A near-field radiative thermal rectification device and its design method

Abstract

The present invention discloses a near-field radiative thermal rectification device and its design method, which relates to the technical intersection field of nanophotonics and micro-nano scale heat transfer, and includes: a thermally sensitive active layer, a first radiative layer, a fixed near-field gap, a second radiative layer, and a rigid substrate are sequentially arranged from top to bottom. The design method involved in the present invention mainly utilizes the steep dependence of near-field radiative heat flux on the gap size of the radiative surface, and can achieve a thermal rectification ratio of 3 to 5 orders of magnitude under different temperature biases; this method can overcome the disadvantages of difficult design and low thermal rectification efficiency of the terminal materials of existing radiative thermal rectifiers, and has the advantages of simple and flexible design, and can realize dynamic modulation of the near-field radiative thermal rectification effect, etc.

Description

Technical Field

[0001] The present invention relates to the technical intersection field of nanophotonics and heat transfer at the micro-nano scale, and particularly relates to a near-field radiative thermal rectification device and a design method thereof. Background Art

[0002] A thermal rectifier is an analogue of an electronic diode that can control the unidirectional flow of heat and has potential application prospects in fields such as thermal logic operations, thermal management, and energy utilization. As a two-terminal thermal device, the magnitude of the heat flux of a thermal rectifier depends on the direction of the applied temperature bias. Usually, the rectification ratio ζ is used to characterize its rectification performance, ζ = (Q F -Q R ) / Q R , where Q F and Q R represent the radiative heat fluxes under forward and reverse temperature biases, respectively. The rectification ratio should be at least higher than 10 to ensure high technical efficiency of the thermal rectifier.

[0003] Traditional thermal rectifiers mainly rely on phonon heat conduction, which is designed by establishing non-linearity in the heat conduction channels between the two terminals. For example, by designing a single-component material with spatial asymmetry and non-linear thermal conductivity, or by designing non-linear phonon heat transport at the interface between different materials. However, due to limitations such as the low group velocity of phonons, strong phonon interface scattering, and multi-phonon collisions, this method has achieved extremely low thermal rectification ratios (ζ < 1) both theoretically and experimentally. In contrast, radiative thermal rectifiers based on near-field photon tunneling have received extensive attention in recent years due to their potential to generate thermal rectification ratios of more than an order of magnitude.

[0004] The key to realizing a near-field radiative thermal rectifier is to design materials or structures with different temperature-dependent electromagnetic properties at the two terminals. The basic idea is that under a given forward bias, spectral overlap of electromagnetic modes between the terminals should be obtained to ensure a significant enhancement of the near-field radiative heat flux; while when the bias is reversed, the spectral overlap is significantly reduced due to the temperature-dependent electromagnetic properties, thereby strongly suppressing heat exchange. In this way, a high contrast of radiative heat fluxes, that is, a high rectification ratio, can be achieved. So far, the literature has widely explored different terminal material pairings, including 3C-SiC and 6H-SiC, SiC and SiO 2 , InSb and graphene / SiO 2 , InSb and h-BN, phase change materials such as VO 2and another heterogeneous material, etc. Obviously, these designs naturally result in an asymmetric terminal configuration, and their mismatched dielectric properties largely hinder the possibility of spectral matching. This paradox greatly limits the transfer of near-field heat flux in the rectifier, thereby leading to a limited increase in the thermal rectification ratio. Therefore, it remains a formidable challenge to achieve an efficient (ζ>100) near-field radiative thermal rectifier through a reasonable design of terminal materials pairs.

[0005] Therefore, it is an urgent problem for those skilled in the art to propose a near-field radiative thermal rectification device and its design method to solve the difficulties existing in the prior art. Summary of the Invention

[0006] In view of this, the present invention provides a near-field radiative thermal rectification device and its design method, which overcome the disadvantages of difficult design of terminal material pairs and low thermal rectification efficiency in existing radiative thermal rectifiers. The design method is simple and flexible, and can realize the dynamic modulation of the near-field radiative thermal rectification effect based on the temperature-controlled gap change.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A near-field radiative thermal rectification device, comprising:

[0009] A heat-sensitive active layer, a first radiation layer, a fixed near-field gap, a second radiation layer, and a rigid substrate are sequentially arranged from top to bottom.

[0010] Optionally, the first radiation layer covers the heat-sensitive active layer to form a forward-biased hot-end heterojunction, and the second radiation layer covers the rigid substrate to form a forward-biased cold-end heterojunction.

[0011] Optionally, the first radiation layer and the second radiation layer are materials that support frustrated total internal reflection or infrared polaritons, and the surface evanescent wave tunneling mediated by them enhances the near-field radiative heat flux.

[0012] Optionally, the gap between the first radiation layer and the radiation layer is the fixed near-field gap, and the gap size is 10 nm to 10 μm.

[0013] Optionally, the heat-sensitive active layer is made of a material with a thermal expansion coefficient β>10 -5 K -1 and the rigid substrate is made of a material with a thermal expansion coefficient β≈10 -7 K -1

[0014] ​Optionally, the thermally sensitive active layer, the first radiative layer, the second radiative layer, and the rigid substrate are all functional layers with a modular design. The first radiative layer and the second radiative layer are a single-material continuous thin film layer, or a thin layer with a specific nanostructure design, or a heterostructure layer with different materials and nanostructure designs.

[0015] A design method for a near-field radiative heat rectification device, which utilizes the steep dependence of near-field radiative heat flux on the radiative surface gap to achieve a large rectification ratio, includes the following steps:

[0016] S101. Design the hot-end heterojunction and the cold-end heterojunction of the near-field radiative heat rectifier;

[0017] S201. Control the gap of the near-field radiative heat rectifier and operate it.

[0018] Optionally, S101 specifically includes the following steps:

[0019] S1011. Select two materials with a thermal expansion coefficient difference Δβ > 10 2 K -1 as the temperature-responsive layers, where the material with a relatively high thermal expansion coefficient is used as the thermally sensitive active layer of the hot-end heterojunction under forward bias, and the material with a relatively low thermal expansion coefficient is used as the rigid substrate of the cold-end or two-terminal heterojunction;

[0020] S1012. Select a thin layer of material that supports frustrated total internal reflection or infrared polariton modes as the radiative layer, and design and cover it symmetrically on the thermally sensitive active layer of the hot-end heterojunction and the rigid substrate of the cold-end heterojunction respectively to obtain the first radiative layer and the second radiative layer;

[0021] S1013. Separate the hot-end heterojunction and the cold-end heterojunction by the fixed near-field gap as the two terminals of the near-field radiative heat rectification device; selectively integrate a rigid substrate at the bottom of the two terminals to provide necessary support for the designed heterostructure.

[0022] Optionally, S201 specifically includes the following steps:

[0023] S2011. The hot-end heterojunction and the cold-end heterojunction are separated by a fixed near-field gap. When the temperature bias is reversed, the first radiative surface of the first radiative layer moves unidirectionally along its normal due to the thermal expansion / contraction of the thermally sensitive active layer;

[0024] S2012. When a positive temperature bias ΔT is applied to the hot - end heterojunction and the cold - end heterojunction, the change in the gap Δd between the first radiation surface and the second radiation surface can be controlled by the thickness t of the thermally sensitive active layer, the thermal expansion coefficient β, and the applied temperature bias ΔT: Δd = βtΔT;

[0025] The gap size corresponding to the forward bias is d f = d r - Δd, where d f and d r are the gap sizes under forward and reverse temperature biases respectively; when controlling d f = 10 - 200 nm, due to the effective coupling of thermally excited infrared polaritons between the surfaces of the first radiation layer and the second radiation layer, the evanescent - field tunneling mediated by them can achieve an enhancement of the near - field radiative heat flux by 3 - 5 orders of magnitude compared to black - body radiation;

[0026] S2013. When the temperature bias is reversed, the gap between the first radiation surface and the second radiation surface increases due to the thermal contraction of the thermally sensitive active layer, reducing the number of electromagnetic modes that mediate photon tunneling through the gap to enhance heat transfer, thereby resulting in a reduction in the order of magnitude of the near - field radiative heat flux amplitude.

[0027] Optionally, the contrast of the thermal expansion coefficients of the materials of the active layer and the rigid substrate > 10 2 ;

[0028] Optionally, the first radiation layer and the second radiation layer separated by the fixed near - field gap are symmetrically arranged, with the same material and structure design.

[0029] Through the above - mentioned technical solutions, compared with the prior art, the present invention provides a near - field radiative heat rectification device and its design method: 1) For the first time, a general design method for achieving an efficient near - field radiative heat rectifier by using the change in the gap size between radiation surfaces caused by thermal expansion of materials is proposed, solving the problems of difficult material pairing and low efficiency in existing heat rectification technologies; 2) For the heat rectification device designed based on this method, materials that support frustrated total internal reflection or infrared polariton modes can be used arbitrarily, thereby achieving an order - of - magnitude increase in the rectification ratio by utilizing the characteristic that the near - field radiative heat flux decays exponentially as the gap size increases; 3) The design method has the characteristics of high modularity, and various material and structure combinations can be used for design, breaking through the limitations of the original device material selection and structure design; 4) The designed heat rectification device is applicable to all temperature ranges that the application materials can withstand, expanding the temperature range of use of the device and improving the practicality of the device; 5) It breaks through the design principle of traditional heat rectification devices and has good practicality and feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the provided drawings.

[0031] Figure 1 Schematic structural diagram of a near-field radiative heat rectification device provided by the present invention;

[0032] Figure 2 Schematic cross-sectional structure diagram of the near-field radiative heat rectification device provided by the present invention;

[0033] Figure 3 Schematic diagram of the working principle of the heat rectification device provided by the present invention: among them, 3.1 is the schematic diagram of the working principle of the heat rectification device under forward temperature bias, and 3.2 is the schematic diagram of the working principle of the heat rectification device under reverse temperature bias;

[0034] Figure 4 Near-field radiative heat flux distribution and corresponding heat rectification ratio of the embodiment of the present invention under different temperature biases in a specific material combination design (graphene / hBN heterostructure as the symmetric radiation layer, PDMS as the thermally expandable active layer, and quartz as the rigid substrate);

[0035] Figure 5 Physical mechanism for achieving a large rectification ratio in the above material combination of the embodiment of the present invention;

[0036] Figure 6 Exponential dependence of the near-field radiative heat flux on the gap change and rectification potential for achieving a rectification ratio of nearly four orders of magnitude in the embodiment of the present invention;

[0037] Figure 7 Flowchart of a design method for a near-field radiative heat rectification device provided by the present invention;

[0038] Figure 8 Specific flowchart of S101 provided by the present invention;

[0039] Figure 9 Specific flowchart of S201 provided by the present invention.

[0040] Wherein: 1 - thermally sensitive active layer, 2 - first radiation layer, 3 - second radiation layer, 4 - rigid substrate, 5 - fixed near-field gap. Detailed implementation manners

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Referring to Figure 1 and Figure 2 as shown, the present invention discloses a near-field radiative thermal rectification device, including:

[0043] An active layer 1, a first radiation layer 2, a fixed near-field gap 5, a second radiation layer 3, and a rigid substrate 4 are sequentially arranged from top to bottom.

[0044] Further, the first radiation layer 2 covers the active layer 1 to form a forward-biased hot-end heterojunction, and the second radiation layer 3 covers the rigid substrate 4 to form a forward-biased cold-end heterojunction.

[0045] Further, the gap between the first radiation layer 2 and the second radiation layer 3 is the fixed near-field gap 5.

[0046] Further, the active layer 1 is made of a material with a coefficient of thermal expansion β>10 -5 K -1 , and the rigid substrate 4 is made of a material with a coefficient of thermal expansion β≈10 -7 K -1 .

[0047] Further, the thermally sensitive active layer 1, the first radiation layer 2, and the second radiation layer 3 are all functional layers that can be modularly designed. The first radiation layer 2 and the second radiation layer 3 can be a continuous thin film layer of a single material, or a thin layer with a fine nanostructure design, or a multi-layer heterostructure layer with different material and nanostructure designs.

[0048] Further, the material of the thermally sensitive active layer 1 can be selected as: flexible polymer materials such as polydimethylsiloxane (PDMS, β≈3×10 -4 K -1 ), polyvinylidene fluoride (PVDF, β≈1.27×10 -4 K -1 ), etc., or other high thermal expansion composite materials;

[0049] The material of the rigid substrate 4 can be selected as a rigid substrate material with a negligible coefficient of thermal expansion (β~10 -7 K -1 ), such as S i , CaF 2 , BaF 2 , SiO 2 , etc.;

[0050] The radiative layer (the first radiative layer 2 and the second radiative layer 3) is a material that supports the frustrated total internal reflection mode, or the infrared-range plasmon or phonon polariton mode, such as conventional bulk materials like intrinsic silicon, doped silicon, or polar dielectric materials such as SiO 2 , SiC, or low-dimensional van der Waals materials such as graphene, black phosphorus, hexagonal boron nitride, molybdenum oxide, and vanadium oxide.

[0051] The first radiative layer 2 and the second radiative layer 3 can be a continuous thin film layer of a single material, or a thin layer with a fine nanostructure design, such as periodic nanobands, nanodisks, etc., or a heterostructure layer with different material and structure designs. The fine nanostructure design can be achieved by means such as ultraviolet lithography, electron beam lithography, and focused ion beam lithography.

[0052] Furthermore, the thickness of the thermally sensitive active layer 1 is specifically determined according to the required gap size change, the actual operating temperature bias, and the material's thermal expansion coefficient; the thickness of the two symmetric radiative layers (the first radiative layer 2 and the second radiative layer 3) is 0.334 nm to 2000 nm.

[0053] Furthermore, the radiative layer (the first radiative layer 2 and the second radiative layer 3) can be covered on the thermally sensitive active layer 1 and the rigid substrate 4 by methods such as chemical vapor deposition growth, magnetron sputtering, thermal oxidation, dry / wet transfer, etc., according to the actually selected materials.

[0054] See Figure 3 As shown, the working principle of the near-field radiative thermal rectifier designed by the present invention mainly includes two processes: as Figure 3 .1 shows, when a forward bias is applied, the thermally sensitive active layer 1 of the hot-end heterojunction makes the vacuum gap 5 smaller due to thermal expansion, resulting in a greatly enhanced near-field radiative heat flux due to the effective coupling of the polariton modes between the first radiative layer 2 and the second radiative layer 3; as Figure 3 .2 shows, when the temperature bias is reversed, the thermally sensitive active layer 1 of the hot-end heterojunction makes the vacuum gap 5 larger due to thermal contraction, resulting in a rapid reduction in the amplitude of the radiative heat flux due to the evanescent field of the polariton mode between the first radiative layer 2 and the second radiative layer 3 decaying exponentially along the surface normal.

[0055] See Figure 4 As shown, it is the distribution of the near-field radiative heat flow and the rectification ratio of the rectifier designed by the present invention using a specific material combination at different temperature biases. The near-field radiative heat flow is calculated by the fluctuation-dissipation theorem. When using a graphene / hexagonal boron nitride heterojunction as the first radiative layer 2 and the second radiative layer 3, PDMS as the thermally sensitive active layer 1, and SiO 2 as the rigid substrate 4, an ultra-high rectification ratio of about 7000 can be achieved at a temperature bias of 200 K.

[0056] See Figure 5 As shown, the photon tunneling cloud map and spectral heat flux distribution of the near-field radiative heat flux mediated by the corresponding thermal rectifier of the present invention are presented. The distribution of the photon bright bands in the cloud map clearly shows that the effective coupling of graphene plasmons and hexagonal boron nitride phonon polaritons leads to a significant enhancement of the near-field radiative heat flux; however, as the gap size increases, the modes with relatively small transverse wave vectors are greatly weakened in radiative heat flux due to their rapid decay. This trend can be further illustrated by Figure 5 .3, where the magnitude of the spectral heat flux under forward bias is about three orders of magnitude higher than that under reverse bias.

[0057] As Figure 6 shown, the dependence of the calculated near-field radiative heat flux on the gap of the present invention and the thermal rectification potential corresponding to different gap changes are presented. Ideally, the radiative thermal rectifier obtained by the present invention can achieve a record-high rectification ratio of about four orders of magnitude. In addition, the trend that the thermal rectification ratio continuously increases with the increase of the gap indicates the possibility of realizing the control of the gap change by applying a time-varying temperature, and further realizing the dynamic modulation of the thermal rectification ratio.

[0058] See Figure 7 shown, the present invention discloses a design method for a near-field radiative thermal rectification device, which utilizes the steep dependence of the near-field radiative heat flux on the gap of the radiative surface to achieve a large rectification ratio, including the following steps:

[0059] S101. Design the hot-end heterojunction and cold-end heterojunction of the near-field radiative thermal rectifier;

[0060] S201. Control the gap and operate the near-field radiative thermal rectifier.

[0061] Furthermore, see Figure 8 shown, S101 specifically includes the following steps:

[0062] S1011. Select two materials with a difference in thermal expansion coefficient Δβ > 10 2 K -1 as the temperature-responsive layers, where the material with a relatively high thermal expansion coefficient is used as the active layer 1 of the hot-end heterojunction under forward bias, and the material with a relatively low thermal expansion coefficient is used as the rigid substrate 4 of the cold-end or both-end heterojunctions;

[0063] S1012. Select a thin layer of material that supports frustrated total internal reflection or infrared polariton modes as the radiative layer, and design it in a symmetric structure to cover the active layer 1 of the hot-end heterojunction and the rigid substrate 4 of the cold-end heterojunction respectively, to obtain the first infrared polariton radiative layer 2 and the second infrared polariton radiative layer 3;

[0064] S1013. Separate the hot - end heterojunction and the cold - end heterojunction by a fixed near - field gap, which serves as the two terminals of the near - field radiative heat rectification device. The fixed gap is in a vacuum state, obtaining a vacuum gap 5.

[0065] Further, as shown in Figure 8 , S201 specifically includes the following steps:

[0066] S2011. Separate the hot - end heterojunction and the cold - end heterojunction by a fixed near - field gap. When the temperature bias of the hot - end heterojunction is reversed, the first radiation surface of the first radiation layer 2 moves unidirectionally along its normal due to the thermal expansion / contraction of the thermally sensitive active layer.

[0067] S2012. When a positive temperature bias ΔT is applied to the hot - end heterojunction and the cold - end heterojunction, the change in the gap Δd between the first radiation surface and the second radiation surface can be controlled by the thickness t, the thermal expansion coefficient β of the first radiation layer 2 and the second radiation layer 3, and the applied temperature bias ΔT: Δd = βtΔT;

[0068] The gap size corresponding to the forward bias is d f = d r -Δd, where d f and d r are the gap sizes under forward and reverse temperature biases respectively. When controlling d f = 10 - 200 nm, due to the effective coupling of the first radiation layer 2 and the second radiation layer 3, the evanescent - field tunneling mediated by them can achieve an enhancement of the near - field radiative heat flux by 3 - 5 orders of magnitude compared to black - body radiation.

[0069] S2013. When the temperature bias is reversed, the gap between the first radiation surface and the second radiation surface increases due to the thermal contraction of the active layer 1, reducing the number of electromagnetic modes that mediate photon tunneling through the gap to enhance heat transfer, thereby resulting in a reduction in the magnitude order of the near - field radiative heat flux.

[0070] Further, the contrast of the thermal expansion coefficients of the materials of the active layer 1 and the rigid substrate 4 > 10 2 ;

[0071] Further, the first radiation layer 2 and the second radiation layer 3 separated by the fixed near - field gap 5 are symmetrically arranged, with the same material and nanostructure design.

[0072] The above description of the disclosed embodiments is presented in a progressive manner so that those skilled in the art can implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A near-field radiative thermal rectification device, characterized in that, it includes: a thermally sensitive active layer, a first radiative layer, a fixed near-field gap, a second radiative layer, and a rigid substrate are sequentially arranged from top to bottom; the first radiative layer and the second radiative layer are two symmetric radiative layers; the first radiative layer and the second radiative layer are materials that support frustrated total internal reflection or infrared polaritons, and the surface evanescent wave tunneling mediated by them enhances the near-field radiative heat flux; The thermally sensitive active layer is made of a material with a coefficient of thermal expansion β > 10 -5 K -1 and the rigid substrate is made of a material with a coefficient of thermal expansion β ≈ 10 -7 K -1 . the first radiative layer covers the thermally sensitive active layer to form a forward-biased hot-end heterojunction, and the second radiative layer covers the rigid substrate to form a forward-biased cold-end heterojunction; the first radiative layer and the second radiative layer are separated by the fixed near-field gap, and the gap size is 10 nm to 10 μm; the thermally sensitive active layer, the first radiative layer, and the second radiative layer are all functionally layered with modular design; the first radiative layer and the second radiative layer are continuous thin film layers of a single material, or thin layers with nanostructure design, or heterostructure layers corresponding to different materials and nanostructure designs.

2. A design method for the near-field radiative thermal rectification device as claimed in claim 1, characterized in that utilize the steep dependence of near-field radiative heat flux on the radiative surface gap to achieve a large rectification ratio, including the following steps: S101. Design the hot-end heterojunction and the cold-end heterojunction of the near-field radiative thermal rectifier; S201. Control the gap of the near-field radiative thermal rectifier and operate it; S101 specifically includes the following steps: S1011. Select two materials with a difference in coefficient of thermal expansion Δβ > 10 2 K -1 as the temperature-responsive layer, where the material with a relatively high coefficient of thermal expansion serves as the thermally sensitive active layer of the hot-end heterojunction under forward bias, and the material with a relatively low coefficient of thermal expansion serves as the rigid substrate of the cold-end or two-terminal heterojunction; S1012. Select a thin layer of material that supports frustrated total internal reflection or infrared polaritons as the radiative layer, and cover it on the thermally sensitive active layer of the hot-end heterojunction and the rigid substrate of the cold-end heterojunction respectively with a symmetric structure design to obtain the first radiative layer and the second radiative layer; S1013. Separate the hot-end heterojunction and the cold-end heterojunction by the fixed near-field gap as two terminals of the near-field radiative thermal rectification device, and selectively add a rigid substrate at the bottom of the two terminals to provide necessary support for designing the heterostructure; S201 specifically includes the following steps: S2011. The hot-end heterojunction and the cold-end heterojunction are separated by the fixed near-field gap. When the temperature bias is reversed, the first radiative surface of the first radiative layer moves unidirectionally along its normal due to the thermal expansion / contraction of the thermally sensitive active layer; S2012. When a positive temperature bias ΔT is applied to the hot-end heterojunction and the cold-end heterojunction, the change Δd in the gap between the first radiation surface and the second radiation surface of the second radiation layer can be controlled by the thickness t, the thermal expansion coefficient β, and the applied temperature bias ΔT of the thermally sensitive active layer: Δd = β t ΔT; The gap size corresponding to the forward bias is d f = d r -Δd, where d f and d r are the gap sizes under forward and reverse temperature biases respectively; when controlling d f = 10 - 200 nm, due to the effective coupling of infrared polaritons between the surfaces of the first radiation layer and the second radiation layer, the evanescent field tunneling mediated by it can achieve an enhancement of the near-field radiative heat flux by 3 - 5 orders of magnitude compared to blackbody radiation; S2013. When the temperature bias is reversed, the gap between the first radiative surface and the second radiative surface increases due to the thermal contraction of the thermally sensitive active layer, so that the number of electromagnetic modes that mediate photon tunneling through the gap to enhance heat transfer decreases, resulting in a reduction in the magnitude order of the near-field radiative heat flux; The thermal expansion coefficient contrast between the materials of the thermally sensitive active layer and the rigid substrate is greater than 10 2 ; the first radiative layer and the second radiative layer separated by the fixed near-field gap are symmetrically arranged, and their material and structure designs are the same.

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