Simulation Of Radiative Heat Transfer Research Articles

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.

Numerical simulation of combined convection and radiation heat transfer in a hybrid nanofluid inside an open fins cavity under a magnetic field

Numerical simulation of combined convection and radiation heat transfer in a hybrid nanofluid inside an open fins cavity under a magnetic field

Adjoint-based shape optimization for radiative transfer in porous structure for volumetric solar receiver

Due to their large surface areas, porous structures are often used for volumetric solar receivers for efficient utilization of the solar energy. However, the precise simulation and optimization of radiative heat transfer inside porous structures are still challenging due to their complex geometries. In the present study, an adjoint-based shape optimization framework for radiative transfer in porous structures is first proposed. Specifically, an arbitrary complex geometry of a porous structure is represented by a level-set function embedded in a Cartesian grid system. The volume penalization method combined with the discrete ordinate method is employed to simulate a forward radiative transfer problem in a porous structure. Then, a cost functional for an adjoint analysis is defined by the volume average of the divergence of the radiative heat flux, which corresponds to the total heat absorbed by the porous structure with a negative sign. The adjoint equations for minimizing the cost functional, and the corresponding shape update formula are derived and implemented in an open-source software, OpenFOAM. The developed adjoint-based shape optimization framework is applied to three types of initial porous structures, i.e., SC Kelvin, BCC Kelvin, and square honeycomb models. For all the initial porous models, the front surface commonly extends towards the direction of the incident radiation, and consequently notable improvements of the absorption efficiency can be achieved through the optimization. In addition, a systematic parametric survey for the initial shape of the SC Kelvin model is conducted to reveal the impacts of the number of unit cells, the solid emissivity, and the solid temperature on the optimal shapes and the resulting absorption efficiencies.

Innovative Tool to Determine Radiative Heat Transfer Inside Spherical Segments

The classic equations used to find the form factor inside fragments of spheres are often unassailable. The main difficulties that they present lie in iterative integrations effected over curved surfaces. The typical simulation software for this kind of issue is not capable of tackling the drawbacks that appear in the process, among them we could cite the impossibility of discretizing curved shapes with equal matching tiles, whether triangles or rectangles, especially when we arrive at the contour elements. The current type of cylindrical tiles employed for the calculation of spheres, due to incoherence in curvature, presents a significant array of gaps that render the whole procedure inadequate and inconsistent. To countermeasure this drawback, the recent finding of some innovative principles by the present author has provided a sure and exact path towards the solution of the problem in the frequent case of a volume enclosed within a spherical fragment and two limiting sections of the said sphere placed at arbitrary positions. The coherent application of such postulates by virtue of form factor algebra leads to an encompassing expression which solely requires the input of the surface areas of the involved shapes and, thus, avoids the lengthy resort to integration. A relevant number of cases in radiative heat transfer simulation, that cannot be solved by any other method, become feasible and accurate. Since the new tool can be implemented as an algorithm for simulation software, pivotal advances emerge in the complex domain of radiation which are applicable for the lighting industry, building simulations, and aerospace technologies, among others.

The efficiency of multithreaded computing in casting simulation software

The utilization of computer simulation software for casting process simulation is becoming essential in the advancement of casting technology in aviation and other high-tech engineering fields. With the increase in the number of computational cores in modern CPUs, the use of multi-threaded computations is becoming increasingly relevant. In this study, the efficiency of multi-threaded computations in modeling casting processes was evaluated using finite element method casting simulation software ProCast and PoligonSoft, which utilize parallel computing architectures with distributed (DMP) and shared (SMP) memory, respectively. Computations were performed on Intel and AMD-based computers, varying the number of computational threads from 4 to 32. The calculation efficiency was evaluated by measuring the calculation speed increase in the filling and solidification of GP25 castings made of ML10 alloy, as well as the complex task of filling and solidification modeling nickel superalloy casing castings with radiation heat transfer simulation. The results indicate that the minimum computation time in ProCast software is observed when using 16 computational threads. This pattern holds true for both computing systems (Intel and AMD processors), and increasing the number of threads beyond this point does not make a practical difference. The performance decrease in this scenario can be attributed to the low-performance energy-efficient cores in systems based on Intel processors or the decrease in core frequency and full loading of physical cores in systems based on AMD processors. Multi-threading the modeling task in PoligonSoft software is less efficient than in ProCast, which is a result of the shared-memory architecture used in PoligonSoft. Despite the significant difference in parallel efficiency, the task of GP25 casting solidification in both PoligonSoft and ProCast is solved in a time close enough to be considered sufficient.

A New Principle for Building Simulation of Radiative Heat Transfer in the Presence of Spherical Surfaces

Radiant heat interchanges are pivotal to assessing the energy use of buildings and facilities that channel some sort of solar radiation. Form factor integrals are needed for an accurate simulation of the main features of the envelope of such buildings. However, the expressions required when the space under analysis is curved, for instance, in domes and vaults, are not feasible. The calculation process of algorithms is usually addressed by cumbersome analytical deductions or else by rough statistical approximations included in the simulations, such as ray-tracing methods. Neither of which works properly under curved geometries. The following article deals with an innovative methodology for employing an exact property that solves any spherical configuration of the radiant surfaces. The newly found relationship is validated by comparison with other solutions previously deducted by the author and by numerical simulations when available. Since there is no other exact method of calculating radiation exchanges within spherical fragments, we consider that this finding represents an advance which contributes to overcoming a variety of unexplained and practical problems of radiative heat transfer applicable to architectural developments, lighting elements and aircraft components.

Approaches to radiative heat transfer simulation in a cavity above melt

Approaches to radiative heat transfer simulation in a cavity above melt

Calculating the view factor of randomly dispersed multi-sized particles using hybrid GRU-LSTM recurrent neural networks regression

This study presents three novel methods for the computational acceleration of simulations of high temperature radiative heat transfer in particulate media. The paper presents a novel algorithm for neighbor searching that can locate and sort multi-sized particles, based on their distance, with minimal computation. The traditional use of regression recurrent neural networks for time series data is modified to a regression function for distance-ordered data. LSTM and GRU cells are used in a deep recurrent neural network to predict radiation view factors of particle and face neighbors through the distance-ordered sequential data. The preprocessing of sequential data is addressed with two new transformation methods. Through the use of the transformation methods, both the particle and face neighbors are regarded as general objects, allowing one regression neural network to predict the view factor of any number of particles and faces sequentially, which represents a unique feature. With neural networks and preprocessing methods, it is possible to predict the view factor of different-sized objects (particles and faces), representing a significant development in the field. The models demonstrate high precision for objects located within the short-range radiation region. Objects located a long distance from the emitting particle have an over-prediction of view factor, but due to their negligible contribution to overall radiation heat transfer, a high coefficient of determination is obtained for particle and face neighbors, with several orders of magnitude improvement in computational speed compared to typical Monte Carlo ray tracing methods.

Modern Methods for Numerical Simulation of Radiation Heat Transfer in Selective Gases (Review)

Modern Methods for Numerical Simulation of Radiation Heat Transfer in Selective Gases (Review)

Numerical simulation of radiative heat transfer in a binary-size granular bed

The radiative heat transfer in a high temperature granular bed of binary-size mixture was explored in this paper. The effective view factor between particles decreases exponentially with the increase in particle interval, increases with the increase in the size of the absorption particle but is hardly affected by the volume ratio of the mixture. The effective thermal conductivity of granular bed was further deduced basing on the characteristic of the effective view factor. It is indicated that the thermal conductivity is proportional to the particle size and temperature cubed, and increases with the increase in the particle size ratio and volume ratio. Finally, modified calculation correlations of the effective view factor and effective thermal conductivity were developed for binary-size bed based on the simulation results, and good accuracy of less than 0.01 and 10% had been achieved, respectively.

Open-source non-gray gas radiation heat transfer solvers for combustion applications based on OpenFOAM

Numerical simulation of non-gray radiation heat transfer is essential for many thermal engineering processes, especially for combustion applications. This work develops open-source non-gray gas radiation solvers based on the OpenFOAM framework. The discrete ordinates method (DOM) and first order spherical harmonics (P1) method are implemented by the advanced numerical discretization utilities provided by the OpenFOAM toolbox. The weighted-sum-of-gray-gases (WSGG) model for the carbon dioxide and water vapor are coupled with the two radiative transfer equation (RTE) solvers. Validations with finite volume method (FVM) are performed to test the accuracy of the developed models. Comparisons show that both solvers can produce very close results to the FVM. The relative error of the DOM and P1 is about 3% and 10% respectively for radiative heat flux calculations.

Effect of oxidation on spectral and integrated emissivity of Ti-6Al-4V alloy at high temperatures

Thermomechanical simulation is challenging for the optimization and virtual monitoring of high temperature shape processes, such as SuperPlastic Forming (SPF) of Titanium alloys alike Ti-6Al-4V (TA6V). Part of this challenge is the accurate and process-representative knowledge of emissivity, which controls radiative heat transfer during the process. In this paper, the characterization of TA6V emissivity, with regards to its oxidation stage, is performed within the [600–1000 °C] thermal range. The main contribution of this work is the use of an in-house characterization bench, enabling the fast radiative heating of samples, and the control of oxide layers thicknesses ranging from 250 nm to 120 µm. An oxidation law is established thanks to post-mortem mass gain and oxide thicknesses measurement, and the various oxide phases are identified. Oxide thicknesses versus heating time were then calculated and implemented in the emissivity analysis. Two patterns are observed for oxide thickness versus temperature: below 900 °C, emissivity values are quasi-continuously increasing with oxide thickness, exhibiting an oxide layer mainly composed by TiO2, above 900 °C, emissivity values are also continuously increasing but with a different trend, due to the formation of alumina, confirmed by X-Ray Diffraction (XRD) measurements. Finally, the dependence of emissivity to temperature and oxide thickness emphasized in this paper constitutes a non-trivial mandatory input to increase the radiative heat transfer simulations codes accuracy.

A Quasi-Monte Carlo method to compute scattering effects in radiative heat transfer: Application to a sooted jet flame

The Monte-Carlo simulation of radiative heat transfer is known to be very accurate. Its convergence can be significantly improved using Randomized Quasi-Monte-Carlo (RQMC) methods that rely on low-discrepancy sequences. The RQMC approach derived recently to deal with thermal radiation is, however, limited to non-scattering media. The present work proposes a methodology aiming at extending this technique to scattering media based on the prior estimation of the low-discrepancy sequence dimension. Firstly, the method is tested on 3D homogeneous fields with various operating points based on the domain’s optical thickness and albedo. It is observed that, for a given number of generated rays, the error can be reduced by up to one order of magnitude. Secondly, the RQMC approach is combined with importance sampling to increase its efficiency further. The number of rays required is even lower, resulting in saving CPU time to reach a given error. The RQMC approach is then applied along with an accurate model for soot particles’ radiative properties: the Rayleigh-Debye-Gans for Fractal Aggregates (RDGFA) theory. The model assumes a complex morphological shape of particles contrary to Rayleigh theory that is valid for spherical particles only. Monte-Carlo simulations are performed on a fixed turbulent sooted flame field taken from coupled calculations with large-eddy simulation. The overall CPU cost is divided by a factor of 2 compared to a standard Monte Carlo calculation. The simulation allows for accurate quantification of soot scattering effects with RDGFA, which eventually appear small in this configuration. On the other hand, the use of Rayleigh theory strongly underpredicts the actual scattering impact.

Many-body effective thermal conductivity in phase-change nanoparticle chains due to near-field radiative heat transfer

In dense systems composed of numerous nanoparticles, direct simulations of near-field radiative heat transfer (NFRHT) require considerable computational resources. NFRHT for the simple one-dimensional nanoparticle chains embedded in a non-absorbing host medium is investigated from the point of view of the continuum by means of an approach combining the many-body radiative heat transfer theory and the Fourier law. Effects of the phase change of the insulator-metal transition material (VO2), the complex many-body interaction (MBI) and the host medium relative permittivity on the characteristic effective thermal conductivity (ETC) are analyzed. The ETC for VO2 nanoparticle chains below the transition temperature can be as high as 50 times of that above the transition temperature due to the phase change effect. The strong coupling in the insulator-phase VO2 nanoparticle chain accounts for its high ETC as compared to the low ETC for the chain at the metallic phase, where there is a mismatch between the characteristic thermal frequency and resonance frequency. The strong MBI is in favor of the ETC. For SiC nanoparticle chains, the MBI even can double the ETC as compared to those without considering the MBI effect. For the dense chains, a strong MBI enhances the ETC due to the strong inter-particles couplings. When the chains go more and more dilute, the MBI can be neglected safely due to negligible couplings. The host medium relative permittivity significantly affects the inter-particles couplings, which accounts for the permittivity-dependent ETC for the VO2 nanoparticle chains.

Numerical Simulation of Solar Radiation and Conjugate Heat Transfer through Cabin Seat Textile

Abstract The solar radiation and the conjugate heat transfer through the cabin seat fabric were investigated numerically with a focus on a comparative analysis of various fabric solar reflectance or reflectivity (SR) and inlet cooling air velocity. For this purpose, 3D compressible Reynolds-averaged Navier–Stokes equations with the low Reynolds number turbulence model were utilized to simulate the airflow in the cabin. The discrete ordinate radiation model was adopted to describe the solar radiation. The conjugate heat transfer between the airflow and the fabric seats was included. The airflow temperature, radiative heat flux, and radiative heat transfer through the fabrics in a fixed cross section were studied. The results demonstrate that the increase in fabric SR leads to the increase in energy reflected to the atmosphere, which will bring about a lower temperature on the seat fabric. The decrease in emissivity and the energy absorbed results in the lower heat transfer and heat radiation and leads to the improvement of the cabin thermal environment. The high-temperature gradient near the seat causes the forced air circulation and is beneficial for the improvement of the thermal comfort. However, the cooling effect is not so obvious near the cabin seats when the inflow speed is increased.

Proposal of an efficient method for handling turbulent fluctuation on numerical simulations of radiative heat transfer in the large-scale industrial furnaces including hydrocarbon flame

Proposal of an efficient method for handling turbulent fluctuation on numerical simulations of radiative heat transfer in the large-scale industrial furnaces including hydrocarbon flame

Numerical modeling of radiation heat exchange in combustion chambers and heat exchangers of power installations

The application of numerical modeling is considered to solve the problems of radiation heat exchange in structurally inhomogeneous two-phase media which are realized during the combustion of fuel in boiler units atmospheric emissions from air carriers when they move at supersonic speeds. The optically active ingredients of the gas phase of the combustion products have a sharp selection of spectral absorption lines (radiation) which causes a difference in the spectral transmission functions for selective radiation from the spectral transmission functions for non-selective radiation (gray body). In the presence of a dispersed phase of the combustion products acute selection is subjected to such a parameter of the radiation propagation medium as the probability of quantum survival. The number of spectral lines determining the spectral transmission functions increases with temperature and is determined by hundreds of thousands of lines at high temperatures. In this paper we consider a closed simulation of radiation heat transfer in combustion chambers when the temperature field in the combustion chambers is calculated first and then the flux of thermal radiation to the tube heat-receiving surfaces.

Hybrid conduction, convection and radiation heat transfer simulation in a channel with rectangular cylinder

The innovation of this study is to investigate the combination effect of thermal radiation and convection in the hybrid heat transfer between solid and fluid in a channel. The lattice Boltzmann method based on the D2Q9 scheme has been utilized for modeling fluid and temperature fields. Streamlines, isotherms, vortices and Nusselt numbers along the wall surfaces have been investigated for different Reynolds numbers (Re = 10, Re = 60, Re = 133.3), Peclet numbers (Pe = 7.1, Pe = 42.6, Pe = 94.7), the emission coefficients (e = 0.3, e = 0.7, e = 1), radiation coefficients (RP = 0.010, RP = 0.015, RP = 0.020) and diffusion coefficients (αs = αf, αs = αf/2, αs = 2αf). The mean Nusselt number (Num) fluctuations have been analyzed for different cases to predict optimal levels of effective factors of this simulation in order to maximize and minimize the heat transfer rate. The results show that by increasing the Reynolds number to Re = 133.3, the maximum average Nusselt number can be changed by more than 9.249 time. Also by increasing the thermal diffusion coefficient to αs = 2αf, the minimum average Nusselt number can be changed by less than − 0.687 time.

Assessment of randomized Quasi-Monte Carlo method efficiency in radiative heat transfer simulations

Radiation can play a central role in turbulent reactive flows where heat transfer is enhanced in applications with high temperature and pressure. The Monte Carlo method is a successful technique to solve the radiative transfer equation accurately with relative ease while retaining detailed properties. However, its drawback is associated to a slow convergence rate. One strategy to improve the efficiency of Monte Carlo method consists in replacing the pseudo-random sequences with an alternative sampling: the low-discrepancy sequences. The introduction of such sequences in Monte Carlo leads to Quasi-Monte Carlo methods. Their advantage lies in a higher convergence rate compared to MC methods which have however not been assessed in 3D participating media. Additionally, in order to get an error estimation which is necessary in practical applications, a randomization of Quasi-Monte Carlo is needed (Randomized-QMC). Such Randomized-QMC methods have not been considered for simulations of radiative heat transfer in participating media before. In the present study, Monte Carlo and Randomized Quasi-Monte Carlo methods are assessed in terms of efficiency and computational cost in radiative heat transfer simulations of three practical 3D configurations. Comparisons in terms of local standard deviation, convergence rate, and final computational cost show that Randomized Quasi-Monte Carlo outperforms Monte Carlo in all the investigated cases.

An improved WSGG model for exhaust gases of aero engines within broader ranges of temperature and pressure variations

Advanced aero engines operate at high temperatures and pressures to improve thermal efficiency and power output, thus thermal radiation becomes a significant mode of heat transfer for exhaust gases. The existing gaseous radiative models for atmosphere are not suitable for the application in aero engines due to the huge pressure variation of exhaust gases. In this work, an improved weighted sum of gray gases (WSGG) model for mixtures of H2O and CO2 within broader ranges of temperature and pressure variations is proposed. The mole ratio of H2O and CO2 is fixed at 1/1, which represents typical products of stoichiometric combustion of kerosene. The weighting factors, which only relate to the temperature in previous WSGG models, are modified by taking into account the effects of both temperatures and pressures. The coefficients of the improved WSGG model are obtained based on the up-to-date HITEMP-2010 database, and they are valid for the temperatures varying from 500 K to 2500 K, pressures ranging from 1 atm to 30 atm, and pressure path-lengths ranging from 0.0001 atm·m to10 atm·m. To access the accuracy of the coefficients, the improved WSGG model and other two traditional WSGG models are applied to the solution of the radiative heat transfer with the discrete ordinate method, and the comparison is conducted with the benchmark line-by-line calculations. The results indicate that the improved WSGG model has much higher accuracy in the simulation of gaseous radiative heat transfer for exhaust gases of aero engines.