Wicking Structures and Multiphase Devices for Heat-Transfer

Abstract

A multiphase heat exchanger includes an evaporator, a condenser, and a liquid-return portion extending between the evaporator and the condenser, such that microstructured wicking structures are electrochemically integrated into one or more of these components. In an evaporator, the wicking structures promote capillary-driven liquid transport and assist in displacing vapor bubbles from the evaporator to improve two-phase cooling performance. By tailoring the geometry, location, and density of the wicking features, localized “dryouts” are mitigated thereby ensuring efficient heat transfer. Wicking structures may be also positioned along sidewalls, at channel bases, or on fin surfaces to maintain fluid distribution and enhance phase-change efficiency. Electrochemical additive manufacturing (ECAM) enables precise, layer-by-layer fabrication of these structures, allowing customization for different flow regimes and heat flux profiles. The resulting device supports higher thermal loads, improved reliability, and consistent manufacturing for advanced heat transfer/cooling applications.

1 . A multiphase heat exchanger for thermal coupling to a heat source, the multiphase heat exchanger comprising:
 an evaporator base comprising a heat-source interface for thermal coupling to the heat source;   a condenser base spaced away from the evaporator base by a cavity configured to contain a heat-transfer fluid, the condenser base comprising an external heat-release interface;   a liquid-return base extending between the evaporator base and the condenser base; and   wicking structures electrochemically deposited on a base surface formed by at least one of (a) the evaporator base forming an evaporator, (b) the condenser base forming a condenser, or (c) the liquid-return base forming a liquid-return portion, wherein:
 the wicking structures protrude into the cavity away from the base surface, 
 the evaporator is configured to evaporate the heat-transfer fluid, from a liquid phase to a gas phase, upon receiving heat from the heat source through the heat-source interface, 
 the condenser is configured to condense the heat-transfer fluid, from the gas phase to the liquid phase, by releasing heat through the external heat-release interface, 
 the liquid-return portion is configured to return the heat-transfer fluid, in the liquid phase, from the condenser to the evaporator, and 
 any two adjacent ones of the wicking structures, attached to the evaporator base, are spaced apart by an average pitch selected to maintain the heat-transfer fluid, in the liquid phase, in contact with at least a part of the evaporator base during operation of the multiphase heat exchanger. 
   
     
     
         2 . The multiphase heat exchanger of  claim 1 , wherein the wicking structures, attached to the condenser base, are configured to facilitate capillary pumping of the heat-transfer fluid, in the liquid phase, away from the condenser base. 
     
     
         3 . The multiphase heat exchanger of  claim 1 , wherein the wicking structures, attached to the liquid-return base, vary in size or pitch along a direction to achieve one or more of (a) to compensate for changes in a gravitational or capillary head in an intended operational environment and (b) to compensate for differences in anticipated heat loads in the intended operational environment. 
     
     
         4 . The multiphase heat exchanger of  claim 1 , wherein:
 the wicking structures are electrochemically deposited on both the evaporator base and the liquid-return base, and   the pitch of the wicking structures electrochemically deposited on the evaporator base is greater than the pitch of the wicking structures electrochemically deposited on the liquid-return base.   
     
     
         5 . The multiphase heat exchanger of  claim 1 , further comprising one or more bridging portions, extending through the cavity between and connected to each of the evaporator base and the condenser base, wherein the one or more bridging portions are parts of the liquid-return portion. 
     
     
         6 . The multiphase heat exchanger of  claim 5 , wherein the wicking structures are electrochemically deposited on the one or more bridging portions. 
     
     
         7 . The multiphase heat exchanger of  claim 5 , wherein the one or more bridging portions are electrochemically deposited on the evaporator base or the condenser base. 
     
     
         8 . The multiphase heat exchanger of  claim 1 , wherein the evaporator base or the condenser base is electrochemically deposited. 
     
     
         9 . The multiphase heat exchanger of  claim 1 , wherein one or more of the wicking structures are a 1-dimensional column comprising a base growth rooted to at least one of the evaporator base, the condenser base, and the liquid-return base by electrochemical deposition. 
     
     
         10 . The multiphase heat exchanger of  claim 9 , wherein:
 the wicking structures are arranged into a set of rows, and   the wicking structures in two adjacent rows in the set of rows are offset relative to each other, forming a straight channel for the heat-transfer fluid.   
     
     
         11 . The multiphase heat exchanger of  claim 1 , wherein one or more of the wicking structures are a 2-dimensional (2D) wall comprising a base growth rooted to the base surface by electrochemical deposition. 
     
     
         12 . The multiphase heat exchanger of  claim 1 , wherein the wicking structures are configured to direct the heat-transfer fluid in all three directions as the heat-transfer fluid is proximate to the base surface. 
     
     
         13 . The multiphase heat exchanger of  claim 12 , wherein:
 one or more of the wicking structures comprise a base and an overhang,   the base is electrochemically deposited on the base surface, positioned between the overhang and the base surface, and supports the overhang relative to the base surface,   the overhang protrudes beyond a footprint of the base thereby forming a lower cavity proximate to the base surface,   the overhang of two adjacent ones of the wicking structures are spaced, forming an upper cavity, fluidically coupled with the lower cavity by an opening.   
     
     
         14 . The multiphase heat exchanger of  claim 1 , wherein:
 the evaporator base and the condenser base define a liquid-flow direction, and   a pitch (P) of the wicking structures changes along the liquid-flow direction.   
     
     
         15 . The multiphase heat exchanger of  claim 14 , wherein the pitch (P) of the wicking structures decreases in the liquid-return portion along a flow direction of the heat-transfer fluid. 
     
     
         16 . The multiphase heat exchanger of  claim 1 , wherein the wicking structures have a nucleation point density of at least 100/mm 2  based on a surface area of the base surface, at least in the evaporator base. 
     
     
         17 . The multiphase heat exchanger of  claim 1 , wherein the wicking structures have an electrochemically-deposited base and one or more structures bonded to the electrochemically-deposited base, and selected from the group consisting of mesh, woven fabric, and sintered powder. 
     
     
         18 . The multiphase heat exchanger of  claim 1 , wherein one or more of the wicking structures are selected from the group consisting of a composite wick, a lattice, a TPMS structure, a uniform and composite structure, a composite gyroid, a body-centered-cubic (BCC), and a composite body-centered-cubic (BCC). 
     
     
         19 . The multiphase heat exchanger of  claim 1 , further comprising the heat-transfer fluid provided in the cavity. 
     
     
         20 . The multiphase heat exchanger of  claim 16 , wherein the heat-transfer fluid is selected from the group consisting of a hydrofluorocarbon refrigerant, a hydrocarbon refrigerant, a chlorofluorocarbon refrigerant, an ammonia refrigerant, and a carbon dioxide refrigerant.