Infrared transparent aerogel composite for deep sub-ambient cooling of virtually any surface

Abstract

An apparatus for cooling a surface includes a composite that includes a porous infrared (IR) transparent material having at least one substance that is transparent to infrared radiation having a wavelength in a range of 8 to 13 μm. In addition, the composite includes a support frame having an opening for exposing a sky-facing surface of the porous IR transparent material and an encapsulant. The encapsulant is positioned on the sky-facing surface of the porous IR transparent material. The composite is configured to be optically reflective to sunlight and is thermally insulating for reducing heating of a surface from surrounding air.

What is claimed is: 
     
         1 . An apparatus for cooling a surface, the apparatus comprising:
 a composite comprising:
 a porous infrared (IR) transparent material comprised of at least one substance that is transparent to infrared radiation having a wavelength in a range of 8 to 13 microns; 
 a support frame having an opening for exposing a sky-facing surface of the porous IR transparent material; and 
 an encapsulant, wherein the encapsulant is positioned on the sky-facing surface of the porous IR transparent material, 
   wherein the composite is configured to be optically reflective to sunlight,   wherein the composite is thermally insulating for reducing heating of a surface from surrounding air.   
     
     
         2 . The apparatus as recited in  claim 1 , wherein the at least one substance is selected from the group consisting of: sodium chloride (NaCl), potassium chloride (KCI), sodium bromide (NaBr), potassium bromide (KBr) cesium iodide (CsI), germanium (Ge), zinc selenide (ZnSe), zinc sulfide (ZnS), barium fluoride (BaF 2 ), and a combination thereof. 
     
     
         3 . The apparatus as recited in  claim 2 , wherein the IR transparent material is comprised of a combination of NaCl and KCl. 
     
     
         4 . The apparatus as recited in  claim 1 , wherein the IR transparent material is comprised of a plurality features, the features having an average diameter of greater than 10 nanometers to less than 500 nanometers. 
     
     
         5 . The apparatus as recited in  claim 4 , wherein the IR transparent material is effective at scattering optical light having a wavelength less than one micron. 
     
     
         6 . The apparatus as recited in  claim 1 , wherein the IR transparent material has a density in a range of 0.5 to 2.0 of the maximum theoretical density. 
     
     
         7 . The apparatus as recited in  claim 1 , wherein the IR transparent material has a porosity in a range of 98 to 99.5% porosity. 
     
     
         8 . The apparatus as recited in  claim 1 , wherein the porous IR transparent material is an IR transparent aerogel. 
     
     
         9 . The apparatus as recited in  claim 1 , wherein the porous IR transparent material is an IR transparent foam. 
     
     
         10 . The apparatus as recited in  claim 1 , wherein the support frame is functional as an optomechanical frame. 
     
     
         11 . The apparatus as recited in  claim 1 , wherein a length from a bottom surface of the composite to the sky-facing surface is in a range of greater than 0.5 centimeters to 5 centimeters. 
     
     
         12 . The apparatus as recited in  claim 1 , wherein the IR transparent material is in the form of an aerogel powder. 
     
     
         13 . The apparatus as recited in  claim 1 , wherein the IR transparent material is in the form of an aerogel monolith. 
     
     
         14 . The apparatus as recited in  claim 1 , wherein the encapsulant is in the form of an IR transparent film. 
     
     
         15 . The apparatus as recited in  claim 1 , wherein the composite further comprises a coating for inhibiting water vapor transmission to the IR transparent material. 
     
     
         16 . The apparatus as recited in  claim 1 , wherein the IR transparent material further comprises an anti-caking agent. 
     
     
         17 . The apparatus as recited in  claim 16 , wherein the anti-caking agent is selected from the group consisting of: sodium ferrocyanide, CTAB, and a cationic surfactant. 
     
     
         18 . A method of forming an apparatus for cooling a surface, the method comprising forming a porous infrared (IR) transparent material comprising at least one substance that is transparent to infrared radiation having a wavelength in a range of 8 to 13 microns; and
 coupling the porous IR transparent material to a support frame structure,   wherein the porous IR transparent material is coated with an IR transparent encapsulant.   
     
     
         19 . The method as recited in  claim 18 , wherein the at least one substance is selected from the group consisting of: sodium chloride (NaCl), sodium bromide (NaBr), potassium chloride (KCl), potassium bromide (KBr), cesium iodide (CsI), germanium (Ge), zinc selenide (ZnSe), zinc sulfide (ZnS), barium fluoride (BaF 2 ), and a combination thereof. 
     
     
         20 . The method as recited in  claim 18 , wherein the at least one substance is a combination of NaCl and KCl. 
     
     
         21 . The method as recited in  claim 18 , wherein the at least one substance is at least one salt selected from the group consisting of: NaCl, KCl, and a combination thereof,
 wherein forming the porous IR transparent material comprises:
 spraying a solution to form droplets, the solution comprising the at least one salt and a solvent; 
 freezing the droplets; and 
 drying the droplets to form a porous material. 
   
     
     
         22 . The method as recited in  claim 21 , wherein a concentration of the at least one salt is in a range of 0.1 M to about 0.4 M. 
     
     
         23 . The method as recited in  claim 18 , wherein a density of the porous IR transparent material is in a range of 0.5 to 2.0 relative density. 
     
     
         24 . The method as recited in  claim 18 , wherein a porosity of the porous IR transparent material is in a range of 98-99.5% porosity. 
     
     
         25 . The method as recited in  claim 18 , wherein the IR transparent material further comprises an anti-caking agent. 
     
     
         26 . The method as recited in  claim 25 , wherein the anti-caking agent is selected from the group consisting of: sodium ferrocyanide, CTAB, and a cation surfactant. 
     
     
         27 . An apparatus for cooling a surface, comprising:
 a composite that is   an infrared (IR) transparent aerogel or foam that is transparent in the 8-13 micron wavelength range,   that is optically reflective to reduce heating from sunlight, and that is thermally insulating to avoid heating from surrounding air.   
     
     
         28 . The apparatus for cooling of  claim 27 , wherein said composite comprises an IR transparent aerogel or foam and a frame that holds said IR transparent aerogel or foam. 
     
     
         29 . The apparatus for cooling of  claim 27 , wherein said composite comprises a frame that holds said IR transparent aerogel or foam, wherein said IR transparent aerogel or foam is configured to concentrate emitted radiation, and wherein said frame is positioned to concentrate said emitted radiation to the sky to improve cooling.