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An unstructured Monte Carlo ray-tracing method for solving radiative heat transfer in 3D gray semitransparent medium
摘要： Monte Carlo ray-tracing method (MCRTM) is widely used for solving the Radiative Transfer equation (RTE) due to its high accuracy and flexibility. In this paper, a MCRTM is developed for solving the radiative heat transfer in gray semitransparent media with complex geometries which are discretized by 3D unstructured grids. A novel algorithm associated to unstructured four-node tetrahedron element is proposed for generating random emitting positions of rays, and the ray tracing process is performed based on Beer's law. Meanwhile, radiation distribution factors are used for calculating radiative source terms which are loaded to the grid. The present method is first validated by comparing the predictive results with those from previous studies on a cubic enclosure, a 3D L-shaped enclosure, and a 3D elliptical enclosure, respectively. Furthermore, a radiation-conduction heat transfer problem is examined in a cylindrical enclosure. All the comparisons show that the present method is in good agreement with these previous cases. This method can be well adapted to various complex geometries. In addition, since the source term is calculated by the radiation distribution factor, which can be reused for different conditions as long as the volumetric radiative properties remain unchanged, this will bring great advantage when coupled with other heat transfer models such as conduction, convection, combustion, etc.
关键词： Monte Carlo ray-tracing method,Radiative heat transfer,Semitransparent medium,Radiation distribution factor,Unstructured grids
更新于2025-09-23 15:23:52
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Radiative thermal conduction of molten tin sulfide estimated from its optical emission spectrum
摘要： Molten semi-conductors have potential utility in thermoelectrics or heat-management at high temperature (900 °C and above), though their development requires further analysis of their thermal conduction mechanisms, in particular radiative heat-transfer. Using a container-less method based on the floating zone furnace, the optical emission properties of a pendant droplet of molten tin sulfide (SnS) are investigated in the UV–visible (200–850 nm) and near IR (900–2050 nm) ranges. The emissivity results suggest a low emissivity for molten SnS at the peak of radiation for the temperature range of 890–950 °C. Corresponding estimates of radiative thermal conductivity suggest its minor contribution to the overall thermal conduction of molten SnS.
关键词： Container-less,Radiation,Melts,Emissivity,Radiative heat-transfer,Molten semi-conductor
更新于2025-09-23 15:23:52
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Evolution of the infrared emissivity of Ni during thermal oxidation until oxide layer opacity
摘要： The mid-infrared (3–22 μm) emissivity of high-purity Ni has been studied in its pure state, during an isothermal oxidation in air at 730 °C and in the fully oxidized state. Measurements in pure Ni were performed in Ar between 200 and 800 °C and a change of slope in the temperature dependence of the total normal emissivity around its Curie temperature (354 °C) was observed. An oxidation process was carried out at 730 °C for 33 days, when the emissivity stopped evolving and the results were representative of NiO. During the ?rst stages, the emissivity evolved forming the usual interference patterns of semi-transparent ?lms. A mixture of oscillatory and monotonic behaviours of the emissivity as a function of wavelength and oxide layer thickness was found, which manifests as a non-trivial evolution of the total normal emissivity, di?erent than that reported in previous studies. Finally, the emissivity of NiO was measured from below its Néel temperature (252 °C) to 850 °C. It showed the typical shape of a ceramic material with an extra vibrational mode due to two-phonon processes and an additional absorption band around 5 μm in the antiferromagnetic phase produced by magnons. The temperature dependence of its total normal emissivity di?ers signi?cantly from that of a lightly oxidized nickel sample from the literature. Overall, the in?uence of the surface characteristics on the thermal radiative properties of oxidized Ni is thoroughly discussed and highlights the importance of accounting for all possible sources of infrared emissivity evolution in order to make accurate radiative heat transfer calculations.
关键词： Nickel oxide,Infrared emissivity,Radiometry,Radiative heat transfer,Magnetic phase transition,Nickel,Oxidation
更新于2025-09-23 15:23:52
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A fully coupled numerical simulation of a hybrid concentrated photovoltaic/thermal system that employs a therminol VP-1 based nanofluid as a spectral beam filter
摘要： The realistic numerical modelling of multiphysics applications is an efficient way to precisely predict the operation of concentrated solar systems. Although many multiphysics conjugating approaches have been proposed in the literature, it is difficult to adopt such methods into simulating complex concentrated solar technologies. Consequently, this study introduces a novel 2D:3D numerical optical, thermal and electric coupling approach for a hybrid compound parabolic concentrator photovoltaic/thermal (CPC-PV/T) collector using a nanofluid as a spectral beam filter. In this approach, the volumetric absorbed radiation in each component of the system obtained from the non-gray 2D model is patched into the 3D model as a volumetric heat source using sophisticated computational tools. The main features of the full coupling method (FCM) are extensively analyzed and compared with the other two coupling methods previously adopted. Further, the module performance has been investigated employing both the nanofluid and base-fluid spectrum filters (BF-filter) compared with a stand-alone concentrated PV cell. From findings, the FCM can be applied to reveal more realistic operation characteristics of the proposed system compared with the other approaches, since the FCM can take into account the non-uniformity of solar illumination and the direction of reflected solar beams upon the receiver, along with the variation in the optical characteristics of utilized materials over the solar irradiance. Additionally, suspending indium tin oxide (ITO) nanoparticles into the Therminol VP1 oil raises the absorption rate over the thermal-bands with 62.5% higher than the use of BF-filter, whilst the cell temperature and the transmitted irradiance within the PV-band are obviously declined.
关键词： Radiative heat transfer,Multiphysics coupling method,Nanofluid,Concentrated photovoltaic/thermal system,Spectral beam filter
更新于2025-09-23 15:21:01
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Near-field radiative heat transfer between black phosphorus and graphene sheet
摘要： Low thermal conductivity of black phosphorus (BP) makes it difficult to cool BP-based electronic or optoelectronic devices. Therefore, developing a cooling strategy for BP-based nano devices is highly required. We theoretically study the near-field radiative heat transfer between BP sheets as well as between BP and graphene. We find that the heat transfer between BP sheets is determined by its electron doping. Plasmons excited by BP in different directions dominate the heat transfer for different electron doping. At optimum electron doping, heat transfer between the BP sheets increases significantly. The heat transfer between BP and graphene is dependent on both the electron doping of BP and chemical potential of graphene. Modulating the chemical potential of graphene can result in a strong coupling between graphene plasmons and BP plasmons, which will lead to a significant enhancement of heat transfer between BP and graphene. Our results are not only meaningful in controlling the heat transfer between BP-based structures but also helpful in developing cooling strategies for BP-based nano devices.
关键词： near-field radiative heat transfer,plasmons,graphene,black phosphorus,chemical potential,electron doping
更新于2025-09-23 15:21:01
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Near-Field Radiative Heat Transfer between Dissimilar Materials Mediated by Coupled Surface Phonon- and Plasmon-Polaritons
摘要： Near-field radiative heat transfer (NFRHT) between dissimilar materials supporting surface polaritons in the infrared is of critical importance for applications such as photonic thermal rectification and near-field thermophotovoltaics. Here, we measure NFRHT between millimeter-size surfaces made of 6H-SiC and doped Si, respectively supporting surface phonon-polaritons (SPhPs) and surface plasmon-polaritons (SPPs) in the infrared, separated by a 150-nm-thick vacuum gap spacing maintained via SiO2 nanopillars. For purpose of comparison, measurements are also performed between two doped Si surfaces. The measured radiative flux is in good agreement with theoretical predictions based on fluctuational electrodynamics. A flux enhancement beyond the blackbody limit of ~ 8.2 is obtained for the SiC-Si sample, which is smaller than the enhancement for the Si-Si sample (~ 12.5) owing to the spectral mismatch of the SiC and Si light lines, and SPhP and SPP resonances. However, due to lower losses in SiC than Si and weaker SPhP-SPP coupling than SPP coupling, the near-field enhancement for the SiC-Si sample exhibits a more pronounced monochromatic behavior with a resonant flux that is ~ 5 times larger than the resonant flux for the Si-Si sample. This work demonstrates that it is possible to modulate NFRHT via surface polariton coupling, and will accelerate the development of energy conversion and thermal management devices capitalizing on the near-field effects of thermal radiation between dissimilar materials.
关键词： radiative flux measurement,doped silicon,near-field radiative heat transfer,dissimilar materials,coupled surface phonon- and plasmon-polaritons,silicon carbide
更新于2025-09-23 15:19:57
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Evaluation of performance of near-field thermophotovoltaic systems based on entropy analysis
摘要： Near-field radiative heat transfer can significantly improve the output power of thermophotovoltaic (TPV) systems. Therefore, it is crucial to explore how to increase the energy conversion efficiencies of near-field TPV systems. In this study, based on the fluctuation–dissipation theorem with the effective medium theory, we evaluate the performance of a near-field TPV system from the formulation of thermodynamics. It is found that a near-field TPV system consisting of InAs or GaSb cell can achieve higher heat flux or efficiency limit, respectively. Moreover, the TPV system with a hyperbolic metamaterial (HMM) emitter composed of nanowire or nanohole arrays can achieve higher heat flux and efficiency limit compared to that of the bulk reference. This is attributable to the HMMs being able to support hyperbolic modes, and the radiation with the HMM emitter exhibits a favorable entropy content for the energy conversion efficiency. This work provides an approach to determine the efficiency limit and establish a target for efficiency of the near-field TPV system without considering how the system works. The results of this study will facilitate the design and application of the HMM emitter and material of the TPV cell to improve the efficiency of near-field TPV systems.
关键词： Thermophotovoltaic systems,Near-field radiative heat transfer,Energy conversion efficiency,Hyperbolic metamaterial,Entropy analysis
更新于2025-09-23 15:19:57
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Radiative Thermal Diode Mediated by Nonreciprocal Graphene Plasmon Waveguides
摘要： A thermal diode based on the asymmetric radiative heat transfer between nanoparticles assisted by nonreciprocal graphene plasmon waveguides is proposed in this work. The thermal diode system consists of two particles and a drift-biased suspended graphene sheet in close proximity of them. Nonreciprocal graphene plasmons are induced by the drift currents in the graphene sheet, and then couple to the waves emitted by the particles in near-field regime. Based on the asymmetry with respect to their propagation direction of graphene plasmons, the thermal rectification between the two particles is observed. The performance of the radiative thermal diode can be actively adjusted through tuning the chemical potential or changing the drift currents in the graphene sheet. With a large drift velocity and a small chemical potential, a perfect radiative thermal diode with a rectification coefficient extremely approaching 1 can be achieved within a wide range of interparticle distance from near to far field. The dispersion relations of the graphene plasmons are adopted to analyze the underlying physics of the rectification effect. In addition, due to the wide-band characteristic of nonreciprocal graphene plasmons, drift-biased graphene can act as a universal platform for the thermal rectification between particles. The particles with a larger particle resonance frequency are preferable to achieve a better thermal diode. This technology could find broad applications in the field of thermal management at nanoscale.
关键词： graphene plasmon waveguides,nonreciprocal,nanoparticles,radiative heat transfer,thermal diode
更新于2025-09-19 17:13:59
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Direct Determination of Total Hemispherical Emittance of Perovskite and Silicon Solar Cells
摘要： Because the performance and lifetime of a solar cell is sensitive to its operating temperature, an accurate knowledge of the total hemispherical emittance as a function of temperature is required. Granados et al. report a rapid transient calorimetry for the direct determination of total hemispherical emittance of perovskite and silicon solar cells over their operating temperature.
关键词： total hemispherical emittance,perovskite solar cells,silicon solar cells,transient calorimetry,radiative heat transfer
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Periodic Amplification of Radiative Heat Transfer
摘要： The thermal excitation of materials with a periodic heat flux or temperature modulated in time is a reliable and accurate tool usually applied to determine thermal properties, through techniques such as thermoreflectance, photothermal radiometry, 3ω, photoacoustics, thermal-wave resonant cavity, etc. Moreover, over the past years, the control of heat flux has been improved by means of phase-change materials (PCMs), whose internal structures are strongly driven by their temperature, which results in significant variations of their thermal, optical, and electrical properties. Thermochromic materials (VO2, nitinol) or superconductors are examples of such PCMs, where the material can be either in an insulator phase, with low thermal/electrical conductivity and high emissivity, or in a metallic one characterized by a high thermal/electrical conductivity and low emissivity. This metal-insulator transition (MIT) occurs at the critical temperature of each PCM and can therefore be used to tune the heat currents that the PCM exchanges with the environment, which paves the wave for novel applications.
关键词： radiative heat transfer,metal-insulator transition,thermochromic materials,thermal excitation,phase-change materials
更新于2025-09-11 14:15:04