阅读说明：本技术 一种辐射制冷织物及其设计方法 (Radiation refrigeration fabric and design method thereof ) 是由 马耀光 片思杰 王铸宁 于 2021-07-02 设计创作，主要内容包括：一种辐射制冷织物,包括层叠的第一层结构和第二层结构,所述第一层结构为反射膜,所述第二层结构为织物层,并且所述第二层结构由复合纤维编织而成,所述复合纤维包括高分子基材和分散于所述高分子基材中的微纳颗粒。该辐射制冷织物的设计方法,包括S1：确定所述第二层结构中微纳颗粒的最佳粒径；S2：确定所述第二层结构的第二厚度为最佳厚度。本发明所述的辐射制冷织物弥补了以往辐射制冷织物固有的漏光严重、紫外吸收严重等问题,其太阳光谱反射率大于90％,中红外波段发射率大于90％。本发明的设计方法,能快速确定填充的微纳颗粒的最佳粒径以及织物的最佳厚度,以实现在预定的体积百分数下,最佳的太阳光谱反射效率以及辐射制冷功率。(The utility model provides a radiation refrigeration fabric, is including range upon range of first layer structure and second floor structure, first layer structure is the reflectance coating, the second floor structure is the fabric layer, and the second floor structure is woven by composite fiber and is formed, composite fiber include the polymer substrate with disperse in receive the nano-particle in the polymer substrate. The design method of the radiation refrigeration fabric comprises the following steps of S1: determining the optimal particle size of micro-nano particles in the second layer structure; s2: determining a second thickness of the second layer structure as an optimal thickness. The radiation refrigeration fabric provided by the invention makes up the inherent problems of serious light leakage, serious ultraviolet absorption and the like of the conventional radiation refrigeration fabric, and has a solar spectrum reflectivity of more than 90% and a mid-infrared band emissivity of more than 90%. The design method can rapidly determine the optimal particle size of the filled micro-nano particles and the optimal thickness of the fabric so as to realize the optimal solar spectrum reflection efficiency and radiation refrigeration power under the preset volume percentage.)

1. A radiation-cooled fabric comprising a first layer structure and a second layer structure which are laminated, wherein:

the first layer structure is a reflective film, and the first layer structure can reflect ultraviolet light;

the second layer structure is a fabric layer, can reflect visible-near infrared light wave bands and emit mid-infrared wave bands, is formed by weaving composite fibers, and comprises a polymer base material and micro-nano particles dispersed in the polymer base material.

2. A radiation-cooled fabric as claimed in claim 1, wherein: the first layer structure is a polymer porous aerosol film, and the polymer can be one or a mixture of polymethyl methacrylate (PMMA), polylactic acid (PLA), polyvinyl alcohol (PVA), polyethylene terephthalate (PET), Polydimethylsiloxane (PDMS), Polytetrafluoroethylene (PTFE), Polyethylene (PE), polypropylene (PP), Polyamide (PA), polymethylpentene (TPX) or polyvinylidene fluoride (PVDF);

the polymer base material in the composite fiber of the second layer structure comprises at least one of polymethyl methacrylate (PMMA), polylactic acid (PLA), polyvinyl alcohol (PVA), polyethylene terephthalate (PET), Polydimethylsiloxane (PDMS), Polytetrafluoroethylene (PTFE), polypropylene (PP), polymethylpentene (TPX) or polyvinyl fluoride (PVDF); the micro-nano particles in the composite fiber of the second layer structure comprise titanium dioxide (TiO)₂) Zinc sulfide (ZnS), zinc oxide (ZnO), silicon carbide (SiC), barium sulfate (BaSO)₄) Silicon nitride (Si)₃N₄) And calcium sulfate (CaSO)₄) At least one of (1).

3. A radiation-cooled fabric as claimed in claim 1, wherein: the first thickness of the first layer structure is 5-200 μm, and the second thickness of the second layer structure is 100-1000 μm;

the diameter range of the composite fiber of the second layer structure is 3-200 mu m, and the diameter range of the micro-nano particles in the composite fiber of the second layer structure is 0.05-5 mu m.

4. A method of designing a radiation-cooled fabric according to any of claims 1 to 3, comprising the steps of:

s1: according to the preset material of the first layer structure (1), the thickness of the first layer structure (1), the high molecular base material, the micro-nano particle material and the preset volume percentage (V) of the micro-nano particles_d) Determining the optimal particle size (D) of the micro-nano particles in the second layer structure (2);

s2: determining a second thickness of the second layer structure (2) as an optimum thickness (D) on the basis of the optimum particle diameter (D) and the above-mentioned predetermined parameters_f)。

5. The design method of claim 4, wherein: the step S1 specifically includes:

s11, determining a first optional range of the micro-nano particle size, obtaining a first group of optional particle sizes with first particle size intervals as intervals in the first optional range according to a predetermined micro-nano particle material in the first optional range, obtaining scattering efficiency curves corresponding to a plurality of micro-nano particles with different particle sizes in the first group of optional particle sizes, and selecting the particle size range of the micro-nano particles with scattering efficiency peaks in visible-near infrared bands as a second optional range;

s12, selecting a group of second optional particle sizes within the second optional range by taking the second particle size interval as an interval, and obtaining the reflectivity and transmittance data of the micro-nano particles with different particle sizes and the fabric with different thicknesses of the second layer structure in the solar radiation waveband by using a first numerical simulation model according to the micro-nano particles with different particle sizes in the group of second optional particle sizes;

s13, obtaining the reflectivity and transmittance data of the micro-nano particles with different particle sizes and the fabric with different second-layer structure thicknesses in the solar radiation wave band according to the obtained data in the step, obtaining the average reflectivity and average transmittance of the radiation refrigeration fabric to the ultraviolet-visible-near infrared wave band under the preset solar spectrum and different particle sizes of the micro-nano particles under different second-layer structure thicknesses and different particle sizes, and selecting the optimal particle size (D) of the micro-nano particles according to the average reflectivity.

6. The design method of claim 5, wherein: the step S2 specifically includes

S21, according to the optimal particle diameter (D) of the micro-nano particles and the preset volume percentage (V) of the micro-nano particles_d) Acquiring emissivity data of the radiation refrigeration fabric in the middle infrared band under different thicknesses of the second layer structure by using a second numerical simulation model;

s22, obtaining net refrigerating power (q) of the fabric with different thicknesses by using a third numerical simulation model according to emissivity data of the radiation refrigerating fabric in the middle infrared band under different thicknesses and the average reflectivity and the average transmissivity of the radiation refrigerating fabric of the micro-nano particles with the optimal particle size under the solar radiation band under different second-layer structure thicknesses obtained in the step S13_cool) Selecting the net refrigeration power (q)_cool) The maximum thickness is the optimal fabric thickness.

7. The design method of claim 5, wherein: in the above step S11, the scattering efficiency Q_sComprises the following steps:

σ_sthe scattering cross section of the micro-nano particles is the scattering cross section (m) of the micro-nano particles²) Total scattered energy (W)/incident light intensity (W/m)²) Wherein A represents the maximum geometric cross section of the particle, and for spherical micro-nano particles, A is pi R²Wherein R is the radius of the sphere;

in step S12, the first numerical simulation model is a numerical simulation model based on monte-carlo simulation;

in the step S13The average reflectivity (p)_fab,sun) Comprises the following steps:

wherein I_sun(λ) is the predetermined solar spectrum, ρ (D, λ, D)_f) Is the diameter D of micro-nano particles and the thickness of a fabric layer is D_fThe reflection spectrum of the lower fabric with respect to the wavelength λ, λ 1 and λ 2 being the lower and upper limits, respectively, of the weighted wavelength range, ρ (D, λ, D)_f) Fitting is performed on the reflectance data in step S12.

8. The design method of claim 6, wherein: in the step S21, the second numerical simulation model is to make the fabric equivalent to a random composite fiber model, and then measure emissivity, reflectivity and transmittance data of the fabric with the second layer structure of different thickness in the middle infrared band;

in step S22, the third numerical simulation model is a dimensionally stable thermal model.

9. The design method of claim 6, wherein:

the fabric is equivalent to a double-layer film structure by the first numerical simulation model, the first layer structure (1) is equivalent to a first layer (6), the second layer structure (2) is equivalent to a second layer (5), the thickness of the first layer (6) is regarded as 0, and the thickness (d) of the second layer (5) is regarded as_eff) With the thickness (d) of the second layer structure (2)_f) The correlation is made by the following equation,

where ρ is_f、ρ_pAnd ρ_sDensity of the second layer structure, micro-nano particles and polymer base material, V_dIs the volume percentage of the micro-nano particles.

10. The design method of claim 8, wherein: obtaining emissivity data of the fabric in a middle infrared band by using a second numerical simulation model, and determining the volume fraction (V) of composite fibers in the fabric layer_fiber) Diameter of composite fiber (D)_fiber) Equivalent refractive index (n) of composite fiber_eff)；

Wherein the diameter (D) of the composite fiber_fiber) Is a measured constant value;

wherein the volume fraction (V) of the composite fiber_fiber) Is defined by the formula:

ρ_f、ρ_pand ρ_sDensity of the second layer structure, micro-nano particles and polymer base material, V_dIs the volume percentage of the micro-nano particles;

equivalent refractive index of composite fiber

Wherein the equivalent dielectric constant ∈ is_effAnd equivalent permeability mu_effObtained from the following equation:

wherein N is the number of micro-nano particles in unit volume of the composite fiber,wherein V_dIs the volume percentage of the preset micro-nano particles, and R is the radius of the micro-nano particles;

∈_sis the dielectric constant, k, of the polymer substrate_hIs the wave number, mu, of light within the polymeric substrate₀Is the magnetic permeability in vacuum, wherein a1, b1 are obtained by the following formula:

where K2 π/λ is the wave number in vacuum, ψ_nAnd xi_nIs a Riccati-Bessel function,

wherein n is a natural number, m0 is the refractive index of the polymer base material, and m1 is the refractive index of the doped micro-nano particles.

11. The design method of claim 8, wherein: the third numerical simulation model comprises four layers of structures, namely a refrigerated object, an air layer with a certain thickness, a radiation refrigeration fabric and an external environment layer.

12. The design method of claim 11, wherein: the net refrigeration power (q)_cool) This can be solved by the following equation:

where ρ is_fab,ir，τ_fab,ir，α_fab,irAnd ε_fab,irRespectively represents the average reflectivity, the transmittance, the absorptivity and the emissivity of the fabric to the infrared radiation spectrum of a human body, I_hbIs a human body infrared radiation spectrum, and can utilize the existing data, R_MIR、T_MIR、E_MIRReflectance, transmittance and emissivity data for the second layer structure fabric of different thicknesses for the optimal particle size at mid-infrared band;

I_eis the atmospheric infrared radiation spectrum, I_e(λ)＝I_bb(T_amb,λ)·E_AT(λ)，I_bb(T_ambλ) is a temperature ofAmbient temperature T_ambBlack body radiation spectrum of time, E_AT(λ) is the atmospheric emissivity spectrum; rho_skin,sun、ρ_fab,sunAnd τ_fab,sunThe average reflectivity of the human body to the solar radiation spectrum, the average reflectivity of the fabric to the solar radiation spectrum and the average transmittance of the fabric to the solar radiation spectrum are represented; q. q.s_genIs human metabolic heat production power density; q. q.s_sunIs the total solar radiation power density; t is_skin、T_toAnd T_tiThe temperatures of the surface of the refrigerated object, the upper surface of the fabric and the lower surface of the fabric are respectively measured; t is t_fab、t_airRespectively, the thicknesses of the fabric layer and the air layer, wherein t can be considered as t since the thickness of the first aerosol film in the radiation refrigeration fabric is negligible_fabIs that d_f；k_fab、k_airRespectively, the thermal conductivity of the fabric and air; sigma 5.67 × 10^-8W·m^-2·K^-4Is the Spander-Boltzmann constant; q. q.s_rad,skin、q_rad,amb、q_rad,ti、q_cond,air、q_rad,to、q_convCalculated by the following formula:

q_conv＝h·(T_to-T_amb) (31)

wherein epsilon_ambAnd h is the air convection coefficient, which is the average infrared emissivity in the atmosphere.

Technical Field

The invention relates to the field of radiation refrigeration, in particular to a radiation refrigeration fabric 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 on the entire building or outside open environment, 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 an 8-13 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 composite fiber state radiation refrigeration material has the air and moisture permeable characteristics 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 composite fiber with 100nm-1000nm air holes, the average infrared transmittance of the fabric manufactured by the composite fiber is over 70 percent, the opacity reaches 90 percent, the skin temperature of the covering nano-porous PE fabric is 2.3 ℃ lower than that of the covering cotton fabric during testing, and opaque personal heat management can be realized. However, the refrigeration principle of the infrared high-transmittance composite fiber adopted by the method needs that the refrigerated surface has high emissivity in an infrared light wave band, the application range of the composite fiber is limited to a certain extent, the emissivity in a solar radiation wave band is limited, and effective radiation refrigeration is difficult to realize under the condition of direct sunlight outdoors.

In the aspect of high-emissivity refrigeration composite fiber, the Yu professor team of university of Columbia also adopts a phase separation method to draw out a composite fiber with the diameter of about 100 mu m and the air hole section hole density of 17 mu m^-2The sunlight reflectivity of the composite fiber can reach 93%, and the composite fiber has an infrared emissivity of 0.91. However, limited to the manufacturing process, this method results in a composite fiber that is relatively thick and reduces the comfort of wear. 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. In another method, for example, a radiation refrigeration composite fiber membrane disclosed in chinese patent publication No. CN110042564A, a preparation method and an application thereof, high-emission radiation particles SiO2 microspheres with good monodispersity are uniformly dispersed in a polymer, such as PE, PA6, PMMA, PVDF solution, and a composite fiber membrane is obtained by electrostatic spinning, which has the capability of radiation cooling for the skin surface of a human body, but the method has low production efficiency, a complex process and high equipment cost, and the produced composite fiber has low strength and cannot be used for radiation refrigeration fabrics for human bodies. Also a radiation refrigeration composite 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 composite fiber, wherein the linear density of the composite fiber is 1dtex-20dtex, the filler particle size is preferably 3 mu m-5 mu m, the visible-near infrared light reflectivity can be more than or equal to 60 percent, and the atmospheric window emissivity of 8 mu m-13 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. In addition, most of the methods only provide the composite fibers, and the fabric obtained by direct weaving cannot effectively improve the reflectivity of solar radiation of the final fabric due to the problems of uneven thickness, fluctuation, pores and the like, and cannot effectively realize outdoor daytime radiation refrigeration.

In summary, a radiation refrigeration fabric structure which is compatible with the prior art, simple in structure and high in efficiency and a design method for optimizing such a composite fiber structure are lacked, so that the fabric 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 composite fiber and the radiation refrigeration composite fiber, so as to solve the problems of complex preparation method, high cost, poor effect and the like in the existing radiation refrigeration composite fiber technology, and obtain a human body cooling fabric with both radiation refrigeration performance and wearable performance.

In order to solve the above problems, the present invention mainly provides the following technical solutions:

a radiation-cooled fabric comprising a first layer structure and a second layer structure which are laminated, wherein:

the first layer structure is a reflective film, and the first layer structure can reflect ultraviolet light;

the second layer structure is a fabric layer, can reflect visible-near infrared light wave bands and emit mid-infrared wave bands, is formed by weaving composite fibers, and comprises a polymer base material and micro-nano particles dispersed in the polymer base material.

Preferably, the first layer structure is a polymeric porous aerosol film having a first thickness and the second layer structure has a second thickness.

Preferably, the first layer structure is a polymer porous aerosol film, and the polymer can be one or a mixture of polymethyl methacrylate (PMMA), polylactic acid (PLA), polyvinyl alcohol (PVA), polyethylene terephthalate (PET), Polydimethylsiloxane (PDMS), Polytetrafluoroethylene (PTFE), Polyethylene (PE), polypropylene (PP), Polyamide (PA), polymethylpentene (TPX) or polyvinylidene fluoride (PVDF);

the polymer base material in the composite fiber of the second layer structure comprises at least one of polymethyl methacrylate (PMMA), polylactic acid (PLA), polyvinyl alcohol (PVA), polyethylene terephthalate (PET), Polydimethylsiloxane (PDMS), Polytetrafluoroethylene (PTFE), polypropylene (PP), polymethylpentene (TPX) or polyvinyl fluoride (PVDF); the micro-nano particles in the composite fiber of the second layer structure comprise at least one of titanium dioxide (TiO2), zinc sulfide (ZnS), zinc oxide (ZnO), silicon carbide (SiC), barium sulfate (BaSO4), silicon nitride (Si3N4) and calcium sulfate (CaSO 4).

The first thickness of the first layer structure is 5-200 μm, and the second thickness of the second layer structure is 100-1000 μm.

Preferably, the diameter range of the composite fiber of the second layer structure is 3 μm to 200 μm, and the diameter range of the micro-nano particles in the composite fiber of the second layer structure is 0.05 μm to 5 μm.

The design method of the radiation refrigerating fabric comprises the following steps:

s1: according to the preset material of the first layer structure (1), the thickness of the first layer structure (1), the high molecular base material, the micro-nano particle material and the preset volume percentage (V) of the micro-nano particles_d) Determining the optimal particle size (D) of the micro-nano particles in the second layer structure (2);

s2: determining a second thickness of the second layer structure (2) as an optimum thickness (D) on the basis of the optimum particle diameter (D) and the above-mentioned predetermined parameters_f)。

Preferably, the step S1 specifically includes:

s11, determining a first optional range of the micro-nano particle size, obtaining a first group of optional particle sizes with first particle size intervals as intervals in the first optional range according to a predetermined micro-nano particle material in the first optional range, obtaining scattering efficiency curves corresponding to a plurality of micro-nano particles with different particle sizes in the first group of optional particle sizes, and selecting the particle size range of the micro-nano particles with scattering efficiency peaks in visible-near infrared bands as a second optional range;

s12, selecting a group of second optional particle sizes within the second optional range by taking the second particle size interval as an interval, and obtaining the reflectivity and transmittance data of the micro-nano particles with different particle sizes and the fabric with different thicknesses of the second layer structure in the solar radiation waveband by using a first numerical simulation model according to the micro-nano particles with different particle sizes in the group of second optional particle sizes;

s13, obtaining the reflectivity and transmittance data of the micro-nano particles with different particle sizes and the fabric with different second-layer structure thicknesses in the solar radiation wave band according to the obtained data in the step, obtaining the average reflectivity and average transmittance of the radiation refrigeration fabric to the ultraviolet-visible-near infrared wave band under the preset solar spectrum and different particle sizes of the micro-nano particles under different second-layer structure thicknesses and different particle sizes, and selecting the optimal particle size (D) of the micro-nano particles according to the average reflectivity.

Preferably, the step S2 specifically includes

S21, according to the optimal particle diameter (D) of the micro-nano particles and the preset volume percentage (V) of the micro-nano particles_d) Acquiring emissivity data of the radiation refrigeration fabric in the middle infrared band under different thicknesses of the second layer structure by using a second numerical simulation model;

s22, according to emissivity data of the radiation refrigeration fabric in the middle infrared band under different thicknesses, and the average reflectivity and the average transmissivity of the radiation refrigeration fabric of the micro-nano particles with the optimal particle size obtained in the step S13 under the solar radiation band under different thicknesses of the second layer structureAnd obtaining the net refrigerating power (q) of the fabrics with different thicknesses by using a third numerical simulation model_cool) Selecting the net refrigeration power (q)_cool) The maximum thickness is the optimal fabric thickness.

Preferably, in the step S11, the scattering efficiency Q is_sComprises the following steps:

σ_sthe scattering cross section of the micro-nano particle is (m2) ═ total scattering energy (W)/incident light intensity (W/m2), A represents the maximum geometric cross section of the particle, and for the spherical micro-nano particle, A ═ π R²Wherein R is the radius of the sphere;

in step S12, the first numerical simulation model is a numerical simulation model based on monte-carlo simulation;

in the step S13, the average reflectance (ρ)_fab，sun) Comprises the following steps:

wherein I_sun(λ) is the predetermined solar spectrum, ρ (D, λ, D)_f) Is the diameter D of micro-nano particles and the thickness of a fabric layer is D_fThe reflection spectrum of the lower fabric with respect to the wavelength λ, λ 1 and λ 2 being the lower and upper limits, respectively, of the weighted wavelength range, ρ (D, λ, D)_f) Fitting is performed on the reflectance data in step S12.

Preferably, in step S21, the second numerical simulation model is obtained by equivalent the fabric to a random composite fiber model, and then measuring emissivity, reflectivity and transmittance data of the fabric with the second layer structure of different thickness in the middle infrared band;

in step S22, the third numerical simulation model is a dimensionally stable thermal model.

Preferably, the first numerical simulation model is used for enabling the fabric to be equivalent to a double-layer film structure, namely a first-layer structure(1) Equivalent to a first layer (6) and a second layer structure (2) equivalent to a second layer (5), wherein the thickness of the first layer (6) is taken as 0 and the thickness (d) of said second layer (5) is taken as_eff) The thickness (df) of the second layer structure (2) is related by,

where ρ is_f、ρ_pAnd ρ_sDensity of the second layer structure, micro-nano particles and polymer base material, V_dIs the volume percentage of the micro-nano particles.

Preferably, the emissivity data of the fabric in the middle infrared band is obtained by using a second numerical simulation model, and the volume fraction (V) of the composite fibers in the fabric layer needs to be determined_fiber) Diameter of composite fiber (D)_fiber) Equivalent refractive index (n) of composite fiber_eff)；

Wherein the diameter (D) of the composite fiber_fiber) Is a measured constant value;

wherein the volume fraction (V) of the composite fiber_fiber) Is defined by the formula:

ρ_f、ρ_pand ρ_sDensity of the second layer structure, micro-nano particles and polymer base material, V_dIs the volume percentage of the micro-nano particles;

equivalent refractive index of composite fiber

Wherein the equivalent dielectric constant ∈ is_effAnd equivalent permeability mu_effObtained from the following equation:

wherein N is the number of micro-nano particles in unit volume of the composite fiber,wherein V_dIs the volume percentage of the preset micro-nano particles, and R is the radius of the micro-nano particles;

∈_sis the dielectric constant, k, of the polymer substrate_hIs the wave number, mu, of light within the polymeric substrate₀Is the magnetic permeability in vacuum, wherein a1, b1 are obtained by the following formula:

where K2 π/λ is the wave number in vacuum, ψ_nAnd xi_nIs a Riccati-Bessel function,

wherein n is a natural number, m0 is the refractive index of the polymer base material, and m1 is the refractive index of the doped micro-nano particles.

Preferably, the third numerical simulation model comprises four layers of structures, which are an object to be refrigerated, an air layer with a certain thickness, a radiation refrigerating fabric, and an external environment layer.

Preferably, said net refrigeration power (q)_cool) This can be solved by the following equation:

where ρ is_fab，ir，τ_fab，ir，α_fab，irAnd ε_fab，irRespectively represents the average reflectivity, the transmittance, the absorptivity and the emissivity of the fabric to the infrared radiation spectrum of a human body, I_hbIs a human body infrared radiation spectrum, and can utilize the existing data, R_MIR、T_MIR、E_MIRReflectance, transmittance and emissivity data for the second layer structure fabric of different thicknesses for the optimal particle size at mid-infrared band;

I_eis atmospheric infraredRadiation spectrum, I_e(λ)＝I_bb(T_amb，λ)·E_AT(λ)，I_bb(T_ambλ) is the ambient temperature T_ambBlack body radiation spectrum of time, E_AT(λ) is the atmospheric emissivity spectrum; rho_skin，sun、ρ_fab，sunAnd τ_fab，sunThe average reflectivity of the human body to the solar radiation spectrum, the average reflectivity of the fabric to the solar radiation spectrum and the average transmittance of the fabric to the solar radiation spectrum are represented; q. q.s_genIs human metabolic heat production power density; q. q.s_sunIs the total solar radiation power density; t is_skin、T_toAnd T_tiThe temperatures of the surface of the refrigerated object, the upper surface of the fabric and the lower surface of the fabric are respectively measured; t is t_fab、t_airRespectively, the thicknesses of the fabric layer and the air layer, wherein t can be considered as t since the thickness of the first aerosol film in the radiation refrigeration fabric is negligible_fabIs that d_f；k_fab、k_airRespectively, the thermal conductivity of the fabric and air; sigma 5.67 × 10^-8W·m^-2·K^-4Is the Spander-Boltzmann constant; q. q.s_rad，skin、q_rad，amb、q_rad，ti、q_cond，air、q_rad，to、q_convCalculated by the following formula:

q_conv＝h·(T_to-T_amb) (31)

wherein epsilon_ambAnd h is the air convection coefficient, which is the average infrared emissivity in the atmosphere.

By the technical scheme, the technical scheme provided by the invention at least has the following advantages:

compared with the prior art, the radiation refrigeration fabric has the advantages that the radiation refrigeration fabric has a double-layer structure, is simple in structure and low in cost, overcomes the problems of serious light leakage, serious ultraviolet absorption and the like of the conventional radiation refrigeration fabric, and has a solar spectrum (0.3-2.5 microns) reflectivity of more than 90% and a middle infrared band (8-13 microns) emissivity of more than 90%.

According to the design method, the optimal particle size of the filled micro-nano particles and the optimal thickness of the fabric are rapidly determined under the conditions of the preset material, the preset composite fiber thickness range and the preset micro-nano particle volume percentage, so that the optimal solar spectrum reflection efficiency and the optimal radiation refrigeration power are achieved under the preset volume percentage.

Drawings

FIG. 1 is a schematic cross-sectional view of a radiation-cooled fabric according to an embodiment of the present invention.

Fig. 2 is a scattering efficiency curve of a plurality of different micro-nano particle sizes according to an embodiment of the present invention.

Fig. 3a is a schematic cross-sectional view of another direction of a radiation-cooled fabric according to an embodiment of the present invention, and fig. 3b is a schematic view of an equivalent double-layer film structure according to a first numerical simulation model.

Fig. 4 is a schematic diagram of a first numerical simulation model according to an embodiment of the present invention.

Fig. 5 is a schematic diagram of the average solar spectrum reflectivity of a plurality of equivalent double-layer thin film structures in the visible-near infrared band under different thicknesses and different micro-nano particle sizes according to the embodiment of the invention.

FIG. 6 is a diagram illustrating an equivalent simulation model according to a second numerical value.

Fig. 7 is a schematic diagram of a radiation-cooled fabric according to an embodiment of the present invention after being equivalent according to a third numerical simulation model.

FIG. 8 is a graph of net cooling power q for a radiation cooled fabric according to an embodiment of the present invention_coolSchematic representation of (a).

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 composite fiber, as shown in figure 1, the radiation refrigeration fabric comprises a double-layer structure, namely a first layer structure 1 and a second layer structure 2 which are arranged in a stacking mode, wherein the first layer structure 1 comprises a polymer porous aerosol film, and the second layer structure is a fabric layer. The fabric layer comprises a composite fiber woven structure, and the composite fiber comprises a polymer base material 3 and micro-nano particles 4 dispersed in the polymer base material.

The porosity of the polymer porous aerosol film is 10% -90%, the thickness of the second layer structure, namely the fabric layer, is 100-1000 microns, the volume percentage of micro-nano particles in the composite fiber is 5% -20%, the diameter of the composite fiber is 3-200 microns, the radiation refrigeration fabric utilizes the first layer structure 1, namely the polymer porous aerosol layer, to reflect ultraviolet light, particularly ultraviolet light in a wave band of 0.3-0.4 microns, utilizes the micro-nano particles in the second layer structure 2 to reflect visible-near infrared light, particularly visible-near infrared light in a wave band of 0.4-2.5 microns, and utilizes the polymer substrate in the second layer structure 2 to radiate infrared light, particularly mid-infrared light in a wave band of 7-14 microns. The reflection of ultraviolet light and the emission of heat of human infrared wave band are realized, and the radiation refrigeration effect is realized.

Optionally, the thickness of the polymer porous aerosol film is 5 μm to 200 μm, preferably 25 μm to 75 μm.

Preferably, the polymer porous aerosol film satisfies the characteristics of low absorptivity in the solar radiation band in the range of 0.3 μm to 2.5 μm and high reflectivity in the ultraviolet band in the range of 0.3 μm to 0.4 μm, and the material that can be used is a thermoplastic polymer having high transmissivity in the solar radiation band in the range of 0.3 μm to 2.5 μm, including one or a mixture of polymethyl methacrylate (PMMA), polylactic acid (PLA), polyvinyl alcohol (PVA), polyethylene terephthalate (PET), Polydimethylsiloxane (PDMS), Polytetrafluoroethylene (PTFE), Polyethylene (PE), polypropylene (PP), Polyamide (PA), polymethylpentene (TPX), or polyvinylidene fluoride (PVDF), and the polymer porous aerosol film is composed of an aerosol film having an internal microstructure of 0.1 μm to 3 μm in size, the microstructure can be at least one of air holes of an aerosol film, polymer micro-nano composite fibers or polymer particles.

Preferably, the polymer substrate 3 satisfies the characteristics of high transmittance in the visible-near infrared band ranging from 0.4 μm to 2.5 μm and high absorptivity (emissivity) in the middle infrared band ranging from 7 μm to 14 μm, and may be made of a thermoplastic polymer having low absorptivity in the visible-near infrared band and high absorptivity in the middle infrared band ranging from 7 μm to 14 μm, such as polymethyl methacrylate (PMMA), polylactic acid (PLA), polyvinyl alcohol (PVA), polyethylene terephthalate (PET), Polydimethylsiloxane (PDMS), Polytetrafluoroethylene (PTFE), polypropylene (PP), polymethylpentene (polymethylpentene, polyvinylidene fluoride), or polyvinylidene fluoride (TPX 1), 1-difluoroethylene), PVDF).

Optionally, the micro-nano particles 4 are made of a material with a high refractive index characteristic in a visible-near infrared band of 0.4-2.5 μm and a refractive index range of 1.6-3, and the micro-nano particles can be in a circular, elliptical or irregular shape. Preferably, the material of the micro-nano particles can be titanium dioxide (TiO)₂) Zinc sulfide (ZnS), oxygenZinc oxide (ZnO), silicon carbide (SiC), barium sulfate (BaSO)₄) Silicon nitride (Si)₃N₄) And calcium sulfate (CaSO)₄) At least one of (1).

The design method of the radiation refrigeration fabric comprises the following steps:

s1: according to the preset material of the first layer structure 1, the thickness of the first layer structure 1, the high molecular base material, the micro-nano particle material and the preset volume percentage v of the micro-nano particles_dDetermining the optimal particle size D of the micro-nano particles in the second layer structure 2;

s2: determining the optimum thickness D of the second layer structure 2 on the basis of the optimum particle diameter D and the above-mentioned predetermined individual parameters_f。

Since the first layer structure is a film and the second layer structure is a fabric layer, the thickness of the first layer structure is much greater than that of the first layer structure, and therefore, in the following design method, the film thickness of the first layer structure is negligible, and preferably, the thickness of the first layer structure is less than 100 μm.

Specifically, the step S1 includes:

s11, first setting a first optional range of the particle size of the micro-nano particles, where the first optional range may be preset and adjusted according to the material of the micro-nano particles that can be selected, for example, the first optional range of the particle size of the micro-nano particles is 0.05 μm to 5 μm, and setting a first particle size interval, where the smaller the first particle size interval, the more accurate the later-stage calculated data is, for example, the first particle size interval may be 0.25 μm.

Then, in the first optional range, selecting a group of first optional micro-nano particle diameters according to the preset particle diameter interval, wherein the group of first optional micro-nano particle diameters comprises a plurality of different micro-nano particle diameters at intervals according to the first particle diameter, then obtaining scattering efficiency curves of the plurality of different micro-nano particle diameters, the abscissa of each scattering efficiency curve is a wavelength, the ordinate of each scattering efficiency curve is a scattering efficiency, and the scattering efficiency Q is_sComprises the following steps:

σ_sthe scattering cross section of the micro-nano particles is the scattering cross section (m) of the micro-nano particles²) Total scattered energy (W)/incident light intensity (W/m)²) Wherein A represents the maximum geometric cross section of the micro-nano particles, and for the spherical micro-nano particles, A is pi R²Wherein R is the radius of the micro-nano particle sphere.

More specifically, in the step, software simulation can be utilized, three-dimensional spherical particles, namely the micro-nano particles in the step, are constructed on the basis of FDTD solutions of a time domain finite difference method, a light source adopts a full-field scattered field light source (TFSF), 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, the boundary condition is set to be a Perfect Matching Layer (PML), so that the 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 power of the scattered light and the absolute value of the absorbed light power. Further, the intermediate scattering energy is obtained, and further, a scattering efficiency curve is obtained according to the above formula (1), as shown in fig. 2, the scattering efficiency curve is a plurality of scattering efficiency curves with different micro-nano particle diameters. Furthermore, from the scattering efficiency curve, the particle size of the micro-nano particles with the scattering efficiency peak value in the visible-near infrared band, namely the 0.4-2.5 μm band, is 0.1-1.6 μm, which is the second optional range.

For example, the material of the micro-nano particles is selected to be TiO₂When the polymer substrate material is PLA, as shown in fig. 2, the scattering efficiency curve of the 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 in the band of 0.4 μm to 2.5 μm is 0.1 μm to 1.6 μm, which is the second optional range.

In the step, the absorption efficiency curves of the micro-nano particles with different particle sizes can be obtained in the same way.

Wherein Q is_aTo the particle absorption efficiency, σ_aIs the absorption cross section of the particle, the absorption cross section (m) of the particle²) Total absorption energy (W)/incident light intensity (W/m)²). The absorption efficiency does not play a role in the preliminary screening of the particle size of the micro-nano particles in the step, but the data can be used in subsequent calculations.

And S12, selecting a group of second optional particle sizes from the second optional range according to the second particle size interval, wherein the group of second optional particle sizes comprises the particle sizes of a plurality of micro-nano particles with the second particle size interval as the interval. And then obtaining a plurality of equivalent double-layer film structures with different thicknesses and different micro-nano particle diameters according to the group of second optional particle diameters. Reflectivity data for the plurality of equivalent structures is then calculated. The second particle size interval may be 0.1 μm.

Because the radiation refrigeration fabric is of a double-layer structure, the radiation refrigeration fabric has the best ultraviolet light reflectivity and the best near-infrared band emissivity after selecting the appropriate micro-nano particles, and if the radiation refrigeration fabric is obtained according to actual measurement, the optimal particle size of the micro-nano particles can be selected only by measuring for countless times. Therefore, by using mathematical modeling, the double-layer fabric structure is equivalent to a double-layer film structure, and then the reflectivity and emissivity under different conditions are measured by using a numerical simulation model and computer simulation software, so that the selection of the optimal particle size of the micro-nano particles can be quickly obtained. The numerical simulation model may be any conventional mathematical model, and may be any analytical model or numerical model that can be used to calculate the physical quantity.

Therefore, in this step, first, the double-layer fabric structure is equivalent to a double-layer film structure, as shown in fig. 3a, which is a schematic diagram of the double-layer fabric, and fig. 3b is a schematic diagram of the equivalent double-layer film, in which the first layer structure 1 is equivalent to the first layer 6, and the second layer structure is equivalent to the second layer 5. Wherein the first layer 6 has a thickness of 0 as the upper surface of the second layer 5. And selecting different thicknesses of the second layer structure to obtain a plurality of equivalent thin film structures with different thicknesses.

On equivalent transformation, the thickness deff of the second layer 5 is correlated with the thickness df of the fabric layer, i.e. the second layer structure 2, by

Where ρ is_f、ρ_pAnd ρ_sDensity of the second layer structure, micro-nano particles and polymer base material, V_dIs the volume percentage of the micro-nano particles. The density of the micro-nano particles and the polymer base material, namely the mass density of the micro-nano particles and the polymer base material is directly determined during material selection. The density of the second layer of fabric is a fixed value independent of the thickness of the fabric layer after determining the volume percentage of the polymer base material and the micro-nano particles, so that a sample with any thickness and any particle size can be prepared, and the density is obtained by measurement and is defined as the mass (g/cm) of the second layer structure, namely the fabric layer in unit area²)/d_f(ii) a The specific measurement method comprises the following steps: taking a fabric sample, measuring its area as A_fabricMeasuring its thickness as d_fMeasuring its mass as m_fabricTo obtain a second layer fabric density

To calculate the reflectivity of an equivalent bilayer film structure, the following parameters also need to be known: reflectivity R of the first layer 6_uvfAnd a transmittance T_uvfThe equivalent scattering coefficient mu of the second layer 5_sλEquivalent absorption coefficient mu_aλAnd equivalent asymmetry parameter g_Tλ. Wherein the reflectivity R_uvfAnd a transmittance T_uvfNamely the reflectivity and the transmittance of the first layer of polymer aerosol film in the radiation refrigeration fabric, after determining which polymer aerosol film to use, the reflectivity R can be measured by an ultraviolet-visible-near infrared (UV-VIS-NIR) spectrophotometer and an integrating sphere_uvfAnd a transmittance T_uvf. The other threeThe parameters are calculated from the following formula:

wherein N (R) is the number of micro-nano particles with the radius of R in a unit volume, and N (R) is 3V_d(R)/(4πR³)，μ_a0Is the absorption coefficient, Q, of the polymeric substrate_sAnd Q_aThe formula (1) and the formula (2) show. g_λIs an asymmetric parameter of the particle that indicates the probability of a photon being scattered by the particle in different directions

Wherein

Where K2 π/λ is the wave number in vacuum, ψ_nAnd xi_nIs a Riccati-Bessel function,

where n is a natural number, m0 is the refractive index of the polymer base material, and m1 is the refractive index of the doped particles.

In this step, we will double layer fabric structure etcIs equivalent to an equivalent double-layer film structure, and obtains all parameters of the equivalent double-layer film structure, including the reflectivity and transmittance of the first layer 6 and the thickness d of the second layer 5_fAnd the equivalent parameter mu of the second layer 5_sλ、μ_aλAnd g_Tλ. The parameters are substituted into the following first numerical simulation model, so that the reflectivity and the transmittance of the equivalent double-layer film structure in the solar radiation wave band can be calculated. The thickness of the first layer 6 is considered to be 0.

In the step, for the simplified equivalent thin film structure, it is still difficult to find an analytic mode to directly solve the reflectivity and the transmissivity of the equivalent thin film structure, that is, the reflectivity of the structure can not be directly calculated by finding one or more formulas, therefore, a first numerical simulation model is used for modeling solution, and a numerical simulation model based on Monte-Carlo simulation is selected as the first numerical simulation model.

The numerical simulation model is a probability statistical model, as shown in fig. 4, in a simple way, a photon energy packet is injected each time, the motion trajectory of photons in the structure is simulated based on some basic parameters of the film, a single photon packet is scattered and absorbed in the film according to a certain probability, and finally emitted from an upper interface/a lower interface, or residual energy is completely absorbed, so that the simulation of the motion of the photon energy packet in the film structure is completed. Thereafter, we can use these simulated statistics as the reflectivity, transmissivity and absorptivity of the structure by simulating the motion of a large number of photon packets in the thin film structure, for example, the process of simulating 2000, 5000, 10000 or even more photon energy packets entering and moving in the thin film structure, and counting the exit of these photon packets from the upper/lower interfaces, corresponding to the reflected and transmitted energy and the absorbed energy, respectively, and calculating the ratio of these energies to the total energy.

Simulating the movement process of the single photon energy package in the film, and running the following steps through a program:

a1, taking certain discrete points at equal intervals in the wavelength range of ultraviolet-visible-near infrared, and driving certain photon energy packets into the points with each wavelength, wherein the number of the photon energy packets can be 5000, and the energy of each photon energy packet is set to be 1;

a2, each photon energy package is first reflected and transmitted at the top surface of the film structure, the reflectance and transmittance of the top surface, i.e., the reflectance and transmittance of layer 6, as measured by a spectrophotometer, as previously described, and the reflected light energy packages cumulatively add to the total reflected energy W_R；

A3, scattering and circulating the transmitted photon energy packet in the equivalent film structure; firstly, a random free path parameter s is given, and when s is 0, s is-ln (xi), xi is a random number with the value between 0 and 1, and further, the free path of photon energy packet in the cycle, namely the distance l of photon linear motion before scattering and absorption is s/mu_tλWherein, mu_tλ＝μ_sλ+μ_aλIs the equivalent extinction coefficient of the film; at the same time, the distance d between the photon energy package and the upper or lower boundary of the film is determined_bThe choice of which boundary depends on the direction of motion of the photon packet, the vertical component of the direction of motion of the photon packet, i.e. the component perpendicular to the direction of the membrane, is the upper boundary, the vertical component is the lower boundary. And use of d_bThe magnitude of l determines whether the photon energy packet meets the boundary at that time.

If the photon is judged not to touch the boundary, the photon energy packet moves for a distance l, and the energy absorption attenuation w is w × exp (-mu)_aλL) the remaining photon energy packet changes the propagation direction due to scattering, the new propagation direction has a deflection angle theta and an azimuth angle psi relative to the original propagation direction

ψ＝2πζ (12)

Where ζ is a random number between 0 and 1.

If it is determined that the photon packet hits the boundary, the photons are reflected and transmitted, the reflectivity and transmissivity of the upper boundary being that of layer 6, and the reflectivity and transmissivity of the lower boundaryThe refractive index is directly given by Snell's law of refraction, and the partial energy of transmission is cumulatively counted as total reflection/transmission energy W according to the fact that the boundary of transmission is an upper/lower boundary_R/W_T(ii) a The reflected part of the energy changes the propagation direction according to the reflection law of the incident angle, namely the reflection angle, and continues to propagate the rest optical path in the film, and then is absorbed and scattered.

A4, by mixing the residual photon packet energy w with the threshold energy w_tComparing to judge whether the photon needs to be propagated and scattered continuously or not, w_tIt may be set to 0.0001, if the energy of the photon packet is higher than the threshold, the next propagation is continued, if the energy of the photon packet is lower than the threshold, the cycle of the photon packet is ended, and the transmission process of the next photon packet is simulated.

In the first numerical simulation model, the simulated propagation process of a single photon energy packet is shown as an arrow in the right diagram, after the photon energy packet is incident, multiple scattering and absorption are performed in the film, the last part of energy escapes from the film structure and is counted into reflection or transmission, and the other part of energy is absorbed in the film, as shown in fig. 3 b.

Finally, the reflectivity, the transmissivity and the absorptivity of the equivalent structure can be obtained by counting the reflection, the transmission and the absorption conditions of a large number of photon energy packets, and as long as the number of the photon energy packets is enough, the numerical value obtained by simulation is infinitely close to the theoretical value.

Therefore, through the step, the reflectivity and transmittance data of the double-layer radiation refrigeration fabric under different thicknesses of the second layer structure 2 of the fabric and different particle sizes of the micro-nano particles can be obtained.

And S13, according to the thicknesses of the second layer structures 2 obtained in the steps and the particle sizes of the micro-nano particles, obtaining the reflectivity and transmittance data of the radiation refrigeration fabric. The average reflectivity of the equivalent double-layer film structures to ultraviolet-visible-near infrared bands under a preset solar spectrum is calculated according to the reflectivity of the equivalent double-layer film structures, and the optimal particle size of the micro-nano particles under the thickness of the second layer structure 2 of different fabrics is obtained according to the average reflectivity.

Preferably, according to the reflectivity data of the equivalent structures obtained in the step S12, calculating the average reflectivity of each equivalent structure to the ultraviolet-visible-near infrared band under a predetermined solar spectrum, and obtaining the optimal particle size of the micro-nano particles under different thicknesses according to the average reflectivity; the average reflectivity is weighted according to the wavelength in the reflectivity formula, namely the average reflectivity is obtained by calculating the weighting of the reflectivity of an ultraviolet-visible-near infrared band under a preset solar spectrum, so that the average reflectivity is related to the thickness of an equivalent structure and the particle size of micro-nano particles.

The average reflectance ρ_fab，sunThe physical meaning is the reflected solar radiation power (W) ÷ incident total solar power (W), which is calculated as follows

Wherein I_sun(λ) is the predetermined solar spectrum, which may be the AM1.5 solar spectrum, and is the intensity of the different light produced by the actual sunlight and its angle of incidence. ρ (D, λ, D)_f) Is the diameter D of micro-nano particles and the thickness of a fabric layer is D_fThe reflection spectrum of the lower fabric with respect to the wavelength λ. λ 1 and λ 2 are the lower and upper limits, respectively, of the weighted wavelength range, for example, in the UV-visible-near infrared range, λ 1 being 0.3 μm and λ 2 being 2.5 μm.

From this we can get ρ_fab，sun(D，d_f) With the distribution diagram of the structure thickness, the micro-nano particle size and the reflectivity, as shown in fig. 5, under different equivalent structure film thicknesses, when the particle size of the micro-nano particles is about 500nm, the average reflectivity is highest, so that the optimal particle size is 500 nm.

In addition, the average transmittance of the radiation-cooled textile to solar radiation, which has no effect on optimizing the particle size, can also be calculated in this step, but is used in the subsequent optimization of the second layer structure, i.e. the thickness of the textile layer.

The physical significance of the average transmittance is the power of solar radiation (W) transmitted by the structure divided by the total incident solar power (W), which is calculated as follows

Wherein I_sun(λ) is the predetermined solar spectrum, which may be the AM1.5 solar spectrum, and is the intensity of the different light produced by the actual sunlight and its angle of incidence. τ (D, λ, D)_f) Diameter D of micro-nano particles and thickness D of fabric_fTransmission spectrum of the lower fabric with respect to wavelength λ. λ 1 and λ 2 are the lower and upper limits, respectively, of the weighted wavelength range, for example, in the UV-visible-near infrared range, λ 1 being 0.3 μm and λ 2 being 2.5 μm.

After obtaining the corresponding optimal grain diameter D. The determination of the optimum thickness d of the second layer structure is continued_f。

S2: determining the optimum thickness D of the second layer structure 2 on the basis of the optimum particle diameter D and the above-mentioned predetermined individual parameters_f. The method comprises the following steps.

S21: and after the optimal particle size is determined, the radiation refrigeration fabric structure is equivalent to a random composite fiber model, and the emissivity data of the radiation refrigeration fabric is calculated by utilizing a second numerical simulation model.

Specifically, emissivity data of the fabric in a middle infrared band is calculated by using a second numerical simulation model. For this purpose, it is necessary to know the volume fraction V of the composite fibers in the fabric layer_fiberDiameter D of the composite fiber_fiberThe equivalent refractive index n of the composite fiber_eff。

Here, the first and second liquid crystal display panels are,all the parameters are defined in the foregoing and can be directly calculated.

Diameter D of the composite fiber_fiberAfter the volume percentage of the selected material and the micro-nano particles is determined, the volume percentage is determined to be a fixed value, and the fixed value is obtained according to measurement. The measuring method comprises the following steps: get oneThese composite fiber samples are directly measured by taking a photograph with a microscope, and the actual sample is measured to be 30 μm, for example.

Equivalent refractive index n of composite fiber_effCan be obtained by using an Equivalent Medium Theory (EMT), and the equivalent dielectric constant epsilon of the composite fiber is calculated by using the following two formulas_effAnd equivalent permeability mu_eff。

Wherein N is the number of micro-nano particles in unit volume of the composite fiber,wherein V_dIs the volume percentage of the preset micro-nano particles, and R is the radius of the micro-nano particles;

∈_sis a dielectric constant, k, of a polymer base material_hIs the wave number, mu, of light within the polymeric substrate₀Is the permeability in vacuum. The composite fiber thus obtained has an equivalent refractive index ofa1 and b1 are defined in equations 9 and 10.

So far, we only need to obtain V_fiber、D_fiber、n_effAnd substituting the three quantities into a second numerical simulation model, and calculating the emissivity of the radiation refrigeration fabric in the middle infrared band.

And a second numerical simulation model, namely, the fabric is equivalent to a random composite fiber model, as shown in fig. 3a and 6, the random composite fiber model is composed of infinite cylindrical composite fibers arranged in parallel, and fig. 6 is a cross-sectional view of the random composite fiber model. Here, we construct a two-dimensional circle using FDTD solutions based on finite-difference time-domain methodsForm construction, i.e. section of the parallel cylindrical composite fibre of indefinite length in the above-mentioned step, in the figure, P_fCan be set to any value, P, greater than 14 μm_fIs the width of the fabric in the simulation. The actual fabric thickness is limited, but the length is very large, up to several meters. Length calculations of a few meters are time consuming for numerical simulations, so it is desirable to be able to simulate with a smaller thickness, but as close to reality as possible. If the distance is too small, less than 14 μm will result in a reduction in calculation accuracy, and if the distance is greater than 14 μm, for example, set to 15,20 μm, the actual situation can be simulated well. Number of cylindrical composite fibersThe refractive index is set to n_effThe light source is a Plane wave light source (Plane wave), the wavelength of the light source is 7-14 μm, namely light in a middle infrared band is selected as the light source, the x boundary of an FDTD region in simulation software, namely the condition parallel to the Plane wave propagation direction, is set as a periodic boundary condition (Period), and the y boundary, namely the condition perpendicular to the Plane wave propagation direction, is set as a Perfect Matching Layer (PML). Respectively adding a power detector in front and back directions of the model for obtaining reflectivity R_MIRAnd transmittance T_MIRObtaining the mid-infrared emissivity E of the second layer structure with different thicknesses_MIR＝1-R_MIR-T_MIR。

S22, average reflectivity and average transmissivity data in the solar radiation band according to the radiation refrigeration fabrics with different thickness, such as obtained in the step S13. And reflectivity, transmissivity, and emissivity data in the mid-infrared band at step S21. Substituting the obtained product into a third numerical simulation model which is a thermal model so as to obtain the net refrigerating power q of the fabrics with different thicknesses_coolThe maximum value achieves the optimum fabric thickness.

The third numerical simulation model is a dimensional stability thermal model, which comprises four layers of structure, namely a refrigerated object, an air layer with a certain thickness, a radiation refrigeration fabric and an external environment, as shown in fig. 7.

In this model, the net refrigeration power q_coolCan be obtained by solving the following equation

Where ρ is_fab，ir，τ_fab，ir，α_fab，irAnd ε_fab，irRespectively represents the average reflectivity, the transmittance, the absorptivity and the emissivity of the fabric to the infrared radiation spectrum of the human body, and respectively represents the infrared total radiation power density (W/m) of the human body²) The ratio of the reflected, transmitted and absorbed power densities of the fabric; and is calculated by the following formula:

wherein, I_hbIs a human body infrared radiation spectrum, and can utilize the existing data, R_MIR、T_MIR、E_MIRWhich has been calculated in step S21. When only the influence of the mid-infrared band is considered, λ 1 is 7 μm and λ 2 is 14 μm.

ρ_fab，ire，τ_fab，ire and alpha_fab，ire，ε_fab，ireIndicating that the fabric is environmental, i.e. largeThe average reflectivity, transmittance, absorptivity and emissivity of the gas infrared radiation spectrum respectively represent the total power density (W/m) of atmospheric infrared radiation²) The ratio of the reflected, transmitted and absorbed power densities of the fabric; and is calculated by the following formula:

wherein, I_eIs the atmospheric infrared radiation spectrum, I_e(λ)＝I_bb(T_amb，λ)·E_AT(λ), here I_bb(T_ambλ) is the ambient temperature T_ambBlack body radiation spectrum of time, E_AT(λ) is the atmospheric emissivity spectrum, and existing data can be directly utilized. When only the influence of the mid-infrared band is considered, λ 1 is 7 μm and λ 2 is 14 μm.

ρ_skin，sun、ρ_fab，sunAnd τ_fab，sunThe average reflectivity of human body to solar radiation spectrum, the average reflectivity of fabric to solar radiation spectrum and the average transmittance of fabric to solar radiation spectrum are respectively expressed as the total solar radiation power density (W/m)²) The ratio of the power density of human body reflection, fabric reflection and fabric transmission; rho_skin，sunCan be directly preset to be 0.36, which is an empirical value in the past research; rho_fab，sunAnd τ_fab，sunIt has been calculated in the equations (13) (14).

q_genIs the power density of human metabolic heat production, and takes a fixed value of 141W/m²；q_sunIs the total solar radiation power density, measured according to a standardization body, of 980W/m²；T_skin、T_toAnd T_tiAre respectively refrigeratedThe temperature of the surface of the object (i.e., the skin surface of the human body), the upper surface of the fabric and the lower surface of the fabric; t is t_fab、t_airRespectively, the thicknesses of the fabric layer and the air layer, wherein t can be considered as t since the thickness of the first aerosol film in the radiation refrigeration fabric is negligible_fabIs that d_f；k_fab、k_airRespectively, the thermal conductivity of the fabric and air; sigma 5.67 × 10^-8W·m^-2·K^-4Is the Spander-Boltzmann constant; thermal radiation power (W/m) of skin²)q_rad，skinThermal radiation power of the environment (W/m)²)q_rad，ambThermal radiation power (W/m) of the inner surface of the fabric²)q_rad，tiThermal conductivity of the air layer between the textile and the skin, or thermal conductivity (W/m)²)q_cond，airThermal radiation power (W/m) of the outer surface of the fabric²)q_rad，toThermal convection power (W/m) of the environment of the outer surface of the fabric²)q_convCalculated by the following formula:

q_conv＝h·(T_to-T_amb) (31)

wherein epsilon_ambFor the average emissivity of infrared in the atmosphere, 0.61 is taken, and h is the air convection coefficient, which is a quantity related to the wind speed, the larger the value, the larger the wind speed.

In which some parameters are predetermined in advance, e.g. given to the object to be cooled, i.e. the skin surface temperature T_skin34 ℃ and ambient temperature T_ambThe remaining values of the predetermined parameters are shown in table 1, 22 ℃.

TABLE 1

By solving the steps (17) to (19), the net refrigerating power q of the radiation refrigerating fabric under different thicknesses can be calculated_coolAs shown in fig. 8.

The four curves in fig. 8 correspond to four thermal convection coefficients, that is, four h values corresponding to 4 wind speeds, although in practice one curve, that is, one h value, is sufficient to judge that the optimal fabric thickness for radiation cooling is about 500 μm, the four curves are calculated to consider that in practical situations, under different wind speed environments, about 500 μm is the optimal fabric thickness condition.

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.