Patent Publication Number: US-2015060021-A1

Title: Heat transfer device and an associated method of fabrication

Description:
This invention was made with Government support under contract number N66001-08-C-2008 awarded by U.S. Department of Defense. The Government has certain rights in the invention. 
    
    
     BACKGROUND 
     The present disclosure relates generally to a heat transfer device and more particularly, to a vapor chamber or a heat pipe having a spatially controlled porosity or pore size and an associated method of fabrication. 
     A heat transfer device is used to transfer heat from a source to a sink. Such heat transfer devices may include a hot end and a cold end to enable transfer of the heat from the hot end to the cold end. Generally, the heat transfer device combines the principle of a thermal conductivity and a phase transition of a working fluid to transfer the heat. In one example, the heat transfer device is a sealed tube or a sealed chamber, fabricated using a material having a high thermal conductivity. The heat transfer device includes the working fluid within the sealed chamber to transfer the heat effectively. Typically, such heat transfer device may further include a wick to enable heat transfer by condensation and evaporation of the working fluid i.e. by changing phase of the working fluid within the sealed chamber. 
     The conventional wick includes a plurality of mono-dispersed sintered particles distributed along the longitudinal direction of the heat transfer pipe. Typically wicks are designed to provide a high fluid transport and phase change capability of the working fluid. Such functions are achieved by designing the wick having a very large pores combined with high surface area for phase change processes. However, such conventional wicks are less effective in performing phase change of the working fluid, because the design and fabrication process are based on mono-dispersed particles. Further, such wick structures provide solid conduction thermal resistance due to low contact area with the chamber walls, or casing material and/or low porosity. 
     Such limitations can be addressed by designing the wick, having pore size variation through the use of varying particle sizes. However, the wicks that are designed with varying particle sizes are fabricated using an organic carrier which is burned completely to generate the sintered particles having varied pore size and/or varied porosity. Such fabrication processes may result in contamination of the heat transfer device, limit the wick fabrication temperature to temperatures high enough to burn-away the organics, and also may lead to generation of a non-condensable fluid during prolonged operation of the heat transfer device. 
     There is a need for an improved heat transfer device and a method for fabricating the heat transfer device. 
     BRIEF DESCRIPTION 
     In accordance with one exemplary embodiment, a heat transfer device is disclosed. The heat transfer device includes a casing and a wick disposed within the casing. The wick includes a first sintered layer disposed proximate to an inner surface of the casing and a second sintered layer disposed on the first sintered layer. The first sintered layer includes a plurality of first sintered particles, having a first porosity and a plurality of first pores. The second sintered layer includes a plurality of second sintered particles, having a second porosity and a plurality of second pores. At least one first sintered particle is smaller than at least one second pore and the first porosity is smaller than the second porosity 
     In accordance with one exemplary embodiment, a method for manufacturing a heat transfer device is disclosed. The method includes filling a mixture of a plurality of first particles and second particles within a first half casing portion. Further, the method includes leveling the plurality of first and second particles within the first half casing portion. The method includes vibrating the first half casing portion to segregate the plurality of first particles from the plurality of second particles such that a first layer portion having the plurality of first particles and a second layer portion having the plurality of second particles are formed. The first layer portion is disposed proximate to an inner surface of the first half casing portion and a second layer portion is disposed on the first layer portion. Further, the method includes sintering the first layer portion and the second layer portion to generate a first sintered layer portion and a second sintered layer portion. The first sintered layer portion includes a plurality of first sintered particles, having a first porosity and a plurality of first pores. The second sintered layer portion includes a plurality of second sintered particles, having a plurality of second pores and a second porosity greater than the first porosity. Further, the method includes forming at least one first sintered particle smaller than at least one second pore. The method further includes forming a first wick portion having the first sintered layer portion and the second sintered layer. The method further includes repeating the filling, the leveling, the vibrating, and the sintering process in a second half casing portion to form a second wick portion within the second half casing portion. Further, the method includes coupling the first half casing portion to the second half casing portion such that the first wick portion is coupled to the second wick portion to form a heat transfer device. 
    
    
     
       DRAWINGS 
       These and other features and aspects of embodiments of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a schematic sectional view of a heat transfer device, for example a vapor chamber in accordance with an exemplary embodiment; 
         FIG. 2   a  is a sectional view of a first half casing portion of a vapor chamber in accordance with an exemplary embodiment; 
         FIG. 2   b  is a sectional view of a second half casing portion of a vapor chamber in accordance with an exemplary embodiment; 
         FIG. 3  is a schematic sectional view of a portion of a vapor chamber having a first sintered layer, a second sintered layer, and a third sintered layer in accordance with an exemplary embodiment; 
         FIG. 4   a  is a perspective view of a portion of a wick having a plurality of first sintered particles and a plurality of second sintered particles in accordance with an exemplary embodiment; 
         FIG. 4   b  is a perspective view of the portion of the wick in  FIG. 4   a  having a plurality of third sintered particles in accordance with an exemplary embodiment; 
         FIG. 4   c  is a perspective view of a portion of a wick having a plurality of third sintered particles in accordance with another exemplary embodiment; 
         FIG. 5   a  is a schematic view of a portion of a wick having a first sintered layer with a uniform thickness of and a second sintered layer having a non-uniform thickness in accordance with another exemplary embodiment; 
         FIG. 5   b  is a schematic view of the portion of the wick in  FIG. 5   a  having a third sintered layer having a non-uniform thickness in accordance with another exemplary embodiment; 
         FIG. 6  is a schematic flow diagram illustrating a method of manufacturing a first sintered layer and a second sintered layer within a casing in accordance with an exemplary embodiment; 
         FIG. 7  is a schematic flow diagram illustrating a method of manufacturing a third sintered layer portion on a second sintered layer portion within a first half casing portion in accordance with an exemplary embodiment; 
         FIG. 8  is a schematic flow diagram illustrating a method of manufacturing a second sintered layer portion having a non-uniform thickness along an evaporator section, a transport section, and a condenser section in accordance with another exemplary embodiment; 
         FIG. 9  is a schematic flow diagram illustrating a method of manufacturing a second sintered layer portion having a non-uniform thickness along an evaporator section, a transport section, and a condenser section in accordance with yet another exemplary embodiment; and 
         FIG. 10  is a schematic flow diagram illustrating a method of manufacturing a third sintered layer portion having a non-uniform thickness along an evaporator section, a transport section, and a condenser section in accordance with another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     While only certain features of embodiments have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as falling within the spirit of the invention. 
     Embodiments discussed herein disclose a heat transfer device and associated methods for manufacturing the heat transfer device. More particularly, certain embodiments disclose a vapor chamber. The vapor chamber includes a casing and a wick having a first sintered layer and a second sintered layer disposed within the casing. The first sintered layer includes a plurality of first sintered particles having a first porosity and a plurality of first pores. The first sintered layer is disposed proximate to an inner surface of the casing. The second sintered layer includes a plurality of second sintered particles having a second porosity and a plurality of second pores. The second sintered layer is disposed on the first sintered layer. At least one first sintered particle is smaller than at least one second pore and the first porosity is smaller than the second porosity. 
     Certain embodiments disclose a method of manufacturing a heat transfer device. More specifically, certain embodiments disclose a method of manufacturing a vapor chamber. The method includes filling a plurality of first particles and second particles within a first half casing portion and leveling the plurality of first and second particles. Further, the method includes vibrating the first half casing portion so as to segregate the plurality of first particles from the plurality of second particles to form a first layer portion and a second layer portion. The segregated first layer portion includes the plurality of first particles disposed proximate to an inner surface of the first half casing portion and the segregated second layer portion includes the plurality of second particles disposed on the first layer portion. The method further includes sintering the first layer portion and the second layer portion to generate a first sintered layer portion and a second sintered layer portion. The first sintered layer portion and the second sintered layer portion together form a first wick portion. 
     Further, the method includes repeating the filling, the leveling, the vibrating, and the sintering process in a second half casing portion to form a second wick portion within the second half casing portion. The method further includes coupling the first half casing portion to the second half casing portion such that the first wick portion is coupled to the second wick portion to form the vapor chamber. 
       FIG. 1  is a schematic sectional view of a heat transfer device  100  in accordance with an exemplary embodiment. In the illustrated embodiment, the heat transfer device  100  is a vapor chamber. It should be noted herein that the terms “heat transfer device” and “vapor chamber” are used interchangeably. In some other embodiments, the heat transfer device is a heat pipe. 
     The vapor chamber  100  includes a casing  102  and a wick  104 . Further, the wick forms a sealed chamber  106  filled with a working fluid  108 . The working fluid  108  transfers the heat from one end  116  to another end  118  of the vapor chamber  100 . Further, the vapor chamber  100  includes an evaporator section  110  disposed proximate to the end  116 , a condenser section  112  disposed proximate to the end  118 , and a transport section  114  disposed between the evaporator section  110  and the condenser section  112 . The evaporator section  110  is used to absorb heat from a source (not shown in  FIG. 1 ) by evaporating the working fluid  108 . The condenser section  112  is used to release heat to a sink (not shown in  FIG. 1 ) by condensing the working fluid  108 . The transport section  114  is used to conduct the heat from one end  116  to the other end  118  via the working fluid  108 . The vapor chamber  100  is fabricated using a material having high thermal conductivity. The material of the vapor chamber  100  may be copper or aluminum nitrate, for example. The vapor chamber  100  has a rectangular shape and a length “L 1 ” in the range of five to ten meters, for example. 
     The casing  102  includes a first half casing portion  102   a  and a second half casing portion  102   b . Each half casing portion  102   a ,  102   b  includes an inner surface  120  and an outer surface  122 . Each half casing portion  102   a ,  102   b  has a U-shape. The first half and second half casing portions  102   a ,  102   b  are coupled to each other by brazing, soldering, or the like. The wick  104  is disposed proximate to the inner surface  120  of the casing  102 . The wick  104  includes a first sintered layer  126  and a second sintered layer  128 . Specifically, the first sintered layer  126  is disposed proximate to the inner surface  120  of the casing  102 . The second sintered layer  128  is disposed on the first sintered layer  126 . The first sintered layer  126  includes a first sintered layer portion  126   a  disposed in the first half casing portion  102   a  and another first sintered layer portion  126   b  disposed in the second half casing portion  102   b . Similarly, the second sintered layer  128  includes a second sintered layer portion  128   a  disposed on the first sintered layer portion  126   a  and another second sintered layer portion  128   b  disposed on the other first sintered layer portion  126   b.    
     The first and second sintered layers  126 ,  128  have a uniform thickness “T 1 ” and “T 2 ” respectively across the length “L 1 ” of the vapor chamber  100 . The casing  102  may be made of a first material and the first sintered layer  126  and the second sintered layer  128  are made of a second material different from the first material. The casing  102 , the first sintered layer  126 , and the second sintered layer  128  may be made of the same material. 
       FIG. 2   a  is a sectional view along ( 2 A- 2 A) of the first half casing portion  102   a  in accordance with the embodiment of  FIG. 1 . The first half casing portion  102   a  includes a first wick portion  104   a  and a coating portion  130   a.    
     The first wick portion  104   a  includes the first sintered layer portion  126   a  disposed proximate to the inner surface  120  of the first half casing portion  102   a  and the second sintered layer portion  128   a  disposed on the first sintered layer portion  126   a . The coating portion  130   a  is disposed between the inner surface  120  of the first half casing portion  102   a  and the first sintered layer portion  126   a . The coating portion  130   a  may include one or more layers depending on the application and design criteria. The coating portion  130   a  may be made of a material having high thermal conductivity such as copper, aluminum nitrate, or the like. The first half casing portion  102   a  may be made of a first material and the coating portion  130   a , the first sintered layer portion  126   a , and the second sintered layer portion  128   a  may be made of a second material different from the first material. 
       FIG. 2   b  is a sectional view along ( 2 B- 2 B) of the second half casing portion  102   b  in accordance with the embodiment of  FIG. 1 . The second half casing portion  102   b  includes a second wick portion  104   b  and a coating portion  130   b.    
     The second wick portion  104   b  includes the first sintered layer portion  126   b  disposed proximate to the inner surface  120  of the second half casing portion  102   b  and the second sintered layer portion  128   b  disposed on the first sintered layer portion  126   b . The coating portion  130   b  is disposed between the inner surface  120  of the second half casing portion  102   b  and the first sintered layer portion  126   b . The coating portion  130   b  includes a material having high thermal conductivity such as copper, aluminum nitrate, or the like. The second half casing portion  102   b  may be made of a first material and the coating portion  130   b , the first sintered layer portion  126   b , and the second sintered layer portion  128   b  may be made of a second material different from the first material. 
       FIG. 3  is a schematic sectional view of a portion of the vapor chamber  100 . In the illustrated embodiment, the vapor chamber  100  includes the casing  102 , the first sintered layer  126 , the second sintered layer  128 , and additionally a third sintered layer  140 . The third sintered layer  140  is disposed on the second sintered layer  128 . The third sintered layer  140  has a uniform thickness “T 3 ” along the length of the vapor chamber  100 . The third sintered layer  140  includes a material having high thermal conductivity, such as copper, aluminum nitrate, or the like. 
       FIG. 4   a  is a perspective view of a portion  134  of the wick  104 . The wick  104  includes the first sintered layer  126  and the second sintered layer  128 . The first sintered layer  126  has a plurality of first sintered particles  142  and the second sintered layer  128  has a plurality of second sintered particles  144 . Further, the first sintered layer  126  has a plurality of first pores  146  and a first porosity  148  and the second sintered layer  128  has a plurality of second pores  150  and a second porosity  152 . 
     Each first sintered particle  142  has a size “S 1 ” and each second sintered particle  144  has a size “S 2 ”. Each first sintered particle  142  has the size “S 1 ” in a range of hundred nanometers to fifty micrometers and each second sintered particle  144  has the size “S 2 ” in a range of ten micrometers to hundred micrometers. The size “S 2 ” of each second sintered particle  144  is greater than the size “S 1 ” of each first sintered particle  142 . 
     Further, each first pore  146  has a size “S 3 ” and each second pore  150  has a size “S 4 ”. Each first pore  146  has the size “S 3 ” in a range of ten nanometers to ten micrometers and each second pore  150  has the size “S 4 ” in a range of one micrometer to fifty micrometers. Each first sintered particle  142  and each second sintered particle  144  has a spherical or oval or circular shape. The size “S 1 ” of each first sintered particle  142  is smaller than the size “S 4 ” of each second pore  150 . The size “S 1 ” of the first sintered particle  142  is at least forty to sixty percent smaller than the size “S 4 ” of the second pore  150 . The first sintered particle  142  having a relatively smaller size than the second pore  150  provides higher heat transfer capability and offers very less thermal resistance along the length of the vapor chamber  100 . 
     The first porosity  148  of the first sintered layer  126  is in a range of five percent to forty percent. The second porosity  152  of the second sintered layer  128  is in a range of eight percent to twenty percent. The first porosity  148  is smaller than the second porosity  152 . The second layer  128  having a relatively greater second porosity  152  facilitates to exert a higher capillary pressure on the working fluid along the length of the vapor chamber  100 . 
       FIG. 4   b  is a perspective view of the third sintered layer  140  in accordance with the exemplary embodiment of  FIG. 4   a . The third sintered layer  140  includes a plurality of third sintered particles  154 . The plurality of third sintered particles  154  is disposed on the plurality of second sintered particles  144 . Each third sintered particle  154  has a dendrite shape. Further, the third sintered layer  140  has a plurality of third pores  156  and a third porosity  158 . Each third sintered particle  154  has a size “S 5 ” and each third pore  156  has a size “S 6 ”. Each third sintered particle  154  has the size “S 5 ” in a range of hundred nanometers to ten micrometers and each third pore  156  has a size “S 6 ” in a range of one nanometer to ten micrometers. The third porosity  158  is in a range of twenty percent to eighty percent. The size “S 5 ” of each third sintered particle  154  is smaller or equal to the size “S 2 ” of each second sintered particle  144  and the third porosity  158  is smaller than the second porosity  152 . The third sintered layer  140  having a relatively smaller third porosity  152  provides a higher heat transfer capability of the wick  104 . 
       FIG. 4   c  is a perspective view of a third sintered layer  139  in accordance with another exemplary embodiment. The third sintered layer  139  is disposed on a second sintered layer (not shown in  FIG. 4   c ). The third sintered layer  141  includes a plurality of third particles  132  having a spherical shape. 
       FIG. 5   a  is a schematic view of a portion  137  of a wick  105  having a first sintered layer  127  and a second sintered layer  129  in accordance with another exemplary embodiment. 
     The second sintered layer  129  is disposed on the first sintered layer  127 . The first sintered layer  127  has a uniform thickness “T 4 ” along an evaporator section  111 , a condenser section  113 , and a transport section  115  of a vapor chamber. The second sintered layer  129  has a non-uniform thickness along the evaporator section  111 , the condenser section  113 , and the transport section  115 . Specifically, the second sintered layer  129  has a thickness “T 5 ” corresponding to the evaporator section  111 , a thickness “T6” corresponding to the condenser section  113 , and a thickness “T 7 ” corresponding to the transport section  115 . The thickness “T 5 ” may be in the range of five millimeters to ten millimeters, the thickness “T 6 ” may be in the range of two millimeters to five millimeters, and the thickness “T 7 ” may be in the range of five millimeters to eight millimeters, for example. The thickness “T 5 ” is greater than the thickness “T 6 ”. The thickness “T 7 ” is greater than the thickness “T 5 ”. 
       FIG. 5   b  is a schematic view of the portion  137  of the wick  105  having an additional third sintered layer  141  in accordance with the exemplary embodiment of  FIG. 5   a.    
     The third sintered layer  141  is disposed on the second sintered layer  129 . The third sintered layer  141  has a non-uniform thickness along the evaporator section  111 , the condenser section  113 , and the transport section  115  of the vapor chamber. Specifically, the third sintered layer  141  has a thickness “T 8 ” corresponding to the evaporator section  111 , a thickness “T 9 ” corresponding to the condenser section  113  and a thickness “T 10 ” corresponding to the transport section  115 . The thickness “T 8 ” may be in the range of two millimeters to three millimeters, the thickness “T 9 ” may be in the range of one millimeter to two millimeters, and the thickness “T 10 ” may be in the range of two millimeters to five millimeters, for example. The thickness “T 8 ” is greater than the thickness “T 9 ”. The thickness “T 10 ” is greater than the thickness “T 8 ”. 
       FIG. 6  is a schematic flow diagram illustrating a plurality of steps involved in a method  160  of manufacturing the first sintered layer  126  and the second sintered layer  128  within the casing  102  in accordance with the embodiment of  FIGS. 1 ,  2   a , and  2   b.    
     The method  160  includes a step  162  of disposing the first half casing portion  102   a  and a step  168  of applying the coating portion  130   a  on the inner surface  120  of the first half casing portion  102   a . A plurality of first particles  164  and a plurality of second particles  166  are filled in the first half casing portion  102   a . The first half casing portion  102   a  is made of a first material and the coating portion  130   a , the plurality of first particles  164 , and the plurality of second particles  166  includes a second material different from the first material. 
     In another embodiment, a coating portion  130   a  may not be applied to the inner surface  120  of the first half casing portion  102   a  and the plurality of particles  164 ,  166  are filled directly within the first half casing portion  102   a  such that the plurality of particles  164 ,  166  are in contact with the inner surface  120  of the first half casing portion  102   a . The first half casing portion  102   a , the plurality of first particles  164 , and the plurality of second particles  166  include the same material. 
     A step  170  includes leveling the plurality of first particles  164  and the plurality of second particles  166  within the first half casing portion  102   a . The plurality of first and second particles  164 ,  166  is leveled using a squeegee device  172 . A uniform contact surface  171  of the squeegee device  172  is used to level the plurality of first particles  164  and the plurality of second particles  166  to generate a uniform thickness. The squeegee device  172  may be made of a material such as nickel-cobalt ferrous alloy or ceramics such as aluminum nitrate, alumina, silicon carbide, silicon nitride or the like. 
     The method  160  further includes a step  174  of vibrating the first half casing portion  102   a  to segregate the plurality of first particles  164  from the plurality of second particles  166  such that a first layer portion  176   a  and a second layer portion  178   a  is formed within the first half casing portion  102   a . The first half casing portion  102   a  is vibrated using a vibrator device  180 . The vibrator device  180  is clamped to the first half casing portion  102   a  and powered via mechanical elements to vibrate the first half casing portion  102   a . The first layer portion  176   a  having the plurality of first particles  164  is disposed proximate to the inner surface  120  of the first half casing portion  102   a  and the second layer portion  178   a  having the plurality of second particles  166  is disposed on the first layer portion  176   a . The first layer portion  176   a  has a uniform thickness “T 01 ” and the second layer portion  178   a  has a uniform thickness “T 02 ”. In another exemplary embodiment, the step  174  of vibrating the half casing portion may be optional. 
     The method  160  further includes a step  182  of sintering the first layer portion  176   a  and the second layer portion  178   a . The step  182  includes disposing a sintering spacer  184  over the second layer portion  178   a  and filling an additional amount of the plurality of second particles  166  in the spaces formed between the sintering spacer  184  and the inner surface  120  of the first half casing portion  102   a . The sintering spacer  184  has a uniform contact surface  187  contacting the second layer portion  178   a . The step  182  further includes disposing the first half casing portion  102   a  with the sintering spacer  184 , in a sintering device  188  to sinter the first layer portion  176   a  and the second layer portion  178   a  so as to generate the first sintered layer portion  126   a  and the second sintered layer portion  128   a  having a uniform thickness as shown in step  190 . 
     The first sintered layer portion  126   a  includes the plurality of first sintered particles  142  having the first porosity  148  and the plurality of first pores  146  (as shown in  FIG. 4   a ). The second sintered layer portion  128   a  includes the plurality of second sintered particles  144  having the plurality of second pores  150  and the second porosity  152  (as shown in  FIG. 4   a ). The sintering step  182  is performed in a controlled environment i.e. at a predefined temperature and pressure so as to generate at least one first sintered particle  142  smaller than at least one second pore  150 . The sintering process is controlled to generate at least forty to sixty percent of the first sintered particles  142  having a size smaller than the plurality of second pores  150 . The sintering pressure is in a range of 50 bars to 60 bars and the sintering temperature is in a range of 648.89 degrees Celsius to 815.56 degrees Celsius. The sintering spacer  184  may be made of a material such as nickel-cobalt ferrous alloy or ceramics including aluminum nitrate, alumina, silicon carbide, and silicon nitride. 
     The first sintered layer  126   a  has a uniform thickness “T 1 ” corresponding to an evaporator section  110 , a condenser section  112 , and a transport section  114 . Similarly, the first sintered layer  128   a  has a uniform thickness “T 2 ” corresponding to the evaporator section  110 , the condenser section  112 , and the transport section  114 . The step  190  further involves removing the sintering device  188  and the sintering spacer  184  such that the first wick portion  104   a  is formed within the first half casing portion  102   a . The first wick portion  104   a  includes the first sintered layer portion  126   a  and the second sintered layer portion  128   a.    
     Similarly, the method further includes a step  192  of repeating the steps  162 ,  168 ,  170 ,  174 ,  182 , and  190  in the second half casing portion  102   b  to form a second wick portion  104   b . The second wick portion  104   b  includes the first sintered layer portion  126   b  disposed proximate to the inner surface  120  of the second half casing portion  102   b  and the second sintered layer portion  128   b  disposed on the first sintered layer portion  126   b . The method also includes applying the coating portion  130   b  on the inner surface  120  of the second half casing portion  102   a.    
     The method  160  further includes a step  194  of coupling the first half casing portion  102   a  to the second half casing portion  102   b  such that the first wick portion  104   a  is coupled to the second wick portion  104   b  to form the heat transfer device  100 . A sealed chamber  106  is formed between the first half casing portion  102   a  and the second half casing portion  102   b . The heat transfer device  100  includes a casing  102  having a wick  104  disposed within the casing  102 . The first half and second half casing portions  102   a ,  102   b  are coupled to each other by brazing, soldering, or the like. 
       FIG. 7  is a schematic flow diagram illustrating the method  360  of manufacturing an additional third sintered layer portion  140   a  on the second sintered layer portion  128   a  within the first half casing portion  102   a  in accordance with the embodiment of  FIGS. 2   a ,  2   b , and  3 . 
     The method  360  includes a step  196  of disposing the first half casing portion  102   a  having the first sintered layer portion  126   a  and the second sintered layer portion  128   a . The method  360  further includes a step  200  of filling the plurality of third particles  198  within the first half casing portion  102   a . Specifically, the plurality of third particles  198  are filled on the second sintered layer portion  128   a . The method  360  further includes a step  202  of leveling the plurality of third particles  198  within the first half casing portion  102   a  so as to form a third layer portion  204   a  having a uniform thickness T 03 . The squeegee device  172  having the uniform contact surface  171  is used for leveling the plurality of third particles  198 . 
     The method  360  further includes a step  206  of sintering the third layer portion  204   a . The sintering step  206  includes disposing the sintering spacer  184  on the third layer portion  204   a  and disposing the first half casing portion  102   a  including the sintering spacer  184 , in the sintering device  188  to sinter the third layer portion  204   a  so as to generate the third sintered layer portion  140   a . The sintering spacer  184  having a uniform contact surface  187 , is used to generate the third sintered layer portion  140   a  having the uniform thickness “T 3 ”. The third sintered layer portion  140   a  includes the plurality of third sintered particles  154  having the third porosity  158  and the plurality of third pores  156  (as shown in  FIG. 4   b ). The sintering process is performed in a controlled environment so as to generate the third porosity  158  smaller than the second porosity  152 . The third sintered particle  154  has a size less than or equal to the size of the second sintered particle  144 . 
     The steps  196 ,  200 ,  202 , and  206  are repeated in the second half casing portion  102   b  to generate another third sintered layer portion  140   b.    
       FIG. 8  is a flow diagram illustrating a method  208  of manufacturing the second sintered layer portion  129   a  having a non-uniform thickness in accordance with the embodiment of  FIG. 5   a.    
     The method  208  includes a step  210  of forming a second layer portion  179   a  having a non-uniform thickness on a first layer portion  177   a  having a uniform thickness “T 04 ”. The step  210  includes leveling a plurality of second particles  167  using a squeegee spacer  212  having a uniform contact surface  214 . Two smaller squeegee spacers  173 ,  175  are disposed on the second layer portion  179   a  corresponding to the position of the evaporator section  111  and the condenser section  113 . The squeegee spacer  212  is disposed on the second layer portion  179   a  and contacting the two smaller squeegee spacers  173 ,  175  so as to form the second layer portion  179   a  having a non-uniform thickness. The second layer portion  179   a  has a thickness “T 05 ” for the evaporator section  111 , a thickness “T 06 ” for the condenser section  113 , and a thickness “T 07 ” for the transport section  115 . The squeegee spacers  212 ,  173 ,  175  may be made of a material including nickel-cobalt ferrous alloy or ceramics such as aluminum nitrate, alumina, silicon carbide, and silicon nitride. 
     The method  208  further includes a step  216  of generating the second sintered layer portion  129   a  having a non-uniform thickness over the first sintered layer portion  127   a  having the uniform thickness “T 4 ”. The step  216  includes replacing the squeegee spacer  212  with a first sintering spacer  213  having a uniform contact surface  218  and the two smaller squeegee spacers  173 ,  175  with second sintering spacers  183 ,  185 . The process further includes sintering the second layer portion  179   a  having non-uniform thickness to form the second sintered layer portion  129   a . The second sintered layer portion  129   a  has the thickness “T 5 ” for the evaporator section  111 , the thickness “T 6 ” for the condenser section  113 , and the thickness “T 7 ” for the transport section  115 . The sintering spacers  213 ,  183 ,  185  may be made of a material including nickel-cobalt ferrous alloy or ceramics such as aluminum nitrate, alumina, silicon carbide, and silicon nitride. 
       FIG. 9  is a flow diagram illustrating a method  220  for manufacturing a second sintered layer portion  229   a  having a non-uniform thickness in accordance with another embodiment. 
     The method  220  includes a step  222  for forming a second layer portion  228   a  having a non-uniform thickness, using a squeegee device  226  having a non-uniform contact surface  224 . The non-uniform contact surface  224  of the squeegee device  226  is disposed over the second layer portion  228   a  and the squeegee device  226  is actuated so as to form the second layer portion  228   a  having a non-uniform thickness. The second layer portion  228   a  has a thickness “T 011 ” corresponding to the position of an evaporator section  221 , a thickness “T 012 ” corresponding to the position of a condenser section  223 , and a thickness “T 013 ” corresponding to the position of a transport section  225 . The squeegee device  226  having the non-uniform contact surface  224  may be manufactured by milling. 
     The method  220  further includes a step  230  of generating the second sintered layer portion  229   a  having a non-uniform thickness. The process  230  includes replacing the squeegee device  226  with a sintering spacer  232  having a non-uniform contact surface  234  and sintering the second layer portion  228   a  in a sintering device to form the second sintered layer portion  229   a  having the non-uniform thickness. The second sintered layer portion  229   a  has a thickness “T 11 ” corresponding to the evaporator section  221 , a thickness “T 12 ” corresponding to the position of the condenser section  223 , and a thickness “T 13 ” corresponding to the position of the transport section  225 . The sintering spacer  232  having the non-uniform contact surface  234  may also be manufactured by milling 
       FIG. 10  is a schematic flow diagram illustrating a method  236  of manufacturing a third sintered layer portion  141   a  having a non-uniform thickness in accordance with the embodiment of  FIG. 5   b.    
     The method  236  includes a step  238  of forming a third layer portion  240   a  having a non-uniform thickness. A plurality of third particles  246  is disposed on the second sintered layer portion  129   a . A squeegee device  244  having a non-uniform contact surface  242 , is actuated over the plurality of third particles  246  so as to form a third layer portion  240   a  having a non-uniform thickness. The third layer portion  240   a  has a thickness “T 08 ” corresponding to the position of the evaporator section  111 , a thickness “T 09 ” corresponding to the position of the condenser section  113 , and a thickness “T 010 ” corresponding to the position of the transport section  115 . The method  236  further includes a step  248  of generating the third sintered layer portion  141   a  having a non-uniform thickness. The step  248  includes replacing the squeegee device  244  with a sintering spacer  252  having a non-uniform surface  254  for sintering the third layer portion  240   a  to form the third sintered layer portion  141   a . The third sintered layer portion  141   a  has the thickness “T 8 ” corresponding to the position of the evaporator section  111 , the thickness “T 9 ” corresponding to the position of the condenser section  113 , and the thickness “T 10 ” corresponding to the position of the transport section  115 . 
     Embodiments of the present disclosure discussed herein facilitate easy and economic manufacturing of the heat transfer device. Further, the heat transfer device of the present disclosure provides lower thermal resistance, higher thermal conductivity, and higher heat transport capability.