Thermal Rectification Research Articles

Influence of Shrinkage on Phase Change Material-based Thermal Rectifiers

Thermal rectifiers have recently emerged as a field of interest because of their potential application in a wide-ranging field. Thermal rectifiers can be employed to shield heat-sensitive electronics components, building thermal management and thermal energy conversion. A thermal rectifier allows heat transfer in a preferred direction while curtailing heat transfer in the reverse direction. Recently, the thermal conductivity differential of Phase Change Materials (PCMs) in their different states has been employed to develop thermal rectifiers. However, these studies are limited to analyzing the effect of change in the thermal conductivity alone, neglecting the influence of change in other thermophysical properties. The difference in PCM density in different states leads to the development of void volume upon phase transition, which can significantly alter thermal rectification. Therefore, this study analyzes the interdependent influence of thermal conductivity and density on thermal rectification under a wide range of temperature biases. The presence of void volume under reverse bias augments thermal rectification, whereas it has an adverse effect when developed under the forward bias. A criterion is developed to identify when the influence of density negates that of thermal conductivity, which requires the design of the thermal rectifier to be altered. Furthermore, optimization criteria and expressions for optimal thermal rectification are developed, incorporating the influence of both thermal conductivity and density.

Thermal rectification effect of pristine graphene induced by vdW heterojunction substrate

As an effective means of thermal management, thermal rectification (TR) has been studied in a variety of complex asymmetric or heterogeneous structures. Due to experimental conditions, many complex structures cannot be realized easily, and the low-temperature thermal bath temperature far below room temperature does not conform to the actual application environment of the device. In this paper, we studied the thermal rectification inside graphene supported by a heterogeneous substrate of SiO2 and GaN alternately. Heat flux is easier to transfer from the graphene covered on the SiO2 side to the GaN side. When the temperature of the cold bath is maintained at 300 K, only the temperature of the high-temperature hot bath is changed, and the maximum TR rate is about 52%. TR rate can be tuned by heat source temperature and size, with heat source size of 2 nm and temperature above 450 K, the highest TR rate can be obtained. The phonon density of states and participation ratio reveal the influence of the substrate and position on the phonon transport in graphene. Besides, the spectral energy density analysis confirmed that the substrate effect caused the shift of the graphene flexural phonon mode and the reconstruction of the phonon spectrum, which was in good agreement with PDOS, and further explain the basic mechanism of TR from the scattering rate and the degree of localization.

Thermal conduction and rectification phenomena in nanoporous silicon membranes.

Non-equilibrium molecular dynamics simulations have been applied to study thermal transport properties, such as thermal conductivity and rectification, in nanoporous Si membranes. Cylindrical pores have been generated in crystalline Si membranes with different configurations, including step-like, ordered and random pore distributions. The effect of interface and overall porosity on thermal transport properties has been investigated as well as the impact of the porosity profile on the direction of the heat current. The lowest thermal conductivity and highest thermal rectification for equal porosity have been found for a step-like pore distribution. Increasing interface porosity resulted in an increase of thermal rectification, which has been found to be systematically higher for random pore distribution with respect to an ordered one. Furthermore, a maximum in rectification of 5.5% has been found for a specific overall porosity (Φtot = 0.02) in samples with constant interface porosity and ordered pore distribution. This has been attributed to an increased effect of asymmetric interface boundary resistance resulting from increased fluctuations of the latter with altering temperature. The average value of the interface boundary resistance has been found to decrease with increasing porosity for samples with ordered pore distribution leading to a decrease in thermal rectification.

Технологии и материалы для ремонта автомобильных дорог в районах распространения много-летнемерзлых грунтов

This paper addressed the selection of overhaul methods for roads in the permafrost area. Ensuring the strength and stability of the road base and engineering structures under the permafrost conditions and deep seasonal freezing of soils remains one of the main scientific and technical challenges of road construction and maintenance in the northern regions. The main factors causing the failure of road structures were reviewed, including both climate change and complex geological and hydrogeological conditions of the area. Since the construction of the Amur Road, the deformation has been observed in many of its sections. In 2012, the Federal State Institution of Road Management “Zabaykalye”, to-gether with engineering and scientific organisations, developed a target programme for inspecting such sections. The article discusses the renovation measures and technologies elaborated under this programme, which include the construction of culverts, rockfills, thermal diodes and cooling layers, awnings, and protective berms. The monitoring of the repaired sections shows insignificant defor-mation of the road surface and road base; 55 % of the sections were fully stabilised. However, the fi-nal assessment of the permafrost stabilisation will take a longer time. The establishment of an effective system of engineering-geocryological monitoring for the Amur Road should become the most im-portant measure, whose implementation will allow dangerous deformations to be prevented and effi-cient measures for protecting the roadbed from their negative impact to be developed.

Anatomical identification and evaluation of improvement on dimensional stability in amazonian species thermal rectification

RESUMO A Termorretificação é um método que se utiliza visando incrementar as propriedades físicas, químicas e mecânicas da madeira, expondo amostras a temperaturas elevadas. No presente estudo, avaliaram-se as melhorias e implicações proporcionadas pela termorretificação nas espécies amazônicas Angelim Vermelho, Cedro, Quaruba e Muiracatiara, quanto às alterações nas propriedades físicas, alterações na coloração, possíveis trincas, além disso, foi realizada a identificação anatômica destas espécies. A termorretificação foi realizada a temperaturas de 130, 150 e 170 °C. As maiores alterações na coloração foram evidenciadas nas espécies Angelim Vermelho e Muiracatiara. O aparecimento de trincas foi observado, principalmente, a 170 °C. A perda de massa foi diretamente proporcional ao emprego de maiores temperaturas. Alterações na densidade da madeira foram verificadas após o processo de termorretificação, com destaque para o Angelim Vermelho, seguindo um padrão linear com redução da densidade de acordo com o aumento das temperaturas aplicadas. Os ensaios da variação volumétrica revelaram uma redução da higroscopicidade das espécies tratadas em relação às testemunhas, exceto para o tratamento do Angelim Vermelho a 130 ºC. A análise anatômica possibilitou a identificação até nível de espécie, sendo as espécies estudadas: Dinizia excelsa Ducke, Cedrela fissilis Vell, Astronium ulei Mattick e Vochysia maxima Ducke, para Angelim Vermelho, Cedro, Muiracatiara e Quaruba.

Highly-efficient radiative thermal rectifiers based on near-field gap variations.

Near-field radiative thermal rectifiers (NFRTRs) enabling directional heat transport hold great promise for various applications, including thermal logic computing, thermal management, and energy conversion. Current NFRTR designs rely on dissimilar terminal materials with high contrasts in their temperature-dependent dielectric properties, which in turn hinders the spectral match for radiative heat transfer and thus limits the device's efficiency. Herein, this dilemma is solved by designing heterostructures where a pair of polaritonic layers are separately stacked on a thermally-expanding layer and a rigid substrate, spaced by a vacuum gap. In this scheme, the symmetric polaritonic layers can provide stable near-field radiative channels for heat transfer, while the thermally-expanding layer can modulate the gap size with flipped temperature bias to allow high contrasts in heat flux. In exemplified implementations, the hBN-based design has achieved a record-high thermal rectification factor (TRF, ∼104) even under small thermal gradients (∼20 K), which can be further boosted by polaritonic hybridizations in the graphene/hBN-based design. This study paves the way to design novel NFRTRs with 2D materials, thus providing enriched polaritons to realize higher TRFs.

Magnetohydrodynamic Thermal Diode Using Natural Convection of In-Ga-Sn Alloy in a Square Enclosure with an Insulating Body

Magnetohydrodynamic Thermal Diode Using Natural Convection of In-Ga-Sn Alloy in a Square Enclosure with an Insulating Body

The Use of a Thermal Diode Bridge for Passive Temperature Control in the Built Environment During the Heating Seasons – an Analytical Study

The Use of a Thermal Diode Bridge for Passive Temperature Control in the Built Environment During the Heating Seasons – an Analytical Study

Energy-Saving Potential of Thermal Diode Tank Assisted Refrigeration and Air-Conditioning Systems

Lowering the condensing temperature of the Refrigeration and Air-conditioning (RAC) system has been proven to effectively increase the system’s Coefficient of Performance (COP). This paper revolves around evaluating the energy-saving generated by applying a Thermal Diode Tank (TDT) in the RAC systems. The TDT is a novel invention, which is an insulated water tank equipped with gravity heat pipes. If the TDT was placed outdoors overnight, its inside water would theoretically be at the minimum ambient temperature of the previous night. When the TDT water is used to cool the condenser of RAC systems that operate during the daytime, a higher COP of this TDT assisted RAC (TDT-RAC) system could be achieved compared with the baseline system. In this study, a steady-state performance simulation model for TDT-RAC cycles has been developed. The model reveals that the COP of the TDT-RAC cycle can be improved by 10~59% over the baseline cycle depending on the compressor types. The TDT-RAC cycle with a variable speed compressor can save more energy than that with a fixed speed compressor. In addition, TDT-RAC cycles can save more energy with a higher day/night ambient temperature difference. There is a threshold tank size for a given TDT-RAC cycle to save energy, and the energy-saving can be improved by enlarging the tank size. A desk-top case study based on real weather data for Adelaide in January 2021 shows that 9~40% energy could be saved by TDT-RAC systems every summer day on average.

Temporally-adjustable radiative thermal diode based on metal-insulator phase change

Thermal diode, which allows heat transfer between two terminals in one direction but blocks it in the opposite direction, has attracted extensive attention in recent years because of its potential applications in thermal management, energy systems, information processing and so on. Compared to the conductive thermal diode, the photon-based radiative thermal diode can break the performance limitations and achieve better thermal rectification effect. In this study, a temporally-adjustable radiative thermal diode consisting of vanadium dioxide (VO2) and blackbody is proposed. Based on the metal-insulator phase change of vanadium dioxide, the thermal rectification could be modulated with time, thus enabling time-dependent heat flow control. The influence of shape factors on the thermal rectification is specifically investigated, revealing that the thermal rectification effect is positively correlated with the ratios of inner and outer radius of cylindrical and spherical radiative thermal diodes, and the thermal rectification effect of planar diode is stronger than that of cylindrical or spherical diode under the same settings. The temporally-adjustable photon-based thermal diode is demonstrated to be more powerful with large thermal rectification ratio, precise control of heat, and configuration adjustability.

Hybrid model combining multivariate regression and machine learning for the rapid prediction of interior temperatures affected by thermal diodes and solar cavities

Sustainable design often requires highly efficient building performance evaluations. This study proposed a hybrid model combining multivariate regression modelling (MRM) and machine learning modelling (MLM) for the rapid prediction of interior temperatures affected by heat pipe thermal diodes and solar cavities based on experimental data. A heat pipe thermal diode can promote unidirectional heat transmission from the solar cavity on the south side of our newly built experimental house to the indoor environment to increase the interior temperature and reduce the heating load in cold climates. Experimental data were collected and then imported, cleaned, and split according to MRM and MLM requirements, respectively. In MRM, linear multivariate formulas were generated according to the thermal diode's two different working conditions. In MLM, a machine-learning model was created and trained using the experimental data. The results our hybrid model produced were comprehensively evaluated via R-square, statistical discrepancies, and complex MRM analyses. The similarity between the prediction and experimental results clearly demonstrates our model's accuracy and efficiency. This research was an original attempt to integrate emerging computational tools and provide a means to perform highly efficient quantitative analysis of indoor thermal environments for environmental studies and sustainable designs in the early stages.

Near-field thermal rectification driven by nonreciprocal hyperbolic surface plasmons

In this work, we theoretically demonstrate a pathway for highly efficient near-field thermal rectification. We propose the use of nonreciprocal hyperbolic surface plasmon polaritons (NHSPPs) supported by a drift-biased graphene grating to rectify the radiative heat flux between the two dielectric particles. At higher chemical potentials, we achieve theoretical rectification ratios over 88.67, which is a 460-fold improvement over the case of a drift-biased graphene sheet. By adjusting the value of the drift current or the orientation of the graphene ribbons, the NHSPPs can be actively manipulated, hence inducing the modulation of the rectification effect. We discuss the influence of the filling ratio of the grating and the height of the particles from its surface on the near-field radiative heat transfer. We find that the rectification ratio and the heat flux between the particles can be adjusted over a broad range by controlling the height of the particles. Compared with a drift-biased graphene sheet, the directional stability of the diode was also enhanced. This work provides an idea for the thermal management of micro- and nanoscale devices.

Thermal Diodes Based on Fractal Structures with Tunable Thermal Threshold

AbstractThe asymmetry of heat conduction in thermal diodes is attributed to the thermal regulation in thermal logic circuits, thermal control devices, etc. Currently, thermal rectification devices, however, are constrained by either specific on/off switching thresholds, or low sensitivity to manufacturing errors, as well as the restrictions for specific roughness and material characteristics. Here, a thermal diode based on fractal structures (inverted tapered branch channel, 5.7 mm branch length, and 4 branches) with liquid metal/insulator interface is proposed to avoid these existing constraints. The thermal rectification coefficient reaches 0.4704 (16.43 times larger than that of the basic structures) when the filling fraction only increases 1.33 times. The maximum temperature difference for the optimized thermal diodes is 18.31 °C when the heating temperature is 80 °C. By different arrangements of two thermal diodes mounted on chambers’ surfaces, the interior temperatures range from 16.06 to 52.34 °C in the same ambient conditions (23.49 °C), indicating the excellent thermal regulation effect of the thermal diodes. These controlled temperature chambers can be applied in greenhouses or cold chain storage devices, more combinations with higher degree of thermal‐threshold tunability offer possibilities in solving complicated thermal management problems and promote the energy utilization efficiency.

Heat transport across graphene/hexagonal-BN tilted grain boundaries from phase-field crystal model and molecular dynamics simulations

We study the interfacial thermal conductance of grain boundaries (GBs) between monolayer graphene and hexagonal boron nitride (h-BN) sheets using a combined atomistic approach. First, realistic samples containing graphene/h-BN GBs with different tilt angles are generated using the phase-field crystal model developed recently [P. Hirvonen et al., Phys. Rev. B 100, 165412 (2019)] that captures slow diffusive relaxation inaccessible to molecular dynamics (MD) simulations. Then, large-scale MD simulations using the efficient GPUMD package are performed to assess heat transport and rectification properties across the GBs. We find that lattice mismatch between the graphene and h-BN sheets plays a less important role in determining the interfacial thermal conductance as compared to the tilt angle. In addition, we find no significant thermal rectification effects for these GBs.

Asymmetrical carbon nanotubes exhibit opposing thermal rectification behaviors under different heat baths

Asymmetrical nanostructures are leading candidates to create efficient thermal rectifiers critical in thermal management and energy conversion systems. Due to their nanoscale size and inherent non-equilibrium nature, their working principles are commonly elucidated through non-equilibrium molecular dynamic simulations. Using asymmetrical carbon nanotubes, the resulting thermal rectification under different heat baths is found to differ in magnitude and direction. We find that nanotubes with the Langevin baths have a higher thermal conductivity in one heat flow direction due to the low-frequency phonons, resulting in a positive rectification. On the other hand, nanotubes with the Nose-Hoover baths show similar thermal conductivity contributions in both heat flow directions across the whole phonon frequency range, culminating in a negative rectification. Our work highlights how asymmetrical carbon nanostructures can rectify heat flow differently under different heat baths and provides strong evidence for the need to consider their non-equilibrium phonon spectrum before analyzing any associated nanoscale thermal transport phenomena.

Radiative Thermal Diode via Hyperbolic Metamaterials

Hyperbolic metamaterials (HMMs) support propagating waves with arbitrarily large wavevectors over broad spectral ranges, and are uniquely valuable for engineering radiative thermal transport in the near field. Here, by employing a rational design approach based on the electromagnetic local density of states, we demonstrate the ability of HMMs to substantially rectify radiative heat flow. Our idea is to establish a forward-biased scenario where the two HMM-based terminals of a thermal diode feature overlapped hyperbolic bands which result in a large heat current, and suppress the reverse heat flow by creating spectrally mismatched density of states as the temperature bias is flipped. As an example, we present a few high-performance thermal diodes by pairing HMMs made of polar dielectrics and metal-to-insulator transition (MIT) materials in the form of periodic nanowire arrays, and considering three representative kinds of substrates. Upon optimization, we theoretically achieve a rectification ratio of 324 at a 100 nm gap, which remains greater than 148 for larger gap sizes up to 1 um over a wide temperature range. The maximum rectification represents an almost 1000-fold increase compared to a bulk diode using the same materials, and is twice that of state-of-the-art designs. Our work highlights the potential of HMMs for rectifying radiative heat flow, and may find applications in advanced thermal management and energy conversion systems.

Thermal rectification on asymmetric suspended graphene nanomesh devices

Graphene-based thermal rectification was investigated by measuring the thermal transport properties of asymmetric suspended graphene nanomesh devices. A sub-10 nm periodic nanopore phononic crystal structure was successfully patterned on the half area of the suspended graphene ribbon by helium ion beam milling technology. The ‘differential thermal leakage’ method was developed for thermal transport measurement without disturbance from the leakage of electron current through the suspended graphene bridge. A thermal rectification ratio of up to 60% was observed in a typical device with a nanopore pitch of 20 nm. By increasing the nanopore pitch in a particular range, the thermal rectification ratio showed an increment. However, this ratio was degraded by increasing the environmental temperature. This experiment suggests a promising way to develop a high-performance thermal rectifier by using a phononic crystal to introduce asymmetry on homogeneous material.

The qutrit as a heat diode and circulator

We investigate the heat transport properties of a three-level system coupled to three thermal baths, assuming a model based on superconducting circuit implementations. The system-bath coupling is mediated by resonators which serve as frequency filters for the different qutrit transitions. Taking into account the finite quality factors of the resonators, we find thermal rectification and circulation effects not expected in configurations with perfectly-filtered couplings. Heat leakage in off-resonant transitions can be exploited to make the system work as an ideal diode where heat flows in the same direction between two baths irrespective of the sign of the temperature difference, as well as a perfect heat circulator whose state is phase-reversible.

Heat rectification by two qubits coupled with Dzyaloshinskii-Moriya interaction.

We investigate heat rectification in a two-qubit system coupled via the Dzyaloshinskii-Moriya (DM) interaction. We derive analytical expressions for heat currents and thermal rectification and provide possible physical mechanisms behind the observed results. We show that the anisotropy of DM interaction in itself is insufficient for heat rectification, and some other form of asymmetry is needed. We employ off-resonant qubits as the source of this asymmetry. We find the regime of parameters for higher rectification factors by examining the analytical expressions of rectification obtained from a global master equation solution. In addition, it is shown that the direction and quality of rectification can be controlled via various system parameters. Furthermore, we compare the influence of different orientations of the DM field anisotropy on the performance of heat rectification. Finally, we investigate the possible interplay between quantum correlations and the performance of the quantum thermal rectifier. We find that asymmetry in the coherences is a fundamental resource for the performance of the quantum thermal rectifier.

Interfacial thermal conductance of graphene/MoS2 heterointerface

The thermal transport performance and thermal rectification characteristics of graphene/MoS2 heterointerface (G/M) are comprehensively studied in this paper. The influence of three different types of vacancy defects on thermal conductance is simulated using Molecular Dynamics method. We find that the single C-vacancy defects greatly enhance the interfacial thermal conductance (G) by 90% at the defect concentration of 5%, resulting from the enhanced interface coupling strength. We also find the temperature plays an important role in G. The interfacial thermal conductance of pristine G/M heterointerface increases of by 80% from 300 K to 700 K. In addition, an increase in both temperature and single C-vacancy defects concentration result in enhanced G/M thermal rectifier effect, and the thermal rectification ratio (TR) can reach 8% because of the superior interface coupling of M/G over G/M. It provides theoretical support for the application of graphene/MoS2 heterojunctions in heat rectifier devices.