artery, provides the benefit of increased wick cross section to facilitate liquid transport to the sidewalls of the wick. The fact that ridge  44  protrudes radially inward toward the center of vapor space  13  makes it less likely to contain vapor that would block liquid flow. Tunnel artery  46  further enhances the ability of ridge  44  to transport liquid to heated portions of wick  42 , and this technique operates for an evaporator in which the entire evaporator is heated when multiple ridges  44  including arteries  46  are included around the evaporator. Tunnel artery  46  is located in the part of ridge  44  that is most remote from heated wall  16  to minimize vapor interference with the liquid flow, and tunnel artery  46  extends longitudinally over a large portion of evaporator wick  42  and opens directly into reservoir  24 . The effect of this structure is essentially to extend reservoir  24  and its liquid supply into close contact with the heated portions of evaporator wick  42 . 
     FIGS. 7-9  are cross section views across a cylindrical evaporator wick  48  showing alternate embodiments of the invention in which the evaporator wick  48  includes high longitudinal ridges  50  with tunnel arteries  52  protruding into vapor space  13 . These alternate embodiments reduce the risk of boiling within the arteries that is sometimes caused when a heat source is too close to the artery. Such boiling causes vapor blockage of the liquid flow in the artery. 
     FIG. 7  shows the basic structure of high ridges  50  within evaporator wick  48 . Arteries  52  are located in the parts of the ridges that are as remote as possible from the heat source located at the outer circumference of evaporator wick  48 , as shown in  FIG. 1 . 
     FIG. 8  shows an enhanced structure for high ridges  50  of evaporator wick  48 . Tunnel arteries  52  of  FIG. 8  are shown with walls that are constructed with isolating wicks  54 . Isolating wicks  54  have finer pore structures than the rest of the ridges. Isolating wicks  54  prevent vapor flow into the arteries because the vapor travels the path of least resistance and moves out of the ridges and into vapor space  13  rather than moving through the more restrictive fine pore structure of isolating wicks  54 . 
     FIG. 9  shows another location for isolating wick structures  56  within high ridges  50  of evaporator wick  48 . Isolating wick structures  56  are located within high ridges  50  and have the same fine pore structure as isolating wicks  54  of  FIG. 8  that prevents vapor flow into the arteries. The essential difference of isolating wicks  56  is that they are located within ridges  50  rather than around the arteries as are isolating wicks  54  of  FIG. 8 . Nevertheless, the action of isolating wicks  56  is the same as those of isolating wicks  54  because isolating wicks  56  span across the entire cross sections of high ridges  50  and therefore divert vapor into vapor space  13  to prevent the vapor from entering arteries  52 . It should be appreciated that isolating wicks can be located anywhere along the height of high ridges  50 . 
     FIG. 10  is a perspective cut away view showing the interior of an alternate embodiment of the invention that is an evaporator  58  with evaporator wick  60  and barrier wick  61 . Evaporator wick  60  includes longitudinal ridges  62  with tunnels  64  and cable arteries  66  within tunnels  64 . However, other high permeability arteries similar to cable arteries, such as those constructed from mesh screen and metal felt can also be used within tunnels  64 . Cable arteries  66  are essentially multiple strand cables running through the length of tunnels  64 . Cables  66  then pump liquid along their lengths by capillary action between the strands, and have the advantage of allowing vapor to vent back into reservoir  68  by means of the open volumes around cables  66  without blocking the liquid flow within the cables. The added benefit of operation in a zero gravity environment can be attained by installing reservoir wick  70  on the interior walls of reservoir  68  and extending cable arteries  66  into contact with reservoir wick  70 . Reservoir wick  70  then collects liquid in reservoir  68  and moves it into evaporator  60  through cable arteries  66 . This action can be enhanced even further by installing an additional wick structure in the reservoir, such as a web across reservoir  68  interconnecting opposite sidewalls, thereby capturing more liquid that can be directed into cable arteries  66 . 
     FIG. 11  is a perspective cut away view showing the interior of another alternate embodiment of the invention with evaporator  72  that has evaporator wick  60  and barrier wick  61 . Evaporator wick  60  includes longitudinal ridges  62  with tunnels  64 . To this extent the evaporator wick structure is the same as shown in  FIG. 10 . However, instead of cable arteries within tunnels  64 , evaporator  72  has tubing  74  that feeds liquid into tunnels  64 . Tubing  74  extends well into each of the tunnels, and all the multiple lengths of tubing are connected to common liquid manifold  76  within reservoir  78 . Manifold  76  receives liquid directly from liquid return line  22  (see  FIG. 1 ), and any vapor in tunnels  64  can escape back into reservoir  78  through the annular gap between tubing  74  and the walls of tunnels  64 . As in  FIG. 10 , reservoir wick  70  then captures and returns liquid condensed from the escaped vapor back to the evaporator wick  60 . An additional wick can also be added to partially occupy the annular space between tubing  74  and tunnel walls and be in contact with reservoir wick  70  to return the reservoir condensed liquid to evaporator wick  60 . 
     FIG. 12  is a perspective cut away view showing the interior of evaporator  80  that is very similar to evaporator  72  of  FIG. 11  except that it does not have a barrier wick or an integrated reservoir as in evaporator  72  of  FIG. 11 . Instead of an integrated reservoir and a barrier wick at the end of evaporator wick  81 , evaporator  80  has sealed end plate  82 , and evaporator  80  is connected to detached and separated reservoir  84  by lengths of connecting tubing  86 . 
   The use of connecting tubing  86  to feed tunnels  64  permits the complete elimination of barrier wick  26  ( FIGS. 1-6 ) because liquid is fed to the evaporator wick through connecting tubing  86 . This structure permits the physical separation of the enclosures of evaporator  80  and reservoir  84 . When the evaporator and reservoir enclosures are separated, all that is needed is that the two enclosures have connecting tubing  86  sealed to both enclosures so that tunnels  64  are fed directly from connecting tubing  86 , and connecting tubing  86  acts as extensions of tunnels  64 . A further advantage of the structure shown in  FIG. 12  is that connecting tubing  86  can also enclose high permeability arteries, cable arteries  66  as shown in  FIG. 10 , or feed tubing  74  as shown in  FIG. 11 , and with such a structure it is quite simple to make the connection between evaporator  80  and reservoir  84  flexible. As indicated by the break lines shown in  FIG. 12 , connecting tubing  86  can span different distances which will essentially be determined by the liquid flow and vapor pressure characteristics of entire capillary loop  10  of  FIG. 1  and the capillary capability of the artery. 
     FIG. 13  is a perspective cut away view showing the interior of an alternate embodiment of the invention with evaporator  90  and reservoir  91 . This embodiment includes barrier  92  formed between easily sintered continuous evaporator wick  94  and reservoir wick  96 . Evaporator wick  94  and reservoir wick  96  are formed as a continuous structure that includes ridges  98 , which also run continuously between evaporator wick  94  and reservoir wick  96 . Barrier  92 , including through passages  93  for wick material, is formed to mate with continuous evaporator wick  94 , reservoir wick  96 , and ridges  98 , so that the only paths available between evaporator wick  94  and reservoir wick  96  for liquid and vapor are within the wick material itself. Such a structure can be formed by sintering in one operation, but barrier  92  can be either capillary material or a previously constructed solid structure sintered in place. The sintering process permits many variations in the structures of barrier  92  and ridges  98  so that the shape of through passages  93  can include, among others, the rectangular slots shown or circular holes. Ridges  98  can also have various shapes and can include tunnel arteries as shown in  FIG. 6 , cable arteries as shown in  FIG. 10 , or feed tubes as shown in  FIG. 11 . In some cases ridges  98  may not be needed with evaporator wick  96  and reservoir wick  96  having smooth inner surfaces. Furthermore, the shape of barrier  92  can be constructed to mate with any enclosure configuration. 
   The present invention thereby provides a capillary loop evaporator that has improved heat transfer from the heat source to the evaporator wick, reduced likelihood of vapor blockage of the liquid supply, and particularly with the separated evaporator and reservoir, reduced parasitic heat loss to the reservoir. 
   It is to be understood that the forms of this invention as shown are merely preferred embodiments. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims. For example, the evaporator and the evaporator wick structures need not be circular cylinders, but could be constructed with planar surfaces and also with a smaller space between two opposite sides to yield a slab-like structure.