Heat pipe with sintered powder wick

Abstract

A heat pipe ( 10 ) includes a casing ( 12 ) and a sintered powder wick ( 14 ) arranged at an inner surface of the casing. The sintered powder wick is in the form of a multi-layer structure of at least three layers and each layer has an average powder size different from that of the other layers, wherein the layer ( 143 ) with large-sized powders is capable of reducing the flow resistance to the condensed liquid to flow back while the layer ( 141 ) with small-sized powders is still capable of providing a relatively large capillary force for the wick.

1 . A heat pipe comprising: 
 a casing; and    a sintered powder wick arranged at an inner surface of the casing;    wherein the sintered powder wick is in the form of a multi-layer structure of at least three layers and each layer has an average powder size different from that of each the other layers.    
   
   
       2 . The heat pipe of  claim 1 , wherein said at least three layers are stacked in such a manner that the average powder sizes thereof increase along a predetermined direction.  
   
   
       3 . The heat pipe of  claim 2 , wherein said direction is a radial direction of the casing.  
   
   
       4 . The heat pipe of  claim 2 , wherein said direction is a longitudinal direction of the casing.  
   
   
       5 . The heat pipe of  claim 1 , wherein the sintered powder wick is one of a sintered metal powder wick and a sintered ceramic powder wick.  
   
   
       6 . A method for manufacturing a heat pipe comprising steps of: 
 providing a hollow casing and at least three groups of powder with each group having an average powder size different from that of each of the other groups;    filling said at least three groups of powder sequentially into said casing at a location adjacent to an inner surface of the casing with the later filled group of powder being stacked on the earlier filled group of powder; and    conducting sintering process to the casing and the filled powder, whereby a sintered powder wick with a multi-layer structure is formed inside the casing.    
   
   
       7 . The method of  claim 6 , wherein said at least three groups of powder are filled into said casing in such an order that the average powder size of the later filled group of powder is larger than that of the earlier filled group of powder.  
   
   
       8 . The method of  claim 6 , wherein a mandrel is used to be inserted into said casing with a space formed between the casing and the mandrel, and said at least three groups of powder are filled into said space to be stacked along a longitudinal direction of the casing.  
   
   
       9 . The method of  claim 6 , wherein said at least three groups of powder are stacked along a radial direction of the casing, and when filling each group of powder, a mandrel is used to control a thickness thereof.  
   
   
       10 . The method of  claim 9  further comprising a step of pre-sintering each group of powder before a corresponding mandrel used to control a thickness thereof is drawn out of the casing.  
   
   
       11 . A heat pipe comprising: 
 a metal casing having an outer surface and an inner surface;    a wick formed on the inner surface of the metal casing; and    working fluid received in the metal casing and capable of becoming into vapor upon receiving heat at a first place of the heat pipe and liquid upon releasing the heat at a second place of the heat pipe, the liquid being drawn by the wick from the second place of the heat pipe to the first place of the heat pipe; wherein    the wick forms capillary pressure in drawing the liquid, the capillary pressure being in gradient along one of radial and longitudinal directions of the heat pipe.    
   
   
       12 . The heat pipe of  claim 11 , wherein the wick is formed by sintering powders having different powder sizes.  
   
   
       13 . The heat pipe of  claim 12 , wherein the powders have three different sizes, with the powders having the largest size being located near the second place of the heat pipe and the powders having the smallest size being located near the first place of the heat pipe.  
   
   
       14 . The heat pipe of  claim 12 , wherein the powders have three different sizes, with the powders having the largest size being located close to the casing and the powders having the smallest size being located close to a center of the heat pipe.  
   
   
       15 . The heat pipe of  claim 12 , wherein the powders have three different sizes, with the powders having the largest size being located close to a center of the heat pipe and the powders having the smallest size being located close to the casing.