High-flux Radiation Research Articles

Solar-Driven Torrefaction of a Lignin-Rich Biomass Residue in a Directly Irradiated Fluidized Bed Reactor

ABSTRACTThe share of energy production from renewable sources is continuously increasing and aims at reaching two-thirds of primary energy supply in 2050. In this scenario, the 2009/28/EC Directive requires that at least 10% of the transportation fuel of every EU Country derives from renewable sources by 2020, thus largely encouraging the production of biofuels. The synthesis of second-generation biofuels is characterized by extensive generation of residues with large lignin content. Torrefaction can be applied to sterilize and stabilize this residue, and to upgrade its properties for subsequent utilization in the energy field. In this study, the use of solar energy via concentrating solar power systems is proposed to perform solar-assisted torrefaction of a lignin-rich residue derived from a second-generation bioethanol production plant. The process was carried out in a lab-scale directly irradiated bubbling fluidized bed (BFB) reactor, a system designed so as to simultaneously operate as a solar receiver and a reactor in real applications. Experiments were also performed in a lab-scale conventional (i.e. electrically heated) BFB test reactor. Chemical and physical analyses were performed on the product materials to investigate changes in the elemental composition and volatile matter content as a function of the reaction temperature. Heating values of the torrefied materials were also characterized. Scanning electron microscopy (SEM) analyses were performed on the torrefied residues to highlight possible differences in the structure of the materials recovered after solar and nonsolar experiments. The influence of operating conditions on the quality of the torrefied biomass has been assessed, with a particular emphasis on the possible overheating of fuel particles under the high radiative flux conditions experienced in solar-driven torrefaction.

Experimental and numerical analysis of the heat transfer in a packed bed exposed to the high thermal radiation flux

This paper investigates temperature profiles and heat fluxes in a packed bed heated by radiation that simulates solar energy flux. For this purpose, the discrete element method (DEM) was used along a heat transfer model (conduction and radiation mechanism). Short-range model is proposed for considering thermal radiation in a discrete elements system, which represents an easy-to-implement and low-computational-cost alternative. As results of the simulations, thermal profiles through the packed bed were obtained, as well as the accompanying heat flux. Experiments were performed in a packed bed of inert ceramic particles (alumina spheres). A radiant porous burner was placed at the bottom of the packed bed to simulate an imposed concentrated solar heat flux. Numerical results show good agreement with experimental data. In addition, the thermal profiles, obtained by the heat transfer model in DEM, were compared with the results obtained by discretizing the conservation of energy equation of the solid phase using finite differences, showing a correlation between the power and temperatures reached. It is concluded that the radiation model proposed provides the basis to continue with the study of granular materials at high temperature, where radiation is the dominant mechanism.

Improving the opto-thermal performance of transmissive laser-based white light sources through beam shaping.

Laser diodes have been proposed as a good replacement for light-emitting diodes in high-luminance white light sources. However, laser diodes typically generate very sharp temperature gradients inside the colour-converting elements (CCE) used to produce white light. This poses a thermal management problem in transmissive configurations, where most of the thermal dissipation occurs at the edges of the CCE. The hot spot in the center of the CCE typically drives the efficiency of the system down due to thermal quenching. In this work, we propose a strategy to tackle this issue that is based purely on optical manipulation. By using a free-form lens, the radiation pattern of the laser diode exciting the CCE is tailored so that its power distribution is skewed towards the periphery of the CCE: the zone with the highest thermal dissipation. With this technique, the maximum temperature inside the CCE can be significantly lower than when uniformly illuminating the CCE. Additionally, by lowering the temperature inside the CCE, this technique excites the CCE with a higher radiant flux, allowing higher luminance to be extracted from the system. These results were obtained with a realistic opto-thermal simulation framework and were then experimentally verified.

Evidence for color dichotomy in the primordial Neptunian Trojan population

In the current model of early Solar System evolution, the stable members of the Jovian and Neptunian Trojan populations were captured into resonance from the leftover reservoir of planetesimals during the outward migration of the giant planets. As a result, both Jovian and Neptunian Trojans share a common origin with the primordial disk population, whose other surviving members constitute today’s trans-Neptunian object (TNO) populations. The cold (low inclination and small eccentricity) classical TNOs are ultra-red, while the dynamically excited “hot” (high inclination and larger eccentricity) population of TNOs contains a mixture of ultra-red and blue objects. In contrast, Jovian and Neptunian Trojans are observed to be blue. While the absence of ultra-red Jovian Trojans can be readily explained by the sublimation of volatile material from their surfaces due to the high flux of solar radiation at 5 AU, the lack of ultra-red Neptunian Trojans presents both a puzzle and a challenge to formation models. In this work we report the discovery by the Dark Energy Survey (DES) of two new dynamically stable L4 Neptunian Trojans, 2013 VX30 and 2014 UU240, both with inclinations i > 30°, making them the highest-inclination known stable Neptunian Trojans. We have measured the colors of these and three other dynamically stable Neptunian Trojans previously observed by DES, and find that 2013 VX30 is ultra-red, the first such Neptunian Trojan in its class. As such, 2013 VX30 may be a “missing link” between the Trojan and TNO populations. Using a simulation of the DES TNO detection efficiency, we find that there are 162 ± 73 Trojans with Hr < 10 at the L4 Lagrange point of Neptune. Moreover, the blue-to-red Neptunian Trojan population ratio should be higher than 17:1. Based on this result, we discuss the possible origin of the ultra-red Neptunian Trojan population and its implications for the formation history of Neptunian Trojans.

Super Broadband Near-Infrared Phosphors with High Radiant Flux as Future Light Sources for Spectroscopy Applications

The near-infrared (NIR) light source is desirable for real-time nondestructive examination applications, which include the analysis of foodstuffs, health monitoring, iris recognition, and infrared cameras. The emission spectra of such an infrared light source should also be as broad as possible for effective performance, in view of the fact that the broad absorption and reflection of light by the organic elements present in foodstuffs and human health fall in the blue and NIR regions of the electromagnetic spectrum, respectively. In this letter, a blue light-emitting diode (LED) excitable super broadband NIR phosphor light source is developed with a high fwhm of 330 nm and radiant flux of 18.2 mW for the first time. The observation of super-broad-band luminescence from two distinct luminescence centers is studied and evidenced by electron paramagnetic resonance, X-ray absorption near-edge structure, steady-state luminescence, and time-resolved luminescence at ambient and high-pressure environments. Finall...

GOBO projection for 3D measurements at highest frame rates: a performance analysis

Aperiodic sinusoidal patterns that are cast by a GOBO (GOes Before Optics) projector are a powerful tool for optically measuring the surface topography of moving or deforming objects with very high speed and accuracy. We optimised the first experimental setup that we were able to measure inflating car airbags at frame rates of more than 50 kHz while achieving a 3D point standard deviation of ~500 µm. Here, we theoretically investigate the method of GOBO projection of aperiodic sinusoidal fringes. In a simulation-based performance analysis, we examine the parameters that influence the accuracy of the measurement result and identify an optimal pattern design that yields the highest measurement accuracy. We compare the results with those that were obtained via GOBO projection of phase-shifted sinusoidal fringes. Finally, we experimentally verify the theoretical findings. We show that the proposed technique has several advantages over conventional fringe projection techniques, as the easy-to-build and cost-effective GOBO projector can provide a high radiant flux, allows high frame rates, and can be used over a wide spectral range.

Ultrahigh temperature processing by concentrated solar energy with accurate temperature measurement

An ultrahigh temperature solar processing platform consisting of a High-Flux Solar Simulator (HFSS) and auxiliary equipments is developed to research high-temperature materials and processes. Refractory metals of zirconium (melting point of 1855 °C), niobium (2477 °C) and tantalum (3017 °C) were successfully melted by concentrated light from xenon lamps of the HFSS. The melting experiment was monitored by a charge-coupled device camera, and the temperature was recorded by a near-infrared multi-wavelength pyrometer. Then the processed metals were examined by SEM and EDS to compare the difference before and after the ultrahigh-temperature experiments. In addition, a numerical model combining Monte-Carlo ray-tracing method and finite-element method was established to simulate the melting process, the results of which agreed well with experimental results. Furthermore, melting temperatures measured by the well-calibrated near-infrared multi-wavelength pyrometer were close to the melting points of the refractory metals (i.e., ±2% relative error). The experimental platform also demonstrates the capability of providing high radiative flux and ultrahigh temperatures (>2000 °C) for the calibration of heat flux gauges and the testing of high-temperature properties of materials. The concentrated solar energy based ultrahigh temperature technology provides an innovative approach for processing refractory materials in general.

Biofluorescent worlds: global biological fluorescence as a biosignature

In this paper, we analyze a new possible biological surface feature for habitable worlds orbiting other stars: biofluorescence. High ultraviolet (UV) and blue radiation fluxes drive the strongest biofluorescence in terrestrial fluorescent pigments and proteins. F stars emit more blue and UV radiation than the Sun, while planets and exomoons orbiting such stars remain in the habitable zone for 2-4 Gyr; a timespan that could allow a complex biosphere to develop. Therefore we propose biofluorescence as a new surface biosignature for F star planets. We investigate how the extra emission from surface fluorescence could cause observable signals at specific wavelengths in the visible spectrum. Using the absorption and emission characteristics of common coral fluorescent pigments and proteins, we simulate the increased emission at specific visible wavelengths caused by strong fluorescence, accounting for the effects of different (non-fluorescent) surface features, atmospheric absorption and cloud-cover. Our model shows that exoplanets with a fluorescent biosphere could have characteristic surface colours that allow the presence of surface life to be inferred from observations with upcoming telescopes.

Four-layer metallodielectric emitter for spectrally selective near-field radiative transfer in nano-gap thermophotovoltaics

A four-layer metallodielectric planar thermal emitter is designed and optimized to tailor the spectral near-field radiative flux in a nano-gap thermophotovoltaic (TPV) system. The structure contains an ultra-thin refractory metallic layer (tungsten) sandwiched by two dielectric (hafnia) layers sitting on a metallic substrate. The theoretical calculation showed that the lossy metallic thin-layer acted as a perfect absorber that stimulated strong thermal emission, with its frequency and amplitude further modulated by the Fabry–Perot resonances in the dielectric layer. The spectral peak of near-field radiative flux can be manipulated by layer thickness to suit different cell bandgaps and emitter temperatures. The combination of optimized emitter and cell layer thickness results in selectively high near-field radiative flux above the bandgap, reaching a conversion efficiency of 50.2% (at radiative limit) with emitter temperature at 1600 K and 200 nm vacuum gap, surpassing or comparing with the efficiency and output power of state-of-the-art plasmonic and hyperbolic emitter designs. By tailoring the radiative heat flux mainly in the propagating and frustrated components, the design also circumvents possible electrical losses due to enhanced surface recombination when the radiative transfer is dominated by surface modes. This study offers a straightforward strategy to manipulate the near-field radiative transfer with great flexibility by a few-layer planar emitter and emphasizes the different consideration for designing a nano-gap TPV emitter from far-field PV/TPV emitter designs.

Research on Nondestructive Examination of Bracket Welds of ITER In-Vessel Coils (IVC)

The ITER in-vessel coils are comprised of edge-localized mode (ELM) and vertical stabilization (VS) coils. There are 27 ELM coils and 2 VS coils. All the ELM and VS coils are supported by the clamped brackets bolted to the rails which are welded to the vacuum vessel wall. The in-vessel environment is severe, characterized by large transient electromagnetic fields, high radiation flux, and high temperature. Therefore, an appropriate nondestructive examination approach should be established and qualified. The difficulty in the development of the bracket weld nondestructive examination is the complex structure which brings space limit and various reflect echoes. Phased array ultrasonic test (PAUT) was studied and developed for nondestructive examination. In order to obtain the appropriate test parameters, CIVA simulation software was utilized to visualize the acoustic field distribution and coverage. The sensitivity of the PAUT method was also demonstrated by using machined defect provided by ITER Organization. Experiment results shows that all of reference defects can be detected with peak amplitude higher than 80% of FSH for both first leg and second leg.

Verification and validation of an advanced model of heat and mass transfer in the protective clothing

The paper presents verification and validation of an advanced numerical model of heat and moisture transfer in the multi-layer protective clothing and in components of the experimental stand subjected to either high surroundings temperature or high radiative heat flux emitted by hot objects. The developed model included conductive-radiative heat transfer in the hygroscopic porous fabrics and air gaps as well as conductive heat transfer in components of the stand. Additionally, water vapour diffusion in the pores and air spaces as well as phase transition of the bound water in the fabric fibres (sorption and desorption) were accounted for. All optical phenomena at internal or external walls were modelled and the thermal radiation was treated in the rigorous way, i.e., semi-transparent absorbing, emitting and scattering fabrics with the non-grey properties were assumed. The air was treated as transparent. Complex energy and mass balances as well as optical conditions at internal or external interfaces were formulated in order to find values of temperatures, vapour densities and radiation intensities at these interfaces. The obtained highly non-linear coupled system of discrete equations was solved by the Finite Volume based in-house iterative algorithm. The developed model passed discretisation convergence tests and was successfully verified against the results obtained applying commercial software for simplified cases. Then validation was carried out using experimental measurements collected during exposure of the protective clothing to high radiative heat flux emitted by the IR lamp. Satisfactory agreement of simulated and measured temporal variation of temperature at external and internal surfaces of the multi-layer clothing was attained.

High coupling efficiency of foam spherical hohlraum driven by 2ω laser light

The majority of solid state laser facilities built for laser fusion research irradiate targets with third harmonic light (0.35 μm) up-converted from the fundamental Nd wavelength at 1.05 μm. The motivation for this choice of wavelength is improved laser-plasma coupling. Significant disadvantages to this choice of wavelength are the reduced damage threshold of optical components and the efficiency of energy conversion to third harmonic light. Both these issues are significantly improved if second harmonic (0.53 μm) radiation is used, but theory and experiments have shown lower optical to x-ray energy conversion efficiency and increased levels of laser-plasma instabilities, resulting in reduced laser-target coupling. In this letter, we propose to use a 0.53 μm laser for the laser ignition facilities and use a low density foam wall to increase the coupling efficiency from the laser to the capsule and present two-dimensional radiation-hydrodynamic simulations of 0.53 μm laser light irradiating an octahedral-spherical hohlraum with a low density foam wall. The simulations show that the reduced optical depth of the foam wall leads to an increased laser-light conversion into thermal x-rays and about 10% higher radiation flux on the capsule than that achieved with 0.35 μm light irradiating a solid density wall commonly used in laser indirect drive fusion research. The details of the simulations and their implications and suggestions for wavelength scaling coupled with innovative hohlraum designs will be discussed.

Neutron/gamma discrimination enhancement: plastic scintillators high dose irradiation and recovery time

In the context of high-energy physics experiments, particle accelerators create a significant dose of radiations, up to 106 Gy for example at the Large Hadron Collider (LHC, Cern). Control detectors, such as scintillators, are affected by these high irradiation levels. The literature mentions that the light yield of organic scintillators dramatically drops when strongly irradiated. However, the tested scintillators can recover some of their light output with time. To the best of our knowledge, only the luminescent properties of plastic scintillators were analyzed under high radiation fluxes. But, plastic scintillators are also able to discriminate fast neutrons from gamma rays. In this work, we characterized neutron/gamma discriminating as well as emissive properties of plastic scintillators after high dose irradiations. Two identical lab-made plastic scintillators containing a polystyrene-based matrix and two fluorophores were analyzed before and after high dose irradiation. Irradiation was performed using a Gamma-Cell 220 Excel with twelve 60Co sources and a 53.7 Gy/min dose rate at isocenter. These two scintillators were irradiated to reach a cumulative dose equal to 104 Gy. In order to measure their neutron/gamma discrimination ability, scintillators were coupled to a Hamamatsu R7724-100 photomultiplier tube and placed in front of a 252Cf source (Activity 580 kBq). The anode signal fed a digitizer. Scintillation pulses were then recorded and post-processed. A charge-comparison method was implemented and FoM was evaluated. Offline treatment allowed the estimation of fast and slow decay times of neutron pulses, as well as their relative intensities. In parallel, characterization of radioluminescence properties of irradiated and non-irradiated samples was performed. Results indicate a strong modification in the neutron/gamma discrimination capability before and after high dose irradiations and a redshift of the radioluminescence spectrum. In fact, a 103 Gy irradiation increases the FoM of both sensors by a factor 2.5 at least. Further, as recovery time passes after a 104 Gy cumulative dose, FoM improves for scintillators and is multiplied by 6 compared to the value at the zero dose. Thanks to evaluated decay times and relative intensities, we could infer that a strong irradiation does not produce a higher yield of triplet excited states but it impacts the slow decay time of the tested scintillator. This leads to a better neutron/gamma discrimination than at the zero dose. These observations lead us to believe that the intrinsic nature of the plastic material is modified under high dose irradiation. In this paper we present the current iteration of this ongoing work. The neutron/gamma discrimination properties are presented for both plastic scintillators and first characterization results are discussed. We show that material modification under high dose irradiation manages to an improvement in neutron/gamma discrimination opening the field to applications of very high dose measurements.

Non-intrusive temperature measurement of particles in a fluidised bed heated by well-characterised radiation

We report an important step towards the in-situ measurement of heat transfer in particle-laden flows via direct measurement of the temperatures of fluidised particles. Laser-induced phosphorescence (LIP) was employed to provide non-intrusive, temporally resolved and in-situ measurement of suspended particles as a function of heat flux and radiation attenuation. Excitation was performed at 355 nm with a repetition rate of 1.67 Hz. Particles were transported with dry air within an optically-accessible fluidised bed and heated with a well-defined source of high-flux radiation from a 3 kW solid-state solar thermal simulator radiation to achieve heating rates in order 23,000°/s. Particle and gas temperatures were measured simultaneously with the former determined from thermo-phosphorescent emissions following excitation at 355 nm. Irradiation flux and mass loading were found to play important roles in particle and gas temperature rise. Confidence in the method was obtained by verifying internal consistency between the energy absorbed by the particles and the temperature rise of the gas phase, taking into account the variability of particle mass loading.

Biomass gasification under high solar heat flux: Advanced modelling

This article presents a new numerical model describing the behaviour of a thermally thick wood sample exposed to high solar heat flux (above 1 MW/m2). A preliminary study based on dimensionless numbers is used to classify the problem and support model building assumptions. Then, a model based on mass, momentum and energy balance equations is proposed. These equations are coupled with liquid-vapour drying model and pseudo species biomass degradation model. By comparing to a former experimental study, preliminary results have shown that these equations are not enough to accurately predict biomass behaviour under high solar heat flux. Indeed, a char layer acting as radiative shield forms on the sample exposed surface. In addition to this classical set of equations, it is mandatory to take into account radiation penetration into the medium. Furthermore, as biomass contains water, medium deformation consecutively to char steam gasification must also be implemented. Finally, with the addition of these two strategies, the model is able to properly capture the degradation of biomass when exposed to high radiative heat flux over a range of sample initial moisture content. Additional insights of biomass behaviour under high solar heat flux were also derived. Drying, pyrolysis and gasification fronts are present at the same time inside of the sample. The coexistence of these three thermochemical fronts leads to char gasification by the steam produced from drying of the sample, which it is the main phenomenon behind medium ablation.

Single-shot planar temperature imaging of radiatively heated fluidized particles

A single-shot, non-intrusive planar technique for measuring the temperature of radiatively heated particles with good spatial resolution has been demonstrated. This technique has been applied to particles with diameters between 10µm and 50µm, suspended in a highly unsteady flow within a fluidized bed. The particles were heated with a high-flux radiation source to provide high and well-characterized heat fluxes ranging from 2.4 MW/m2 ≤ Ф ≤ 21.1 MW/m2. Each measurement is derived from two images with an area of 15mm × 10.8mm using an image splitter and a single ICCD camera. An average of 30 particles were recorded in each image with a spatial resolution of 51 pixels/mm. A maximum temperature rise of 350°C was recorded with a heat flux of 21.1 MW/m2, with a corresponding heating rate of up to 23,000°C/s, given the maximum residence time of the particles in the heating region of 0.05s. The normalized temperature distribution within an individual particle agglomerate was found to be up to ± 4%, which is attributable to ICCD noise so that the mean temperature is well resolved.

Effects of Irradiation on the Evolution of Ultracompact X-Ray Binaries

Abstract Using the Modules for Experiments in Stellar Astrophysics code, we investigate the influences of irradiation on ultracompact X-ray binary (UCXB) evolution. Although the persistent UCXBs have short orbital periods that result in high irradiation flux, the irradiation hardly affects the evolution of persistent sources because the white dwarfs (WDs) in these binaries have large masses that lead to very low irradiation depth. The irradiation has a significant effect on the transient sources during outburst phase. At the beginning of the outburst, high X-ray luminosity produces high radiation flux, which results in the significant expansion of WDs. Then, the irradiation triggers high mass-transfer rates, which can last several days for the transient sources with WDs whose masses are larger than or several hundred years for those sources with WDs whose masses are less than . The observed three persistent UCXBs, XTE J0929-314, 4U 1916-05, and SWIFT J1756.9-2508, may belong to the latter.

Evaporation, boiling and explosive breakup of oil–water emulsion drops under intense radiant heating

An experimental study on conditions and main characteristics for high-temperature (more than 700K) evaporation of oil–water drops is presented. The high-temperature water purification from impurities can be the main practical application of research results. Thus, the heating of drops is implemented by the two typical schemes: on a massive substrate (the heating conditions are similar to those achieved in a heating chamber) and in a flow of the heated air. In the latter case, the heating conditions correspond to those attained while moving water drops with impurities in a counter high-temperature gaseous flow in the process of water purification. Evaporation time and rate as functions of heating temperature and conditions for the heat energy supply to an emulsion drop are illustrated. The influence of oil product concentration in an emulsion drop on evaporation characteristics is discussed. The conditions for intensive flash boiling of an emulsion drop and its explosive breakup (fragmentation) with formation of the fine droplets cloud are pointed out. High radiant heat fluxes required in the boundary layer of a drop for intensive flash boiling and explosive breakup of drops with further formation of the fine aerosol. The fundamental differences between flash boiling and explosive breakup of an emulsion drop when heated on a substrate and in a flow of the heated air are described. The main prospects for the development of the high-temperature water purification technology are detailed taking into account the fast emulsion drop breakup investigated in the paper.

Approximate analytical solutions for temperature based transient mass flux and ignition time of a translucent solid at high radiant heat flux considering in-depth absorption

Most studies, employing ignition temperature as the ignition criterion, utilized surface absorption of radiant incident heat flux in analytical models when investigating the ignition mechanism of solid combustibles. However, in-depth absorption exerts its influence on ignition time significantly for translucent solid, especially at high radiant heat flux. In this work, we extend the previous researches from surface absorption to in-depth absorption to develop an approximate analytical ignition model using critical mass flux instead of critical temperature. An approximation methodology is proposed during derivation to study the in-depth absorption scenario. The comparison among this model, available experimental data of black PMMA in the literature and previous numerical simulations indicates that the proposed model provides relatively high accuracy in predicting ignition time. Furthermore, the pure surface absorption circumstance is also reexamined and compared with the classical ignition theory. The results show that surface absorption hypothesis accelerates the total mass flux, which consequently shortens the ignition time. However, in-depth absorption assumption eliminates the heat accumulation on surface and results in good prediction for ignition time at high heat flux. For in-depth absorption, the absorption coefficient affects the heat penetration depth and temperature distribution in this layer which consequently affects the thermal degradation reaction rate, mass flux and finally ignition time. Meanwhile, the ignition time considering both surface and in-depth absorption is discussed, and the relationship with pure surface and in-depth absorption conditions is obtained.

High-flux optical systems for solar thermochemistry

High-flux optical systems (HFOSs) are optical concentrators used to increase the radiative flux of the natural terrestrial solar irradiation. High radiative flux concentration leads to high energy density in solar receivers which allows to obtain high temperatures. In solar thermochemical applications, the high-temperature heat drives endothermic thermochemical reactions. HFOSs have been deployed for research and development of solar thermochemical devices and systems, from solar reacting media to solar reactors. Here, we review the designs and characteristics of HFOSs as well as challenges and opportunities in the area of high-flux optical systems for solar thermochemical applications.