Radiation Heat Transfer Model Research Articles

Finite-rate chemistry Favre-Averaged Navier-Stokes based simulation of a non-premixed SynGas/Air flame

Abstract The present paper is devoted to the study of the influence of chemical mechanisms, turbulence models and gas radiative properties models on the characteristics of a turbulent diffusion CO/H2/N2 -air flame, i.e., the so-called syngas flame in a Favre-averaged Navier-Stokes (FANS) environment. For this purpose, a transient FANS solver for combustion is used. The simulations are carried out using three distinct turbulence models, i.e., the standard k-ε (SKE), the renormalization group (RNG) k-ε, and the Shear Stress Transport (SST) models. The turbulence-chemistry interaction is modeled using the Partially Stired Reaction (PaSR) model. The chemical mechanisms used in the present study are: (i) a compact skeletal C2 mechanism, (ii) a mechanism developped by Frassoldati-Faravelli-Ranzi (FFR) containing 14 species and 33 reactions and (iii) the optimised syngas mechanism by Varga. Radiation heat transfer is handled by the P-1 method. In addition, the performances of two gas radiative properties models, i.e., the grey mean gas and the weighted-sum-of-gray-gases (WSGG) models, are assessed in radiative heat transfer modeling of the syngas flame. The predicted results reveal that the combination of the RNG turbulence model and the C2 skeletal mechanism shows the best agreement with measurements. The WSGG model used predicts results with the same level accuracy as the grey gas model in modeling of the syngas flame.

Расчеты сжатия сферической слоистой системы ударными волнами с учетом переноса тепла излучением в различных приближениях

Numerical modeling is one of the basic tools to investigate physical phenomena that occur in materials compressed by shock waves. A study of the behavior of shock waves using simplified models is helpful in the analysis of more complex systems, for instance, in the problems of inertial thermonuclear fusion on laser facilities. Mathematical simulation of the nonstationary radiative heat transfer in a spectral kinetic statement is rather complicated because the system of equations is nonlinear and large in size. Generally, the kinetic transport equation is solved in 7D phase space, which requires huge computational resources. The initial system is often approximated under certain assumptions but this immediately causes questions as to whether the simplified model is applicable to particular calculations. In this study, several economic radiative heat transfer models were implemented in a 2D hydrodynamic code. Based on these models, test calculations were performed to simulate the compression of a layered spherical system by shock waves, taking into account radiative heat transfer. When the shock wave reaches the center of the sphere, it is focused and reflected. In the neighborhood of the focal point of a converging wave, temperature gradients increase; therefore, thermal conduction and radiation become the main mechanisms of energy dissipation to be considered when taking into account heat transfer. Maximum densities and temperatures at the center of the sphere and their average values in its regions were calculated. In addition, the time when shock and heat waves cross the sphere center was determined, and their behavior before and after focusing at the sphere center was estimated. It is shown that solutions to such problems can be found much faster and with adequate accuracy when applying simplified models.

Study on the flame radiative heat transfer and near-field radiation heat flux predictive model of vehicle fires in a tunnel

As a major form of heat transfer, flame thermal radiation has an important effect on the ignition of adjacent energy, fire spread and environmental damage. Forecasting the flame radiation heat flux can provide theoretical basis for fire hazard assessment, fire extinguishing and salvation. Meanwhile, the distinctive structure of the arc tunnel can result in significant variations in the local heat and mass transfer processes during tunnel fires compared to those in rectangular tunnels, leading to different fire characteristics parameters. In this study, experiments and theoretical analyses were conducted to investigate the flame length scale and near-field radiation heat flux on the lower surface of an arc-shaped ceiling induced by vehicle fires in a tunnel. The findings reveal that the flame length scale in the transverse direction beneath the arc-shaped ceiling decreases with an increasing burner aspect ratio and increases with the increasing heat release rate. A dimensionless model of the flame length scale under the arced ceiling with various burner aspect ratios was proposed based on the amount of remaining unburned fuel after flame impingement and the buoyancy component along the arc-shaped ceiling. Simultaneously, radiative heat fluxes on the lower surface also increase with rising heat release rate. The flame geometry beneath the arc-shaped ceiling is assumed to be a combination of a cuboid and an arc plate model based on the actual flame length scale. Subsequently, the view factor, radiative fraction, and flame surface area are analyzed to predict the radiative heat fluxes on the lower surface. The predictions of the cuboid and arc plate flame model show good agreement with the current experimental data. This work presents a dimensionless correlation of the flame length scale and calculates the view factor between the target and the arc plate to predict the near-field radiative heat flux more accurately. This approach also facilitates the understanding of flame spreading behavior and thermal hazards impacted by arced ceiling.

Greatly Enhanced Radiative Transfer Enabled by Hyperbolic Phonon Polaritons in α‐MoO3

AbstractOrthorhombic molybdenum trioxide (α‐MoO3) is a highly anisotropic hyperbolic material in nature. Within its wide Reststrahlen bands, α‐MoO3 has hyperboloidal dispersion that supports bulk propagation of high‐k phonon polariton modes. These modes can serve as energy transport channels to greatly enhance radiative heat transfer inside the material. In this work, large radiative transfer enabled by phonon polaritons in α‐MoO3 is demonstrated. The study first determines the temperature‐dependent permittivity of α‐MoO3 from polarized Fourier‐Transform Infrared (FTIR) spectroscopy measurements and then uses a many‐body radiative heat transfer model to predict the equivalent radiative thermal conductivity of hyperbolic phonon polariton. Contribution of radiative transfer to the total thermal transport is experimentally determined from the Time‐Domain Thermoreflectance (TDTR) measurements in a temperature range from −100 to 300 °C. It is found that radiative transfer can account for ≈60% of the total thermal transport at a temperature of 300 °C. That is, conductive thermal transport is enhanced by >100% by radiative transfer, or radiation inside α‐MoO3 is greater than that of conduction. These additional energy pathways will have important implications in thermal management in new materials and devices.

CFD simulations of helium layer erosion in one PANDA vessel following cooler activation

We performed CFD simulations of the two H2P6 cooler tests conducted in the PSI PANDA vessel as part of the OECD/NEA HYMERES-2 project. Initially, the vessel atmosphere consists of a 60/40 % vol. steam- air mixture. Then, a helium stratification (15 % vol.) is introduced in the upper half of the vessel. The two experiments H2P6_1 and H2P6_2 are characterized by the activation respectively of 3 and 1 cooler(s) in the upper part of the vessel. In the course of the experiments, condensation takes place, resulting in a gradual pressure decay and erosion of the helium layer until complete mixing is achieved.The URANS k-ε is used to model turbulence. CFD Best Practice Guidelines are followed to minimize numerical errors, with preliminary mesh sensitivity studies. A correlation based on the heat-and-mass transfer analogy is employed to estimate steam condensation rates.Each cooler consisting of 18 tubes is simplified into a cuboid with equivalent heat transfer area. In a further simplification, it is assumed that the cooler wall has a thickness of zero and is initially at the temperature of the coolant. The small initial energy stored in the mass of the cooler at time zero is therefore neglected.The simulation for H2P6_1 matches the main experimental parameters (heat removal rate, pressure, species concentrations) almost perfectly. For H2P6_2 the heat removal rate is slightly under-predicted, with a corresponding over-prediction of the pressure by a maximum of 3 %. The inclusion of radiative heat transfer modeling improves the accuracy of the temperature field but has little influence on the pressure or heat removal histories.These results show that CFD allows accurate predictions of containment mixing when coolers are activated. Moreover, the simulations also indicate that multiple cooler units can be represented by one larger equivalent unit.

Numerical investigations and design optimization of cryogenic plate-fin heat exchanger in Electric Arc Furnace using radiative heat transfer model

The most crucial element affecting cryogenic systems’ energy efficiency is heat exchangers. In this article, a model for cryogenic plate-fin heat exchanger (PFHE) under thermal-hydraulic performance with various blends is proposed. To reduce five objective functions total heat transfer rate, total weight, total mass flow rate, number of entropy generating units, and whole annual cost the study carried out the PFHE’s optimal design. This study innovatively focuses on optimizing PFHE design for cryogenic conditions using Opposition Learning with the Beetle Swarm algorithm. The proposed geometry addresses non-uniform temperature distribution, emphasizing thermal-hydraulic properties in various blends. Additionally, a second-order semi-discretization radiative heat transfer approach enhances boiler simulation accuracy. A multi-objective optimization of Opposition Learning with Beetle Swarm (MO-OBBS) optimization approach was suggested in the article for the design of PFHE. Despite the significant potential for renewable energy the low-temperature waste heat treatment process is rarely examined from a sustainability perspective. Consequently, the study proposed a second-order semi-discretization radiative heat transfer method to simulate a furnace using a water heat recovery process. The cooling panel’s numerical analysis was conducted using computed temperature fields. The performance of the various algorithms is compared using the Freidman rank-sum test to determine the statistical significance of the findings obtained. In logarithmic coordinates, the proposed method’s faster convergence is compared to GQB-PSO, SLTLBO, Jaya, CKKO, and OLE-SCA algorithms. The proposed method exhibits a maximum average increase of 115.39% for PFHE design. When the numerical simulation results are compared to measurements of output water temperature, the accuracy is highly improved.

Heat Transfer through Double-Chamber Glass Unit with Low-Emission Coating

The numerical modeling of radiation and convective heat transfer through a double-chamber glass unit was carried out to substantiate the increase in the heat transfer resistance of this unit via the application of low-emission coatings to glass surfaces. In the space between the panes of a window without low-emission coatings, the amount of heat transferred via radiation exceeds the amount of heat transferred via thermal conductivity and convection. The question of the effect of low-emissivity coatings on reducing heat loss through a window has not yet been sufficiently studied. This problem is also not sufficiently reflected in the literature. In this regard, this paper presents the results of numerical simulation aimed at studying the effect of low-emissivity coatings on heat transfer through a double-chamber glass unit. Simulation is carried out by numerically solving a system of equations of fluid dynamics and energy for the air gap and glass. Boundary conditions of the fourth kind are set on the internal surfaces of the chambers, taking into account the radiation and conduction components of the total heat flux emanating from the glass. The results of modeling heat transfer through a glass unit with ordinary glass show that about 60% of the heat is transferred by radiation. Therefore, an effective measure to reduce heat loss through windows is to reduce the radiation component of the total heat flux by applying a low-emissivity coating to the internal surfaces of the glass unit. This allows for the reduction of the overall heat flux (and, accordingly, heat loss to the environment) by 20–34%, depending on the number of glass surfaces with such a coating.

Predictive radiation heat transfer modeling in fibrous insulation at high temperature

The modeling of heat transfer in fibrous materials is important for designing and improving thermal insulation systems. At high temperatures and low sample density, thermal radiation is expected to be the primary mode of heat transfer in fibrous insulation. Currently, the most common and successful models for modelling heat transfer in insulation at high temperatures require the use of semi-empirical methods. The main limitation of this approach is that the model parameters need to be determined from thermal measurements for each possible material and re-determined if the morphological structure is modified, even for the same material. This paper presents a predictive model for radiation heat transfer based solely on physical and morphological properties. The model was validated using experimental determinations of the effective thermal conductivity in a low-density alumina-based insulation. The model demonstrates good agreement with experimental measurements, and its predictions fall within the experimental uncertainty limits for temperatures between 800 K and 1700 K.

GPU-DEM-based heat transfer model for an HTGR pebble bed

Based on the discrete element method (DEM) and GPU parallel computing, a particle heat transfer model is developed to simulate the heat transfer in a pebble bed of the high-temperature gas-cooled reactor (HTGR). The model is implemented based on a previously developed GPU-DEM program by our team and uses the mesh-based neighbor searching algorithm for the heat transfer calculation. This model couples the conduction and radiative heat transfer between the pebbles and incorporates neural networks and empirical fittings to calculate the radiation view factors, which can improve computational efficiency. The effective thermal conductivity of different models and experimental data are used to verify the accuracy of the model, and the influence of different radiation heat transfer models on the results is also compared. The results show that the effective thermal conductivity derived from the current model is comparable to the classical models at different temperatures, and the numerical simulation results based on the current model are in good agreement with the corresponding experimental data. Additionally, the model achieves a single-core speedup ratio of 126–395 times with GPU acceleration, significantly enhancing computational efficiency. In conclusion, the current model has been effectively verified for accuracy and computational efficiency, and it demonstrates great potential in dealing with large-scale pebble flow and heat transfer challenges in HTGRs.

Reduced integration coupled with Monte Carlo ratios method for zone modeling of radiative heat transfer in reheating furnaces

Reduced integration coupled with Monte Carlo ratios method for zone modeling of radiative heat transfer in reheating furnaces

Assessing the impact of wet and dry flue gas recycling on heat transfer in oxygen-fired circulating fluidized bed furnaces

Oxygen-driven circulating fluidized bed combustion (oxy-CFB) has been suggested as a potential technique for facilitating carbon capture in large-scale power generation. Precise modeling of radiative heat transfer is vital for forecasting the thermal performance of such processes. This research examines the impact of wet and dry flue gas recycling on the thermal behavior of a large-scale oxy-CFB furnace, utilizing a combined modeling strategy that merges a three-dimensional furnace process model with a thermal radiation solver. The semi-empirical furnace model operates in steady-state conditions, accounting for fluid dynamics, reactions, and heat transfer phenomena. The radiation solver, based on the zone method, employs novel correlations for radiative heat exchange between optically thick zones. The radiation solver employs a weighted sum of the gray gases model, developed specifically for oxy-combustion, and geometric optics to determine the radiative characteristics of combustion gases and particles, respectively.This research covers various process conditions and boiler loads to evaluate the influence of wet versus dry flue gas recycling on heat transfer and temperature profiles. Model results were successfully compared against small-scale oxygen-fired CFB tests and large-scale measurements in a supercritical air-fired CFB. Utilizing an external radiation solver allows for a more precise representation of radiative heat transfer and the influence of varying process conditions. The insights from this research can aid in the design of large-scale oxy-CFB facilities, and the demonstrated modeling approach can be employed for additional model development, such as integrating the external radiation solver with other modeling tools.

Simulating Radiative Heat Transfer in Multi‐Scattering Irregular Surfaces: Application to Snow and Ice Morphologies on Europa

AbstractWe developed a Monte‐Carlo‐based radiative heat transfer model capable of simulating solar exposure and subsequent warming of rough snow and ice surfaces on ice‐covered airless solar system bodies. The model accounts for wavelength‐dependent internal light scattering and heat conduction in the snow interior down to meter‐scale depths. We validated the model against analytical and experimental test cases with relevant applications to Europa, one of Jupiter's moons. We examined differential heating across the surface, from the centimeter to meter scale, to reveal potential patterns of preferential sublimation that could lead to rough ice morphologies, such as penitentes. An exploration of parameters such as penitente height‐width ratios, shape, size, snow grain size, and thermal properties revealed that taller, thinner, larger penitentes with sharper peaks, coarser snow grain sizes, and lower thermal inertias are more likely to grow in Europa's environment near the equator.

Neutronic-thermalhydraulic coupling analysis of heat pipe failure accidents of a new type of megawatt heat pipe reactor

Heat pipe cooled reactors featured with high energy density, long lifecycle, modularity, and compact structure could be ideal power sources for large unmanned undersea vehicles (UUVs). In the early stage of reactor concept design, heat pipe failure accident is usually one of the design basis accidents that need to be considered. In this study, a set of transient analysis models for heat pipe failure accidents of a new type of megawatt heat pipe reactor is established. The models include the point kinetics model, Core Matrix module and Fuel-Heat Pipe module heat conduction models, and radiation heat transfer model for the inner core cavity. 2D-3D combined method is used to solve the heat conduction model in the Fuel-Heat Pipe module. Based on the models, a transient analysis code for heat pipe failure accidents is developed using FORTRAN. The models are separately validated based on the analytical solutions, the experimental data or the CFD results by FLUENT. Neutronic-thermalhydraulic coupling calculation is conducted in normal operation condition and heat pipe failure accidents. The peak temperatures of each region are below their melting points in all presumed heat pipe failure accidents which reflects the good inherent safety of the core. Meanwhile, the calculation results by the code are in good agreement with those of FLUENT, and the maximum relative error of the peak temperature does not exceed 1.5%. The code calculation time is 1/8 of FLUENT ensuring the accuracy of important parameters, effectively reducing the computation costs and improving the computation efficiency. The code also provides a basis for subsequent transient operation condition and typical accidents analysis of this reactor.

Modelling and effects of fuel radiation in methanol pool fires

This article proposes a computationally affordable radiative heat transfer model to predict accurately the feedback toward the fuel surface. It combines the multi-scale full-spectrum k (MSFSK) approach to model accurately the radiative interaction between CO2/H2O and the fuel and the rank correlated (RCFSK) scheme. The model achieves the narrow band correlated-k model accuracy with only five quadrature points for each of the two scales. The predictions are also weakly dependent on the Planck temperature which allows to store efficiently the MSRCFSK parameters in a flamelet library. The model is implemented in a well-validated numerical model to provide large eddy simulations of 30 cm and 1 m diameter methanol pool fires. The heat feedback predictions are improved when methanol radiation is considered. The overall radiative contribution of methanol results from two competitive mechanisms: an increase in emission in the hot part of the fuel dome and an increase in absorption close to the pool surface. For both pool fires, the enhancement in emission overall dominates, leading to higher radiative loss and heat feedback. The contribution of absorption increases with the pool size and, as a result, the effects of methanol radiation are more pronounced for the 30 cm pool than for the 1 m one.

The Effect of Fuel Aerosol Particle Size on Aerosol Release Potential in Energetic Core Disruptive Accident Studies

In nuclear reactor accident safety studies, the radiological source term is a metric that quantifies the release of radiological material from the reactor to the environment. The present work evaluates heat transfer between high-temperature vapor bubbles and the surrounding coolant and the effect these interactions have on the source term for postulated core disruptive accident scenarios associated with an oxide-fueled, liquid metal–cooled fast reactor class. It is shown that aerosol particle size can influence heat transfer, and it is suggested that the extent of the influence depends on the fineness of the particles in the aerosol. The results are consistent with legacy experiments conducted in the Fuel Aerosol Simulant Test (FAST) facility at Oak Ridge National Laboratory and offer a more comprehensive assessment of vapor condensation by treating the bubble constituents, in the context of radiation heat transfer, as participating media. The model, which couples classical scattering theory to the equation of radiative transfer and the energy equation, provides a means for estimating size-affected radiative cooling times. Solutions are obtained via the P-1 method of spherical harmonics with improved, higher-order boundary conditions. Outcomes include the development of an “extinction-time ratio” criterion for assessing whether ejection of aerosol from the bubble to the cover region is likely. Aerosol release from the coolant pool is evaluated using this criterion with the potential to extend this work to reactor-scale accidents. A baseline evaluation is provided that shows that omission of participatory effects could lead, in a relative sense, to cooling time offsets in excess of 14%. In addition to enhancing previous evaluations of FAST results, these modeling outcomes contribute to knowledge management efforts aimed at developing a more mechanistic assessment of the source term while suggesting potential enhancements to severe accident safety analysis through the use of more comprehensive radiative heat transfer models.

Radiation-Induced Thermal Runaway Propagation in a Cylindrical Li-Ion Battery Pack: Non-Monotonicity, Chemical Kinetics, and Geometric Considerations

Li-ion batteries play a key role in energy storage and conversion in engineering systems such as electric vehicles and grid energy storage, with critical impact on electrification and storage of renewable energy. A key unresolved technological challenge in Li-ion batteries pertains to thermal runaway initiation and propagation in a battery pack, which can lead to subsequent fire and explosion. Despite significant past work, there remains a critical need to understand how thermal runaway propagates in a pack. This work presents a comprehensive investigation of the effect of radiative heat transfer on thermal runaway propagation. Radiation can be important when a battery is exposed to adjacent heat and fire sources, as well as in thermal runaway propagation from one hot cell to another. A theoretical radiative heat transfer model based on view factor theory is developed. Calculations based on this model for a simple 2D cylinder-to-cylinder geometry are found to be in very good agreement with analytical expressions. Radiation-induced thermal runaway propagation between two cylindrical 18650 batteries is evaluated. It is shown that radiation may play a key role in thermal runaway propagation, depending strongly on the triggering temperature. It is found that radiative effects in thermal runaway propagation exhibit both nonlinear and non-monotonic characteristics. At high temperatures, thermal runaway is triggered rapidly in the region close to the battery surface, where the chemical reactions are strongly coupled, and radiation plays a dominant role. In contrast, at lower temperatures, thermal runaway is triggered much more slowly and towards the core of the cell, where some chemical reactions may be decoupled, and pre-runaway chemical heat release plays an increasingly important role. The results presented here suggest that radiation can either facilitate or mitigate thermal runaway. The net radiation heat flux has a cross-over instant, beyond which radiation starts to retard thermal runaway. Additionally, the blocking effect in radiative heat transfer between cells arranged in equal-spacing homogenous or orthogonal arrangements in a battery pack is investigated, along with the effect of the hot spot size. Results from this work help understand the role of radiation in thermal runaway propagation and provide useful insights into the thermal runaway control and design of safe Li-ion battery packs.

Impact Assessment of Radiative Heat Transport in ARC-Class Reactor FLiBe Liquid Immersion Blanket

Molten salt systems have become of growing interest in the energy industry due to a wide range of applications (concentrated solar power systems, energy storage, Generation IV fission reactors, and high magnetic field fusion reactors). Because of the high temperature that characterizes such materials, radiative heat transfer (RHT) may become a nonnegligible heat transfer mechanism in molten salt components. In this paper, an investigation of FLiBe RHT has been conducted, with a focus on Affordable, Robust, Compact (ARC)–class fusion reactors, a preconceptual design proposed by Commonwealth Fusion Systems and the Plasma Science and Fusion Center. This class of reactors largely employs FLiBe molten salt due to its thermal and neutronic properties. The reactor is characterized by high temperatures, and its 0.5-m-thick liquid immersion blanket is a component where RHT contribution to the temperature distribution is yet to be evaluated. Therefore, this study is the first work that quantifies the contribution of RHT in ARC-class reactor FLiBe systems. FLiBe optical property spectral-banding assessment is carried out, and the impact of RHT in FLiBe systems is assessed in operational ARC-class scenarios through computational fluid dynamics models by taking advantage of COMSOL® Multiphysics. Heat transfer, thermal-dependent properties, and buoyancy effects are considered in a comparison between scenarios with and without RHT modeling. The flow field in the tank is unaffected by RHT effects, even when considering buoyancy effects. The external layer of the vacuum vessel shows an average decrease in the temperature of 5.4 K and an average decrease in temperature on the surface in contact with the FLiBe tank of 8.1 K. Results indicate that for ARC-class reactors, RHT phenomena are negligible (<1% increase in heat transfer) in operational conditions.

Experimental study of the thermal and burning characteristics of 15 cm pool fires fueled by heptane-toluene mixtures

This article presents an experimental investigation of the effects of the fuel sooting propensity on the thermal and burning characteristics of 15 cm diameter pool fires burning in air. Heptane is used as reference fuel and two other heptane/toluene blends with toluene volume concentration of 5% and 10% are considered to vary the fuel sooting propensity. An exhaustive characterization of the pool fires is performed with measurements of the flame geometry, puffing frequency, mass burning rate, combustion efficiency, local temperature statistics from a dual thermocouple technique, local mean soot volume fraction from laser light extinction, radiative loss to the surroundings and total heat flux to the center of the pool surface. This comprehensive dataset can be used to develop and validate models for soot formation and radiative heat transfer. The experimental results show that the increase in fuel sooting propensity, characterized by a smoke point height decreasing from 12.5 cm to 4.9 cm, results in a significant enhancement in soot production, with the peak of mean soot volume fraction increasing from 0.62 ppm to 1.11 ppm. Radiative loss to the surroundings is also affected, as radiant fraction and total heat flux to the center of the fuel surface increase from 0.37 to 0.45 and 18.5 to 22.2 kW/m2 respectively. This is accompanied by a significant reduction in combustion efficiency from 0.95 to 0.83. In an opposite way, the impact on the temperature statistics is minor.

Near-field thermal modulator between nanoparticles based on the multilayered structure

• We develop the calculation model for radiative heat flux between arbitrary multiple nanoparticles placed on opposite sides of the multilayered slab. • The coupling of particle resonance and excited multilayered surface polaritons plays a dominant role in RHT between particles. • The phase change feature of VO 2 can achieve the dramatically active modulation of the RHT between two particles. • The impacts of particle-slab distance and the thickness of the multilayered slab on the thermal control effect are studied. • We can achieve various thermal modulation effects between particle clusters, including thermal switching, thermal modulation, and thermal amplification. We propose a near-field thermal modulator between nanoparticles based on a multilayered slab consisting of the phase change material. Initially, we present a calculation model for radiative heat transfer (RHT) between multiple nanoparticles placed on opposite sides of the multilayered slab. Subsequently, we proceed to analyze the case of two particles, demonstrating that the multilayered slab is capable of providing a robust transmission channel for RHT between the particles. This is achieved through the coupling of particle resonance and excited surface polaritons of the multilayer. Furthermore, the phase change feature can be utilized to switch the transmission channel, thereby achieving active modulation of the RHT. The impact of particle-slab distance and the thickness of the multilayered slab on the thermal control effect is investigated. Moreover, we explore the thermal modulation functions of the RHT in a more complex system where particle clusters are located on opposite sides of the multilayered slab, achieving various thermal modulation effects between particle clusters, including thermal switching, thermal modulation, and thermal amplification.

A numerical and experimental comparison of heat transfer in a quasi two-dimensional packed bed

Heat transfer plays a major role in many industrial processes taking place in packed beds. An accurate and reliable simulation of the heat exchange between particles is therefore crucial for a reliable operation and to optimize the processes in the bed. The discrete ordinates method (DOM) provides an established numerical technique to model radiative heat transfer in granular media that offers the possibility to consider the directional dependence of the radiation propagation. In this work, DOM is compared with Monte Carlo ray tracing, which provides an alternative method for heat transfer simulations. Geometrically simple configurations are used to investigate the influence of the angular discretization on the accuracy of the results and the computation time in both methods. The obtained insights are then transferred to a more complex configuration of a quasi two-dimensional test rig consisting of metal rods for which also experimental results are available. Our results show that both DOM and Monte Carlo ray tracing allow for an accurate simulation of heat transfer in packed beds. Monte Carlo ray tracing requires thereby computation times that are surprisingly competitive (although still somewhat slower) compared to DOM and allows for an easier computation of highly accurate reference solutions. In our preliminary comparison to the experimental test rig, Monte Carlo ray tracing also provides the advantage that it can more easily model highly specular materials such as stainless steel. Both methods are comparable for diffuse materials such as magnesium oxide.