Abstract
The invention relates to a passive radiant cooler (1) having a substrate and a layer structure which is applied to the substrate (2) and comprises the at least one reflection layer (3) and at least one emission layer (4), the emission layer (4) comprising an at least partially crosslinked polymer and/or a ceramic material derived from this polymer which are produced in order to form the emission layer (4) from at least one crosslinkable, silicon-based prepolymer, the prepolymer being composed of at least one type of monomer unit according to formula (I).
Claims
1. A passive radiant cooler (1), comprising: a substrate; a layer structure applied to the substrate (2) and comprising at least one reflection layer (3) and at least one emission layer (4); wherein the emission layer (4) comprises at least one of an at least partly crosslinked polymer or a ceramic material derived from said polymer, which are produced to form the emission layer (4) from at least one crosslinkable, silicon-based prepolymer, wherein the prepolymer is composed of at least one type of monomer units of Formula (I), ##STR00011## in which A is selected from the group consisting of the elements nitrogen, carbon and boron or a carbodiimide group; E is selected from the group consisting of the elements oxygen and silicon; D is the element boron; p1, p2, p3, p4, p5 and p6 are independently the numbers 0 or 1; m1 and m2 are independently the numbers 0 or 1; and R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are independently selected from the group consisting of the element hydrogen, a linear saturated or branched saturated hydrocarbyl group, a linear unsaturated or branched unsaturated hydrocarbyl group, a functionalized linear or a functionalized branched hydrocarbyl group, an unsaturated cyclic hydrocarbyl group or a saturated cyclic hydrocarbyl group, and a hydroxyl group; and wherein the reflection layer (3) in a first spectral wavelength range has a reflectivity of 0.60 to 1.00.
2. The passive radiant cooler (1) as claimed in claim 1, wherein the layer structure is formed such that either the reflection layer (3) is applied to the substrate (2) and the emission layer (4) to the reflection layer (3), or the emission layer (4) is applied to the substrate (2) and the reflection layer (3) to the emission layer (4).
3. The passive radiant cooler (1) as claimed in claim 1, wherein the first electromagnetic spectral wavelength range is between 200 nm and 3000 nm.
4. The passive radiant cooler (1) as claimed in claim 1 wherein the reflection layer (3) is formed from a metal selected from the group by consisting of silver, aluminum, rhodium and magnesium; or from a metal alloy selected from the group consisting of steel, an aluminum-magnesium alloy and an aluminum-zinc alloy; or from a metal oxide selected from the group consisting of titanium dioxide in the form of TiO.sub.2, titanium dioxide in the form of TiO.sub.x and barium sulfate (BaSO.sub.4); or from a polymer selected from the group consisting of tetrafluoroethylene-hexafluoropropylene copolymer and polytetrafluoroethylene.
5. The passive radiant cooler (1) as claimed in claim 1, wherein the reflection layer (3) has a layer thickness in the range from 20 nm to 1 mm.
6. The passive radiant cooler (1) as claimed in claim 1, wherein the reflection layer comprises multiple reflection layers (31, 32, 33, 34) arranged one on top of another, wherein the emission layer (4) is disposed either on uppermost (31) one of the reflection layers (31, 32, 33, 34) or between the reflection layers (31, 32, 33, 34) and the substrate (2).
7. The passive radiant cooler (1) as claimed in claim 1, wherein the reflection layer (3) contains at least one additive (7) which is a pigment or a dye.
8. The passive radiant cooler (1) as claimed in claim 1, wherein the emission layer (4) has an emissivity in a second electromagnetic spectral wavelength range in a range from 0.50 to 1.00.
9. The passive radiant cooler (1) as claimed in claim 8, wherein the second electromagnetic spectral wavelength range is within a range from 7 m to 14 m.
10. The passive radiant cooler (1) as claimed in claim 9, wherein the emission layer (4) has an emissivity in a third electromagnetic spectral wavelength range in the range from 0.20 to 1.00.
11. The passive radiant cooler (1) as claimed in claim 10, wherein the third electromagnetic spectral wavelength range is within a range from 16 m to 26 m.
12. The passive radiant cooler (1) as claimed in claim 1 wherein, in the Formula (I), A is the element nitrogen, p1 is the number 1, and p2, m1, p3, p4, m2, p5 and p6 are the number 0.
13. The passive radiant cooler (1) as claimed in claim 12, wherein, in the Formula (I), A is the element nitrogen, p1 is the number 1, and p2, m1, p3, p4, m2, p5 and p6 are the number 0, R.sup.1 is a methyl group, R.sup.2 is a vinyl group or the element hydrogen, and R.sup.3 is the element hydrogen.
14. The passive radiant cooler (1) as claimed in claim 1, wherein the prepolymer is composed of two kinds of monomer units of the following Formulae (II) and (III): ##STR00012## in which y and z are respective proportions of monomer units in the prepolymer and where y has a value of 0.8 and z has a value of 0.2.
15. The passive radiant cooler (1) as claimed in claim 1, wherein the at least partly crosslinked polymer is crosslinked by at least one of covalent SiOSi, SiCH.sub.2CH.sub.2Si, SiNSi, SiOB, SiBN, SiCB or SiBSi polymer crosslinks.
16. The passive radiant cooler (1) as claimed in claim 1 wherein the emission layer (4) is in microstructured form.
17. The passive radiant cooler (1) as claimed in claim 1, wherein the emission layer (4) comprises at least one filler (6) which is embedded into the at least partly crosslinked polymer and is selected from the group consisting of SiO.sub.2, TiO.sub.2, Al.sub.2O.sub.3, BN, PTFE, ZrO.sub.2, MgO and CeO.sub.2.
18. The passive radiant cooler (1) as claimed in claim 1, wherein the emission layer (4) has a layer thickness in a range from 0.1 m to 600 m.
19. The passive radiant cooler (1) as claimed in claim 1, wherein the substrate (2) is a glass substrate, a silicon wafer, a film or foil, a metal sheet or a ceramic plate.
20. The passive radiant cooler (1) as claimed in claim 1, wherein an interlayer (5) which is disposed between the substrate (2) and the reflection layer (3, 31, 32, 33, 34) and is formed from silicon dioxide, germanium, chromium, titanium, a transparent conductive oxide, or an inorganic oxide.
Description
BRIEF DESCRIPTION FO THE DRAWINGS
[0049] Further preferred features and advantageous embodiments are described hereinafter with reference to working examples in the figures and experimental examples. The figures show:
[0050] FIG. 1 a first working example of a passive radiant cooler in a schematic side view;
[0051] FIG. 2 a second working example of a passive radiant cooler in a schematic side view;
[0052] FIG. 3 the absorbance of electromagnetic radiation in the range from 4000 cm.sup.1 to 500 cm.sup.1 by an emission layer;
[0053] FIG. 4 the coefficient of absorption of the emission layer and the incident power of solar radiation, each as a function of wavelength;
[0054] FIG. 5 the atmospheric transmissivity and emissivity of the first working example of the passive radiant cooler 1 from FIG. 1, each as a function of wavelength;
[0055] FIG. 6 a third working example of the passive radiant cooler in a schematic side view;
[0056] FIG. 7 a fourth working example of the passive radiant cooler in a schematic side view;
[0057] FIG. 8 a fifth working example of the passive radiant cooler in a schematic side view;
[0058] FIG. 9 a sixth working example of the passive radiant cooler in a schematic side view;
[0059] FIG. 10 a seventh working example of the passive radiant cooler in a schematic side view;
[0060] FIG. 11 an eighth working example of the passive radiant cooler in a schematic side view;
[0061] FIG. 12 a ninth working example of the passive radiant cooler in a schematic side view;
[0062] FIG. 13 a tenth working example of the passive radiant cooler in a schematic side view;
[0063] FIG. 14 a high-rise building in a schematic perspective view; and
[0064] FIG. 15 cooling by a passive radiant cooler in an outdoor experiment.
DETAILED DESCRIPTION
[0065] FIG. 1 shows a first working example of a passive radiant cooler 1 in schematic side view. This radiant cooler 1 comprises a reflection layer 3 applied to a substrate 2, and an emission layer 4 applied to the reflection layer 3. The substrate 2 in this first working example is a glass substrate. The reflection layer 3 applied to the glass substrate 2 is formed from silver (Ag) and has a layer thickness of 300 nm. The emission layer 4 applied to the reflection layer 3 comprises a partly crosslinked polymer produced from the crosslinkable silicon-based prepolymer, which is composed of two types of monomer units of the Formulae (II) and (III), where y has the value of 0.8 and z has the value of 0.2 in the Formulae (II) and (III). This prepolymer in the form of a polysilazane is commercially available under the Durazane 1800 brand from Merck KGAA from Germany. The emission layer in the present first working example has a layer thickness of 3
[0066] Example 1: Production of the Passive Radiant Cooler 1
[0067] The procedure for the production of the first working example of the passive radiant cooler 1 is as follows:
[0068] In a first method step, the reflection layer 3 of silver with a layer thickness of 300 nm is applied to the glass substrate 2 by an electron beam evaporator (DREVA LAB 450, VTD Vakuumtechnik Dresden GmbH, Germany). In a second method step, the crosslinkable silicon-based prepolymer composed of two types of monomer units of the Formulae (II) and (III), in which y has the value of 0.8 and z has the value of 0.2, is mixed with the di-n-butyl ether solvent, so as to form a liquid solution having a proportion of the prepolymer of 50 percent by weight (% by weight). Thereafter, in a third method step, the glass substrate 2 coated with the reflection layer 3 of silver is coated with the solution produced in the second method step using a dip-coater produced by the applicant. For this purpose, the glass substrate 2 coated with the reflection layer 3 of silver is dipped gradually into a trough of the dip-coater filled with the solution, and the glass substrate 2 coated with the reflection layer 3 of silver is kept in the trough for a defined period of 10 seconds, such that the glass substrate 2 coated with the reflection layer 3 of silver is surrounded by the solution. Thereafter, the glass substrate 2 coated with the solution and the reflection layer 3 of silver is pulled gradually back out of the trough of the dip-coater at a speed of 0.5 m/min. After being pulled out, a still-liquid layer of the prepolymer dissolved in di-n-butyl ether is present on the glass substrate 2 coated with the reflection layer 3 of silver. In a further method step, the glass substrate coated with the liquid layer of the prepolymer and the reflection layer 3 is dried in a drying cabinet under an air atmosphere at a temperature of 180 C. for one hour. This thermal treatment leads to crosslinking of the prepolymer with simultaneous evaporation of the di-n-butyl ether solvent, which result in formation of covalent polymer crosslinks between individual polysilazane molecules and also within a polysilazane molecule. The formation of these covalent polymer crosslinks leads to formation of a three-dimensional polymer network and the emission layer 4. Since the thermal treatment is conducted under an air atmosphere, the oxygen from the air atmosphere is incorporated into the three-dimensional polymer network of the emission layer 4, which result in formation of SiOSi polymer crosslinks and release of ammonia gas. This production method can also be employed for other prepolymers, for example polycarbosilanes or polyborosiloxanes.
[0069] FIG. 2 shows a second working example of the passive radiant cooler 1 in a schematic side view. This second working example of the passive radiant cooler 1 differs from the first working example from FIG. 1 in that the substrate 2 is an aluminum sheet (Alanod GmbH & Co. KG, Germany) having a thickness of 0.04 cm. This aluminum sheet has good thermal conductivity. A further difference is that the reflection layer 3 has a layer thickness of 230 nm.
[0070] FIG. 3 shows a diagram showing the absorbance of electromagnetic radiation in the range from 4000 cm.sup.1 to 500 cm.sup.1 by the emission layer 4. This emission layer 4 comprises the at least partly crosslinked polymer produced to form the emission layer 4 from the above-described polysilazane having the name Durazane 1800, and applied directly to a substrate 2 in the form of a silicon wafer, i.e. without a reflection layer 3 disposed between the emission layer 4 and the substrate 2 (so-called PSZ-coated silicon wafer). This layer structure serves for analysis of the absorbance properties of the emission layer 4. Peaks or local maxima in the spectrum indicate the absorbance caused by factors including absorption of infrared radiation by covalent bonds in the partly crosslinked polymer of the emission layer 4. This infrared radiation is absorbed either by an SiNSi polymer backbone of the polymer, by covalent polymer bonds SiOSi, or by other covalent bonds NH, CH, SiH and SiCH.sub.3. This absorption of infrared radiation induces vibration in the respective bonds. In FIG. 3, each peak is labeled with the corresponding vibration.
[0071] FIG. 4 shows a diagram showing the incident power of solar radiation as a function of wavelength (dotted line; labeled as AM1.5G incident power). The same diagram shows the coefficient of absorption of the second working example of the passive radiant cooler 1 from FIG. 2, likewise as a function of wavelength (solid line, labeled as Absorption factor of PSZ-coated sample). The wavelength range between 300 nm and 2500 nm which is shown in the diagram corresponds to the first electromagnetic spectral wavelength range. This diagram shows that the emission layer 4 absorbs solar radiation in this first spectral wavelength range only to a very small degree. This is because the emission layer 4 is transparent in this first spectral wavelength range. This diagram was recorded with the aid of a UV-VIS-NIR spectrometer (Cary 500, Agilent Technologies, Inc., USA).
[0072] FIG. 5 shows a diagram showing atmospheric transmissivity as a function of wavelength (dotted line, labeled as Atmospheric transmissivity). The same diagram shows the emissivity of the second working example of the passive radiant cooler 1 from FIG. 2 (solid line, labeled as PSZ-coated substrate (with Ag reflector)) as a function of wavelength. Atmospheric transmissivity corresponds to the transparency of the Earth's atmosphere for electromagnetic radiation. As becomes clear from the dotted line on this diagram, the Earth's atmosphere has two atmospheric transmission windows. A first transmission window is in the second electromagnetic spectral wavelength range between 8 m and 14 m. In addition, the Earth's atmosphere is also transparent to infrared radiation between about 16 m and 25 m. In these spectral wavelength ranges, infrared radiation emitted by the emission layer 4 can be released into cold outer space without heating the Earth's atmosphere in the process. The emission layer 4 of the second working example of the passive radiant cooler 1 emits infrared radiation in the second electromagnetic spectral wavelength range between 8 m and 14 m, and in a third electromagnetic spectral wavelength range between 20 m and 25 m. This second and third electromagnetic spectral wavelength range are respectively in the first and second atmospheric transmission windows.
[0073] FIG. 6 shows a third working example of the passive radiant cooler 1. This third working example differs from the first working example of the passive radiant cooler 1 shown in FIG. 1 in that the emission layer 4 is microstructured. This microstructuring of the emission layer 4 was applied by stamping to the reflection layer 3.
[0074] FIG. 7 shows a fourth working example of the passive radiant cooler 1. This fourth working example differs from the second working example shown in FIG. 2 in that the emission layer 4 is formed from a partly crosslinked polymer produced from a crosslinkable polycarbosilane. This emission layer 4 of polycarbosilane has a layer thickness of 4 m.
[0075] FIG. 8 shows a fifth working example of the passive radiant cooler 1. This fifth working example differs from the fourth working example of the passive radiant cooler shown in FIG. 7 in that an interlayer 5 of silicon oxide (SiO.sub.2) is disposed between the substrate 2 and the reflection layer 3. This interlayer 5 can prevent the mixing of silver and aluminum atoms at an interface between the substrate 2 and the reflection layer 3.
[0076] FIG. 9 shows a sixth working example of the passive radiant cooler 1 in a schematic side view. This sixth working example differs from the fifth working example of the passive radiant cooler 1 from FIG. 8 in that the emission layer 4 contains a filler 6 which is embedded in the partly crosslinked polymer and takes the form of silicon dioxide particles (SiO.sub.2). These silicon dioxide particles take the form of microparticles having a diameter of 10 m5 m. They serve to prevent cracking in the emission layer 4 on exceedance of the critical layer thickness. For that reason, the emission layer 4 in the sixth working example has a higher layer thickness than the emission layer 4 shown in the second working example, namely 60 m. These silicon dioxide particles are additionally capable of emitting heat in the form of infrared radiation.
[0077] FIG. 10 shows a seventh working example of the passive radiant cooler 1 in a schematic side view. This seventh working example differs from the second working example of the passive radiant cooler 1 shown in FIG. 2 in that the reflection layer 5 is formed from tetrafluoroethylene-hexafluoropropylene copolymer and contains an additive 7 which is a pigment. This pigment 7 is embedded in the reflection layer 5 in the form of nanoparticles. The effect of the embedding of this pigment 7 in the reflection layer 5 is that a subregion of the first spectral wavelength range of incident solar radiation is not reflected by the reflection layer 5 but instead absorbed by the pigment. As a result, the pigment 7 emits electromagnetic radiation in the visible region of the electromagnetic spectrum, such that the reflection layer 5 is colored. The embedding of the pigment 7 in the reflection layer 5 has the advantage that this causes the passive radiant cooler 1 to appear colored. In this way, it is possible to match the color of the passive radiant cooler 1 to the color of the object on which it is to be mounted.
[0078] FIG. 11 shows an eighth working example of the passive radiant cooler 1 in a schematic side view. This eighth working example differs from the first working example of the passive radiant cooler 1 shown in FIG. 1 in that the passive radiant cooler 1 comprises multiple reflection layers 31, 32, 33, 34 of a dielectric material arranged one on top of another. The layer thicknesses of the individual reflection layers 31, 32, 33, 34 arranged one on top of another are chosen here such that the reflection layers 31, 32, 33, 34 reflect the incident radiation in the first electromagnetic spectral wavelength range.
[0079] FIG. 12 shows a ninth working example of the passive radiant cooler 1 in a schematic side view. This ninth working example differs from the first working example of the passive radiant cooler 1 shown in FIG. 1 in that the substrate 2 is a metal sheet of copper having a thickness of 0.2 cm. In addition, the reflection layer 2 comprises titanium dioxide in the form of TiO.sub.2.
[0080] FIG. 13 shows a tenth working example of the passive radiant cooler 1 in a schematic side view. This tenth working example differs from the eighth working example of the passive radiant cooler 1 shown in FIG. 11 in that the emission layer 4 is applied directly to the substrate 2, with multiple reflection layers 31, 32, 33, 34 of a dielectric material that are disposed one on top of another being disposed on the emission layer 4.
[0081] FIG. 14 shows a high-rise building 9 in a schematic perspective view. On a building roof 10 of said building 9 is disposed the second working example of the passive radiant cooler 1 from FIG. 2, which serves to cool the building 9. The basis of the cooling by the passive radiant cooler 1 is that the passive radiant cooler 1 can firstly reflect incident solar radiation in the first electromagnetic spectral wavelength range and additionally emit heat in the form of infrared radiation in the second and third spectral wavelength ranges. The reflection of incident solar radiation prevents the passive radiant cooler 1 and hence the building 9 from heating up. The emission of infrared radiation and the resultant release of heat leads to cooling of the building roof 10 provided with the passive radiant cooler 1 and consequently also to cooling of the building 9 itself.
[0082] Example 2: Cooling by a Passive Radiant Cooler 1
[0083] FIG. 15 shows a diagram showing the cooling of the building 9 by way of example by an outdoor experiment. In this outdoor experiment, a simple petri dish without a lid was covered with a thin polyethylene (PE) clingfilm having a thickness of 13 m thickness, which serves as convection barrier. The PE clingfilm ensures limited convection losses between a sample to be examined, disposed in the petri dish, and the atmosphere outside the petri dish. The sample in the inner region of the was fixed on a small block of Styropor with a small piece of double-sided adhesive tape in order to ensure minimal convection losses. The sample is the second working example of the passive radiant cooler 1 from FIG. 2. Continuous external temperature measurements were conducted using a first calibrated Pt100 sensor of class A with 4-wire configuration [Heraeus Nexensos M222, Kleinostheim, Germany], also called Pt100 temperature sensor. The first Pt100 sensor was positioned between the Styropor block and the sample. In order to assure a good physical connection between the sample and the first Pt100 sensor, a little thermal paste was applied between the first Pt100 sensor and the sample. The ambient temperature was measured by means of a second Pt100 sensor, which was positioned freely suspended alongside the sample in the petri dish. The Pt100 sensors were connected to an Agilent 34972A LXI data recording unit that reads out the temperature every 5 seconds. The data recording unit was connected to a laptop running a Python script in order to detect and to store the measured temperature from all sensors. The petri dish was then secured with double-sided adhesive tapes to an upturned glass beaker, i.e. to the base of the upturned glass beaker, in order to keep it clear of any surface. The petri dish was arranged in such a way that its base was aligned parallel to the sky without any tracking of the sun, shielding or emitting mounts. Multiple measurements were conducted on a building roof at the Deutsches Zentrum fr Luft- and Raumfahrt (DLR, German Aerospace Centre), Institute of Networked Energy Systems (N530905.1 E81001.1) on Oct. 10, 2020. For the continuous measurements of temperature, a day with a clear blue sky was chosen. The global horizontal irradiation intensity resulting from the solar radiation was collected by a pyranometer at the DLR's permanent weather station that is 166 m away from the site where we conducted the present outdoor experiment. The diagram from FIG. 15 shows the ambient temperature measured by the second Pt100 sensor as a function of the time of day during the outdoor experiment (thick dotted line, labeled as Ambient temperature). In addition, this diagram shows the sample temperature of the sample measured by the first Pt100 sensor, likewise as a function of the time of day during the outdoor experiment (dashed and dotted line, labeled as Sample temperature). The diagram also shows the incident power of solar radiation as a function of time of day during the outdoor experiment (thin dotted line, referred to as incident solar power). The difference between the ambient temperature and the sample temperature is likewise shown in the diagram as a function of the time of day during the outdoor experiment (solid line, labeled as Temperature differential), and illustrates that the sample, i.e. the second working example of the passive radiant cooler 1 from FIG. 2, has a colder temperature by an average of 5 C. than the environment. At maximum, the sample, i.e. the second working example of the passive radiant cooler 1 from FIG. 2, had a lower temperature by a maximum of 6.8 C. than the environment.
