Intense Thermal Radiation Research Articles

Combining node-centered parallel radiation transport and higher-order multi-material cell-centered hydrodynamics methods in three-temperature radiation hydrodynamics code TRHD

Higher-order cell-centered multi-material hydrodynamics (HD) and parallel node-centered radiation transport (RT) schemes are combined self-consistently in three-temperature (3T) radiation hydrodynamics (RHD) code TRHD (Sijoy and Chaturvedi, 2015) developed for the simulation of intense thermal radiation or high-power laser driven RHD. For RT, a node-centered gray model implemented in a popular RHD code MULTI2D (Ramis et al., 2009) is used. This scheme, in principle, can handle RT in both optically thick and thin materials. The RT module has been parallelized using message passing interface (MPI) for parallel computation. Presently, for multi-material HD, we have used a simple and robust closure model in which common strain rates to all materials in a mixed cell is assumed. The closure model has been further generalized to allow different temperatures for the electrons and ions. In addition to this, electron and radiation temperatures are assumed to be in non-equilibrium. Therefore, the thermal relaxation between the electrons and ions and the coupling between the radiation and matter energies are required to be computed self-consistently. This has been achieved by using a node-centered symmetric-semi-implicit (SSI) integration scheme. The electron thermal conduction is calculated using a cell-centered, monotonic, non-linear finite volume scheme (NLFV) suitable for unstructured meshes. In this paper, we have described the details of the 2D, 3T, non-equilibrium, multi-material RHD code developed with a special attention to the coupling of various cell-centered and node-centered formulations along with a suite of validation test problems to demonstrate the accuracy and performance of the algorithms. We also report the parallel performance of RT module. Finally, in order to demonstrate the full capability of the code implementation, we have presented the simulation of laser driven shock propagation in a layered thin foil. The simulation results are found to be in good agreement with the known solutions of RHD problems.

Narrowband thermal radiation from closed-end microcavities

High spectral selectivity of thermal radiation is important for achieving high-efficiency energy systems. In this study, intense, narrowband, and low directional absorption/radiation were observed in closed-end microcavity which is a conventional open-end microcavity covered by a semi-transparent thin metal film. The quality factor (Q factor) of optical absorption band strongly depended on the film electrical conductivity. Asymmetric and narrow absorption band with a Q factor of 25 at 1.28 μm was obtained for a 6-nm-thick Au film. Numerical simulations suggest that the formation of a fixed-end mode at the cavity aperture contributes to the narrowband optical absorption. The closed-end microcavity filled with SiO2 exhibits intense and isotropic thermal radiation over a wide solid angle according to numerical simulation. The narrow and asymmetric absorption spectrum was experimentally confirmed in a model of closed-end microcavity.

Rapid Sintering of Ceramics with Gradient Porous Structure by Asymmetric Thermal Radiation

In this study, thermal radiation was employed for sintering silicon carbide foams that achieved a gradient porous structure. The simultaneous use of graphite and carbon fiber reinforced carbon composite (Cf/C) radiators resulted in an axial temperature gradient of ~600°C along the cylindrical sample, as confirmed by both numerical simulation and experimental measurement. By sintering the cylinder top at 1600°C for 5 min, the porous SiC body achieved an axial pore size gradient from ~106 ± 36 μm to ~250 ± 84 μm and an open porosity from 41.4 to 79.8 vol%. This work indicates the potential of sintering by intense thermal radiation technique for rapid manufacturing functionally graded materials through asymmetric assembly of thermal radiators.

Sintering by intense thermal radiation (SITR): A study of temperature distribution by simulation and experiments

The modeling and a confirming experimental study of a sintering process by using intense thermal radiation (SITR) is demonstrated. Experiments were conducted in a modified spark plasma sintering set-up for the purpose of rapid consolidation of porous SiC ceramics. A finite element method based software package, COMSOL Multiphysics, was employed to simulate the temperature distributions with two different die geometries. Experimental verifications were performed by sintering of SiC foams and measuring the temperature differences between two fixed points on the die and samples at 1000–1800°C. SiC foams sintered under two geometries with 10min’ dwell resulted in the formation of grain necks. The compressive strengths are 19.2±0.7MPa (65.0±0.1vol% porosity) and 15.3±1.9MPa (69.0±0.3vol% porosity), respectively. The simulation and experimental results showed that the temperature distributions are strongly related to these geometries.

Silicon nitride foams from emulsions sintered by rapid intense thermal radiation

Open cell Si3N4 foams were fabricated by an emulsification process and subsequent sintering. Emulsification took place in an aqueous environment by using octane as alkane phase and a surfactant as stabilizer. Effects of different octane concentrations (50vol% and 70vol%) and stirring velocities (700rpm and 1000rpm) on porosity and pore size distribution were investigated. The shaped foams were pressureless sintered at 1600°C inside a modified SPS set-up. Si3N4 foams decorated with SiC nanowires and with an average cell size of 8–41μm and total porosity of 80–86vol% were obtained. The compressive strength ranged from 2.0MPa up to 9.9MPa. Both the foaming and sintering processes contributed to the development of different microstructures.

TRHD: Three-temperature radiation-hydrodynamics code with an implicit non-equilibrium radiation transport using a cell-centered monotonic finite volume scheme on unstructured-grids

Three-temperature (3T), unstructured-mesh, non-equilibrium radiation hydrodynamics (RHD) code have been developed for the simulation of intense thermal radiation or high-power laser driven radiative shock hydrodynamics in two-dimensional (2D) axis-symmetric geometries. The governing hydrodynamics equations are solved using a compatible unstructured Lagrangian method based on a control volume differencing (CVD) scheme. A second-order predictor–corrector (PC) integration scheme is used for the temporal discretization of the hydrodynamics equations. For the radiation energy transport, frequency averaged gray model is used in which the flux-limited diffusion (FLD) approximation is used to recover the free-streaming limit of the radiation propagation in optically thin regions. The proposed RHD model allows to have different temperatures for the electrons and ions. In addition to this, the electron and thermal radiation temperatures are assumed to be in non-equilibrium. Therefore, the thermal relaxation between the electrons and ions and the coupling between the radiation and matter energies are required to be computed self-consistently. For this, the coupled flux limited electron heat conduction and the non-equilibrium radiation diffusion equations are solved simultaneously by using an implicit, axis-symmetric, cell-centered, monotonic, nonlinear finite volume (NLFV) scheme. In this paper, we have described the details of the 2D, 3T, non-equilibrium RHD code developed along with a suite of validation test problems to demonstrate the accuracy and performance of the algorithms. We have also conducted a performance analysis with different linearity preserving interpolation schemes that are used for the evaluation of the nodal values in the NLFV scheme. Finally, in order to demonstrate full capability of the code implementation, we have presented the simulation of laser driven thin Aluminum (Al) foil acceleration. The simulation results are found to be in good agreement with the known solutions of RHD problems.

About the temperature of the thing under the influence of heat radiation of high intensity

The study of the nature of radiant heat, refers to one of the young branches of physics. Broad scientific interest in the study of the invisible heat rays associated with the beginning of transformation in the metallurgical and chemical production of Europe ‐ is in industrialization. The use of steam machines and the associated interest to thermal phenomena influenced in development of the doctrine of the heat. For the first time the concept of thermal radiation is referred to Swedish chemist Carl C. Scheele in his Chemical treatise on air and fire (1777 y.o.) based on many observations. In 1779 y.o. in proceedings of the Pyrometry, German mathematician and physicist Johann Lambert, were described experiments, consistent with the observations Scheele and for the first time experimentally proved that heat rays propagate rectilinearly, and their intensity decreases inversely to the square of the distance. In 1790 y.o. Mark O. Pictet continued the experiment through experiments which were of great importance to determine the nature of radiant heat and the further development of her theory. It is now known that the thermal radiation is electromagnetic radiation emitted by the substance and emerging due to the energy of thermal motion of atoms and molecules, is one of the modes of transmission of heat energy, along with such species as the thermal conductivity and convection. Recently, the importance of the study of thermal radiation was connected with natural and technogenic processes, for example, fire risk assessment and the prevention of such emergencies [1, 2]. Open fire is a source of highly intensity thermal radiation. When it is flow of heat radiation significantly affects the rate of spread of fire. As a rule, in view of substantial economic costs, such studies are carried out on numerical models. Therefore, to obtain reliable experimental data in the study of heat sources, open flame of the surrounding objects is an important practical task. The aim of the present work is an experimental studying of an influence of distance from the source with the heat radiance density 130 · 10 3 Bt 2 on studying sample. The objectives of the study are to measure the temperature of the sample from different distances of the source of thermal radiation, as well as the definition of the analytical dependence of the temperature of the sample at different distances from the source of thermal radiation. A scheme of the experimental setup area on which the research was conducted in accordance with figure 1. The installation consists of a source of thermal radiation (T0), sample temperature sensor (T2), two sliding screens, and measuring the distance from the source of thermal radiation to the sample with temperature sensor.

Rapid sintering of silicon nitride foams decorated with one-dimensional nanostructures by intense thermal radiation

Silicon nitride foams were prepared by direct foaming and subsequent rapid sintering at 1600 °C. The intense thermal radiation generated under the pressureless spark plasma sintering condition facilitated necking of Si3N4 grains. The prepared foams possessed a porosity of ∼80 vol% and a compressive strength of ∼10 MPa, which required only ∼30 min for the entire sintering processes. Rapid growth of one-dimensional SiC nanowires from the cell walls was also observed. Thermodynamic calculations indicated that the vapor–liquid–solid model is applicable to the formation of SiC nanowires under vacuum.

Multiphysics well-stirred reactor modeling of coal gasification under intense thermal radiation

Gasification of carbonaceous materials using concentrated solar radiation can be an efficient and cost-effective way of supporting the endothermic reactions. To understand the effect of concentrated solar energy on the gasification process, we applied a multiphysics constant-volume well-stirred reactor model. The model considers detailed gas-phase chemistry, devolatilization kinetics, particle-phase reactions, film diffusion, pore evolution, as well as full coupling between the two phases at multiple scales for mass, species, and energy exchange. Numerical simulations were conducted using an in-house code to understand the effects of concentrated solar energy flux on conversion time, syngas yield, solar-to-fuel conversion efficiency, and solar-to-chemical enthalpy conversion percentage.

Radiation of light from powder materials under shock compression

Intense radiation of light, covering the visible region and extending into the infrared region, has been observed when powder materials are shock compressed in plate-impact experiments. The time duration of the radiation is on the order of 10ns, and the intensity increases with the shock strength, but intense radiation is still observed in the visible region for very weak shocks. Thermal radiation from the shock-compressed powder cannot explain the observed radiation spectrum. Adiabatic compression of the residual gas in the shock-compressed powder appears to generate high temperatures and intense thermal radiation.

Design and development of a SPMB (self-aspirating, porous medium burner) with a submerged flame

This work reports design and development of a SPMB (self-aspirating porous medium burner) for replacing the self-aspirating, CB (conventional gaseous fuel, free flame burners), which are widely used in heating process of SMEs (small and medium scale enterprises) in Thailand but they have relatively low thermal efficiency of about 30 percent. Design of the SPMB relies on the same important characteristics of the CB, i.e. using the same mixing tube and the same fuel nozzle. The SPMB is formed by a packed bed of alumina spheres. The pressure drop across the packed bed, diameter of particles and a combustion chamber diameter are estimated by Ergun’s equation in combination with Pe (Peclet number). The SPMB yields a submerged flame with an intense thermal radiation emitted downstream. An output radiation efficiency as high as 23 percent can be achieved at relatively high turn-down ratio of 2.65 and firing rate ranging from 23 to 61 kW. The SPMB shows a more complete combustion with relatively low CO emission of less than 200 ppm and acceptably high NO x emission of less than 98 ppm as compared with the CB throughout the range of firing rate studied, suggesting the possibility of the SPMB in replacing the CB.

Laser heated high density fluids probed by coherent anti-Stokes Raman spectroscopy

We describe experiments integrating coherent anti-Stokes Raman spectroscopy (CARS), laser-heating and diamond-anvil cell (DAC) technologies for probing molecular vibrations of transparent molecular fluids at the pressure–temperature conditions of energetic detonation and interiors of giant planets. In these experiments, we use a microfabricated metal toroid and a cw Nd:YLF laser to conductively heat a surrounding transparent sample in a DAC. The laser is operated at a TEM01* mode to match the shape of the toroid and thus produces a uniform heating area. The CARS probe utilizes two pulsed lasers with similar cavity lengths: a commercial narrow-band mode-locked Q-switched Nd:YAG laser and a homebuilt broadband dye laser. A strong CARS signal is then produced from the sample in the central region of laser-heated metal toroid where the two laser pulses spatially and temporally coincide. In this article, we demonstrate that this technique is capable of producing high quality vibrational spectra from nitrogen fluid above 2000 K and 13 GPa, where the application of spontaneous Raman spectroscopy is limited because of intense thermal radiation.

Three-Dimensional Simulation for Urban Warming and Proposal of an Environmental Index for Urban Environment.

In most cities, it is becoming evident that the increase in energy consumption is causing environmental problems, including a temperature rise in the urban atmosphere (an urban heat island) and air pollution. The present paper reports on the results of a three-dimensional computer simulation of the urban heat island in the Tokyo metropolitan area, as well as moisture migration. The three-dimensional governing equations for the urban atmospheric boundary layer were formulated by virtue of the vorticity-velocity vector potential method. Particular attention was focused on the representation of a buoyancy term in the equation of motion in the vertical direction, thereby describing the cross-over effect and stratified inversion layer near the ground surface. According to a recent computer simulation for urban warming in the Tokyo metro area in 2031, the maximum ambient temperature in the evening (18 : 00) at Otemachi will exceed 42°C. In contrast to the interior thermal comfort in residential and office buildings, the urban outdoor comfort is strongly affected by intense thermal radiation coming from the surface of the structures, as well as solar radiation. Motivated by the above facts, we propose a new standard effective temperature index (USET*), which is applicable to urban comfort. By using this comfort index, assessment of the urban environment is made for both presentday Tokyo and Tokyo around 2030. Furthermore, it is suggested that a comprehensive urban environmental index (UEI). which includes pollutants and ultraviolet rays, is adopted for the future urban environment.

X-ray reemission from CH foils heated by laser-generated intense thermal radiation.

X-ray emission and burn through of radiatively heated plastic foils have been investigated in a gold cavity heated by eight beams of the Gekko XII laser up to a radiation temperature of 140 eV. We measured the temporally resolved reemission spectra of carbon. The time and frequency integrated reemission was 23% of the gold reemission. The measurements are in good agreement with numerical simulations.

Uniform multimegabar shock waves in solids driven by laser-generated thermal radiation.

Uniform shock waves were driven into solid gold and aluminum samples via ablation of material by intense thermal radiation. The radiation was generated by laser heating of 1--3 mm size gold cavities to radiation temperatures of up to 150 eV. Shock wave velocity and uniformity were measured using flat, single-step, double-step, and wedge samples. Pressures of up to 20 Mbar were achieved.

X-ray-based displacement measurement for hostile environments

A completely new method of noncontacting, hostile-environment displacement measurement based on the focus and scanning of X rays has been developed and shows promise of overcoming many of the limitations associated with available techniques. The chief advantage lies in the ability to make undisturbed measurements through stratified or flowing gases, smoke and flame. The system is based on the focus and scanning of lowenergy, hard X rays such as those emanating from copper or molybdenum sources. The X rays are focused into a narrow and intense line image which can be swept onto targets that fluoresce secondary X-ray radiation. This radiation is monitored and target-edge position can be determined by measuring the focused image position when the marker begins to fluoresce. The final goal for the system is to be able to conduct macroscopic strain measurement in hostile environments by utilizing two or more fluorescing targets. Current work has been limited to displacement measurement of a single target with a resolution of 0.5 micron. Tests have also been conducted at target temperatures of 1200°C, directly through an open flame. The main advantage of the technique lies in the penetrating nature of X rays, which are not affected by the presence of refracting gas layers, smoke, flame or intense thermal radiation, all of which could render conventional extensometry methods inoperative or greatly compromise their performance.

Experimental investigation of radiation heat waves driven by laser-induced Planck radiation.

The propagation of a radiation heat wave through a thin foil of solid gold was investigated experimentally. The wave is driven by the intense thermal radiation in 1--3-mm-diam gold cavities heated by an intense laser pulse (duration 0.8--0.9 ns, wavelength 0.35 \ensuremath{\mu}m) to temperatures ranging from 80 to 240 eV. Evidence of the propagating wave was obtained from the delayed onset of thermal emission from the outer side of the foil. A detailed comparison of the results with the self-similar solution for the ablative heat wave and with numerical simulations is presented.

Experimental observation of laser-induced radiation heat waves.

The propagation of a radiation heat wave through a thin foil of solid gold was investigated experimentally. The wave is driven by the intense thermal radiation in 1--3-mm-diam gold cavities heated by an intense laser pulse (duration 0.8--0.9 ns, wavelength 0.35 \ensuremath{\mu}m) to temperatures of more than 200 eV. Evidence of the propagating wave was obtained from the delayed onset of intense thermal emission from the outer side of the foil. The results agree with theoretical predictions for a self-similar ablative heat wave and with numerical simulations.

On the Feasibility of Secondary Atomization of Small Slurry Droplets Exposed to Intense Thermal Radiation

Abstract Feasibility of fragmentation of small slurry droplets in combustors caused by absorption of high-temperature thermal radiation is studied theoretically. The first model of explosive vaporization of the liquid assumes uniform radiant heating of the slurry droplet according to the computed absorption efficiency for black body radiation. The subsequent analysis of transient heat conduction inside the droplet provides estimates for threshold intensities of the radiation necessary for explosive evaporation at the hottest spot inside the droplet. The second model applies the extended effective medium theory together with Mie scattering theory in computations of absorption patterns of black body radiation inside the slurry droplet. The calculated absorption profiles are used subsequently in analysis of transient heat conduction and droplet swelling due to internal boiling. Explicit results of computations and predictions of secondary atomization are given for ultrafine coal-water slurry.

Results of Onsite and Research-Facility Dioxin Destruction Tests Using the Advanced Electric Reactor

The Advanced Electric Reactor (AER), is an electrically heated, pyrolytic process which uses a unique graphite reactor core to heat reactants to 2100°-2500°C using intense thermal radiation in the near infrared. Three test series were conducted to demonstrate the AER's capability to treat dioxin-contaminated soil. One test series, conducted at Times Beach, MO using a transportable AER with a 3-inch diameter core (AER-3), represents the first time 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been destroyed in the field. This test series is supported by tests conducted at Huber's Borger, TX research facility with the AER-3 and a 12-inch pilot unit (AER-12) using octachlorodibenzo-p-dioxin (OCDD) as a waste surrogate. Tests conducted at Times Beach and Borger with the AER-3 yielded destruction and removal efficiencies (DRE) ≥99.998% with dioxin concentrations at the process stack which were below detection limits in all cases. Higher DREs could not be demonstrated due to low feed dioxin concentrations (80 -250 ng/g) and low feedrates. The AER-12 test series, conducted with high OCDD concentrations (17,200 - 18,900 ng/g) and high feedrates, yielded DREs from 99.99996% - ≥99.999994%, demonstrating the AER's capability to obtain very high DREs for dioxins. Treated feed dioxin concentrations were <0.45 ng/g for all test series. Chlorine and particulate loading were below detection limits for all test series.