CN110600087A - Isotropic double-shell structure presenting thermal chameleon phenomenon and implementation method thereof - Google Patents
Isotropic double-shell structure presenting thermal chameleon phenomenon and implementation method thereof Download PDFInfo
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- 238000002845 discoloration Methods 0.000 abstract description 4
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- G—PHYSICS
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
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Abstract
The invention belongs to the technical field of thermal discoloration, and particularly relates to an isotropic double-shell structure presenting a thermal discoloration dragon phenomenon and an implementation method thereof. The isotropic double-shell structure comprises a core and two thermal color-changing dragon shell layers coated outside the core; the thermal conductivities of the two shell layers are opposite numbers, and the area fraction of the inner shell layer in the core-inner shell layer structure is equal to the area fraction of the outer shell layer in the core-double shell layer structure. When both conditions are satisfied simultaneously, the thermal conductivity of the double shell structure does not have an effect on the thermal conductivity of the core. When there is temperature gradient at the two ends of the whole structure, the temperature distribution of the core cannot be influenced by the existence of the double-shell structure, and because the double-shell structure is an accurate solution, the effect can be realized no matter how the core material changes, namely, the double-shell structure achieves the effect of thermal chameleon. The invention has simple structure, does not need anisotropic materials, and has guiding significance for the development of the thermal camouflage field and the thermal intelligent field.
Description
Technical Field
The invention belongs to the technical field of thermal discoloration, and particularly relates to an isotropic double-shell structure presenting a thermal discoloration dragon phenomenon and an implementation method thereof.
Background
Thermal metamaterials are artificial materials that exhibit novel thermal properties according to their complex geometry. The earliest examples of thermal metamaterials were thermal cloaks designed based on the theory of coordinate transformation, which can direct the heat flow around an object to bypass the object as if it were not present. In principle, thermal metamaterials can effectively control heat flow, however due to lack of suitable theory, almost all existing thermal metamaterials, except materials that are bifunctional or thermoresponsive, do not have active regulation functionality, which means that the corresponding devices cannot sense and respond to external or internal stimulus changes in a controlled manner. Therefore, in this invention we propose an isotropic double-shell structure capable of exhibiting the phenomenon of thermal chameleon, which, like chameleon in the biological world, can sense and respond to one type of internal change, i.e. a change in the thermal conductivity of the background material. The equivalent thermal conductivity of the double-shell structure can be equal to that of the background no matter the thermal conductivity of the background material is isotropic or anisotropic, and no matter the variation range of the thermal conductivity of the background material, so that the double-shell structure is hidden in the background and does not influence the temperature distribution of the background. Of course, the conventional double-shell structure cannot meet the requirement, and the thermal conductivity and the area fraction of the double shell are designed correspondingly.
Disclosure of Invention
The invention aims to provide an isotropic double-shell structure capable of accurately presenting a thermal chameleon phenomenon and an implementation method thereof.
The isotropic double-shell structure presenting the thermal chameleon phenomenon comprises a core and two thermal chameleon shell layers coated outside the core; the heat conductivities of the two shell layers are opposite numbers, and the area fraction of the inner shell layer in the core-inner shell layer structure is equal to the area fraction of the outer shell layer in the core-double shell layer structure.
In the invention, for the thermal chameleon double-shell structure, the heat conductivity of the two shells needs to satisfy the specific relation, and meanwhile, the area fraction of the inner shell in the core-inner shell structure and the area fraction of the outer shell in the core-double-shell structure need to satisfy the specific relation, so that the thermal chameleon effect is realized, namely, the double shells can well adapt to the background no matter how the background is changed, and the temperature distribution of the double shells is not influenced.
The invention provides a realization method of an isotropic double-shell structure showing a thermal chameleon phenomenon, which comprises the following steps: accurately calculating the shell layer thermal conductivity and constructing a two-dimensional model shown in figure 1; the area fraction of the shell layer in the core-shell structure is accurately calculated, and the equivalent thermal conductivity of the double-shell structure is calculated, so that the thermal chameleon effect is realized, namely the thermal conductivity of the shell layer does not influence the temperature distribution in the background.
In the invention, the condition that the thermal conductivities are opposite to each other needs to utilize the apparent negative thermal conductivity, and a method of additionally adding a heat source can be adopted to realize the condition. Specifically, the temperature distribution conditions inside and outside the shell layer can be accurately obtained by using the uniqueness theorem, and the apparent negative thermal conductivity is realized by adding a point heat source or a linear heat source.
According to the Fourier heat conduction law, the equivalent thermal conductivity of the core-double-shell structure can be accurately calculated, and when the thermal conductivity condition and the area fraction condition are simultaneously met, the equivalent thermal conductivity of the whole structure is irrelevant to the double-shell structure. The specific derivation is as follows:
for an isotropic double-shell structure, let the thermal conductivity and radius of the core be κcAnd rcThe thermal conductivity of the inner and outer shell layers is kappas1、κs2The radius of the inner and outer shell layers is rs1、rs2(ii) a Using Fourier's law, the equivalent thermal conductivity κ of all core-shell structureseExpressed as:
wherein p is12＝(rs1/rs2)2，κ12Is the overall equivalent thermal conductivity of the core and the inner shell layer, and is expressed as:
wherein p isc＝(rc/rs1)2。
In order to realize the effect of thermal chameleon, the equivalent thermal conductivity kappa of the double-layer core-shell structure is required to be ensuredeThermal conductivity with the core κcAnd (3) consistent, namely:
κe＝κc (3)
substituting equation (3) into equation (1) to obtain the specific condition that the double-shell layer needs to satisfy:
(κ12+κs2)2+(pc-p12)2＝0 (4)
namely, simultaneously: kappa12+κs20 and pc-p12When the temperature is 0, the thermal chameleon can be realized.
The invention provides a method for realizing an isotropic double-shell structure showing a thermal chameleon phenomenon, which comprises the following specific steps:
(1) applying a temperature field to the isotropic double-shell structure along the horizontal direction, wherein the temperature field has a certain temperature difference (for example, the temperature difference is 50K) so as to generate a heat conduction process, and the heat conduction process is described by Fourier law;
(2) radius r of the design nucleuscRadius r of inner and outer shellss1、rs2(ii) a To satisfy the area fraction condition: p is a radical ofc-p120; wherein p isc＝(rc/rs1)2，p12＝(rs1/rs2)2；
(3) Setting the thermal conductivity of the inner and outer shell layers: kappas1、κs2To satisfy the thermal conductivity condition: kappa12+κs20; wherein the content of the first and second substances,κcthermal conductivity of the nucleus, pc＝(rc/rs1)2。
For example, a temperature field is applied in a horizontal direction to the structure shown in fig. 3(a1) to produce a heat conduction process with a temperature difference of 50K, which is described by fourier law. In order to meet the area fraction condition, the radius of the core is set to be 2cm, and the radius of the inner shell layer and the radius of the outer shell layer of the chameleon shell layer are respectively set to beAnd 3 cm. In order to meet the thermal conductivity condition, the thermal conductivity of the inner shell layer and the thermal conductivity of the outer shell layer are respectively set to be-10 Wm-1K-1And 10Wm-1K-1The isotropic double-shell structure showing the thermal chameleon phenomenon can be obtained, and at this time, no matter how the external environment changes, the shell can be hidden in the external environment. The parameters given above are not the only parameters that can be achieved, as long as the conditions given in the derivation process, i.e., equation (4), are met.
In the present invention, when both conditions are satisfied simultaneously, the thermal conductivity of the double-shell structure does not have an influence on the thermal conductivity of the core (background). Phenomenologically, when temperature gradients exist at two ends of the whole structure, the temperature distribution of the core (background) cannot be influenced by the existence of the double-shell structure, and the effect can be met no matter how the core (background) material changes due to the fact that the double-shell structure is an accurate solution, so that the effect of thermal chameleon is achieved by the double-shell structure. The invention has simple structure, does not need anisotropic materials, and has guiding significance for the development of the thermal camouflage field and the thermal intelligent field.
The above discussion is two-dimensional calculation results, and for the double-shell layer, the three-dimensional calculation result shows that the thermal conductivity kappa of the core is dependent in the specific condition that the equivalent thermal conductivity of the double-layer core-shell structure is consistent with the thermal conductivity of the corec. This defeats the purpose of achieving the effect by designing the shell only, so two-dimensional discussions cannot be generalized to three-dimensional ones.
The invention has the advantages that:
(1) the method proposed by the invention is an accurate solution;
(2) the invention provides a solution scheme using an isotropic structure, which is simple and easy to obtain;
(3) the method provided by the invention can be applied to various background environments.
Drawings
Fig. 1 is a schematic structural diagram.
FIG. 2 isAnd kappacAnd (4) a functional relation schematic diagram.
FIG. 3 is a temperature distribution diagram of chameleon double-shell, common double-shell and background materials under different background thermal conductivities. Wherein (a1, b1, c1) has a background thermal conductivity of 0.1Wm-1K-1The background thermal conductivity of (a2, b2, c2) was 100Wm-1K-1。
FIG. 4 shows that the background thermal conductivity of chameleon double-shell (a), common double-shell (b) and background material (c) is diag (10,20) Wm-1K-1Lower temperature profile.
Detailed Description
The present invention will be described in detail below with reference to specific examples and drawings, but the present invention is not limited thereto. In the embodiment, the temperature difference of the system is 50K, and the system is in a steady state.
FIG. 1 shows the temperature gradient from left to right in a schematic diagram of a thermal chameleon double-shell structure. The theoretical calculation results can be verified using finite element simulation results, as shown in fig. 3-4.
FIG. 2 isAnd kappacAnd (4) a functional relation schematic diagram.
In FIG. 3, (a1-c1) are a thermal chameleon double-shell simulation, a thermal double-shell general shell simulation and a pure background control simulation, respectively. In the figure, the background thermal conductivity and the thermal conductivity of the core are both 0.1Wm-1K-1The radius of the core is 2cm, and the system size is 10 x 10cm2. (a1) The thermal conductivity parameters of the inner shell layer and the outer shell layer are respectively-10 Wm-1K-1And 10Wm-1K-1Radius is respectivelyAnd 3 cm. (b1) The thermal conductivity of the medium and common shell layers is 5Wm-1K-1The other parameters are the same as in (a 1). (c1) Is a pure background distribution chart. With (a1), (b1), (c1), it was confirmed that: after the chameleon double-shell layer is introduced, the temperature distribution of the background is not changed, and the introduction of a common double-shell layer structure can influence the temperature distribution of the background, so that the chameleon double-shell layer has the effect of adapting to the background thermal conductivity.
In FIG. 3, (a2-c2) are a thermal chameleon double-shell simulation, a thermal double-shell general shell simulation and a pure background control simulation, respectively. The background thermal conductivity and the thermal conductivity of the core are both 100Wm in the figure-1K-1. The other parameters are the same as in FIG. 3(a 1-c 1). Similarly, with (a2), (b2), (c2) it was demonstrated that: after the chameleon double-shell layer is introduced, the temperature distribution of the background is not changed, and the introduction of a common double-shell layer structure can influence the temperature distribution of the background, so that the chameleon double-shell layer has the effect of adapting to the background thermal conductivity. All background thermal conductivity variation ranges can be accommodated by using the comparative visible chameleon double-shell layers of (a1-c1) and (a2-c2) in fig. 3.
In FIG. 4, both background and core thermal conductivities are diag (10,20) Wm-1K-1The other parameters are the same as in fig. 3. The chameleon double-shell layer can adapt to the change of the background material with isotropic thermal conductivity and the change of the background material with anisotropic thermal conductivity.
Claims (3)
1. An isotropic double-shell structure showing a thermal chameleon phenomenon comprises a core and two thermal chameleon shell layers coated outside the core; the thermal conductivity of the two shell layers is opposite to each other, and the area fraction of the inner shell layer in the core-inner shell layer structure is equal to the area fraction of the outer shell layer in the core-double shell layer structure.
2. The isotropic double-shell structure exhibiting thermal chameleon according to claim 1, wherein the core has a thermal conductivity and a radius kcAnd rcThe thermal conductivity of the inner and outer shell layers is ks1、ks2The radius of the inner and outer shell layers is rs1、rs2；
Simultaneously, the following requirements are met: k is a radical of12+ks20 and pc-p12＝0；
Here, pc＝(rc/rs1)2，p12＝(rs1/rs2)2；
k12Is the overall equivalent thermal conductivity of the core and the inner shell layer, and is expressed as:
3. the method for realizing the isotropic double-shell structure exhibiting thermal chameleon phenomenon according to claim 1 or 2, comprising the following steps:
(1) applying a temperature field to the isotropic double-shell structure along the horizontal direction, wherein the temperature field has a certain temperature difference so as to generate a heat conduction process, and the heat conduction process is described by a Fourier law;
(2) radius r of the design nucleuscRadius r of inner and outer shellss1、rs2(ii) a To satisfy the area fraction condition: p is a radical ofc-p120; wherein p isc＝(rc/rs1)2，p12＝(rs1/rs2)2；
(3) Setting the thermal conductivity of the inner and outer shell layers: k is a radical ofs1、ks2To satisfy the thermal conductivity condition: k is a radical of12+ks20; wherein the content of the first and second substances,kcthermal conductivity of the nucleus, pc＝(rc/rs1)2。
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Cited By (4)
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| CN111457236A (en) * | 2020-03-21 | 2020-07-28 | 复旦大学 | Full-thermal super surface presenting infrared thermal illusion and being invisible under visible light |
| CN112257316A (en) * | 2020-10-22 | 2021-01-22 | 华中科技大学 | Method for predicting sealing life of fuel cell |
| CN113160908A (en) * | 2021-04-30 | 2021-07-23 | 华中科技大学 | Dynamic thermal stealth device and method |
| CN113158457A (en) * | 2021-04-16 | 2021-07-23 | 太原理工大学 | Hot spoofing method and hot spoofing structure |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111457236A (en) * | 2020-03-21 | 2020-07-28 | 复旦大学 | Full-thermal super surface presenting infrared thermal illusion and being invisible under visible light |
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| CN112257316A (en) * | 2020-10-22 | 2021-01-22 | 华中科技大学 | Method for predicting sealing life of fuel cell |
| CN112257316B (en) * | 2020-10-22 | 2024-02-02 | 华中科技大学 | Method for predicting sealing life of fuel cell |
| CN113158457A (en) * | 2021-04-16 | 2021-07-23 | 太原理工大学 | Hot spoofing method and hot spoofing structure |
| CN113160908A (en) * | 2021-04-30 | 2021-07-23 | 华中科技大学 | Dynamic thermal stealth device and method |
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