Simulation Of Radiative Heat Transfer Research Articles

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.

A numerical simulation of MHD ow and radiation heat transfer of nano uids through a porous medium with variable surface heat ux and chemical reaction

In this paper, the problem of MHD ow and radiation heat transfer of nanouids against a at plate in porous medium with the eects of variable surface heat ux and rst-order chemicalreaction is investigated numerically. Three dierent types of nanoparticles, namely Cu, Al2O3 andAg are considered by using water as a base uid with Prandtl number Pr = 6:2. The governingpartial dierential equations can be written as a system of nonlinear ordinary dierential equationsover a semi-innite interval using a similarity transformation. A new eective collocation methodis proposed based on exponential Bernstein functions to simulate the solution of the resultingdierential systems. The advantage of this method is that it does not require truncating ortransforming the semi-innite domain of the problem to a nite domain. In addition, this methodreduces the solution of the problem to the solution of a system of algebraic equations. Graphicaland tabular results are presented to investigate the inuence of the solid volume fraction, types ofnanoparticles, radiation and suction/blowing, magnetic eld, permeability, Schmidt number andchemical reaction, on velocity, temperature and concentration proles. The obtained results ofthe current study are in excellent agreement with previous works.

Demonstrating GPU code portability and scalability for radiative heat transfer computations

High performance computing frameworks utilizing CPUs, Nvidia GPUs, and/or Intel Xeon Phis necessitate portable and scalable solutions for application developers. Nvidia GPUs in particular present numerous portability challenges with a different programming model, additional memory hierarchies, and partitioned execution units among streaming multiprocessors. This work presents modifications to the Uintah asynchronous many-task runtime and the Kokkos portability library to enable one single codebase for complex multiphysics applications to run across different architectures. Scalability and performance results are shown on multiple architectures for a globally coupled radiation heat transfer simulation, ranging from a single node to 16,384 Titan compute nodes.

MESH: A free electromagnetic solver for far-field and near-field radiative heat transfer for layered periodic structures

We describe MESH (M ultilayer E lectromagnetic S olver for H eat transfer), a free software that combines rigorous coupled wave analysis (RCWA) and scattering matrix formalism to simulate the radiative heat transfer both in the near-field and far-field regimes for layered three-dimensional structures made of planar layers. Each layer can have in-plane one-dimensional or two-dimensional periodicity. In this paper, we provide detailed discussions of the algorithms of MESH, which enables it to be a flexible tool for different types of radiative heat transfer simulations. We also discuss aspects of the codes related to parallelization and user scripting. Program summaryProgram Title: MESHProgram Files doi:http://dx.doi.org/10.17632/zx9v3bf3hf.1Licensing provisions: GNU General Public License 3 (GPL)Programming language: C, C++.External routines: Lua[1], Python[2] and LAPACK and BLAS linear-algebra software[3], and optionally MPI message-passing interface[4]. Armadillo[5] is already contained in MESH.Nature of problem: Far-field and near-field radiative heat transfer in layered periodic structures.Solution method: Fourier modal method (rigorous coupled wave analysis) and the scattering matrix method.[1] R. Ierusalimschy, L.H. de Figueiredo, W.C. Filho, Lua an extensible extension language, Software: Practice and Experience 26 (1996) 635652. http://www.lua.org.[2] Python Software Foundation. Available at http://www.python.org[3] MKL: https://software.intel.com/en-us/intel-mkl[4] T.M. Forum, MPI: A Message Passing Interface, in: Supercomputing 93, Portland, OR, 878883, 1993[5] Conrad Sanderson and Ryan Curtin. Armadillo: a template-based C++ library for linear algebra. Journal of Open Source Software, Vol. 1, pp. 26, 2016. http://dx.doi.org/10.21105/joss.00026

Entrained flow gasification. Part 2: Mathematical modeling of the gasifier using RANS method

CFD (RANS based) simulations of REGA-1 experimental campaign concerning gasification of glycol in an oxygen-nitrogen mixture have been carried out. The reacting flow-field has been computed using a number of turbulence models while turbulence-chemistry interactions have been modeled using either the Eddy Dissipation Concept (EDC) or the presumed PDF approach. Two global-chemistry schemes have been used: the (HVI1) scheme for glycol gasification and the extended Jones-Lindstedt scheme. Radiation has been computed using the Discrete Ordinate Method with a comprehensive analysis concerning absorption/emission of infrared radiation by gaseous molecules as well as absorption and scattering on droplets. The CFD-predictions of the near-atomizer region have been sensitive to and strongly dependent on the sub-models used; the spray sub-model and the chemical schemes are the most important. Good quality predictions of temperature and chemical species (CO,H2,CO2,H2O,CH4) concentrations at 300 mm and 680 mm distances from the atomizer have been obtained. The HVI1 global chemistry scheme has predicted very well not only the CO/CO2 ratios but also the trace concentrations of methane. The paper shows how to simplify the radiative heat transfer simulations without a significant loss in accuracy.

Моделирование переноса тепла излучением в движущейся плазме с учетом доплеровского сдвига линий

Моделирование переноса тепла излучением в движущейся плазме с учетом доплеровского сдвига линий

Simulation of combined conductive, convective and radiative heat transfer in moving irregular porous fins by spectral element method

A spectral element method (SEM) is developed to solve coupled conductive, convective and radiative heat transfer in moving porous fins of trapezoidal, convex parabolic and concave parabolic profiles. In these irregular porous fins, non-uniform heat generation, heat transfer coefficient and surface emissivity vary with temperature. In the SEM model, the solution domain is decomposed into non-overlapping elements by mesh tools of finite element method, and Chebyshev polynomials are used to establish basis functions on each element. A case of nonlinear heat transfer in the irregular porous fin is taken as an example to verify the performance of SEM. Compared with available data in the literature, SEM can provide a good accuracy. The h and p convergence characteristics of SEM are also studied. The p convergence rate is faster than the h convergence rate and approximately follows an exponential law. In addition, a volume adjusted fin efficiency is developed to evaluate the thermal performance of irregular porous fin. The effects of porous materials, irregular profiles and other thermo-physical parameters, such as Peclet number, surface emissivity coefficient, power index of heat transfer coefficient, convective-conductive parameter, radiative-conductive parameter, non-dimensional heat generation at ambient temperature, heat generation parameters, porosity and non-dimensional ambient temperature on non-dimensional temperature and fin efficiency are also studied.

The Development and Application of an Integrated VAR Process Model

The VAR ingot has been the focus of several modelling efforts over the years with the result that the thermal regime in the ingot can be simulated quite realistically. Such models provide important insight into solidification of the ingot but present some significant challenges to the casual user such as a process engineer. To provide the process engineer with a tool to assist in the development of a melt practice, a comprehensive model of the complete VAR process has been developed. A radiation heat transfer simulation of the arc has been combined with electrode and ingot models to develop a platform which accepts typical operating variables (voltage, current, and gap) together with process parameters (electrode size, crucible size, orientation, water flow, etc.) as input data. The output consists of heat flow distributions and solidification parameters in the form of text, comma-separated value, and visual toolkit files. The resulting model has been used to examine the relationship between the assumed energy distribution in the arc and the actual energy flux which arrives at the ingot top surface. Utilizing heat balance information generated by the model, the effects of electrode-crucible orientation and arc gap have been explored with regard to the formation of ingot segregation defects.

The Development and Application of an Integrated VAR Process Model

The VAR ingot has been the focus of several modelling efforts over the years with the result that the thermal regime in the ingot can be simulated quite realistically. Such models provide important insight into the solidification of the ingot but present some significant challenges to the casual user such as a process engineer. To provide the process engineer with a tool to assist in the development of a melt practice, a comprehensive model of the complete VAR process has been developed. A radiation heat transfer simulation of the arc has been combined with electrode and ingot models to develop a platform which accepts typical operating variables (voltage, current, and gap) together with process parameters (electrode size, crucible size, orientation, water flow, etc.) as input data. The output consists of heat flow distributions and solidification parameters. Utilizing heat balance information generated by the model, the effects of electrode-crucible orientation and arc gap have been explored with regard to the formation of ingot segregation defects.

Numerical simulation of radiative heat transfer in indoor environments on programmable graphics hardware

The efficient use of energy for heating and cooling of indoor environments requires an accurate prediction and analysis of radiative heat transfer. Therefore it is necessary to use modern computer methods as otherwise the computational costs may become higher than for convective heat transfer, which is known to be a huge computational problem. A key problem in calculations of radiative heat transfer is the problem of mutual visibility arising in the determination of view factors. This is the same challenge that global illumination has to cope with which is one of the fundamental topics in computational graphics. The visibility problem is efficiently solved by modern graphics hardware. Therefore an OpenGL-based algorithm is developed to quickly and accurately calculate view factors for arbitrary, complex geometries. Theoretical and implementation details of the applied methods are given. We demonstrate the advantages of the developed computational method by a virtual test room for a tubular radiator, a heating of a warehouse by ceramic infrared heaters and the heat transfer in a car cabin.

Combined non-gray conductive and radiative heat transfer simulation of a single glass window subjected to solar and thermal radiation

Combined nongray conductive and radiative heat transfer in single glass window using the Radiation Element Method by Ray Emission Model REM2, has been investigated in one dimensional case. The optical constants of the glass window have been determined by using Fourier Transform Infrared Spectrophotometer (FTIR). The absorption and emission within the glass layer are taken into consideration. The boundary surfaces of the glass are specular. Spectral dependence of radiation properties of the glass is taken into account. Both collimated and diffuse solar and thermal irradiations are applied at boundary surfaces, using the spectral solar model proposed by Bird. The simulation has been performed for one position of the sun at noon true solar time on the 5th of July for three locations in Japan, Sendai, Tokyo, and Sapporo cities. Steady state temperature and heat flux distributions within the glass layer for each position of the sun of the three locations are obtained. The radiative heat flux through the glass mediums is the predominant mode compared with the conductive one. Therefore, the temperature distributions within the glass layer are not linear in shape.

Numerical simulation of the flue gas side of refining vacuum furnace using CFD

In this work, we aimed to predict the flue gas side performance of a refining vacuum furnace with floor gas burners. The computational fluid dynamics (CFD) approach was employed to simulate the flow, combustion, heat transfer and NO emission. Detailed insights into the flue gas velocity, temperature field and NO mass concentration distribution were obtained with the aid of velocity vectors and contour snapshots. The standard k-ε model was applied to turbulence simulation. The non-premixed turbulent flames and NO emission were predicted using the Laminar Flamelet model. The discrete transfer model (DTM) was applied to the radiative heat transfer simulation. Comparative simulation cases were carried out to investigate the effect of excess air amount on the flue gas temperature distribution and NO emission. Calculations were performed using the commercial packages ANSYS CFX 14.0.

Simplified thermo-fluid model of an engine cowling in a small airplane

Purpose – The purpose of this study is to developed a simplified thermo-fluid model of an engine cowling in a small airplane. An aircraft engine system is composed of different elements operating at various temperatures and in conjunction with the composite nacelle creates a region with high intensity of heat transfer to be covered by the cooling/ventilation systems. Therefore a thermal analysis, accounting for the complex heat transfer modes, is necessary in order to verify that an adequate cooling is ensured and that temperatures of the nacelle are maintained within the operating limits throughout the whole aircraft's flight. Design/methodology/approach – Simplified numerical simulations of conductive, convective and radiative heat transfer in the engine bay of the small airplane I-23 in a tractor arrangement were performed for different air inlet and outlet configurations and for varying conditions existing in air inlets during the flight. The model is based on the control volume approach for heat and ...

A line by line based weighted sum of gray gases model for inhomogeneous CO2–H2O mixture in oxy-fired combustion

The HITEMP 2010 spectral emissivity database has been employed in line by line (LBL) calculation to produce an accurate total emissivity database for H2O–CO2 mixtures of the composition characteristics for the oxy-fired combustion. A wide range of temperatures, pressure-path length products and molar fraction ratios have been covered in the database. By using the LBL based emissivity database, an accurate set of coefficients has been obtained for the weighted sum of gray gases model (WSGGM). Compared to the standard WSGGM, the present model includes the molar ratio of H2O–CO2 mixtures in its formulation which leads to one set of coefficients required to represent the entire range of molar ratio. This simplifies the implementation of the model in the simulation of radiative heat transfer in high inhomogeneous media providing higher accuracy. The model is validated against the benchmark solutions for oxy-fired conditions. Obtained results have been compared with some of the previously reported WSGGMs.

Accuracy evaluation of the gray gas radiation model in CFD simulation

Gaseous combustion product, a mixture of radiating gas CO2, H2O and nonradiating gas N2, O2, absorbs and emits radiation spectrally selectively. Accurate simulation of radiation heat transfer inside a combustion chamber requires the line-by-line radiation model which is impossible for engineering practice because of the prohibitive computation time cost. The simplified gray gas model is the most popular model used in engineering CFD simulation. However, the accuracy of this model has not been systematically evaluated. Several radiation heat transfer cases have been simulated with the gray gas model and the simulation accuracy has been evaluated by the simulation result with the more accurate Statistical Narrow Band model. It is shown that the CFD simulation with the gray gas model can predict the peak heat transfer flux location accurately, but will over predict the heat flux and the heat transfer rate by as much as 23% for the tested cases.

Full-scale-model tests of materials and coatings at simulation of intense radiation and convective heat transfer of heat power equipment elements

There is presented the development of the experimental thermal booth for research and model (similar to full-scale) testing of materials and coatings for simulating complex heat transfer with a substantial portion of the radiant components in various types of combustion chambers during operation turbine elements, a variety of heat and power units, aero-space vehicles.

Extension of weighted sum of gray gas data to mathematical simulation of radiative heat transfer in a boiler with gas-soot media.

In this study an expression for soot absorption coefficient is introduced to extend the weighted-sum-of-gray gases data to the furnace medium containing gas-soot mixture in a utility boiler 150 MWe. Heat transfer and temperature distribution of walls and within the furnace space are predicted by zone method technique. Analyses have been done considering both cases of presence and absence of soot particles at 100% load. To validate the proposed soot absorption coefficient, the expression is coupled with the Taylor and Foster's data as well as Truelove's data for CO2-H2O mixture and the total emissivities are calculated and compared with the Truelove's parameters for 3-term and 4-term gray gases plus two soot absorption coefficients. In addition, some experiments were conducted at 100% and 75% loads to measure furnace exit gas temperature as well as the rate of steam production. The predicted results show good agreement with the measured data at the power plant site.

The Thermal Discrete Dipole Approximation (T-DDA) for near-field radiative heat transfer simulations in three-dimensional arbitrary geometries

A novel numerical method called the Thermal Discrete Dipole Approximation (T-DDA) is proposed for modeling near-field radiative heat transfer in three-dimensional arbitrary geometries. The T-DDA is conceptually similar to the Discrete Dipole Approximation, except that the incident field originates from thermal oscillations of dipoles. The T-DDA is described in details in the paper, and the method is tested against exact results of radiative conductance between two spheres separated by a sub-wavelength vacuum gap. For all cases considered, the results calculated from the T-DDA are in good agreement with those from the analytical solution. When considering frequency-independent dielectric functions, it is observed that the number of sub-volumes required for convergence increases as the sphere permittivity increases. Additionally, simulations performed for two silica spheres of 0.5μm-diameter show that the resonant modes are predicted accurately via the T-DDA. For separation gaps of 0.5μm and 0.2μm, the relative differences between the T-DDA and the exact results are 0.35% and 6.4%, respectively, when 552 sub-volumes are used to discretize a sphere. Finally, simulations are performed for two cubes of silica separated by a sub-wavelength gap. The results revealed that faster convergence is obtained when considering cubical objects rather than curved geometries. This work suggests that the T-DDA is a robust numerical approach that can be employed for solving a wide variety of near-field thermal radiation problems in three-dimensional geometries.

Multiscale Numerical Simulation of Radiation Heat Transfer in Participating Media

In this article, a numerical method for the simulation of radiative heat transfer is presented. The multiscale radiative exchange method (MREM) calculates the radiative source terms in a mesh structure that is coarser than the structures that are typically used in computational fluid flow calculations. To consider the effects of smaller scales on the overall predictions of the model, two dimensionless exchange factors are defined. An accurate simulation of self-extinction and rescattering in coarse volume cells is achieved if the exchange factors are used in the radiative energy balance. According to the location and size of each pair of coarse cells, integration elements of different sizes are used for the calculation of exchange factors. Therefore, the MREM takes into account the effects of a wide range of optical scales in its prediction. On the other hand, the MREM considers the radiative interaction between all of the geometric points in a quick and accurate manner. To improve the accuracy and the performance of the model, a mesh size analysis is performed and some sizes for various mesh structures are suggested for use in the MREM calculations. The model is verified by comparing it against some benchmarks. The predictions and computational cost of the method are compared to the results of other numerical methods, and the effects of different spatial scales on the accuracy of the method are addressed.

FDTD Simulation of Near-Field Radiative Heat Transfer between Thin Films Supporting Surface Phonon Polaritons: Lessons Learned

Abstract We present the numerical simulation, using the finite difference time domain (FDTD) method, of the radiative heat transfer between two thin SiC slabs. We aim to explore the ability of the FDTD method to reproduce the analytical results for the Surface Phonon Polariton (SPhP) assisted near field radiative energy transfer between two SiC slabs separated by a nano/micro-metric vacuum gap. In this regard, we describe the key challenges that must be addressed for simulating general near-field radiative energy transfer problems using the FDTD method. FDTD is a powerful technique for simulating the near-field radiative energy transfer because it allows simulating arbitrary shaped nano-structured bodies, like photonic crystals, for which an analytical solution is not readily obtained. Key words : Near-Field Radiative Heat Transfer, Fluctuation Electrodynamics, Thermal Radiation, Surface Phonon Polariton, FDTD 1. Introduction When two bodies are located at short distance (in the nano/micro scale) the evanescent modes can tunnel between each other and contribute to the radiative energy transfer, which can exceed the black body radiation by several orders of magnitude [1–3]. Besides, at nano-metric distance, the excitation of surface plasmon polaritons (SPP) in metals or surface phonon polaritons (SPhP) in polar materials, produce even further enhancement of the radiative energy transfer at the resonance frequencies [4–7], allowing for quasi-monochromatic near-field radiative heat transfer. These phenomena have got rising attention in the recent years due to the strong development of nano/micro-technologies, where near-field effects have to be considered in the thermal analysis. Some of the key applications that has been proposed so far are nano-lithography [8], near-field imaging [9], thermophotonic heat pumping [10], and thermophotovoltaic (TPV) energy conversion [3], [11–16] . Most of the theoretical studies on near-field radiative heat transfer presented so far are based on fluctuation electrodynamics theory [17–19]. This theoretical framework assumes that the origins of thermal radiation are the fluctuating currents originated by the random motion of charges within the material, and the problem can be solved analytically by means of the Green’s functions [20], which provides the spatial transfer function between current sources and the corresponding electro-magnetic fields in a given location of the space. However, the complexity of Green’s function formalism limits the theoretical development on near-field radiative heat transfer to relatively simple geometries; mainly infinite extended multilayered structures [19], for which a closed analytical solution is available.