Passive radiative dry cooling module/system using metamaterials
A passive radiative cooling system in which an ultra-black emitter includes metamaterial nanostructures disposed on the top surface of a metal sheet, and a conduit structure channels the flow of coolant against a bottom surface of the metal sheet. The metamaterial nanostructures (e.g., tapered nanopores) are configured to dissipate heat from the coolant in the form of emitted radiant energy having wavelengths/frequencies that fall within known atmospheric transparency windows (e.g., 8-13 μm or 16-28 μm), the emitted radiant energy being transmitted through a reflective layer into cold near-space. The ultra-black emitter is formed using a modified Anodic Aluminum Oxide (AAO) self-assembly technique followed by electroless plating that forms metal-plated tapered nanopores, and the reflective layer includes a distributed Bragg reflector. The cooling system is made scalable by way of modular cooling units (modules) that are configured for connection in series and parallel to form dry cooling systems suitable for large power plants.
1. A passive radiative cooling system comprising:
a metal sheet having a plurality of metamaterial nanostructures disposed on a first surface thereof;
a reflective layer mounted over the first surface of the metal sheet; and
a conduit structure disposed under the metal sheet and configured to conduct a coolant such that the coolant flows against a second surface of the metal sheet, whereby thermal energy is conducted from the coolant through the metal sheet to said plurality of metamaterial nanostructures,
wherein said plurality of metamaterial nanostructures are arranged in an ultra-black metamaterial-based pattern and configured to emit radiant energy having wavelengths in the range of 8 μm to 13 μm; and
wherein said reflective layer is configured both to reflect incident solar radiation and to transmit said radiant energy,
wherein said plurality of metamaterial nanostructures comprises an array of tapered nanopores disposed on the top surface of the metal sheet, and
wherein a nominal width of each said tapered nanopore is less than 1 micron.
2. The passive radiative cooling system according to claim 1 , wherein the plurality of metamaterial nanostructures are further configured to generate said radiant energy having wavelengths in the range of 16 μm to 28 μm.
3. The passive radiative cooling system according to claim 1 , wherein said metal sheet comprises a first metal, and wherein a plated metal layer is disposed on the upward-facing surface of the metal sheet and inside each said tapered nanopore, said plated metal layer comprising a second metal different from the first metal.
4. The passive radiative cooling system of claim 3 , wherein said metal sheet comprises aluminum, and wherein said plated metal layer comprises one or more of nickel (Ni) copper (Cu) and gold (Ag).
5. The passive radiative cooling system of claim 4 ,
wherein said metal sheet comprises aluminum base layer and an aluminum oxide layer disposed on the aluminum base layer,
wherein said tapered nanopores are entirely defined within said aluminum oxide layer, and
wherein said plated metal layer is entirely disposed on a surface of said aluminum oxide layer.
6. The passive radiative cooling system of claim 1 , wherein the reflective layer comprises a plurality of sublayers forming a distributed Bragg reflector that is configured to reflect incident solar radiation having wavelengths in the range of 0 to 2 μm, and configured to pass therethrough radiation having wavelengths in the range of 8 μm to 13 μm.
7. The passive radiative cooling system of claim 1 ,
wherein the conduit structure comprises a box-like frame including a lower wall and peripheral side walls, and
wherein the conduit structure is fixedly connected to the metal sheet such that the lower wall and peripheral side walls of the conduit structure and the second surface of the metal sheet form a substantially enclosed heat-exchange channel configured to facilitate said coolant flow against said second surface of the metal sheet.
8. The passive radiative cooling system of claim 7 , wherein one of said lower wall and said peripheral side walls define an inlet port configured to facilitate flow of said coolant into said heat-exchange channel, and an outlet port configured to facilitate flow of said coolant out of said heat-exchange channel.
9. The passive radiative cooling system of claim 8 , wherein the conduit structure further includes a plurality of baffles mounted on one of said lower wall and said peripheral side walls configured such that a flow direction of said coolant through said heat-exchange channel is controlled by said plurality of baffles.
10. The passive radiative cooling system of claim 1 , wherein the conduit structure comprises a corrugated sheet attached to the second surface of the metal sheet such that a plurality of parallel heat-exchange channels are defined between an upward-facing surface of said conduit structure and said second surface of the metal sheet.
11. A passive radiative cooling system comprising:
a plurality of modules, each said module including:
an ultra-black emitter including a metal sheet and a plurality of metamaterial nanostructures arranged in an ultra-black metamaterial-based pattern on a first surface of the metal sheet, said plurality of metamaterial nanostructures being configured to emit radiant energy having wavelengths in the range of 8 μm to 13 μm;
a reflective layer mounted on the first surface of the emitter layer and configured to reflect incident solar radiation; and
a conduit structure disposed under the metal sheet emitter layer and configured to conduct a coolant between an inlet port and an outlet port such that thermal energy is conducted from the coolant through the metal sheet to said plurality of metamaterial nanostructures; and
a flow control system configured to pass said coolant through said plurality of modules,
wherein said metal sheet comprises aluminum base layer and an aluminum oxide layer disposed on the aluminum base layer,
wherein said plurality of metamaterial nanostructures comprises an array of tapered nanopores entirely defined within said aluminum oxide layer,
wherein said ultra-black emitter further comprises a plated metal layer entirely disposed on said aluminum oxide layer and inside each said tapered nanopore, and
wherein said plated metal layer comprises one or more of nickel (Ni) copper (Cu) and gold (Ag).
12. The passive radiative cooling system of claim 11 ,
wherein the conduit structure comprises a box-like frame including a lower wall and peripheral side walls defining an upper opening,
wherein the conduit structure is fixedly connected to the metal sheet such that the lower wall and peripheral side walls of the conduit structure and the second surface of the metal sheet form a substantially enclosed heat-exchange channel configured to facilitate said coolant flow against said second surface of the metal sheet, and
wherein one of said lower wall and said peripheral side walls define said inlet port and said outlet port.
13. The passive radiative cooling system of claim 11 , wherein flow control system comprises an inflow pipe configured to conduct heated coolant from an object to said plurality of modules, an outflow pipe configured to conduct cooled coolant from said plurality of modules to said object, and a pump operably coupled to at least one of said inflow pipe and said outflow pipe.
14. The passive radiative cooling system of claim 13 , wherein a first row group of said plurality of modules are operably connected in series between said inflow pipe and said outflow pipe such that said coolant passes from said inflow pipe sequentially through the conduit structure of each said module of said first row group to said outflow pipe.
15. The passive radiative cooling system of claim 14 , wherein one or more second row groups of said plurality of modules are operably connected in series between said inflow pipe and said outflow pipe such that said coolant simultaneously passes in parallel from said inflow pipe through said first row group and said one or more second row groups to said outflow pipe.