Metal-Based Microchannel Heat Exchangers Made by Molding Replication and Assembly

Abstract

Compression molding of metals is used to make microchannel heat exchangers. Heat transfer can be improved by employing controlled microchannel surface roughness. Flux-free bonding is achieved using a eutectic thin-film intermediate layer. Seals are leak-tight, mechanically strong, and uniform across multiple contact areas. The metal heat exchangers may be mass-produced inexpensively, and are useful for applications including the cooling of computer chips and other high-power electronic devices, air conditioning, refrigeration, condenser plates, radiators, fuel cell heat management, and instant water heating.

1 . A process for making a metal microchannel heat exchanger, said process comprising the steps of:
 (a) forming one or more open microchannels on a surface of a first homogeneous metal piece, wherein at least one of the microchannels has a width between about 30 μm and about 1000 μm, and a depth between about 30 μm and about 1000 μm;   (b) providing a second homogeneous metal piece that, when bonded to the first metal piece, will convert one or more open microchannels on the first metal piece into one or more closed microchannels, wherein the one or more closed microchannels are adapted to transport liquid without substantial leakage;   (c) providing a eutectic layer or eutectic precursor layer at one or more of the following locations: a surface of the first metal piece, a surface of the second metal piece, or between the first and second metal pieces;   (d) simultaneously applying pressure to and heating the first and second metal pieces, wherein: (i) the pressure pushes the first and second metal pieces toward each other, with the eutectic layer or eutectic precursor layer between the first and second metal pieces; (ii) the pieces are heated to a temperature at which the eutectic layer or eutectic precursor layer melts, or at which the eutectic layer or eutectic precursor layer interacts with the metal pieces to form a molten eutectic composition between the first and second metal pieces; and (iii) the temperature to which the metal pieces are heated is sufficiently below the melting temperature of the first and second metal pieces that no substantial deformation of the one or more microchannels occurs;   (e) cooling the first and second metal pieces to a temperature substantially below the eutectic melting temperature, while maintaining the pressure during at least a portion of said cooling; such that the first and second metal pieces fuse together; such that the one or more open microchannels are converted into one or more closed microchannels, wherein the one or more closed microchannels are adapted to transport liquid without substantial leakage; and wherein no substantial blockage of the one or more closed microchannels occurs as a result of said heating, applying pressure, and cooling;   and wherein:   (f) the one or more closed microchannels are enclosed entirely by the fused first and second metal pieces and eutectic layer; whereby the fused first and second homogeneous pieces and eutectic layer, together with the enclosed one or more closed microchannels, form a microchannel heat exchanger.   
     
     
         2 . A process as in  claim 1 , wherein the heat exchanger is capable of withstanding an internal pressure in the one or more closed microchannels of 100 atmospheres or greater. 
     
     
         3 . A process as in  claim 1 , wherein said microchannel-forming step comprises compression molding of one or both metal pieces with a refractory metal mold insert. 
     
     
         4 . A process as in  claim 1 , wherein at least one of the closed microchannels has a surface roughness between about 3 μm and about 15 μm. 
     
     
         5 . A metal microchannel heat exchanger produced by the process of  claim 1 . 
     
     
         6 . A metal microchannel heat exchanger comprising one or more closed microchannels; wherein at least one of said microchannels:
 (a) is enclosed entirely by a first homogeneous metal piece, a second homogeneous metal piece, and a eutectic layer; wherein said first and second homogeneous metal pieces are brazed to one another by said eutectic layer;   (b) has a width between about 30 μm and about 1000 μm, and a depth between about 30 μm and about 1000 μm; and   (c) is adapted to transport liquid without substantial leakage.   
     
     
         7 . A heat exchanger as in  claim 6 , wherein said heat exchanger is capable of withstanding an internal pressure in said one or more closed microchannels of 100 atmospheres or greater. 
     
     
         8 . A heat exchanger as in  claim 6 , wherein at least one of said closed microchannels has a surface roughness between about 3 μm and about 15 μm.