Synergistic passive cooling fin

Abstract

A cooling film for passively cooling modular data centers, power transformers, and other surfaces. The cooling film includes a specular reflective multilayer mirror film attached to a passive cooling heat transfer fin. The anti-fouling layer is secured to the first major surface of the specular reflective multilayer film. The specular reflective multilayer film may include a metal layer and specularly reflects electromagnetic radiation over a majority of wavelengths in the range of 400 nm to 2500 nm. The specular reflective multilayer film may also include a multilayer optical film including a first optical layer and a second optical layer that constructively reflect electromagnetic radiation over a majority of wavelengths in the range of 400 nm to 2500 nm while absorbing electromagnetic radiation over a majority of wavelengths in the range of 4000 nm to 20000 nm.

Description

Background Technology

[0001] Passive cooling can be achieved using reflective and reflective films attached to the surface to be cooled. Applying innovative radiative cooling materials, in addition to convective cooling materials, to data centers, power transformers, heat transfer panels, and other surfaces to be cooled will enable them to operate more effectively. Summary of the Invention

[0002] Synergistic passive cooling fins for use with data centers, power transformers, heat transfer panels, and other surfaces to be cooled include a specularly reflective multilayer film attached to the passively cooled heat transfer fins. An anti-fouling layer is fixed to a first main surface of the specularly reflective multilayer film. The specularly reflective multilayer film may include a metal layer and specularly reflects electromagnetic radiation over most wavelengths in the 400 nm to 2500 nm range. The specularly reflective multilayer film may also include a multilayer optical film comprising a first optical layer and a second optical layer, which constructively reflect electromagnetic radiation over most wavelengths in the 400 nm to 2500 nm range, while absorbing electromagnetic radiation over most wavelengths in the 4000 nm to 20000 nm range. Attached Figure Description

[0003] Figure 1 This is a schematic side view of an exemplary composite cooling film.

[0004] Figure 2 This is a perspective view of the synergistic passive cooling fins.

[0005] Figure 3 This is a perspective view of a modular data center with radiator cooling fins.

[0006] Figure 4 This is a perspective view of a power transformer with radiator cooling fins.

[0007] Figure 5 This is a cross-sectional side view of the passive cooling fin design.

[0008] Figure 6 This is a cross-sectional side view of multiple passive cooling fins spliced ​​together on the surface to be cooled.

[0009] Figure 7 This is a cross-sectional side view of a modular data center with passive cooling fins. Detailed Implementation

[0010] The implementation plan includes a cooling film on passive radiative cooling fins for cooling modular data centers, power transformers, and other surfaces.

[0011] Cooling film

[0012] As used in this article:

[0013] "Fluoropolymers" refers to any organic polymer that contains fluorine;

[0014] Unless otherwise specified, “infrared” (IR) refers to infrared electromagnetic radiation with wavelengths >700 nm to 1 mm;

[0015] Unless otherwise specified, “visible” (VIS) means visible electromagnetic radiation with wavelengths from 400 nm to 700 nm, including the end values.

[0016] Unless otherwise specified, “ultraviolet” (UV) means ultraviolet electromagnetic radiation with a wavelength of at least 250 nm and at most 400 nm but not including 400 nm;

[0017] "Microporous" refers to an internal porosity (continuous and / or discontinuous) with an average pore size of 50 nm to 10,000 nm.

[0018] "Micro-void" refers to internal discrete voids with an average void diameter of 100 nm to 3000 nm;

[0019] "Multilayer optical film" refers to a multilayer film with multiple first optical layers with high refractive index and multiple second optical layers with low refractive index, wherein the multiple first optical layers and the multiple second optical layers work together in a constructive manner to reflect electromagnetic radiation.

[0020] "Non-fluorinated polymers" refers to any organic polymer that does not contain fluorine;

[0021] Unless otherwise specified, “radiation” means electromagnetic radiation;

[0022] "Fixed to" means directly or indirectly attached to (e.g., directly in contact with or bonded to by an adhesive layer).

[0023] "Average reflectance" refers to the average reflectance over a specified wavelength range;

[0024] "Reflection" and "reflectivity" refer to the properties of reflected light or radiation, especially reflectivity measured independently of material thickness; and

[0025] "Reflectivity" is a measure of the proportion of light or other radiation that strikes a surface at a perpendicular angle of incidence and is reflected by it. Reflectivity typically varies with wavelength and is reported as the percentage of incident light reflected from the surface (0% – no reflection, 100 – all light is reflected). Reflectivity, reflection, and reflectance ratio are used interchangeably in this document;

[0026] "Specular reflection" refers to electromagnetic radiation being reflected at the same angle as the incident light into a single outgoing direction;

[0027] "Diffuse reflection" refers to electromagnetic radiation being reflected in multiple outgoing directions.

[0028] Absorbance can be determined using the method described in ASTM E903-12, "Standard Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres." The absorptance measurement described herein is performed by measuring transmittance as previously described, followed by calculating the absorptance using Equation 1.

[0029] As used herein, the term "absorptivity" refers to the logarithm to base 10 of the ratio of incident radiant power to transmitted radiant power through the material. This ratio can be described as the radiant flux received by the material divided by the radiant flux transmitted through the material. Absorptivity (A) can be calculated based on transmittance (T) according to the following formula 1:

[0030] A = -log 10 T(1)

[0031] Emissivity can be measured using an infrared imaging radiometer in accordance with the method described in ASTM E1933-14 (2018), "Standard Practice for Measuring and Compensating for Emissivity Using Infrared Imaging Radiometers".

[0032] like Figure 1 As shown, the exemplary composite cooling film includes a reflective multilayer film 110, on which an antifouling layer 160 is fixed. The antifouling layer 160 is fixed to the main surface 112 of the specular reflective multilayer film 110, such that the outward-facing antifouling surface 162 is opposite to the specular reflective multilayer film 110.

[0033] Optional metal layer 150 is fixed to reflective microporous layer 110 opposite to antifouling layer 160. Optional adhesive layers 170, 172 can adhere various components together, such as... Figure 1 As shown. Optional adhesive layer 174 can be peelably bonded to optional liner 180. In one embodiment, after removing optional liner 180, optional adhesive layer 174 can be bonded to a substrate to be cooled (e.g., cooling fins, RF antenna surface).

[0034] The composite cooling film according to this disclosure preferably has an average absorption rate of at least 0.80, more preferably at least 0.85, and more preferably at least 0.90 in the wavelength range of 4 micrometers to 20 micrometers, but this is not required.

[0035] Reflective microporous layer

[0036] The reflective microporous layer may comprise a network of interconnected and / or discrete voids, which may be spherical, oval, or some other shape. The primary functions of the reflective microporous layer include reflecting at least a portion of the visible and infrared radiation of the solar spectrum and emitting thermal radiation in atmospheric windows (i.e., wavelengths of 8 to 13 micrometers).

[0037] Therefore, the reflective microporous layer has voids that are appropriately sized to diffusely reflect light with wavelengths in the range of 400 nm to 700 nm, preferably 300 nm to 2500 nm. Generally, this means that the void size should be within a range (e.g., 50 nm to 3000 nm) capable of reflecting light in the 300 nm to 2500 nm wavelength range. Preferably, there exists a range of void sizes corresponding to those sizes to achieve effective broadband reflection.

[0038] The reflectivity of a reflective microporous layer typically depends on the number of polymer film / void interfaces, as reflection (usually diffuse reflection) occurs at those locations. Therefore, the porosity and thickness of the reflective microporous layer are important variables. Generally, higher porosity and greater thickness are associated with higher reflectivity. However, for cost reasons, film thickness is preferably minimized, but this is not mandatory. Therefore, the thickness of the reflective microporous layer is typically in the range of 10 micrometers to 500 micrometers, preferably in the range of 10 micrometers to 200 micrometers, but this is not mandatory. Similarly, the porosity of the reflective microporous layer is typically in the range of 10 vol% to 90 vol%, preferably in the range of 20 vol% to 85 vol%, but this is not mandatory.

[0039] Exemplary materials that can be used in at least one (preferably only one) of a reflective microporous layer (which contains at least one fluoropolymer) or an auxiliary reflective microporous layer (which does not contain a fluoropolymer) are shown below. Based on the preceding discussion, the choice of which microporous material to include in which layer will become apparent.

[0040] Microporous polymer membranes suitable for use as reflective microporous layers are known in the art and described, for example, in U.S. Patent Nos. 8,962,214, 10,240,013, and 4,874,567. These membranes may have an average pore size of at least 0.05 micrometers.

[0041] In some embodiments, the reflective microporous layer comprises at least one thermally induced phase separation (TIPS) material. Due to the ability to selectively stretch the layer, the pore size of the TIPS material can typically be controlled. The preparation of TIPS materials is relatively inexpensive, and methods for preparing such membranes are known to those skilled in the art. For example, various materials and methods are described in detail in U.S. Patent Nos. 4,726,989, 5,238,623, 5,993,954, and 6,632,850. Reflective microporous layers used in various aspects of this disclosure also include solvent-induced phase separation (SIPS) materials (e.g., U.S. Patent No. 4,976,859) and other reflective microporous layers prepared by extrusion, extrusion / stretching, and extrusion / stretching / extraction processes. Suitable reflective microporous layers that can be formed from SIPS include, but are not limited to, polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PS), polyacrylonitrile (PAN), nylon (i.e., polyamide), cellulose acetate, cellulose nitrate, regenerated cellulose, and polyimide. Suitable reflective microporous layers that can be formed by stretching techniques (e.g., U.S. Patent No. 6,368,742) include, for example, but not limited to, polytetrafluoroethylene (PTFE) and polypropylene.

[0042] In some embodiments, the reflective microporous layer comprises a thermoplastic polymer, such as polyethylene, polypropylene, 1-octene, styrene, polyolefin copolymer, polyamide, poly-1-butene, poly-4-methyl-1-pentene, polyethersulfone, ethylene tetrafluoroethylene, polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyamide, cellulose acetate, nitrocellulose, regenerated cellulose, polyvinyl chloride, polycarbonate, polyethylene terephthalate, polyimide, polytetrafluoroethylene, ethylene trifluorochloroethylene, polytetrafluoroethylene, or combinations thereof.

[0043] In some implementations, the solar reflective microporous polymer layer comprises GORE-TEX, purchased from WL Gore, Inc.

[0044] Materials suitable for use as reflective microporous layers include nonwoven fiber layers.

[0045] Polymer nonwoven layers can be fabricated using a meltblown process. Meltblown nonwoven fiber layers can comprise microfibers. In meltblowing, one or more streams of thermoplastic polymer are extruded through a die containing densely arranged orifices. These polymer streams are refined by a converging stream of high-speed hot air to form fine denier fibers, which are then collected on a surface to provide a meltblown nonwoven fiber layer. Depending on the selected operating parameters, the collected fibers can be semi-continuous or substantially discontinuous.

[0046] Polymer nonwoven layers can also be prepared by a process known as melt spinning. In melt spinning, nonwoven fibers are extruded as filaments outside a set of orifices and allowed to cool and solidify to form fibers. The filaments pass through an air space that can accommodate a moving airflow to aid in cooling the filaments and pass through a drawing (i.e., stretching) unit to at least partially lengthen the filaments. Fibers prepared by the melt spinning process can be "spunbonded," whereby a web containing a set of melt-spun fibers is collected as a fiber web and optionally subjected to one or more bonding operations to fuse the fibers together. The diameter of melt-spun fibers is generally larger than that of melt-blown fibers.

[0047] Polymers suitable for meltblown or melt spinning processes include polyolefins such as polypropylene and polyethylene, polyesters, polyethylene terephthalate, polybutylene terephthalate, polyamides, polyurethanes, polybutene, polylactic acid, polyphenylene sulfide, polysulfones, liquid crystal polymers, ethylene-vinyl acetate copolymers, polyacrylonitrile, cyclic polyolefins, and copolymers and blends thereof. In some embodiments, the polymer, copolymer, or blend thereof constitutes at least 35% of the total weight of the directly formed fibers present in the nonwoven fiber layer.

[0048] Nonwoven fibers can be made from thermoplastic semi-crystalline polymers, such as semi-crystalline polyesters. Available polyesters include aliphatic polyesters. Nonwoven materials based on aliphatic polyester fibers are particularly advantageous in high-temperature applications due to their resistance to degradation or shrinkage. This property can be achieved by preparing nonwoven fiber layers using a meltblown process, wherein the meltblown fibers undergo a controlled air heat treatment operation immediately upon exiting from multiple orifices. The controlled air heat treatment operation is carried out at a temperature below the melting temperature of a portion of the meltblown fiber and lasts for a time sufficient to allow at least a portion of the molecules within the portion of the fiber undergoing the controlled air heat treatment operation to achieve stress relaxation. Details of the air heat treatment are described in U.S. Patent Application Publication 2016 / 0298266.

[0049] Nonwoven fiber layers that can be used for reflective microporous layers comprise nonwoven fiber layers made using an air-blowing process, wherein air walls blow fibers onto a perforated collection cylinder with negative pressure inside. Air is drawn through the cylinder, collecting the fibers outside, where they are removed as fiber webs. An exemplary embodiment of a microporous membrane made from nonwoven fibers is a highly reflective white paper containing polysaccharides. Microporous polysaccharide white paper with a reflectivity greater than 90% for visible wavelengths from 400 nm to 700 nm is available under the trade names IP ACCENT OPAQUE DIGITAL (100 lbs), IP ACCENT OPAQUE DIGITAL (100 lbs), HAMMERMILL PREMIUM COLOR COPY (80 lbs), and HAMMERMILL PREMIUM COLOR COPY (100 lbs) from International Paper, Memphis, Tennessee. Titanium dioxide, BaSO4, and other white pigments are often added to paper to increase its reflectivity to visible light (400nm to 700nm).

[0050] Other nonwoven fiber layers that can be used for reflective microporous layers include those prepared using a wet web-forming process. A wet web-forming or “wet web-type” process includes: (a) forming a dispersion in at least one dispersion liquid (preferably water) comprising one or more types of fibers, optional polymer binders, and optional particle fillers; and (b) removing the dispersion liquid from the dispersion.

[0051] Fibers suitable for air-laid and wet-laid processes include those made from natural polymers (animal or plant) and / or synthetic polymers (including thermoplastic polymers and solvent-dispersible polymers). Available polymers include wool; silk; cellulose polymers (e.g., cellulose and cellulose derivatives); fluorinated polymers (e.g., copolymers of polyvinylidene fluoride, polyvinylidene fluoride, and poly(vinylidene fluoride-co-hexafluoropropylene) and trifluorochloroethylene (e.g., poly(ethylene-co-trifluorochloroethylene)); chlorinated polymers; polyolefins (e.g., copolymers of polyethylene, polypropylene, poly-1-butene, ethylene and / or propylene with 1-butene, 1-hexene, 1-octene and / or 1-decene (e.g., poly(ethylene-co-1-butene), poly(ethylene-co-1-butene-co-1-hexene)); polyisoprene; polybutadiene; polyamides (e.g., nylon 6, nylon 6,6, nylon 6...). 12. Poly(iminohexamethylene adipamide), poly(iminohexamethylene adipamide), or polycaprolactam; polyimide (e.g., poly(pyromellitic tetroxide)); polyether; polyethersulfone (e.g., poly(diphenyl ether sulfone) or poly(diphenyl sulfone-co-diphenyl ether sulfone)); polysulfone; polyvinyl acetate; copolymers of vinyl acetate (e.g., poly(ethylene-co-vinyl acetate), wherein at least some of the acetate groups have been hydrolyzed to provide a variety of poly(vinyl alcohol) (including poly(ethylene-co-vinyl alcohol))); polyphosphazene; polyvinyl ester; polyvinyl ether; poly(vinyl alcohol); polyaramid (e.g., poly-p-aramid, such as poly(p-phenylene terephthalamide) and DuPont of Wimington, Delaware). KEVLAR (Co., Wilmington, Delaware) sells fibers under the trade name KEVLAR, whose slurries are commercially available in various grades based on the fiber length from which the slurry is made, such as KEVLAR 1F306 and KEVLAR 1F694, both of which contain polyaramid fibers with a length of at least 4 mm; polycarbonate; and combinations thereof. The nonwoven fiber layers may be calendered to adjust the pore size.

[0052] Using a reflective microporous polymer film as a reflective microporous layer can provide even greater reflectivity than a silvered mirror. In some embodiments, the reflective microporous polymer film reflects the maximum amount of solar energy in the range of 300 nanometers (nm) to 2500 nanometers. Specifically, the use of fluoropolymer blends in this microporous polymer film can provide greater reflectivity than other conventional multilayer optical films. Furthermore, inorganic particles comprising barium sulfate, calcium carbonate, silica, alumina, aluminum silicate, zirconium oxide, and titanium dioxide can be blended into the microporous polymer film to provide high solar reflectivity in the solar radiation spectrum from 0.3 μm to 2.5 μm and high absorptivity in the atmospheric window from 8 μm to 13 μm, or even 4 μm to 25 μm. An outer layer can be used to protect the reflective microporous layer, especially in outdoor environments. Including an outer layer also helps reduce surface contamination and facilitates surface cleaning.

[0053] Exemplary polymers that can be used to form reflective microporous polymer films include polyethylene terephthalate (PET), available from 3M Company. Modified PET copolyesters are also available high-refractive-index polymers, including PETG, such as SPECTAR 14471 and EASTAR GN071, available from Eastman Chemical Company, Kingsport, Tennessee, NY, and PCTG, such as TIGLAZEST and EB0062, also available from Eastman Chemical Company. Stretching can increase the molecular orientation of PET and PET-modified copolyesters, which increases the in-plane refractive index of PET and PET, thereby providing even higher reflectivity in multilayer optical films. Generally, prior to stretching, incompatible polymer additives or inorganic particulate additives are blended into the PET bulk polymer during extrusion at a content of at least 1% by weight, at least 10% by weight, at least 20% by weight, at least 40% by weight, or even at least 49% by weight, to nucleate voids during stretching. Incompatible polymer additives suitable for PET include fluoropolymers, polypropylene, polyethylene, and other polymers that do not adhere well to PET. Similarly, if polypropylene is the host polymer, incompatible polymer additives such as PET or fluoropolymers can be added to the polypropylene host polymer during extrusion at a content of at least 10%, at least 20%, at least 30%, at least 40%, or even at least 49% by weight prior to stretching to nucleate voids during stretching. Exemplary suitable inorganic particulate additives for nucleating voids in microporous polymer films include titanium dioxide, silica, alumina, aluminum silicate, zirconium oxide, calcium carbonate, barium sulfate, and glass beads and hollow glass bulbs, but other inorganic particles and combinations of inorganic particles may also be used. Crosslinked polymer microspheres may also be used instead of inorganic particles. Inorganic particles can be added to the host polymer during extrusion at a content of at least 10%, at least 20%, at least 30%, at least 40%, or even at least 49% by weight prior to stretching to nucleate voids during stretching. If present, inorganic particles preferably have a volume average particle size of 5 nm to 1 micrometer, but other particle sizes may also be used. Hard particles, including glass beads and / or glass bubbles, may be present on the surface layer of the UV reflector or anti-fouling layer to provide scratch resistance. In some embodiments, glass beads and / or glass bubbles may even protrude from the surface as hemispheres or even quarter-spheres.

[0054] In some embodiments, the microporous polymer membrane comprises a continuous phase of a fluoropolymer. Exemplary suitable polymers include ECTFE, PVDF, PTFE, and copolymers of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride, such as those available, for example, from 3M Company under the trade name THV.

[0055] Exemplary microporous PET films containing barium sulfate, such as LUMIRROR XJSA2, are available from Toray Plastics (America) Inc., North Kingstown, Rhode Island. LUMIRROR XJSA2 contains CaCO3 inorganic additives to increase its reflectivity in the visible light range (400 nm to 700 nm). Other exemplary reflective microporous polymer films, such as HOSTAPHAN V54B, HOSTAPHAN WDI3, and HOSTAPHAN W270, are available from Mitsubishi Polymer Film, Inc., Greer, South Carolina.

[0056] Exemplary microporous polyolefin sheets are described, for example, in U.S. Patent No. 6,261,994.

[0057] The reflective microporous layer diffusely reflects visible light radiation over most wavelengths in the range of, for example, 400 nm to 700 nm, including the end values. In some embodiments, the reflective microporous layer may have an average reflectivity of at least 85% (in some embodiments, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or even at least 99.5%) in the wavelength range of at least 400 nm to at most 700 nm.

[0058] The reflectivity of the microporous layer can be reflective over a wide wavelength range. Therefore, in some embodiments, the microporous polymer layer may have an average reflectivity of at least 85% (in some embodiments, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or even at least 99.5%) over a wavelength range of at least 400 nm to at most 2.5 μm, preferably at least 300 nm to 3.0 μm, but this is not required.

[0059] Antifouling layer

[0060] The anti-fouling layer provides a degree of protection against dirt buildup on the surface, which may hinder the function of the composite cooling film (e.g., by absorbing solar radiation).

[0061] Typically, the antifouling layer is a polymer film, which preferably comprises one or more repellent polymers, such as, for example, fluoropolymers. Examples of comonomers used to prepare usable fluoropolymers include TFE, HFP, THV, and PPVE. Exemplary fluoropolymers used as antifouling layers include PVDF, ECTFE, ETFE, PFA, FEP, PTFE, HTE, and combinations thereof. In some embodiments, the fluoropolymer includes FEP. In some embodiments, the fluoropolymer includes PFA.

[0062] In some embodiments, an antifouling layer is applied as a coating onto the reflective microporous layer. Numerous applied antifouling compositions are known in the art, including, for example, those described in U.S. Patent Application Publications 2015 / 0175479 and 2005 / 0233070, U.S. Patent No. 6,277,485, and PCT Publication WO 02 / 12404.

[0063] In some implementations, suitable antifouling coatings include cross-linked siloxane coatings available from Momentive under the trade name SilFORT AS4700 or from California HardCoating Company under the trade name Perma-New 6000.

[0064] In some embodiments, the outward-facing surface of the antifouling layer (i.e., the antifouling surface) may be microstructured and / or nanostructured on some or all of its surface; for example, as described in PCT International Application PCT / IB2018 / 060527 entitled “ANTISOILINGSURFACE STRUCTURES” filed on December 21, 2018.

[0065] An exemplary antifouling agent is THV815, which can be co-extruded with THV221 to form a bilayer film having a high-melting-point THV815 and a low-melting-point THV221. The THV221 layer can be used as a hot-melt adhesive by co-extruding the THV815 / THV221 bilayer film onto a microporous solar reflective layer or by thermally laminating the THV815 / THV221 bilayer film onto the microporous solar reflective layer. Alternative fluoropolymers of THV815 with a melting point greater than 150°C can also be used as the antifouling layer. Alternative fluoropolymers of THV221 with a melting point less than 150°C can also be used as the hot-melt adhesive.

[0066] In some implementations, nanostructures can be superimposed on microstructures on the surface of the antifouling layer.

[0067] The antifouling layer has a host surface (i.e., the antifouling surface) that may include microstructures and / or nanostructures. The microstructures can be arranged as a series of alternating micropeaks and microspaces. The size and shape of the microspaces between the micropeaks can mitigate the adhesion of dirt particles to the micropeaks. The nanostructures can be arranged as at least a series of nanopeaks disposed on at least the microspaces. Micropeaks may be more resistant to environmental effects than nanopeaks. Because the micropeaks are separated only by microspaces, and the microspaces are significantly higher than the nanopeaks, the micropeaks can be used to protect the nanopeaks on the surface of the microspaces from abrasion.

[0068] Referring to the antifouling layer, the term or prefix "micro" refers to at least one dimension of a structure or shape defined in the range of 1 micrometer to 1 millimeter. For example, a microstructure may have a height or width in the range of 1 micrometer to 1 millimeter.

[0069] As used herein, the term or prefix “nano” refers to at least one dimension defining a structure or shape less than 1 micrometer. For example, a nanostructure may have at least one of a height or width less than 1 micrometer.

[0070] The composite cooling film according to this disclosure preferably has an average absorption rate of at least 0.85, preferably at least 0.9, and more preferably at least 0.95 in the wavelength range of 8 to 13 micrometers, but this is not required.

[0071] An exemplary antifouling layer includes a crosslinked hard coating containing a UV-absorbing additive. Suitable materials for the crosslinked hard coating include acrylates, siloxanes, and urethanes, or combinations thereof. An exemplary antifouling layer comprising both acrylate and siloxane comonomers is described in U.S. Patent No. 10,072,173.

[0072] Specular reflective multilayer optical film

[0073] Specular reflective multilayer optical films, as described in U.S. Patent 9,523,516 and PCT Publication WO 2019 / 130199, can be applied to antenna surfaces to minimize solar energy absorption and thus enhance their ability to cool electronics within the antenna. Such multilayer optical films can also be applied to cooling fins for surface cooling.

[0074] The specular reflective multilayer film may be composed of a material that provides at least 90% average reflectivity in a wavelength range of at least 400 nm to 1000 nm, and preferably 400 nm to 2000 nm, and more preferably 350 nm to 2500 nm.

[0075] For reasons of film thickness, flexibility, and economy, the number of layers in a specular reflective multilayer optical film is selected to achieve the desired optical properties using the minimum number of layers. For reflective films such as mirrors, the number of layers is preferably less than about 2,000, more preferably less than about 1,000, and even more preferably less than about 750. In some embodiments, the number of layers is at least 150 or 200. In other embodiments, the number of layers is at least 250.

[0076] Specular reflective multilayer optical films comprise multiple pairs of low / high refractive index layers, wherein the combined optical thickness of each low / high refractive index layer pair is half the center wavelength of the spectral band it is designed to reflect. Stacks of these films are often referred to as quarter-wavelength stacks. In some embodiments, different low / high refractive index layer pairs can have different combined optical thicknesses, such as in the case of optical films requiring broadband reflection.

[0077] The optical layer may contain fluorinated polymers (i.e., fluoropolymers), non-fluorinated polymers, and blends thereof.

[0078] Examples of usable fluoropolymers include copolymers of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (e.g., available under the trade name 3M DYNEON THV from 3M Company); copolymers of TFE, HFP, vinylidene fluoride, and perfluoropropyl vinyl ether (PPVE) (e.g., available under the trade name 3M DYNEON THVP from 3M Company); polyvinylidene fluoride (PVDF) (e.g., available under the trade name 3M DYNEON PVDF 6008 from 3M Company); ethylene-trifluorochloroethylene polymer (ECTFE) (e.g., available under the trade name HALAR 350LC ECTFE from Solvay, Brussels, Belgium); and ethylene-tetrafluoroethylene copolymer (ETFE) (e.g., available under the trade name 3M DYNEON ETFE 6235 from 3M Company). (Company)); perfluoroalkoxyalkane polymers (PFA); fluorinated ethylene propylene copolymers (FEP); polytetrafluoroethylene (PTFE); copolymers of TFE, HFP, and ethylene (HTE) (e.g., 3MDYNEON HTE1705, available from 3M Company). Combinations of fluoropolymers may also be used. In some embodiments, the fluoropolymer includes FEP. In some embodiments, the fluoropolymer includes PFA.

[0079] Examples of non-fluorinated polymers that can be used in at least one layer of a specular reflective multilayer optical film include at least one of the following: polyethylene terephthalate, polypropylene, polyethylene, polyethylene copolymers, polymethyl methacrylate, methyl methacrylate copolymers (e.g., copolymers of ethyl acrylate and methyl methacrylate), polyurethane, extended-chain polyethylene polymers (ECPE), or combinations thereof. Generally, combinations of non-fluorinated polymers can be used. Exemplary non-fluorinated polymers, particularly those for low-refractive-index optical layers, may include homopolymers of polymethyl methacrylate (PMMA), such as those available from Ineos Acrylics, Inc., Wilmington, Delaware (CP71 and CP80); and polyethyl methacrylate (PEMA) having a lower glass transition temperature than PMMA. Other available polymers include copolymers of methyl methacrylate, such as copolymers made of, for example, 75% by weight of methyl methacrylate and 25% by weight of ethyl acrylate, such as those available as PERSPEX CP63 from Ineos Acrylics, Inc., Wilmington, Delaware, or those available as ALTUGLAS 510 from Arkema, Philadelphia, Pennsylvania, and copolymers of methyl methacrylate monomer units and n-butyl methacrylate monomer units.

[0080] Blends of PMMA and PVDF can also be used.

[0081] Suitable triblock acrylic copolymers may be available, for example, as Kuraire LA4285 from Kuraray America Inc., Houston, Texas. Other suitable polymers for optical layers, particularly for low-refractive-index optical layers, may include at least one of the following: polyolefin copolymers, such as poly(ethylene-co-octene) (e.g., available as ENGAGE 8200 from Dow Elastomers, Midland, Michigan); polyethylene methacrylate (e.g., available as ELVALOY from Dow Elastomers); poly(propylene-co-ethylene) (e.g., available as Z9470 from Atofina Petrochemicals, Inc., Houston, Texas); and copolymers of atactic and isotactic polypropylene. Materials may be selected based on the absorptivity or transmittance characteristics described herein and based on refractive index. Generally speaking, the greater the refractive index between two materials, the thinner the film can be, which is ideal for effective heat transfer.

[0082] For solar reflective multilayer optical films, a quarter-wavelength stack design preferably results in each layer in the multilayer stack having an average thickness of no more than about 0.7 micrometers, but this is not necessary.

[0083] Multilayer optical films (including reflective polarizers and mirrors) can be prepared by co-extruding alternating polymer layers with different refractive indices, as described, for example, in U.S. Patents 6,045,894, 6,368,699, 6,531,230, 6,667,095, 6,783,349, 7,271,951, 7,632,568, and 7,952,805, and PCT Publications WO 95 / 17303 and WO 99 / 39224.

[0084] Optional IR reflective layers that can be vapor-coated beneath a solar reflective multilayer optical film also include: a metal layer, such as aluminum, copper, gold, or silver; and a layer of metal oxides or metal sulfides, such as cerium oxide, aluminum oxide, magnesium oxide, titanium dioxide, and indium tin oxide.

[0085] Exemplary materials used as the first and second optical layers in a multilayer optical film absorb more than 50% of electromagnetic radiation across most wavelengths in the 4000 nm to 20000 nm range. An exemplary first optical layer comprises PET (polyethylene terephthalate) and copolymers thereof.

[0086] Optional adhesive layer

[0087] Optional adhesive layers may include any adhesive (e.g., thermosetting adhesives, hot-melt adhesives, and / or pressure-sensitive adhesives). If present, optional adhesive layers preferably contain pressure-sensitive adhesives. In some embodiments, the adhesive is resistant to UV radiation damage. Exemplary adhesives that are typically resistant to UV radiation damage include silicone adhesives and acrylic adhesives containing UV-stabilizing / blocking additives, such as those described above. An exemplary optional adhesive is polyisobutylene, which minimizes moisture transport into the micropores and micropores of the solar reflective layer.

[0088] The optional adhesive layer may be a hot melt adhesive. An example hot melt adhesive is THV221.

[0089] Optional adhesive layers may contain thermally conductive particles to facilitate heat transfer. Exemplary thermally conductive particles include alumina particles, alumina nanoparticles, hexagonal boron nitride particles and aggregates (e.g., purchased from 3M Company as 3M boron nitride), graphene particles, graphene oxide particles, metal particles, and combinations thereof.

[0090] Optional peelable liners may include, for example, polyolefin films, fluoropolymer films, coated PET films, silicone films, or paper.

[0091] UV stabilizer additives

[0092] UV stabilizing additives can be added to any component of the composite cooling film (e.g., UV reflective multilayer optical film, optional antifouling layer, optional adhesive layer, reflective microporous layer, and / or IR reflective layer).

[0093] UV stabilization using ultraviolet absorbers (UVA) and / or hindered amine light stabilizers (HALS) can intervene to prevent photo-oxidative degradation of PET, PMMA, and CoPMMA. Exemplary UVAs used for incorporation into PET, PMMA, or CoPMMA polymer layers include benzophenone, benzotriazole, and benzotriazine. Commercially available UVAs used for incorporation into PET, PMMA, or CoPMMA optical layers include those available as Tinuvin 1577 and Tinuvin 1600 from BASF Corporation, Florham Park, New Jersey. Typically, UVA is incorporated into the polymer at concentrations ranging from 1% to 10% by weight.

[0094] Exemplary HALS compounds used for incorporation into PET, PMMA, or CoPMMA optical layers include those available from BASF Corporation as Chimmasorb 944 and Tinuvin 123. Typically, the HALS compound is incorporated into the polymer at a rate of 0.1% to 1.0% by weight. A UVA to HALS ratio of 10:1 is preferred.

[0095] UVA and HALS compounds can also be incorporated into fluoropolymer layers. U.S. Patent No. 9,670,300 and U.S. Patent Application Publication No. 2017 / 0198129 describe exemplary UVA oligomers compatible with PVDF fluoropolymers.

[0096] Other UV-blocking additives may be included in the fluoropolymer layer. For example, non-pigment-grade microparticles of zinc oxide and titanium dioxide may be used. Nanoscale particles of zinc oxide, calcium carbonate, and barium sulfate reflect or scatter UV light while being transparent to visible and near-infrared light. Small zinc oxide and barium sulfate particles ranging in size from 10 nanometers to 100 nanometers that can reflect UV radiation are available, for example, from Kobo Products Inc., SouthPlainfield, New Jersey.

[0097] Antistatic additives can also be incorporated into any polymer film / layer to reduce unwanted attraction to dust, dirt, and debris. Ionic salt antistatic additives, available from 3M Company, can be incorporated into PVDF fluoropolymer layers to provide static dissipation. Exemplary antistatic additives for PMMA and CoPMMA are available as STAT-RITE from Lubrizol Engineered Polymers, Brecksville, Ohio, or as PELESTAT from Sanyo Chemical Industries, Tokyo, Japan.

[0098] Examples of cooling films are described in U.S. Provisional Patent Application Serial No. 63 / 333152 entitled “Passive Radiative Cooling Film for Antennas”, filed April 21, 2022, which is incorporated herein by reference as if fully described.

[0099] Other examples of cooling films are described in PCT publications WO 2020 / 240447, WO 2020 / 240366 and WO 2019 / 130199.

[0100] Passive cooling fins

[0101] The synergistic passive cooling fins described below can be used to passively cool modular data centers, power transformers, and other surfaces. Figure 2 This is a perspective view of a passively cooled fin with cooling fins 200, wherein a passive radiative cooling film 201 is laminated to the main surface of the fins 200, a heat sink 202 is attached to and supports the cooling fins 200, and a fluid heat transfer panel 204 is attached to the heat sink 202 on a side opposite to the cooling fins 200. The fluid heat transfer panel 204 includes a fluid inlet 206 to the panel 204 and a fluid outlet 208 from the panel 204, the fluid outlet being configured to allow fluid circulation through the panel 204. The cooling fins 200 can be implemented using metal fins such as aluminum. The heat sink 202 and the panel 204 can be implemented using, for example, a metal material such as aluminum. The cooling film 201 laminated to the cooling fins can be, for example, as described above. Figure 1 The composite cooling film described herein is used to achieve this. The cooling film 201 preferably covers all or a substantial portion of the main surface of each cooling fin. The cooling film 201 is preferably laminated or otherwise attached to each cooling fin in the cooling fins; alternatively, the cooling film 201 may be laminated to fewer than all cooling fins.

[0102] Figure 3 This is a perspective view of a modular data center 214 with heat sink cooling fins 210. A heat sink 212 is attached to the cooling fins 210 and the modular data center 214. The heat sink cooling fins 210 include a passive radiative cooling film laminated to the fins, and can be referenced as shown in the reference. Figure 2 Implemented as described. Figure 2 The fluid transfer panel 204 shown can optionally be implemented between the heat sink 212 and the modular data center 214.

[0103] Figure 4 This is a perspective view of a power transformer 220 with heat sink cooling fins 216. A heat sink 218 is attached to the cooling fins 216 and the power transformer 220. The heat sink cooling fins 216 include a passive radiative cooling film laminated to the fins, and can be referenced as shown in the reference. Figure 2 Implemented as described. Figure 2 The fluid transfer panel 204 shown can optionally be implemented between the radiator 218 and the power transformer 220.

[0104] Figure 5This is a cross-sectional side view of a passive cooling fin design. The design includes a passive radiative cooling film 222 attached to an aluminum (or other metal) sheet shaped as a cooling fin 224. A thermally conductive adhesive 226 is attached between the cooling fin 224 and the substrate 228 to be cooled. Figure 5 The passive cooling fins shown can be used Figures 2 to 4 The cooling fins are shown in the image.

[0105] Figure 6 This is a cross-sectional side view of multiple passive cooling fins joined together on a surface to be cooled. Cooling fin 230 includes a passive radiative cooling film 232 attached to an aluminum (or other metal) sheet shaped as cooling fin 234. Cooling fin 240, having the passive radiative cooling film 233, is attached to and joined to cooling fin 230 at interface 241. Cooling fin 242, having the passive radiative cooling film 235, is attached to and joined to cooling fin 240 at interface 243. Thermally conductive adhesive 236 is attached between the cooling fins (230, 240, 242) and the substrate 238 to be cooled. Additional passive cooling fins may be joined together in the same manner.

[0106] Figure 7 This is a cross-sectional side view of a modular data center with passive cooling fins. Cooling fin 244 includes a passive radiative cooling film 246 attached to an aluminum (or other metal) sheet shaped as cooling fin 248. Cooling fin 252 with passive radiative cooling film 247 is attached to and spliced ​​with cooling fin 244 at interface 253. Cooling fin 254 with passive radiative cooling film 249 is attached to and spliced ​​with cooling fin 252 at interface 255. Thermally conductive adhesive 250 is attached between the cooling fins (244, 252, 254) and the modular data center 256 to be cooled. Additional passive cooling fins can be spliced ​​together on the modular data center 256 in the same manner.

[0107] Figures 5 to 7 The cooling film described in the reference above can be used, for example. Figure 1 The composite cooling film described is used to achieve this. Figures 5 to 7 The cooling film described herein is laminated or otherwise attached to the main surface of the corresponding cooling fins. Figures 5 to 7 The cooling film described herein preferably covers all or a substantial portion of the main surface of each cooling fin. Alternatively, the cooling film may be attached to fewer than all cooling fins.

Claims

1. A passive cooling fin, the passive cooling fin comprising: Cooling fins; A passive radiative cooling film is attached to the main surface of the cooling fins; and A radiator, the radiator being attached to the cooling fins, The passive radiation cooling film includes: An anti-fouling layer is fixed to the first main surface of a specular reflective multilayer optical film, wherein the specular reflective multilayer optical film includes a plurality of first optical layers and a plurality of second optical layers, and specularly reflects electromagnetic radiation in most wavelengths in the range of 400 nm to 2500 nm, and absorbs electromagnetic radiation in most wavelengths in the range of 4000 nm to 20000 nm.

2. The passive cooling fin according to claim 1, wherein the passive cooling fin further comprises: A fluid heat transfer panel is attached to the radiator on the side opposite to the cooling fins. A fluid inlet, which is attached to the fluid heat transfer panel; and A fluid outlet, which is attached to the fluid heat transfer panel. The fluid inlet and the fluid outlet are configured to allow fluid to circulate through the fluid heat transfer panel.

3. A modular data center having cooling fins as described in claim 1.

4. A power transformer having cooling fins according to claim 1.

5. The cooling fin of claim 1, wherein the specular reflective multilayer has an average absorption rate of at least 80% in the wavelength range of 8 micrometers to 13 micrometers.

6. The cooling fin according to claim 1, wherein the cooling fin further comprises a thermally conductive adhesive layer, the thermally conductive adhesive layer being fixed to a second main surface of the membrane opposite to the first main surface.

7. The cooling fin of claim 1, wherein the thermally conductive adhesive layer is fixed to the cooling fin opposite to the reflective multilayer optical film.

8. The cooling fin according to claim 1, wherein the cooling fin further comprises an auxiliary reflective metal layer, the auxiliary reflective metal layer being fixed to the reflective multilayer optical film opposite to the anti-fouling layer.

9. The cooling fin of claim 1, wherein the reflective metal layer comprises one of silver, aluminum, and copper.

10. The cooling fin of claim 1, wherein the outward-facing surface of the antifouling layer comprises a nanostructured surface superimposed on the microstructured surface.

11. The cooling fin of claim 1, wherein the antifouling layer comprises an ultraviolet-absorbing crosslinked hard coating.

12. The cooling fin according to claim 1, wherein the reflective multilayer optical film comprises a multilayer optical film.

13. The cooling fin of claim 12, wherein the microporous polymer film further comprises a siloxane.

14. A passive cooling fin, the passive cooling fin comprising: Cooling fins; A passive radiative cooling film is attached to the main surface of the cooling fins; and A radiator, the radiator being attached to the cooling fins, The passive radiation cooling film includes: An antifouling layer is fixed to a first main surface of a specular reflective multilayer film, wherein the specular reflective multilayer film comprises an organic polymer, a metal layer, and specularly reflects electromagnetic radiation over most wavelengths in the range of 400 nm to 2000 nm. The antifouling layer has an outward-facing antifouling surface opposite to a second main surface, and a metallization layer is fixed to the second main surface of the film opposite to the first main surface.

15. The passive cooling fin according to claim 14, wherein the passive cooling fin further comprises: A fluid heat transfer panel is attached to the radiator on the side opposite to the cooling fins. A fluid inlet, which is attached to the fluid heat transfer panel; and A fluid outlet, which is attached to the fluid heat transfer panel. The fluid inlet and the fluid outlet are configured to allow fluid to circulate through the fluid heat transfer panel.

16. A modular data center having cooling fins as claimed in claim 14.

17. A power transformer having cooling fins according to claim 14.

18. The cooling fin of claim 14, wherein the solar reflective multilayer film has an average absorption rate of at least 50% in the wavelength range of 8 micrometers to 13 micrometers.

19. The cooling fin according to claim 14, wherein the cooling fin further comprises an infrared absorbing layer fixed to a second main surface of the membrane opposite to the first main surface.

20. The cooling fin of claim 19, wherein the infrared absorbing layer has an average absorption rate of at least 50% in the wavelength range of 4 micrometers to 20 micrometers.

21. The cooling fin of claim 19, wherein the infrared absorbing layer is fixed to the solar reflective multilayer film opposite to the antifouling layer.

22. A passive cooling fin, the passive cooling fin comprising: Cooling fins; A passive radiative cooling film is attached to the main surface of the cooling fins; A thermally conductive adhesive is attached to the cooling fins on the side opposite to the passive radiative cooling film. and The substrate to be cooled is attached to the thermally conductive adhesive on the side opposite to the cooling fins. The passive radiation cooling film includes: An antifouling layer is attached to a first main surface of a reflective microporous layer, wherein the reflective microporous layer diffusely reflects electromagnetic radiation over most wavelengths in the range of 400 nm to 2500 nm, and the antifouling layer has an outward-facing antifouling surface.

23. A passive cooling fin, the passive cooling fin comprising: Cooling fins; A passive radiative cooling film is attached to the main surface of the cooling fins; A thermally conductive adhesive is attached to the cooling fins on the side opposite to the passive radiative cooling film. and The substrate to be cooled is attached to the thermally conductive adhesive on the side opposite to the cooling fins. The passive radiation cooling film includes: An antifouling layer is attached to a first main surface of a specular reflective multilayer film, wherein the specular reflective multilayer film includes a metal layer and specularly reflects electromagnetic radiation over most wavelengths in the range of 400 nm to 2000 nm. The antifouling layer has an outward-facing antifouling surface opposite to the second main surface, and optionally a thermally conductive adhesive is attached to the second main surface of the film opposite to the first main surface.

24. The passive cooling fin according to claim 22 or 23, wherein the passive cooling fin further comprises another passive cooling fin spliced ​​with the cooling fin.

25. A modular data center having passive cooling fins according to any one of claims 22 to 24.

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