CN111575823A - Design method of radiation refrigeration fiber and radiation refrigeration fiber - Google Patents
Design method of radiation refrigeration fiber and radiation refrigeration fiber Download PDFInfo
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Abstract
A design method of radiation refrigeration fiber and the radiation refrigeration fiber comprise: s1, selecting micro-nano particle materials with different particle sizes in a preset range, and calculating scattering efficiency curves of the micro-nano particle materials with different particle sizes; s2, forming a plurality of equivalent structures, and calculating the reflectivity data of the equivalent structures corresponding to the visible-near infrared bands; s3, fitting the reflectivity data obtained in the step S2 according to a preset reflectivity formula, and further extrapolating to obtain more reflectivity data; and S4, calculating the weighted reflectivity of each equivalent structure to the visible-near infrared band under the preset solar spectrum according to the reflectivity data obtained by extrapolation in S3, and obtaining the optimal particle size of the micro-nano particles under different thicknesses according to the weighted reflectivity. According to the design method, the optimal particle size of the filled micro-nano particles is rapidly determined within the range of the preset material and the preset fiber thickness, so that the highest solar spectrum reflection efficiency is realized under the preset volume percentage.
Description
Technical Field
The invention relates to the field of radiation refrigeration, in particular to a radiation refrigeration fiber and a design method thereof.
Background
The energy promotes the civilized development and progress, and the modern life enjoyed by the people is not based on the energy consumption. However, the high consumption of energy causes excessive emission of greenhouse gases, which leads to global warming and disturbs the climate balance. Global warming not only presents a healthy high temperature extreme weather threatening humans, but also limits the development of industrial labor and productivity. According to the statistics of the U.S. department of energy and the national energy agency, building space heating and cooling consumes 15% of the electricity worldwide and generates 10% of the greenhouse gas emissions worldwide, which is a major part of residential and commercial energy consumption. With the increasing "greenhouse effect" and global warming, the energy demand for refrigeration is increasing, and by 2050 the demand for cooling systems is expected to increase by 10 times, which results in a large energy consumption and further poses a huge challenge to human sustainability. In the face of the enormous energy consumption problem, it is desirable to seek an efficient and economical way to provide localized cooling to the human body without wasting excess electricity throughout the building, and to achieve low energy consumption and low pollution personal thermal management.
The radiation refrigeration technology realizes high reflectivity of an object in a wavelength range of 0.3-2.5 mu m under solar radiation through material selection and structure design, greatly blocks heat input through solar radiation, and realizes high emissivity in a human body thermal radiation waveband and a 7-14 mu m waveband, thereby maximizing the thermal radiation loss of a human body, effectively realizing the purpose of zero energy consumption cooling, and having important energy-saving significance.
Compared with the prior common film state, the fiber state radiation refrigeration material has the air and moisture permeability and flexibility, and is more suitable for human body heat management and application of living goods such as ceilings, car covers, sunshade umbrellas and the like. The professor group Cui of Stanford university in America utilizes industrial extrusion and phase separation processes to prepare the PE fiber with air holes of 100nm-1000nm, the average infrared transmittance of the fabric manufactured by the PE fiber is over 70 percent, the opacity reaches 90 percent, the skin temperature of the PE fabric covering the nanometer holes is 2.3 ℃ lower than that of the PE fabric covering the cotton fabric during testing, and opaque personal heat management can be realized. However, the infrared high-transmittance fiber adopted by the method needs the refrigerated surface to have high emissivity in an infrared light band by the refrigeration principle, and the application range of the fiber is limited to a certain extent.
In the high emissivity refrigerant fiber, the Yu professor of university of Columbia, USA, also uses phase separation method to draw out the fiber with diameter of about 100 μm and air hole section with hole density of 17 μm-2The fiber has a solar reflectance of 93% and an infrared emissivity of 0.91. However, limited to the manufacturing process, this method results in thicker fibers, which reduces the wearing comfort. And the mode of scattering sunlight by adopting the air holes needs a phase separation process, the size of the air holes is not easy to control, and the flow is relatively complex. Another method, such as a radiation refrigeration fiber membrane disclosed in Chinese patent publication No. CN110042564A, and its preparation method and application, is to prepare high-emission radiation particle SiO with good monodispersity2The microspheres are uniformly dispersed in a polymer, such as PE, PA6, PMMA and PVDF solution, and a fiber membrane is obtained through electrostatic spinning, so that the fiber membrane has the capability of cooling the surface of human skin by radiation. Also a radiation refrigeration fiber as disclosed in Chinese patent publication No. CN110685031A, its preparation method and application, such as TiO2And ZnO and the like are mixed with polymer substrates such as PMMA, PE and the like, and the mixture is subjected to melt spinning and drawing to obtain the radiation refrigeration fiber, wherein the linear density of the fiber is 1dtex-20dtex, the filler particle size is preferably 3 mu m-5 mu m, the visible-near infrared light reflectivity can reach more than or equal to 60 percent, and the atmospheric window emissivity of 7 mu m-14 mu m is more than or equal to 80 percent. However, the structure of micron-sized medium particles and a polymer substrate adopted by the method is not ideal in sunlight wave band reflection effect and cannot achieve good daytime radiation refrigeration effect. Furthermore, the above-mentioned methods lack optimization of particle size, fabric thickness, and make the product cost or efficiency deficient.
In summary, a fiber structure which is compatible with the prior art, simple in structure and efficient, and a design method for optimizing the fiber structure are lacked, so that the fiber has the advantages of excellent radiation refrigeration performance, low cost, high production efficiency and the like.
Disclosure of Invention
In view of the above, the invention provides a design method of a radiation refrigeration fiber and the radiation refrigeration fiber, so as to overcome the problems of complex preparation method, high cost, poor effect and the like in the existing radiation refrigeration fiber technology, and obtain a human body cooling fabric with radiation refrigeration performance and wearable performance.
In order to solve the above problems, the present invention mainly provides the following technical solutions: a design method of radiation refrigeration fiber comprises the following steps:
s1, selecting micro-nano particles with different particle sizes in a preset range according to the preset micro-nano particle material, the preset polymer substrate material and the preset volume percentage of the micro-nano particles, calculating scattering efficiency curves of the micro-nano particles with different particle sizes, and selecting the particle size range of the micro-nano particles with scattering efficiency peaks in visible-infrared bands as an optional range;
s2, combining micro-nano particles with different particle sizes in an optional range with a preset polymer substrate material and the preset volume percentage of the micro-nano particles to form a plurality of equivalent structures, and calculating reflectivity data of the equivalent structures corresponding to a visible-near infrared band in a first thickness range;
s3, fitting the reflectivity data obtained by calculation in the step S2 by using a preset reflectivity formula, and further extrapolating to obtain reflectivity data of the equivalent structures in a second thickness range;
and S4, calculating the weighted reflectivity of each equivalent structure to the visible-near infrared band under the preset solar spectrum according to the reflectivity data of the equivalent structures in the second thickness range obtained in the step S3, and obtaining the optimal particle size of the micro-nano particles under different thicknesses according to the weighted reflectivity.
Preferably, the step S4 is followed by a verification step S5, and the step S5 includes obtaining a plurality of radiation refrigerating fibers with different thicknesses according to the optimal particle size obtained in the step S4, the volume percentages of the predetermined micro-nano particle material, the predetermined polymer base material and the predetermined micro-nano particles, and measuring the reflectivity of the plurality of radiation refrigerating fibers with different thicknesses in the visible-near infrared band and the emissivity in the mid-infrared band.
Preferably, in step S1, the scattering ratios of the micro-nano particles with different particle diameters are shown as follows:
wherein σeffFor particle scattering efficiency, σ is the scattering cross-section of the particle, scattering cross-section (m)2) Total scattered energy (W)/incident light intensity (W/m)2) Where A denotes the maximum geometric cross-section of the particle, and for the spherical particle model, A ═ π R2Wherein R is the radius of the sphere.
Preferably, in step S3, the predetermined reflectance formula is
D is the particle size of the micro-nano particles, lambda is the wavelength, h is the thickness of the equivalent structure, and R (D, lambda, h) is the reflectivity; m, N is a constant needing fitting, and the reflectivity formula represents the relation between the reflectivity and the particle size, wavelength and equivalent structure thickness of the micro-nano particles.
Preferably, in step S4, the weighted reflectivity is:
wherein Isun(λ) is the predetermined solar spectrum, λ1And λ2Respectively, the lower and upper limits of the weighted wavelength range.
Preferably, the predetermined range is 0.2 μm to 3 μm.
Preferably, the visible-near infrared band is 0.4-2.5 μm, and the mid-infrared band is 7-14 μm
Preferably, the first thickness ranges from 3 μm to 30 μm, and the second thickness ranges from 100 μm to 600 μm.
A radiation refrigeration fiber comprises a polymer substrate and micro-nano particles, wherein the micro-nano particles are randomly and uniformly distributed in the polymer substrate according to a preset volume percentage, visible-near infrared light is scattered by the radiation refrigeration fiber through the micro-nano particles, mid-infrared light is radiated by the polymer substrate, and the particle size of the micro-nano particles is selected according to the steps of the design method.
Preferably, the diameter of the radiation refrigerating fiber is 3 μm to 600 μm, and the predetermined volume percentage is 5% to 20%.
Preferably, the polymer substrate is made of a material which has high transmittance in a visible-near infrared band and high emissivity in a middle infrared band, and the micro-nano particle material has high reflectivity in the visible-near infrared band.
Preferably, the material of the polymer substrate comprises one or a mixture of at least two of PMMA, F-PMMA, PVDF, PET, PVA and PDMS; the material of the micro-nano particles comprises TiO2、ZnS、ZnO、SiC、BaSO4And Si3N4Or a combination of at least two thereof.
By the technical scheme, the technical scheme provided by the invention at least has the following advantages:
1. the polymer substrate material designed by the invention is combined with the radiation refrigeration fiber structure of the micro-nano particle material, complex manufacturing steps are not needed, the concentration and the particle size of the micro-nano particles as scattering media can be accurately controlled, parameters such as the concentration and the size of the micro-nano particle material cannot be changed in the fiber preparation process, the structure is stable, and the visible-near infrared light reflection performance and the emission performance of a middle infrared band are better.
2. According to the design method, the optimal particle size of the filled micro-nano particles is rapidly determined within the range of the preset material and the preset fiber thickness, so that the highest solar spectrum reflection efficiency is realized under the preset volume percentage.
Drawings
FIG. 1 is a schematic view of a radiation-cooled fiber according to an embodiment of the present invention.
Fig. 2 is a scattering efficiency curve of micro-nano particles with different particle diameters in the design method of the radiation refrigeration fiber according to the embodiment of the invention.
FIG. 3 is a schematic diagram of an equivalent structure of a radiation-cooled fiber according to an embodiment of the present invention.
Fig. 4 is a fitting curve diagram of reflectivity data of equivalent structures with different thicknesses under the same wavelength and the same micro-nano particle size in the design method of the embodiment of the invention.
Fig. 5 is a schematic diagram of an equivalent structure in the design method according to the embodiment of the present invention, showing the solar spectrum weighted reflectivity in the visible-near infrared band at different fiber thicknesses and different micro-nano particle sizes.
Fig. 6 is a graph of reflectance in the visible-near infrared band and emissivity in the mid-infrared band for the radiation refrigeration fibers of examples 1, 2, and 3 of the present invention.
Fig. 7 is a reflectance curve in the visible-near infrared band and an emissivity curve in the mid-infrared band for the radiation refrigeration fibers of example 2 of the present invention and additional comparative examples 1, 2.
Detailed Description
Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The invention provides a radiation refrigeration fiber, as shown in figure 1, the radiation refrigeration fiber comprises a polymer substrate 1 and micro-nano particles 2 randomly distributed in the substrate, the volume percentage of the micro-nano particles in the radiation refrigeration fiber is 5% -20%, the diameter of the radiation refrigeration fiber is 3-600 μm, the radiation refrigeration fiber scatters visible-near infrared light by using the micro-nano particles, particularly visible-near infrared light in a wave band of 0.4-2.5 μm, and radiates infrared light by using the polymer substrate, particularly mid-infrared light in a wave band of 7-14 μm.
Preferably, the polymer substrate satisfies high transmittance in the visible-near infrared band ranging from 0.4 μm to 2.5 μm and at the same time has high absorptivity (emissivity) characteristic in the mid-infrared band ranging from 7 μm to 14 μm, and a material that can be used is a thermoplastic polymer having high transmittance in the visible-near infrared band and high absorptivity in the mid-infrared band ranging from 7 μm to 14 μm, such as one or a mixture of at least two of PMMA, F-PMMA, PVDF, PET, PVA, PDMS, etc.
Preferably, the micro-nano particles have high reflectivity in a visible-near infrared band of 0.4-2.5 μm, and the shape of the micro-nano particles can be round, oval or irregular. The micro-nano particle material comprises TiO2、ZnS、ZnO、SiC、BaSO4、Si3N4Or a combination of at least two thereof.
The design method of the radiation refrigeration fiber comprises the following steps:
s1: selecting micro-nano particles with different particle diameters in a preset range according to a preset micro-nano particle material, a preset polymer substrate material and a preset volume percentage, calculating a scattering efficiency curve of the micro-nano particles with different particle diameters, and selecting a particle diameter size range of the micro-nano particles with scattering efficiency peaks in a visible-near infrared band as an optional range.
S2: combining micro-nano particles with different sizes in an optional range with a predetermined polymer substrate material and a predetermined volume percentage to form a plurality of equivalent structures, and calculating reflectivity data of the plurality of equivalent structures in a visible-near infrared band within a first thickness range. The first thickness range is a smaller range, thinner dimension, and the first thickness range is the thickness of the equivalent structure, i.e., the thickness of the radiation refrigeration fiber.
S3: the data obtained from the preliminary calculation in S2 is fitted using a predetermined reflectance formula and further extrapolated to obtain reflectance data for a second thickness range. The second thickness range is a larger thickness range, typically larger than the first thickness range, and may encompass the first thickness range, either partially overlapping the first thickness range, or not overlapping at all. The reflectivity formula reflects the reflectivity of the equivalent structure in a visible-near infrared band and the relation between the thickness, the wavelength and the particle size of the micro-nano particles of the equivalent structure.
S4: and calculating the weighted reflectivity of the visible-near infrared band under the preset solar spectrum according to the reflectivity data in the second thickness range obtained in the step S3, and obtaining the optimal particle size of the micro-nano particles under the common thickness according to the weighted reflectivity.
The weighted reflectivity is weighted according to the wavelength in the reflectivity formula, namely the weighted reflectivity of the visible-near infrared band is calculated under the preset solar spectrum to obtain the weighted reflectivity, so that the weighted reflectivity is related to the thickness of the equivalent structure and the particle size of the micro-nano particles, and different equivalent structures, different weighted reflectivities and the particle size of the corresponding micro-nano particles can be obtained from the weighted reflectivity.
And after the step S4, a verification step S5 may be further included to perform verification, the optimal particle size obtained in the step S4 is combined with the predetermined micro-nano particle material, the predetermined polymer substrate material and the predetermined volume percentage of the micro-nano particles, fiber thicknesses of different sizes are selected and combined to obtain radiation refrigeration fibers of different thicknesses, and the reflectivity of the plurality of radiation refrigeration fibers in a visible-near infrared band and the emissivity in a middle infrared band are measured, so as to determine whether the requirements are met.
The visible-near infrared band can be selected from a band of 0.4-2.5 μm, or other bands within the visible-near infrared band. The infrared band can be selected from 7-14 μm band or other bands in the infrared band.
Preferably, in step S1, the predetermined range is generally a range of particle sizes of micro-nano particles that can be selected by design, and is generally selected to be 0.2 μm to 3 μm, and within the predetermined range, a plurality of micro-nano particles with a first interval, where the first interval is about 0.25 μm, are generally selected, and then scattering efficiency curves of the micro-nano particles with different particle sizes are calculated respectively.
More specifically, in the step S1, the particle size of the micro-nano particles is scanned within a predetermined range, scattering cross-section curves of the micro-nano particles with different particle sizes are calculated, and a scattering efficiency curve is further calculated by using the scattering cross-section.
Wherein σeffFor particle scattering efficiency, σ is the scattering cross-section of the particle, the scattering cross-section of the particle (m)2) Total scattered energy (W)/incident light intensity (W/m)2) Where A denotes the maximum geometric cross-section of the particle, and for spherical particles, A ═ π R2Wherein R is the radius of the sphere. Selecting the particle size of the micro-nano particles with the scattering efficiency peak value within a visible-near infrared band of 0.4-2.5 μm as an optional range.
For example, the micro-nano particle material is selected to be TiO2When the polymer substrate material is PMMA, as shown in fig. 2, a scattering efficiency curve of micro-nano particles with different particle sizes is shown, the abscissa is the wavelength, the ordinate is the scattering efficiency, and each line represents the particle size of different micro-nano particles, so that the particle size of the micro-nano particles with the scattering efficiency peak value within a band of 0.4 μm to 2.5 μm is 0.2 μm to 1.7 μm, that is, the optional range.
More specifically, in the step, software simulation can be used, the three-dimensional spherical particles are constructed based on the FDTDsolutions of the time domain finite difference method, namely the micro-nano particles in the step, a full-field scattered field light source (TFSF) is selected as the light source, so that part of light of the light source which is not reflected cannot enter a power detector, the wavelength of the light source is 0.4-2.5 microns, namely, light of a visible light-near infrared band is selected as the light source, convenient conditions are set to be a Perfect Matching Layer (PML), light is not reflected by a test boundary, and further, the test space is equal to an infinite space. A cross-sectional analysis group, i.e. a power detector, is added to measure the absolute value of the power of the scattered light.
In step S2, the micro-nano particles with different particle sizes in the selectable range are divided into a plurality of types according to a second interval, where the second interval may be 0.1 μm, and a plurality of equivalent structures are formed by combining a predetermined polymer base material and a predetermined volume percentage.
As shown in fig. 3, the thickness range of the plurality of equivalent structures is selected to be 3 μm to 30 μm, i.e., the first thickness range. In the first thickness range, the equivalent structure 3 may be a three-dimensional cube constructed by using FDTD sources based on a finite difference time domain method, and micro-nano particles 4 with the same diameter are randomly distributed in the three-dimensional cube. The volume percentage of the micro-nano particles 4 in the equivalent structure 3 is a fixed value, namely the preset volume percentage.
For the plurality of equivalent structures, the reflectance in the visible-near infrared band is calculated. As shown in fig. 4, the data shown in the figure is a reflectance curve of equivalent structures with the same micro-nano particle size to the same wavelength, where the abscissa is the equivalent structure thickness and the ordinate is the reflectance.
In step S3, fitting the reflectivity data obtained in step S2, specifically, fitting a curve by using the reflectivities of the same micro-nano particle size, the same wavelength, and different equivalent structure thicknesses as a data set, where the fitting is the following reflectivity formula:
d is the particle size of the micro-nano particles, lambda is the wavelength, h is the thickness of the equivalent structure, and R (D, lambda, h) is the reflectivity; m, N is the constant to be fitted. The reflectivity formula represents the relation between the reflectivity and the particle size, wavelength and equivalent structure thickness of the micro-nano particles. After fitting to obtain the M and N, the reflectance data can be extrapolated to a larger range, i.e., a second thickness range, of the equivalent structure. For example, the second thickness is in the range of 100 μm to 600 μm. The second thickness range may include the first thickness range, may partially overlap the first thickness range, or may not overlap the first thickness range. The skilled person can choose it at will according to needs.
In step S4, weighting is performed in the visible-near infrared band, specifically 0.4 μm to 2.5 μm, within the second thickness range, to obtain the following weighted reflectance under the solar spectrum:
wherein Isun(λ) is the predetermined solar spectrum, which may be the AM15 solar spectrum, and is the intensity of the different light produced by the actual sunlight and its angle of incidence. Lambda [ alpha ]1And λ2For lower and upper weighted wavelength ranges, respectively, e.g. visible-near infrared bands, lambda1Is 0.4 μm, λ2At 2.5 μm, the above equation becomes:
according to the formula (3), the weighted reflectivity under the conditions of different micro-nano particle diameters D and different thicknesses h of equivalent structures can be obtained, and the optimal micro-nano particle diameter D in a certain material thickness range can be determined. For example, as shown in fig. 5, the optimal particle size of the micro-nano particles is 0.6 μm within the thickness of the radiation refrigeration fiber material of 200 μm to 600 μm shown in the figure. As shown in fig. 5, the diagram is a schematic diagram of the solar spectrum weighted reflectivity of the visible-near infrared band under different fiber thicknesses and different micro-nano particle sizes. As can be seen from the figure, in the range of the thickness of the radiation refrigeration fiber being 200-600, when the particle size of the corresponding micro-nano particles is 0.6 μm, the sunlight weighted reflectivity is the highest regardless of the thickness.
Therefore, through the steps, under the conditions of a certain preset volume percentage, a certain micro-nano particle material and a certain polymer substrate material, the optimal micro-nano particle size corresponding to different thicknesses of the refrigeration fiber material is obtained.
After the step S4, a verification step S5 may be further included, in which the software simulation of the radiation refrigeration fiber is performed on the parameters determined in the above steps S1 to S4, and then the actual reflectance of the radiation refrigeration fiber in the 0.4 μm to 2.5 μm wavelength band and the ir emissivity curve in the 7 μm to 14 μm wavelength band are measured to see whether the expected requirements are met.
For example, the simulation analysis is specifically carried out on an equivalent model of the fabric formed by the radiation refrigeration fibers by adopting a finite difference time domain numerical method, FDTD sources are utilized to construct a three-dimensional PMMA cube with a specific thickness, and TiO with the diameter of 600nm is randomly distributed in the three-dimensional PMMA cube2And (3) granules. The light source selects plane wave, which is incident from z direction, the wavelength is 0.4 μm-2.5 μm, the boundary condition of x and y direction is periodic boundary condition, the z direction is Perfect Matching Layer (PML), and adds power monitor to calculate the reflectivity. Changing the wavelength of the incident plane wave to 7-14 μm, and simulating again to obtain the corresponding emissivity.
The first embodiment is as follows:
the polymer substrate material is PMMA, and the micro-nano particle material is TiO2According to the method, the optimal particle size of the micro-nano particles is 600nm, the volume fraction of the micro-nano particles in the fiber is determined to be 10%, the radiation refrigeration fiber is obtained, and the thickness of the fabric formed by the fiber is 50 micrometers.
A three-dimensional PMMA cube was constructed using FDTD Soulions, the thickness of which was determined to be 50 μm, in which TiO with a volume fraction of 10% and a diameter of 600nm was randomly distributed2And (3) granules. By using the simulation setup in step S5, the visible-near infrared light reflectance curve and the emissivity of the fabric with 7 μm to 14 μm wavelength band are calculated, as shown by the chain line in fig. 6.
According to the reflectivity and emissivity curves, the corresponding solar spectrum weighted reflectivity is calculated to be 0.84, and the average emissivity of an atmospheric window, namely the average emissivity of 7-14 mu m wave band is 0.93.
Example two:
the polymer substrate material is PMMA, and the micro-nano particle material is TiO2According to the method, the optimal particle size of the micro-nano particles is 600nm, the volume fraction of the micro-nano particles in the fiber is determined to be 10%, the radiation refrigeration fiber is obtained, and the thickness of the fabric formed by the fiber is 100 micrometers.
A three-dimensional PMMA cube was constructed using FDTD sources, the thickness of which was determined to be 100 μm, in which the PMMA cube was randomly orientedTiO with 10% volume fraction distribution and 600nm diameter2And (3) granules. Using the simulation setup described in step S5, the visible-near infrared light reflectance curve and the 7 μm-14 μm waveband emissivity of the fabric made of the fibers are calculated, as shown by the dotted line in fig. 6 and the solid line in fig. 7.
According to the reflectivity and emissivity curves, the corresponding solar spectrum weighted reflectivity is calculated to be 0.92, and the average emissivity of an atmospheric window, namely the average emissivity of 7-14 mu m wave band is 0.95.
Example three:
the polymer substrate material is PMMA, and the micro-nano particle material is TiO2According to the method, the optimal particle size of the micro-nano particles is 600nm, the volume fraction of the micro-nano particles in the fiber is determined to be 10%, the radiation refrigeration fiber is obtained, and the thickness of the fabric formed by the fiber is 200 micrometers.
A three-dimensional PMMA cube was constructed using FDTD Soulions, the thickness of which was determined to be 200 μm, in which TiO with a volume fraction of 10% and a diameter of 600nm was randomly distributed2And (3) granules. By using the simulation setup described in step S5, the visible-near infrared light reflectance curve and the emissivity of the fabric made of the fibers in the 7 μm-14 μm waveband are calculated, as shown by the solid line in fig. 6.
According to the reflectivity and emissivity curves, the corresponding solar spectrum weighted reflectivity is calculated to be 0.96, and the average emissivity of an atmospheric window, namely the average emissivity of 7-14 mu m wave band is 0.96.
Comparative example 1:
selecting a micro-nano particle material with the particle size of 300nm, a polymer substrate material of PMMA, and a micro-nano particle material of TiO2And determining the volume fraction of the micro-nano particles in the fiber to be 10% to obtain the radiation refrigeration fiber, wherein the thickness of the fabric formed by the fiber is 100 micrometers.
The simulation process of the radiation refrigeration fiber is also implemented by the step of S5, and a visible-near infrared light reflectivity curve and a 7-14 μm waveband emissivity of the fabric formed by the fiber are calculated, as shown by a dotted line in FIG. 7.
The corresponding solar spectrum weighted reflectivity is calculated to be 0.88, and the average emissivity of the atmospheric window is 0.95.
Comparative example 2:
selecting micro-nano particles with the particle size of 1.6 mu m, wherein the polymer substrate material is PMMA, and the micro-nano particle material is TiO2And determining the volume fraction of the micro-nano particles in the fiber to be 10% to obtain the radiation refrigeration fiber, wherein the thickness of the fabric formed by the fiber is 100 micrometers.
The simulation process of the radiation refrigeration fiber is also implemented by the step S5, and the visible-near infrared light reflectivity curve and the 7-14 μm waveband emissivity of the fiber are calculated, as shown by the chain line in FIG. 7.
The corresponding solar spectrum weighted reflectivity is calculated to be 0.80, and the average emissivity of the atmospheric window is 0.95.
The above examples 1 to 4 and comparative examples 1 to 2 were tabulated to obtain the following table 1.
Table 1:
as can be seen from Table 1, in the embodiment obtained by the design method of the invention, under the condition of proper refrigeration fiber thickness (>100 μm), the reflectivity of visible light and near infrared light can reach more than 90% theoretically, and the average emissivity of 7 μm-14 μm wave band can reach 95%, so that the embodiment has good radiation refrigeration effect.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in the process, method, article, or apparatus that comprises the element.
The above are merely examples of the present application and are not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.
Claims (12)
1. A design method of radiation refrigeration fiber comprises the following steps:
s1, selecting micro-nano particles with different particle sizes in a preset range according to the preset micro-nano particle material, the preset polymer substrate material and the preset volume percentage of the micro-nano particles, calculating scattering efficiency curves of the micro-nano particles with different particle sizes, and selecting the particle size range of the micro-nano particles with scattering efficiency peaks in visible-infrared bands as an optional range;
s2, combining micro-nano particles with different particle sizes in an optional range with a preset polymer substrate material and the preset volume percentage of the micro-nano particles to form a plurality of equivalent structures, and calculating reflectivity data of the equivalent structures corresponding to a visible-near infrared band in a first thickness range;
s3, fitting the reflectivity data obtained by calculation in the step S2 by using a preset reflectivity formula, and further extrapolating to obtain reflectivity data of the equivalent structures in a second thickness range;
and S4, calculating the weighted reflectivity of each equivalent structure to the visible-near infrared band under the preset solar spectrum according to the reflectivity data of the equivalent structures in the second thickness range obtained in the step S3, and obtaining the optimal particle size of the micro-nano particles under different thicknesses according to the weighted reflectivity.
2. The design method of claim 1, wherein: the step S4 is followed by a verification step S5, and the step S5 includes obtaining a plurality of radiation refrigeration fibers with different thicknesses according to the optimal particle size obtained in the step S4, a predetermined micro-nano particle material, a predetermined polymer base material, and a predetermined volume percentage of micro-nano particles, and measuring the reflectivity of the plurality of radiation refrigeration fibers with different thicknesses in a visible-near infrared band and the emissivity in a middle infrared band.
3. The design method of claim 1, wherein: in the step S1, the scattering rates of the micro-nano particles with different particle diameters are shown by the following formula:
wherein σeffFor particle scattering efficiency, σ is the scattering cross-section of the particle, scattering cross-section (m)2) Total scattered energy (W)/incident light intensity (W/m)2) And a represents the maximum geometric cross section of the particle.
4. The design method of claim 1, wherein: in the step S3, the predetermined reflectance formula is
D is the particle size of the micro-nano particles, lambda is the wavelength, h is the thickness of the equivalent structure, and R (D, lambda, h) is the reflectivity; m, N is a constant needing fitting, and the reflectivity formula represents the relation between the reflectivity and the particle size, wavelength and equivalent structure thickness of the micro-nano particles.
5. The design method of claim 1, wherein: in step S4, the weighted reflectivity is:
wherein Isun(λ) is the predetermined solar spectrum, λ1And λ2Respectively, the lower and upper limits of the weighted wavelength range.
6. The design method of claim 1, wherein: the predetermined range is 0.2 μm to 3 μm.
7. The design method of claim 1, wherein: the visible-near infrared band is 0.4-2.5 μm, and the mid-infrared band is 7-14 μm.
8. The design method of claim 1, wherein: the first thickness is in the range of 3 μm to 30 μm, and the second thickness is in the range of 100 μm to 600 μm.
9. The radiation refrigeration fiber comprises a polymer substrate and micro-nano particles, wherein the micro-nano particles are randomly and uniformly distributed in the polymer substrate according to a preset volume percentage, and the radiation refrigeration fiber is characterized in that: the radiation refrigeration fiber is characterized in that visible-near infrared light is scattered by micro-nano particles, mid-infrared light is radiated by a polymer substrate, and the particle size of the micro-nano particles is selected according to the steps of the design method of any one of claims 1 to 8.
10. A radiation-cooled fiber as set forth in claim 8, wherein: the diameter of the radiation refrigeration fiber is 3-600 μm, and the predetermined volume percentage is 5-20%.
11. A radiation-cooled fiber as set forth in claim 10 wherein: the polymer substrate is made of a material which has high transmittance in a visible-near infrared band and high emissivity in a middle infrared band, and the micro-nano particle material has high reflectivity in the visible-near infrared band.
12. A radiation-cooled fiber as set forth in claim 11, wherein: the material of the polymer substrate comprises one or a mixture of at least two of PMMA, F-PMMA, PVDF, PET, PVA and PDMS; the material of the micro-nano particles comprises TiO2、ZnS、ZnO、SiC、BaSO4And Si3N4Or at leastA combination of the two.
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