Abstract:
A heat pipe system for an automobile comprising: a separator layer, at least one wick layer in contact with the separator layer, at least two outer walls enclosing the separator layer and the at least one wick layer, one of the at least two outer walls being spaced away from the at least one wick layer to form a vapor space therebetween.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method and apparatus for reducing the interior temperature of automobile cabins by employing a heat pipe system.  
         DESCRIPTION OF THE RELATED ART  
         [0002]    A basic heat pipe comprises a closed or sealed envelope or a chamber containing an isotropic liquid-transporting wick and a working fluid capable of having both a liquid phase and a vapor phase within a desired range of operating temperatures. When one portion of the chamber is exposed to relatively high temperature it functions as an evaporator section. The working fluid is vaporized in the evaporator section causing a slight pressure increase forcing the vapor to a relatively lower temperature section of the chamber defined as a condenser section. The vapor is condensed in the condenser section and returned through the liquid-transporting wick to the evaporator section by capillary pumping action.  
           [0003]    Because it operates on the principle of phase changes rather than on the principles of conduction or convection, a heat pipe is theoretically capable of transferring heat at a much higher rate than conventional heat transfer systems. Consequently, heat pipes have been utilized to cool various types of high heat-producing apparatus, such as electronic equipment (See, e.g., U.S. Pat. Nos. 5,884,693, 5,890,371, and 6,076,595).  
           [0004]    Traditional heat pipes are constructed with rigid metal casings and internal sintered wicks which, after manufacture, are expected to remain in essentially the same configuration as when they were originally manufactured. Some such heat pipes have been constructed with thin casings to permit some reconfiguration, and there have been a number of patents for heat pipes which include flexible segments to enable repeated bending of certain parts of the heat pipe.  
           [0005]    There are also a number of patents which have issued for heat pipes which are considered to be flexible in that their entire casings are constructed of thin flexible materials. Some patents also describe wicks which are flexible. For example, U.S. Pat. No. 5,560,423 to Larson et al. discloses a flexible heat pipe  10  with a thin metal sheet forming one side of a heat pipe casing, and a thin plastic sheet for the other side of the casing, with sheet screen wicking between them. U.S. Pat. No. 5,343,940 to Jean discloses a flexible heat pipe  21  formed of laminated plastic material.  
           [0006]    However, there is presently no available heat pipe system, flexible or otherwise, for cooling the interior cabin of an automobile. It is well known and understood that solar radiation from the sun tends to heat the interior cabins of automobiles, especially when the automobiles are left in one position for an extended period (e.g., in an uncovered parking lot while one is at work, shopping, etc.). It is also well known and understood that air conditioners are used to cool the interior cabins of automobiles, but that often times, because of heated air trapped in the automobile, or because of the prolonged startup time of an air conditioning units, it make take upwards of 5-15 minutes to cool the interior cabin of an automobile to an acceptable temperature.  
           [0007]    Therefore, there is currently a need for a heat pipe system for effectively keeping cool, and cooling, the interior cabin of an automobile.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is a heat pipe system for an automobile comprising: a separator layer, at least one wick layer in contact with the separator layer, at least two outer walls enclosing the separator layer and the at least one wick layer, one of the at least two outer walls being spaced away from the at least one wick layer to form a vapor space therebetween.  
           [0009]    The above and other advantages and features of the present invention will be better understood from the following detailed description of the exemplary embodiments of the invention which is provided in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1( a ) is side elevation view showing a heat pipe according to a first exemplary embodiment of the present invention.  
         [0011]    [0011]FIG. 1( b ) is top plan view showing the heat pipe of FIG. 1( a ).  
         [0012]    [0012]FIG. 2 is side elevation view showing the heat pipe of FIGS.  1 ( a ) and  1 ( b ) installed in an automobile.  
         [0013]    [0013]FIG. 3 is an enlarged cross sectional view of the heat pipe shown in FIGS.  1 ( a ) and  1 ( b ).  
         [0014]    [0014]FIG. 4 is an enlarged cross sectional view of a heat pipe according to a second exemplary embodiment of the present invention.  
         [0015]    [0015]FIG. 5 is an enlarged cross sectional view of a heat pipe according to a third exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]    A first exemplary embodiment of the present invention comprises a heat pipe structure  100  for reducing the interior temperature of automobiles. The heat pipe structure  100  reduces interior heat in two significant ways, by limiting the amount of solar radiation which is transferred to the automobile cabin, and by efficiently removing any heat trapped within the automobile cabin through a heat pipe. In particular, the heat pipe structure  100  acts as a thermal diode, by prohibiting heat entry in one direction (i.e., from the automobile roof to the automobile cabin), and by allowing heat exit in an opposing direction (i.e., from the automobile cabin to the roof).  
         [0017]    [0017]FIG. 1( a ) shows a side view of the heat pipe structure  100  according to a first exemplary embodiment of the present invention. The heat pipe structure  100  comprises a housing  105 , preferably made of metal (e.g., Copper (Cu)) which encases a wick structure  110  and which forms a vapor space  115  therebetween. A lower portion  120  of the housing  105  forms an evaporator section of the heat pipe structure  100 , and an upper portion  130  of the housing  105  forms a condenser section of the heat pipe structure. As is well known in the art, the wick structure  110  may also be made of metal (e.g., Copper felt; see FIG. 3 description below), and saturated with a fluid which has both liquid and vapor phases (e.g., water). A height (d,) of the heat pipe structure  100  may be selected according to the heat dissipation requirements, but is preferably in a range from {fraction (1/8)} inch to {fraction (1/4)} inch.  
         [0018]    [0018]FIG. 1( b ) shows a top view of the heat pipe structure  100 . The width (d 2 ) and length (d 3 ) of the heat pipe structure  100  may be selected based on the roof size of the automobile.  
         [0019]    [0019]FIG. 2 shows an automobile  200  with the heat pipe structure  100  according to the exemplary embodiment of the present invention installed therein. The automobile includes a roof  210  and a cabin area  220  where passengers are seated when the automobile is in use. When the automobile is not in use (i.e., when it is sitting in a parking lot or otherwise), incident solar radiation  245  (i.e., from the sun) tends to produce heated air  225  inside the cabin area  220 . However, when the car is in operation and moving in a direction  240 , air passes across a top surface (i.e., roof  210 ) of the automobile in a direction  230 .  
         [0020]    The heat pipe structure  100  is attached beneath the roof  210  of the automobile  200 , between the roof and the cabin area  220 . The heat pipe structure  100  may be attached to the roof  210  in various ways, but is preferably attached through known attachment means (e.g., clips, screws, etc.) disposed at opposite ends of the heat pipe structure  100 . In the exemplary embodiment, the heat pipe structure  100  includes at least four (4) such attachment means, one disposed at each corner of the rectangular housing  105  of the heat pipe structure  100 .  
         [0021]    In operation, the heat pipe structure  100  significantly reduces cabin heat  225  buildup, and quickly and efficiently dissipates any cabin heat. The heat pipe structure  100  reduces cabin heat  225  buildup by presenting a virtual vacuum to incident solar radiation  245  through vapor space  115 . In particular, incident solar radiation  245  can only travel to the automobile cabin  220  through convection or conduction. Convection is substantially eliminated as a method of transferring the incident solar radiation  245  to the automobile cabin  220  by the vapor space  115  between the automobile roof  210  and the cabin. Additionally, conduction will only occur in those areas where the automobile roof  210  is directly connected to the cabin  220  (i.e., in the small areas where the heat pipe structure  100  is secured to the roof  210  of the automobile. Plastic attachments between the roof  210  and the heat pipe structure  100  may be used to further decrease the conduction of heat to the automobile cabin  220 .  
         [0022]    The heat pipe structure  100  also rapidly dissipates cabin heat  225 . In particular, cabin heat  225  rises to the top of the cabin  220  (a well known thermodynamic principle) and contacts the evaporator portion  120  of the heat pipe structure  100 . This causes the fluid in the wick structure  110  to evaporate and take gaseous form and travel upward. As the gas reaches the condenser section  130  of the heat pipe structure  100  it returns to liquid form, and the liquid returns to the wick structure  110  as is well known in the art. In this manner, cabin heat  225  is removed from the cabin.  
         [0023]    The heat pipe structure  100  dissipates cabin heat  225  even more rapidly when the car is in motion. In particular, when the automobile  200  is moved in direction  240 , air passes across the roof  210  of the automobile at a specified rate dependent upon the speed of the automobile. The air passing across the roof  210  serves to cool the condenser section  130  of the heat pipe structure  100  and also serves to remove any cabin heat  225  which rises towards the roof. Thus, depending upon the external air temperature at the roof  210 , more or less cabin heat  225  can be removed from the automobile  200 .  
         [0024]    Experiments performed by the present applicants have shown that with an internal cabin temperature of approximately 80° C., and an external air temperature of approximately 37° C., approximately 400 watts of power can be transferred from the cabin  220  utilizing the heat pipe structure  100  according to the exemplary embodiment of the present invention.  
         [0025]    [0025]FIG. 3 shows a cross section of the heat pipe  100 , taken along lines  3 - 3  in FIG. 1( a ). As will be understood, the housing  105  of the heat pipe structure  100  is formed by lower and upper housing layers  121 ,  131 . As stated above, these layers are preferably formed of metal such as Copper, but may be formed from any suitable material known to those skilled in the art. The wick structure  110  is disposed on the lower layer  121 , and a vapor space  115  is disposed therebetween. As is known in the art, the vapor space  115  comprises an area in which vapor evaporated at the heat input point (i.e., evaporator side  120 ) can migrate to cooler parts of the heat pipe structure (i.e., condenser side  130 ) to be condensed.  
         [0026]    The wick structure  110  are preferably made of Copper felt wick which is in a range from 0.010 to 0.040 inch thick. This Copper felt is typically constructed of fibers which are 0.00002 inch in diameter, and 0.20 inch in length, wherein Copper forms 20-60% of the wick structure  115  volume. The wick structure  110  is held in place by a partial vacuum created when the heat pipe structure  100  is operating below the working fluid&#39;s (e.g., water) normal boiling point. It is also possible to melt, press or otherwise adhere the wick structure  110  to the housing layer  121 , thereby improving the thermal conductance between the housing layer and the adjoining wick structure. In an alternative construction, one or more layers of fine mesh screen can also serve as wick structure  110 .  
         [0027]    Thus, the heat pipe structure  100  described above provide for a thin, flexible and reliable heat pipe which may be utilized to control the interior temperature of an automobile. The heat pipe structure  100  may also include a layer of adhesive applied to either side thereof (e.g., on either or both of housing layers  121 ,  131 ) for allowing easy placement of the heat pipe structure against a heat producing member.  
         [0028]    In an alternative embodiment of the present invention, an additional compartment situated between the cabin  220  and the heat pipe structure  100  may be added for increasing temperature dissipation capabilities. For example, an additional compartment including fans disposed at either end thereof may be used to more efficiently move heated cabin air  225  across the across the evaporator portion  120  of the heat pipe structure  100 .  
         [0029]    In another alternative embodiment, the heat pipe structure  100  may include heat-dissipating fins as are well known in the art for further increasing the heat dissipation capabilities of the heat pipe structure by increasing the surface area of the heat pipe structure. Preferably, such fins would be disposed on the evaporator section  120  of the heat pipe  100 .  
         [0030]    [0030]FIG. 4 shows a cross section of the heat pipe structure  300  according to a second exemplary embodiment of the present invention. The heat pipe structure  300  is similar to the heat pipe structure  100  shown in FIG. 3, except that instead of single-layer housing wall layers (e.g.,  121 ,  131  in FIG. 3), the heat pipe structure  300  includes lower and upper housing walls  310 ,  320  which each include multiple layers. The heat pipe structure  300  also includes a wick  330 , and a separator layer  340  (explained below) for maintaining a gap or vapor space  345  between the wick and the upper housing wall  320 . Like the heat pipe structure  100  described above, the heat pipe structure  300  includes both an evaporator section  350 , and a condenser section  360 .  
         [0031]    The wick structure  330  is disposed on lower housing wall  310 , and the separator layer  340  is in turn disposed on the wick structure  330 . The separator layer  340  is constructed of one or more layers of either metal or plastic screen, although plastic is preferred in that it makes the heat pipe structure  300  more flexible. The function of the separator layer  340  is to provide interconnected spaces  342  within the heat pipe structure  300  to function as a vapor space  345  within which vapor evaporated at the heat input point (i.e., evaporator side  350 ) can migrate to cooler parts of the heat pipe structure (i.e., condenser side  360 ) to be condensed. In the second exemplary embodiment of the present invention, separator layer  340  is formed of 10-mesh polypropylene screen with 0.030 inch wire thickness, although a screen formed of any suitable material (and of any suitable wire thickness) may be utilized. Since wires  341  of the separator layer  340  overlap and contact one another, the screen provides a minimum separation of about 0.040 inch between the wick structure  330  and the separator layer.  
         [0032]    Lower and upper housing walls  310 ,  320  are formed as laminates which include five separate layers, including a first reinforcing layer  311  (preferably made of polypropylene), a first adhesive layer  312 , a metal layer  313 , a second adhesive layer  314 , and a second reinforcing layer  315  (also preferably made of polypropylene). In the exemplary embodiment, the reinforcing layers  311 ,  315  are approximately 0.004 inch thick. The reinforcing layers  311 ,  315  function both to support the metal layer  313 , and to bond the lower and upper walls  310 ,  320  together to form the heat pipe structure  300 . The bond is accomplished by pressing the edges of the walls  310 ,  320  together while heat is applied, a process well known to those skilled in the art.  
         [0033]    As will be understood by those skilled in the art, metal layer  313  is attached to the first reinforcing layer  311  by the first adhesive layer  312 . In the exemplary embodiment, metal layer  313  comprises a Copper foil which is approximately 0.001 inch thick, and first adhesive layer  312  is approximately 0.0005 inch thick and made of polyethylene terepthalate. The second reinforcing layer  315  is attached to the metal layer  313  by the second adhesive layer  314 . In the exemplary embodiment, second reinforcing layer  315  is 0.004 inch thick and made of polypropylene, and second adhesive layer  312  is approximately 0.0005 inch thick and made of polyethylene terepthalate.  
         [0034]    The metal layers  313  of the housing walls  310 ,  320  act as barriers to prevent gas leakage into the vacuum space  345  of the heat pipe structure  300 . The metal layers  313  also serve to prevent the vapor pressure inside the vacuum space  345  from leaking out of the heat pipe structure  300 .  
         [0035]    [0035]FIG. 5 shows a cross section of the heat pipe structure  400  according to a third exemplary embodiment of the present invention. The heat pipe structure  400  is similar to the heat pipe structure  100  shown in FIG. 3, except that instead of single-layer housing wall layers (e.g.,  121 ,  131  in FIG. 3), the heat pipe structure  400  includes lower and upper housing walls  410 ,  420  which each include multiple layers. The heat pipe structure  400  also includes a wick  430 , and a separator layer  440  (explained below) for maintaining a gap or vapor space  445  between the wick and the upper housing wall  420 . Like the heat pipe structure  100  described above, the heat pipe structure  400  includes both an evaporator section  450 , and a condenser section  460 .  
         [0036]    The wick structure  430  is disposed on lower housing wall  410 , and the separator layer  440  is in turn disposed on the wick structure  430 . The separator layer  440  is constructed of one or more layers of either metal or plastic screen, although plastic is preferred in that it makes the heat pipe structure  400  more flexible. The function of the separator layer  440  is to provide interconnected spaces  442  within the heat pipe structure  400  to function as a vapor space  445  within which vapor evaporated at the heat input point (i.e., evaporator side  450 ) can migrate to cooler parts of the heat pipe structure (i.e., condenser side  460 ) to be condensed. In the third exemplary embodiment of the present invention, separator layer  440  is formed of 10-mesh polypropylene screen with 0.030 inch wire thickness, although a screen formed of any suitable material (and of any suitable wire thickness) may be utilized. Since wires  441  of the separator layer  440  overlap and contact one another, the screen provides a minimum separation of about 0.040 inch between the wick structure  430  and the separator layer.  
         [0037]    Lower and upper housing walls  410 ,  420  are formed as laminates which include nine separate layers, including a first reinforcing layer  411  (preferably made of polypropylene), a first adhesive layer  412 , a metal layer  413 , a second adhesive layer  414 , a second reinforcing layer  415  (also preferably made of polypropylene), a third adhesive layer  416 , a second metal layer  417 , a fourth adhesive layer  418 , a third reinforcing layer  419  (preferably made of plastic), a fifth adhesive layer  420 , and a fourth reinforcing layer  421  (also preferably made of polypropylene).  
         [0038]    In the exemplary embodiment, the reinforcing layers  411 ,  415 ,  419  and  421  function both to support the metal layers  413 ,  417 , and to bond the lower and upper walls  410 ,  420  together to form the heat pipe structure  400 . The bond is accomplished by pressing the edges of the walls  410 ,  420  together while heat is applied, a process well known to those skilled in the art.  
         [0039]    The metal layers  413  and  417  of the housing walls  410 ,  420  act as barriers to prevent gas leakage into the separator layer  440  of the heat pipe structure  400 . The metal layers  413 ,  417  also serve to prevent vapor pressure inside the vapor space  445  from leaking out of the heat pipe structure  400 .  
         [0040]    Moreover, the reliability of the seal is increased by the use of two metal barrier layers (e.g., first and second metal layers  413 ,  417 ), as opposed to just one (e.g., housing layer  121  in FIG. 3; metal layers  313  in FIG. 4). Additionally, since metal foil sheets occasionally have random pinholes therethrough (due to manufacturing defects), the use of two metal foil layers (e.g., first and second metal layers  413 ,  417 ) reduces the likelihood of leaks because of the very low probability that one or more such pinholes in separate metal foil sheets will align in the final structure.  
         [0041]    Thus, the use of two metal layers  413 ,  417 , and a plurality of strengthening plastic layers  411 ,  415 ,  419 ,  421  for support produces a very reliable and very flexible heat pipe structure. The heat pipe structure  400  may also include a third layer of adhesive applied to either side thereof (e.g., on either or both of fourth reinforcing layers  421 ) for allowing easy placement of the heat pipe structure against a heat producing member.  
         [0042]    With any of the heat pipe structures  100 ,  300 ,  400  described above, additional coatings may be applied to either or both of the heat pipe housing outer layers (i.e., layers  121 ,  131  in FIG. 3; layers  315  in FIG. 4; layers  421  in FIG. 5) to facilitate various applications. For example, in some applications it may be desirable to coat the outer layers with an electrically insulating layer to prevent the heat pipe from creating shorts across adjacent electrical connectors.  
         [0043]    Further more, as described above with reference the heat pipe structure  100 , heat pipe structures  300  and  400 , may include heat-dissipating fins as are well known in the art for further increasing the heat dissipation capabilities of the heat pipe structures by increasing the surface area of the heat pipe structures. Preferably, such fins would be disposed on the evaporator sections  350 ,  450  of the heat pipe structures.  
         [0044]    Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.