Frequency-Selective Surfaces (FSS) type metasurfaces consist of periodic arrays of antenna elements. They can be scaled from microwave frequencies to the infrared wavelengths where they allow the scattering response to be engineered. This includes the spectral absorptance/emittance. At IR wavelengths, the features sizes of the metasurface are sub-micron which poses manufacturing issues for the meter squared scales required for most heat transfer applications. In this paper, we investigate the use of Microsphere Photolithography for creating spectrally selective metasurfaces. This approach uses a self-assembled array of microspheres as a lens array to focus a lattice of photonic jets into photoresist. These can be used with lift-off to create metal-insulator-metal (MIM) or even five-layer of resonant structures. We study the design constraints and synthesize a broadband emitter in the mid-infrared. The spectral absorptance is measured experimentally using FTIR. The structures are then tested at moderate temperatures to demonstrate the ability to affect surface temperature/heat flux in practical applications.

In this work, we present a new formula for the near-field thermal radiative transfer between two spheres. The formula is identical for coated or uncoated spheres and captures the effect of the coatings in the effective Mie reflection coefficients of the spheres. We also numerically demonstrate that silica coated silver spheres transition from silver-like conductance in the far-field to surface phonon polariton dominated silica-like behavior in the extreme near-field.

Near-field thermal radiation and van der Waal force between flat plates and curved surfaces have been probed in the past; however the peculiarities of radiative heat transfer and van der Waals stress due to fluctuations of electromagnetic fields for micro/nano-sized spherical objects have not been studied in great details. We demonstrate how fluctuational electrodynamics can be used to determine emissivity and van der Waals contribution to surface energy for various spherical shapes in a homogeneous and isotropic medium. The dyadic Green’s function formalism of radiative energy and fluctuation-induced van der Waals stress for different spherical configurations has been developed. We present the calculations for a single sphere, a bubble, a spherical shell and a coated sphere. We observe that emission spectrum ofmicro/nanoscale spheres displays several sharp peaks as the size of object reduces. Our calculations indicate that surface energy becomes size dependent (r-3) due to van der Waals phenomena for small radii.

Microscopic thin films are known to have narrow band selective thermal radiation whch have potential applications in selective emitter and absorbers. We propose a methodology to shift the wavelength selectivity in the desired location. Calculation of emissivity and near field radiation for different materials and structures is presented. Emissivity calculations are performed using the standard expressions for Fresnel reflection coefficients. For the near field thermal radiation, we use the analytical expression for transitivity between two half spaces obtained using the dyadic Greens function formalism. We use Maxwell-Garnett-Mie theory to calculate effective dielectric function of media doped with nanoparticles. We observe that spectrum of thermal radiation in far-field and in near-field can be altered using nanoparticles. Moreover spectral properties of mixtures can be characterized using refractive indices. Influence of nanoparticle size and concentration is also studied.

The M-1 radiation model is a thermal radiation transport model that is derived from a maximum entropy approximation to the radiative transport equation. It involves the solution of four hyperbolic equations for conservation of radiative energy. The M-1 model has similarities to the classical diffusion approximations (like P-1), but is able to better predict directed flux. Consequently, shadowing and long-range transport can be well resolved for a fraction of the cost of methods with exponentially increasing accuracy costs like the method of discrete ordinates and Monte Carlo ray-tracing. The M-1 method is mostly used historically in astronomical radiation transport, but has recently been shown to work for combustion applications of smaller scale. Past work has shown it to give good comparisons to fire problems with length scales of interest. Because of the potential for the model to predict radiation transport more cost-effectively, it is being examined for implementation as an option in our fire codes. We present the theory behind the model. The Eddington factor is used to partition directed and diffuse radiation. It is normally modeled since it is derived from a transcendental functional relationship. We analyze Eddington factor models presented in previous work, and present a new model that we show to be superior in most ways to all the previously presented models. Some 1-dimensional calculations are also shown that illustrate the potential accuracy and challenges with implementing the M-1 model. Such challenges include the specification of boundary conditions and the development of robust solver methods.

This paper reports a numerical study on the thermal radiative transport in a cloud of dry water particles. Dry water is a water-in-air inverse foam which consists of micrometer-sized water droplets encapsulated by hydrophobic fumed-silica nanoparticles. The radiative properties of this novel material were estimated using the Mie theory for coated spheres. The radiative transport equation (RTE) was solved for a one-dimensional geometry using the discrete ordinates method. The effects of silica particle and water droplet size as well as the volume fraction of dry water particles on reducing radiative heat transfer were studied numerically. The results were compared with respect to two limiting cases: (i) system with no particles and (ii) silica particles with no water. The results showed that dry water reduced the local radiative heat flux as much as 20% more than that by silica particles alone. Additionally, reduction of the diameter of dry water particles from 75 to 25 μm reduced the radiative heat flux by 17%. Finally, parametric analysis showed that increasing the volume fraction of dry water by 10 times decreased the radiative heat flux by about 30% at the receiver end.

This study compares several band models for calculating the thermal radiation from the plume of a simulated rocket motor. First, a non-scattering plume is considered allowing one to use the line-of-sight integration (LOS). The results for three band models are compared. Next we study a scattering plume. The radiative heat transfer equation is solved numerically using the axisymmetric finite volume method (FV). Detailed analysis of the numerical scheme of the FV method demonstrated that it has a large numerical diffusion term which, although formally of the first order, in practice can cause large errors in calculating thermal signatures of hot jets. The numerical scheme was hence modified using what we call the “quasi-Cartesian” approach. We demonstrate that for a non-scattering media in the first order the numerical diffusion term vanishes and the modified scheme formally reduces to the integration along the line of sight resulting in a very good agreement between the FV and LOS predictions. The new method is then used to calculate radiation from a scattering plume and the results for two band models are compared.

This study is focused to the heat transfer analysis in air cooled rooms, which is important to achieve pleasant indoor comfort conditions, fundamentally in terms of air velocity, temperature and air quality. Three dimensional numerical results of a rectangular ventilated room with three different inlet configurations are presented. The study was carried out considering a turbulent flow and the radiative exchange between the walls. The assumed heat flux on a vertical wall was 300 W/m 2 (Rayleigh number of 1.07×10 12 ). The inlet velocity was 0.5 m/s (Reynolds number of 3145) and the emissivity of the walls was fixed as 0.8. The mathematical model was solved numerically with Computational Fluid Dynamics software. The temperature fields, flow patterns, heat transfer coefficients and temperature distribution effectiveness are presented and discussed. It was found that the heat transfer due the radiative effect is around 50% for the three studied cases.

The structure and soot formation characteristics of a coflow laminar methane/air diffusion flame under conditions of constant p 2 g and mass flow rates of the air and fuel streams were numerically investigated in order to examine the validity of the p 2 g scaling relationship. The p 2 g scaling relationship has been used to experimentally investigate soot formation in weakly-buoyant laminar diffusion flames by conducting experiments at reduced pressures. Detailed numerical calculations were conducted by solving the elliptic conservation equations of mass, momentum, species, and energy in axisymmetric cylindrical coordinates using a standard control volume method. Detailed multi-component thermal and transport properties and detail combustion chemistry were employed in the modelling. Soot formation was modeled using a semi-empirical acetylene based model in which two transport equations for the soot mass fraction and soot number density per unit mass were solved. Thermal radiation was calculated using the discrete-ordinates method and a 9-band non-grey model for the radiative properties of the CO-CO 2 -H 2 O-soot mixture. The flame structure and soot formation characteristics exhibit strong dependence on the ambient pressure even though p 2 g and the mass flow rates are kept constant. Significantly more soot is produced with increasing the pressure and decreasing the gravity level. Numerical results clearly demonstrate that the p 2 g scaling relationship is invalid as far as soot formation is concerned.

The recently developed model for thermal radiation in multiphase flows typical of melt-coolant interactions is generalized to account for transient temperature profile in large semi-transparent particles of solidifying melt. A modification of the Large-Cell Radiation Model (LCRM) is based on approximate solution for coupled radiation and conduction in optically thick spherical particles of a refractive material. The simplicity of the suggested approximation enables one to implement the modified model in a multiphase CFD code. The LCRM extension makes possible the use of this approach not only for the core melt in nuclear fuel-coolant interactions (FCI’s) but also for other melt substances which are widely used in the laboratory experiments. The numerical data demonstrate an effect of absorption coefficient of the particle substance on the rate of particle cooling and solidification.

A series of comprehensive large eddy simulations of non-premixed turbulent hydrocarbon flames of different sizes in a typical fire scenario have been carried out to compute the flame radiative heat transfer. In the simulation, considerations include the modelling of sub-grid turbulence, turbulent combustion, soot formation, thermal radiation and interactive heat transfer inside solid walls, etc. The instantaneous thermal radiation was calculated using the discrete transfer method with the radiation property evaluated by both an approximated fast narrow band model and an integral model. Simulation was validated against experimental data. Flame radiation heat transfer was compared for flames of different sizes. The effect of thermal radiation property evaluation model on calculation of radiation and the role of thermal radiation in total heat transfer are analyzed.

The present paper is concerned with the numerical computation of flow, heat transfer and chemical reactions in porous burners. The porous solid matrix acts as a host for redistributing the thermal energy transferred to it from the hot reacting gases. Inside the porous matrix, heat is transferred down stream by conduction and radiation. This thermal energy is then transferred to the incoming cold fuel/air mixture to initiate the chemical reaction processes and thus stabilize the flame. One of the important features of porous burners is its presumed low levels of NO concentration. In the present work, the computed NO x is compared with experimental data and open premixed flames. In order to accurately compute the nitric oxide levels in porous burners, both prompt and thermal NO x mechanisms are included. In the present work, the porous burner species mass fraction source terms are computed from an ‘extended’ reaction mechanism, controlled by chemical kinetics of elementary reactions. The porous burner has mingled zones of porous/nonporous reacting flow, i.e., the porosity is not uniform over the entire domain. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Up-wind differencing is used to insure that the influence coefficients are always positive. Finite-difference equations are solved, iteratively, for velocity components, pressure correction, gas enthalpy, species mass fractions and solid matrix temperature. A non-uniform (80×80) computational grid is used. The grid used to solve the solid energy equation is extended inside the solid annular wall of the porous burner, to improve its modeling. A discrete-ordinate model with S4 quadrature is used for the computation of thermal radiation emitted from the solid matrix. The porous burner uses a premixed CH 4 -air mixture, while its radiating characteristics are required to be studied numerically under equivalence ratios 0.6 and 0.5. Twenty-five species are included, involving 75 elementary chemical reactions. The computed solid wall temperature profiles are compared with experimental data for similar porous burners. The obtained agreement is fairly good. Some reacting species, such as H 2 O, CO 2 , H 2 , NO and N 2 O increase steadily inside the reaction zone. However, unstable products, such as HO 2 , H 2 O 2 and CH 3 , increase in the preheating zone to be depleted afterward.

In modeling catalytic combustion in a monolithic catalytic converter, it is generally assumed that the gas within the individual monolith channels does not interfere with thermal radiation. To date, no quantitative study has been undertaken to validate this assumption. Past studies for carbon monoxide combustion also appear to indicate that the emissivity of the washcoat has little effect on the thermal radiation field. In order to investigate these two issues, methane-air combustion on platinum is modeled inside a single channel of a monolith using a detailed surface reaction mechanism comprised of 24 reactions between 19 species. Radiation transport is modeled using the Discrete Ordinates Method and a gray formulation. Planck-mean absorption coefficients of the gases, calculated from the HITEMP and HITRAN databases, are used to investigate participating medium effects. All calculations were performed using the commercial CFD code, CFD-ACE+™, supplemented by user-subroutines for calculating the absorption coefficient of the gas mixture. Results show that the conversion percentages and temperature distributions are unaltered by the inclusion of participating medium radiation effects, verifying the commonly held belief, stated earlier. However, in strong contrast with carbon monoxide combustion, the emissivity of the washcoat was found to significantly affect flammability limits in the case of methane combustion—the flame being hotter and more stable for smaller values of emissivity.

The Kirchhoff’s law on emission and absorption of thermal radiation is a law driven deductively for the energy equilibrium of thermal radiation. First, we consider on the basis of spectroscopic experiments and an electromagnetism whether the Kirchhoff’s law is valid for the spectra of emission and absorption of an electromagnetic wave which are characterized by the phase as well as the amplitude of the wave. The interference of radiation caused by the phase matching is a key for this problem. Second, we consider the possibility of systematic coherency of spherical waves emitted by a number of dipoles which are the sources of thermal radiation. This consideration is related to the validity of the assumption that emission sources of thermal radiation move randomly.

Spectral control of thermal radiation emitted from micro-cavities made on a mirror-like-polished Ni metal surface was investigated through numerical simulation and experiment. In simulation, thermal radiation from solid surface was dealt as hemispherical emission from point sources, and Maxwell’s equations were solved using CIP (Cubic Interpolated Propagation) method. It was demonstrated that the emittance could be increased around the wavelength corresponding to the standard mode of cavity resonance, while the emittance at wavelengths corresponding to the higher modes was much the same as that of smooth flat surface. Furthermore, in experiment using rectangular micro-cavities (0.5×0.5×0.5μm 3 ) made periodically on Ni smooth surface, spectral emittance was measured in the near-infrared region. The experimental results disclosed that the emissive power only in the range of shorter wavelength than 1.2μm was increased by the micro-cavities that played a role of a wave guide to produce cutoff effect clearly.

A thermal model was constructed to simulate the combined heat transfer phenomena, including thermal radiation in the heating chamber, during the sputtering process. The changes in thermal characteristics when thermal radiation occurred within the chamber system were analyzed using CFD (Computational Fluid Dynamics) method. The research emphasis in this paper was to explore the temperature distribution on the large glass panel. In order to achieve the temperature uniformity criterion (±15°C), the chamber design was improved to prevent a significant difference between temperature distributions. Several design factors were made to observe the effect on temperature distribution. After optimizing the chamber structure, the IR heater settings were in the end determined to meet the standards of three different sputtering circumstances.

The present paper is concerned with the numerical computation of flow, heat transfer and chemical reactions in porous burners. One of the important features of porous burners is their presumed low levels of nitrogen oxides. In the present work, the computed NO x is compared with similar conventional premixed burners and measured nitrogen oxides in porous burners. In order to accurately compute the nitrogen oxides levels in porous burners, both prompt and thermal NO x mechanisms are included. In the present work, the porous burner species mass fraction source terms are computed from an ‘extended’ reaction mechanism, controlled by chemical kinetics of elementary reactions. The porous burner has mingled zones of porous/nonporous reacting flow, i.e. the porosity is not uniform over the entire domain. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Up-wind differencing is used to ensure that the influence coefficients are always positive to reflect the real effect of neighboring nodes on a typical central node. Finite-difference equations are solved iteratively for velocity components, pressure correction, gas enthalpy, species mass fractions and solid matrix temperature. The grid used to solve the solid energy equation is extended inside the zero-porosity solid annular wall of the burner porous disk. This was found useful for computing the solid wall temperature with high accuracy. A two-dimensional, discrete-ordinate, model is used for the computation of thermal radiation emitted from the solid matrix. The porous burner uses a premixed CH4-air mixture, while its radiating characteristics are studied numerically under equivalence ratio ranging from 0.5 to 0.8. Twenty-one species are included, involving 55 chemical reactions. The computed solid wall temperature profiles are compared with experimental data of similar porous burners. The obtained agreement is fairly good. The present numerical results show that as the equivalent ratio decreases, the reaction zone moves downstream. Moreover, as the flame speed increases, the NO x mole fraction increases. Some reacting species, such as H 2 O, CO 2 and H 2 increase steadily inside the reaction zone; they stay appreciable in the combustion products. However, unstable products, such as HO 2 , H 2 O 2 and CH 3 , first increase in the preheating region of the reaction zone; they are then consumed in the remaining part of the reaction zone. The numerical results show that most of the formed NO x is composed of nitric oxide. The velocity and temperature profiles were accurately predicted using a grid of 80×80 while the nitrogen oxides were computed accurately utilizing a finer grid of 160×160.

Much attention has been paid recently by research and development engineers on performing multi-physics calculations. One way to do this is to couple commercial tools for examining complex systems. Since the proposal of an software architecture for coupling programs as published in a previous paper significant changes have led to an improved performance for large-scale industrial applications. This architecture is being described and as a proof of concept a simulation is being conducted by coupling two commercial solvers. The speed-up of the new system is being presented. The simulation results are then compared with measurements of surface temperatures of an exhaust system of an actual sports utilities vehicle (SUV) and conclusions are being drawn. The proposed architecture is easily adaptable to various programs as it is implemented in C++ and changes for a specific code can be restricted to a view classes.

A numerical model of a direct fired generator is presented. The objective is to provide a baseline for designing the prototype of a gas fired generator, aimed to drive a GAX absorption cooling system. The model was carried out using Fortran 90. The gas fired generator will be part of the hybrid 10.5 kW GAX cooling system, which is being designed to operate with solar energy and direct fired by LPG combustion. The prototype is designed in two sections. In the first section, the “U” form combustion chamber is flooded with ammonia-water solution, the heat radiation from the flame and the hot combustion gases are absorbed by the tube walls and transferred to the solution. In the second section (the convection zone), the combustion gases are used to increase the concentration of the ammonia refrigerant. Thermal design results in the radiation, boiling and convection zones are presented and discussed, while the manufacturing strategies are being analyzed to produce a compact and efficient prototype.

Thermal radiation and conduction are the main modes of heat transfer in a packed bed with internal heat generation during a loss of forced cooling incident. Due to the large number of spheres, the only feasible way of treating the bed in Computational Fluid Dynamics is through a porous medium approach. Traditionally, CFD treats a porous medium as a fluid zone, whilst fluid properties are adjusted to account for the presence of the solids. In this work, the bed is treated as a gray gass, emitting and absorbing thermal radiation at the solid temperature. A unit cell approach is used to determine the absorption and scattering coefficients. This approach prevents direct radiation between surfaces on opposite sides of the bed, but allows the free surface of the bed to exchange radiation with surrounding structures. Results generated with the proposed model were compared to modelling results using an effective conductivity (Zehner-Schlu¨nder model [1]) to combine the contributions of conduction and radiation.