Producing Passive Radiative Cooling Panels And Modules

Abstract

Passive radiative cooling panels are produced by anodizing an aluminum foil sheet to form metamaterial nanostructures and then forming a plated metal over the metamaterial nanostructures to produce an ultra-black emitter, and then securing a reflective layer (e.g., a solar mirror film) onto the ultra-black emitter. The process is implementable in a roll-to-roll-type fabricating system in which a continuous aluminum foil ribbon extends from a feed roll through an anodization station to a reflector mounting station such that a first ribbon section undergoes anodization while a second ribbon section undergoes plating and a reflective layer is mounted onto a third ribbon section. A modified Anodic Aluminum Oxide (AAO) self-assembly technique is utilized to generate tapered nanopores that are then plated to generate an ultra-black emitter capable of generating broadband radiant energy with an emissivity close to unity. Modules are produced by mounting the panels onto conduit structures.

1 . A method for producing passive radiative cooling panels on an aluminum foil, the method comprising:
 anodizing said aluminum foil using a first chemical bath such that metamaterial nanostructures disposed in an ultra-black metamaterial-based pattern are generated on said aluminum foil;   forming a plated metal layer over said metamaterial nanostructures using a second chemical bath, thereby forming metal-plated metamaterial nanostructures on said aluminum foil; and   mounting a reflective layer onto said aluminum foil such that the reflective layer covers said metal coated metamaterial nanostructures,   wherein anodizing and forming said plated metal layer are performed such that said metal-plated metamaterial nanostructures are configured to generate radiant energy having wavelengths in the range of 8 μm to 13 μm with an emissivity of at least 0.998, and   wherein the reflective layer is configured to have a reflectance of at least 90% for radiant energy having wavelengths of 2 μm or less, and is also configured to have a reflectance of 10% or less for radiant energy having wavelengths in the range of 8 μm to 13 μm.   
     
     
         2 . The method of  claim 1 , wherein said method includes training an aluminum foil ribbon from a feed roller sequentially through said first chemical bath and said second chemical bath such that said anodizing is performed on a first section of said aluminum foil ribbon while forming said plated metal is performed on a second section of said aluminum foil ribbon. 
     
     
         3 . The method of  claim 2 , wherein said anodizing comprises controlling the formation of an aluminum oxide layer on the first section of said aluminum foil ribbon such that said metamaterial nanostructures comprise one of nanopores and nanotubes formed by said aluminum oxide layer. 
     
     
         4 . The method of  claim 2 , wherein forming said plated metal comprises disposing said second section of said aluminum foil ribbon in a solution and electroplating one or more of nickel (Ni) copper (Cu) and gold (Ag) from said solution onto said second section of said aluminum foil ribbon. 
     
     
         5 . The method of  claim 2 , wherein said anodizing comprises controlling the formation of an aluminum oxide layer on the first section of said aluminum foil ribbon by varying an applied voltage over time such that said metamaterial nanostructures comprise tapered nanopores formed by said aluminum oxide layer. 
     
     
         6 . The method of  claim 5 , wherein forming said plated metal comprises disposing said second section of said aluminum foil ribbon in a solution comprising one or more of nickel (Ni) copper (Cu) and gold (Ag) such that said one or more of Ni, Cu and Ag form metal-plated surfaces on said tapered nanopores by electroless plating. 
     
     
         7 . The method of  claim 2 , wherein mounting said reflective layer comprises training a reflector layer ribbon from a second feed roller such that reflector layer ribbon is secured to a third section of said aluminum foil ribbon while forming said plated metal is performed on said second section and said anodizing is performed on said first section. 
     
     
         8 . The method of  claim 1 , wherein said anodizing comprises controlling the formation of an aluminum oxide layer on the aluminum foil using an Anodic Aluminum Oxide (AAO) self-assembly template technique such that said metamaterial nanostructures comprise tapered nanopores formed in said aluminum oxide layer and disposed in a hexagonally packed array. 
     
     
         9 . The method of  claim 8 , wherein controlling the formation of said aluminum oxide layer comprises gradually changing a voltage applied between said aluminum foil and said cathode during said anodizating. 
     
     
         10 . The method of  claim 8 , wherein controlling the formation of said aluminum oxide layer comprises varying at least one process parameter such that each said tapered nanopore has a nominal width in the range of 100 nm to 1 μm. 
     
     
         11 . The method of  claim 8 , wherein said electroless plating comprises depositing a plated metal layer selected from Ni, Cu and Ag such that said plated metal layer is formed on tapered side walls disposed inside said tapered nanopores. 
     
     
         12 . The method of  claim 11 , wherein said electroless plating comprises immersing said aluminum foil in a nickel-phosphorous bath. 
     
     
         13 . The method of  claim 11 , wherein said electroless plating comprises pre-treating said aluminum foil using PdCl 2  before immersion in said a nickel-phosphorous bath. 
     
     
         14 . A fabrication system for producing passive radiative cooling panels on an aluminum ribbon drawn from a feed roller, the system comprising:
 an anodization station including a first guide mechanism configured to guide a first section of said ribbon through a first chemical bath, said anodization station being configured to generate metamaterial nanostructures disposed in an ultra-black metamaterial-based pattern on said first ribbon section;   a metal plating station disposed downstream from said anodization station including a second guide mechanism configured to guide a second section of said ribbon through a second chemical bath, said metal plating station being configured to deposit a plated metal over previously formed metamaterial nanostructures to produce metal-plated metamaterial nanostructures configured to generate radiant energy having wavelengths in the range of 8 μm to 13 μm with an emissivity of at least 0.998; and   a reflector mounting station configured to mount a reflective layer onto a third section of said ribbon such that the reflective layer covers said metal-plated metamaterial nanostructures, wherein the reflective layer is configured to have a reflectance of at least 90% for radiant energy having wavelengths of 2 μm or less, and is also configured to have a reflectance of 10% or less for radiant energy having wavelengths in the range of 8 μm to 13 μm.   
     
     
         15 . A method for producing a passive radiative cooling module, the method comprising:
 anodizing an aluminum foil while the controlling the formation of an aluminum oxide layer on the aluminum foil using an Anodic Aluminum Oxide (AAO) self-assembly template technique such that tapered nanopores disposed in a hexagonally packed array are formed in said aluminum oxide layer on a first surface of said aluminum foil;   forming a plated metal layer onto the first surface of said aluminum foil such that said plated metal layer is formed on tapered side walls disposed inside said tapered nanopores, thereby forming metal-coated tapered nanopores;   mounting a reflective layer onto said first surface of said aluminum foil; and   mounting a conduit structure under aluminum foil such that said conduit structure and a second surface of said aluminum foil define a flow channel configured to contain a coolant such that the coolant contacts the second surface of said aluminum foil, whereby thermal energy from the coolant is transferred through said aluminum foil to said metal-coated tapered nanopores.   
     
     
         16 . The method of  claim 15 , wherein said anodizing comprises disposing the aluminum foil in a first tank containing an acid solution and a cathode, and gradually changing a voltage applied between said aluminum foil and said cathode during said anodizating. 
     
     
         17 . The method of  claim 16 , wherein forming said plated metal layer comprises removing the aluminum foil from the first tank and disposing the aluminum foil in a second tank containing a plating solution including one or more of Ni, Cu and Ag. 
     
     
         18 . The method of  claim 17 , wherein forming said plated metal layer comprises immersing said aluminum foil in a nickel-phosphorous solution. 
     
     
         19 . The method of  claim 18 , wherein said electroless plating comprises pre-treating said aluminum foil using PdCl 2  after removing the aluminum foil from the first tank and before disposing the aluminum foil in a second tank. 
     
     
         20 . The method of  claim 19 ,
 wherein said anodizing and said electroless plating are performed such that said metal-plated metamaterial nanostructures are configured to generate radiant energy having wavelengths in the range of 8 μm to 13 μm with an emissivity of at least 0.998, and   wherein mounting the reflective layer comprising securing onto said first surface of said aluminum foil a solar mirror film material configured to have a reflectance of at least 90% for radiant energy having wavelengths of 2 μm or less, and is also configured to have a reflectance of 10% or less for radiant energy having wavelengths in the range of 8 μm to 13 μm.