Incident Radiation Flux Research Articles

Fire performance of continuous glass fibre reinforced polycarbonate composites: The effect of fibre architecture on the fire properties of polycarbonate composites

The fire performance of polycarbonate resin and the role of glass fibre reinforcement in altering the fire performance was investigated. Three different fibre weaves with comparable surface density, plain, twill, and unidirectional glass fabrics, were used as reinforcements. E-glass fabrics were solution-impregnated with polycarbonate/dichloromethyl, laid up, and compression-moulded to consolidate the glass fibre reinforced polycarbonate composite. Cone calorimetry tests with an incident radiant flux of 35 kW/m2 were used to investigate the fire properties of polycarbonate resin and its composites. Results showed that glass fibre reinforcement improves polycarbonate performance by delaying its ignition, decreasing its heat release rate, and lowering the mass loss rate. The three fibre weave types exhibited similar time to ignition. However, unidirectional fibre had a 35% lower peak heat release rate followed when compared to plain and twill weave fibres.

Pressure effects on radiative heat transfer in hydrogen/air turbulent diffusion flames

The effects of pressure on radiative heat transfer and turbulence–radiation interaction (TRI) in hydrogen/air turbulent diffusion flames are numerically investigated by using state of the art chemical mechanism, combustion and radiation models. A transported PDF method is used to close properly the emission TRI term and a narrow-band correlated-K (NBCK) model is considered. Absorption TRI term is modelled by considering the optically-thin fluctuation approximation (OTFA). Stochastic time and space series are used to confirm a posteriori the validity of this approximation. Artificial high-pressure flames have been designed based on the Froude modelling in order to isolate the effects of pressure on radiative heat transfer and TRI. Model predictions are in good agreement with available experimental data at atmospheric pressure. As the pressure rises, total absorption is found to increase at a higher rate than total emission, limiting the increase in radiative loss and incident radiative flux which are found to grow with pressure as Pn with n of the order of 0.8. One of the consequences of this phenomenon is that the radiant fraction decreases with pressure. Modelling results also show that the effects of TRI on radiative losses and radiative fluxes cannot be neglected and are enhanced by pressure rises.

Heat transfer in a falling laminar liquid film with in-depth radiation absorption

A heat transfer problem involving a steady-state falling liquid film along a vertical wall with an imposed constant heat flux on the liquid film surface and an in-depth thermal radiation absorption in the film layer is analyzed. The liquid film is assumed to be normal to the incident radiative heat flux, and the heat flux is assumed to be parallel and unidirectional. Nondimensionalized governing equations are formulated and solved numerically. Sample calculations are provided. The effects of pertinent dimensionless parameters on the heat transfer process are demonstrated. The calculated results reveal that the in-depth thermal radiation absorption would play a key role in the heat transfer in the liquid film.

Spontaneous ignition of wildland fuel by idealized firebrands

The spontaneous ignition of a forest fuel layer by idealized firebrands was carried out experimentally in a bench scale apparatus designed to understand the relationship between the time to ignition and incident radiative heat flux on a ring-shaped forest fuel litter. Time to ignition, mass loss, radial temperatures and incident radiative heat flux were measured. The fuel samples were Radiata Pine needles, representative of Chilean forests and the influence of the physical characteristics of the fuel load were analyzed. The firebrand was idealized using a cylindrical electric heater capable of releasing heat flux up to 26.7 kW/m2. For the fuel beds considered the inverse of ignition time was found to be linearly dependent on the incident radiative heat flux, typically observed for thermally thin solid fuels. Several tests were carried out in order to estimate the critical (minimum) heat flux for spontaneous ignition for two forest fuel loads. Additionally, a quasi-linear relationship between mass loss rate and incident radiative heat flux was experimentally determined.

Artificial intelligence unfolding for space radiation monitor data

The reliable and accurate calculation of incident particle radiation fluxes from space radiation monitor measurements, i.e. count-rates, is of great interest and importance. Radiation monitors are relatively simple and easy to implement instruments found on board multiple spacecrafts and can thus provide information about the radiation environment in various regions of space ranging from Low Earth orbit to missions in Lagrangian points and even interplanetary missions. However, the unfolding of fluxes from monitor count-rates, being an ill-posed inverse problem, is not trivial and prone to serious errors due to the inherent difficulties present in such problems. In this work we present a novel unfolding method which uses tools from the fields of Artificial Intelligence and Machine Learning to achieve good unfolding of monitor measurements. The unfolding method combines a Case Based Reasoning approach with a Genetic Algorithm, which are both widely used. We benchmark the method on data from European Space Agency’s (ESA) Standard Radiation Environment Monitor (SREM) on board the INTEGRAL mission by calculating proton fluxes during Solar Energetic Particle Events and electron fluxes from measurements within the outer Radiation Belt. Extensive evaluation studies are made by comparing the unfolded proton fluxes with data from the SEPEM Reference Dataset v2.0 and the unfolded electron fluxes with data from the Van Allen Probes mission instruments Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron Proton Telescope (REPT).

Impact of nanofluids, radiation spectrum, and hydrodynamics on the performance of direct absorption solar collectors

The coupled radiative transfer and thermal energy equations were numerically solved for a nanofluid-based, direct absorption solar collector (DASC) using a Rayleigh scattering approximation for the optical properties of the nanofluid. The flow field was solved using a vorticity-stream function formulation. The numerical model was validated against published results in the literature. The effects of collector aspect ratio, incident radiative flux, heat loss coefficient, inlet flow velocity, nanoparticle size, and nanoparticle concentration were determined for four different types of nanoparticles. It was established that the impact of these parameters on collector performance was determined by the extent to which they affected the outlet temperature gain and thermal losses to the ambiance. Through the exact solution of the flow field, it was established that performance deviations from the fully-developed assumption were encountered for small collector aspect ratios, especially with high Reynolds numbers (Re > 1500). Moreover, with the exception of cases with very low Reynolds numbers (Re < 40), assuming a plug flow profile throughout the collector was shown to cause performance overestimations. Sensitivity of DASC performance to the type of incident radiation spectrum was also investigated and it was found to be largely dependent on spectral distribution of the extinction coefficient of the nanoparticle. The common assumption of a blackbody incident spectrum results in performance overestimations for certain types of nanoparticle suspensions (e.g., silver) more than others (e.g., graphite). Using a higher nanoparticle volume fraction causes the efficiency of the collector to be more insensitive to the incident spectrum type. For a given nanofluid material and thickness, it was established that an optimum nanoparticles concentration existed.

Analysis of radiation heat transfer and temperature distributions of solar thermochemical reactor for syngas production

This paper investigated radiation heat transfer and temperature distributions of solar thermochemical reactor for syngas production using the finite volume discrete ordinate method (fvDOM) and P1 approximation for radiation heat transfer. Different parameters including absorptivity, emissivity, reflection based radiation scattering, and carrier gas flow inlet velocity that would greatly affect the reactor thermal performance were sufficiently investigated. The fvDOM approximation was used to obtain the radiation intensity distribution along the reactor. The drop in the temperature resulted from the radiation scattering was further investigated using the P1 approximation. The results indicated that the reactor temperature difference between the P1 approximation and the fvDOM radiation model was very close under different operating conditions. However, a big temperature difference which increased with an increase in the radiation emissivity due to the thermal non-equilibrium was observed in the radiation inlet region. It was found that the incident radiation flux distribution had a strong impact on the temperature distribution throughout the reactor. This paper revealed that the temperature drop caused by the boundary radiation heat loss should not be neglected for the thermal performance analysis of solar thermochemical reactor.

Molecular photoeffect in single- and multi-wall carbon nanotubes with physisorbed oxygen molecules

The EPR spectra of high purity single-walled and multi-walled semiconducting carbon nanotubes exhibit wide resonance lines (154 ± 5 mT and 159 ± 5 mT, respectively, at room temperature). The broadening of EPR lines is due to magnetic dipole-dipole interaction with the spin-triplet ground state oxygen molecules physisorbed on the carbon nanotubes surface. Here we show that the emission of O2 molecules occurs under the photons with energy of 2.33 eV that leads to narrowing of the EPR line. The number of molecules emitted from nanotubes is proportional to the flux of incident radiation, in full analogy with the first law of the classical photoelectric effect.

Assessing uncertainties in prevailing methodologies for modeling radiative transfer in simulations of oxygen-enriched methane flames

The fidelities and uncertainties associated with prevailing radiative transfer modeling methodologies and practices during simulations of oxygen-enriched flames where the gas temperature exceeds 2500 K are examined. Reference data in representative furnace environments characteristic of methane combustion at oxidizer oxygen concentrations of 30–100% were generated employing the spectral-line-based-weighted-sum-of-gray-gas model (SLWSGGM). Parametric uncertainties associated with two commonly employed WSGGM were assessed. While predictions from the exponential wide band model (EWBM) based WSGGM formulation agreed very well against reference data, significant errors in the radiative source term predictions resulted when the HITEMP-based WSGGM formulation was employed in high temperature regions beyond its intended application. The epistemic uncertainties associated with the wall temperature profiles decreased with oxygen enrichment. However, fully coupled combustion simulations of 100% O2–methane flames for a range of fuel inlet Reynolds numbers (2600–14,000) resulted in identical gas temperature profiles employing both the EWBM and HITEMP WSGG models. Further, their incident wall radiative flux predictions were within 10% of each other. Epistemic errors resulting from neglecting CO as a radiatively participating specie could become significant. Aleatoric uncertainties resulting from turbulence radiation interaction modeling were pronounced when flame radiation was the dominant contributor to the wall fluxes.

Integral Design Methodology of Photocatalytic Reactors for Air Pollution Remediation.

An integral reactor design methodology was developed to address the optimal design of photocatalytic wall reactors to be used in air pollution control. For a target pollutant to be eliminated from an air stream, the proposed methodology is initiated with a mechanistic derived reaction rate. The determination of intrinsic kinetic parameters is associated with the use of a simple geometry laboratory scale reactor, operation under kinetic control and a uniform incident radiation flux, which allows computing the local superficial rate of photon absorption. Thus, a simple model can describe the mass balance and a solution may be obtained. The kinetic parameters may be estimated by the combination of the mathematical model and the experimental results. The validated intrinsic kinetics obtained may be directly used in the scaling-up of any reactor configuration and size. The bench scale reactor may require the use of complex computational software to obtain the fields of velocity, radiation absorption and species concentration. The complete methodology was successfully applied to the elimination of airborne formaldehyde. The kinetic parameters were determined in a flat plate reactor, whilst a bench scale corrugated wall reactor was used to illustrate the scaling-up methodology. In addition, an optimal folding angle of the corrugated reactor was found using computational fluid dynamics tools.

Mechanically Robust, Stretchable Solar Absorbers with Submicron-Thick Multilayer Sheets for Wearable and Energy Applications.

A facile method to fabricate a mechanically robust, stretchable solar absorber for stretchable heat generation and an enhanced thermoelectric generator (TEG) is demonstrated. This strategy is very simple: it uses a multilayer film made of titanium and magnesium fluoride optimized by a two-dimensional finite element frequency-domain simulation, followed by the application of mechanical stresses such as bending and stretching to the film. This process produces many microsized sheets with submicron thickness (∼500 nm), showing great adhesion to any substrates such as fabrics and polydimethylsiloxane. It exhibits a quite high light absorption of approximately 85% over a wavelength range of 0.2-4.0 μm. Under 1 sun illumination, the solar absorber on various stretchable substrates increased the substrate temperature to approximately 60 °C, irrespective of various mechanical stresses such as bending, stretching, rubbing, and even washing. The TEG with the absorber on the top surface also showed an enhanced output power of 60%, compared with that without the absorber. With an incident solar radiation flux of 38.3 kW/m2, the output power significantly increased to 24 mW/cm2 because of the increase in the surface temperature to 141 °C.

Assessment of thermal performance of protective garments

PurposeThe paper aims to present the advanced mathematical and numerical models of conjugated heat and mass transfer in a multi-layer protective clothing, human skin and muscle subjected to incident external radiative heat flux.Design/methodology/approachThe garment was made of three layers of porous fabric separated by the air gaps, whereas in the tissue, four skin sublayers and muscle layer were distinguished. The mathematical model accounted for the coupled heat transfer by conduction and thermal radiation with the associated phase transition of the bound water in the fabric fibres and diffusion of the water vapour in the clothing layers and air gaps. The skin and muscle were modelled with two equation model which accounted for heat transfer in the tissue and arterial blood. Complex thermal and mass transfer conditions at the internal or external boundaries between the fabric layers, air gaps and skin were assumed. Special attention was paid to modelling of thermal radiation emitted by external heat source, for example, a fire, penetrating through the protective clothing and being absorbed by the skin and muscle.FindingsTemporal and spatial variations of temperature in the protective garment, skin and muscle, as well as volume fractions of the water vapour and bound water in the clothing, were calculated for various intensity of incident radiative heat flux. The results of numerical simulation were used to estimate the risk of the first-, second- and third-degree burns.Research limitations/implicationsBecause of the small thickness of the considered system in comparison to its lateral dimensions, the presented model was limited to 1D heat and moisture transfer. The convective heat transfer through the clothing was neglected.Practical implicationsThe model may be applied for design of the new protective clothing and for assessment of thermal performance of the various types of protective garments. Additionally, the proposed approach may be used in the medicine for estimation of degree of thermal destruction of the tissue during treatment of burns.Originality/valueThe novel advanced thermal model of the multi-layer protective garment, skin and muscle layer was developed. For the first time, non-grey optical properties and various optical phenomena at the internal or external boundaries between the fabric layers, air gaps and skin were accounted for during simulation of thermal interactions between the external heat source (e.g. a fire), protective clothing and human skin.

Incident Radiative Heat Flux Based Method for the Coupled Run Length Simulation of Steam Cracking Furnaces

Due to the significant economic penalty associated with decoking steam cracking furnaces, accurate run length predictions are crucial for assessing their techno-economic performance. Therefore, for the first time, a full coupled run length simulation of an industrial naphtha steam cracking furnace was performed using detailed computational fluid dynamics (CFD) simulations for the furnace side. The results show that the unevenly deposited coke layer within the reactors leads to a redistribution of the thermal power over the time on stream, which is beneficial for the uniformity of the coke growth in the reactor. These effects were not observed in traditional standalone run length simulations, which justifies the high computational cost. However, the high computational cost of these CFD iterations can be overcome by using a novel method which correlates the incident radiative heat flux (IRHF) to the flue gas bridge wall temperature obtained from an overall zero-dimensional heat balance. This so-called IRHF ...

An approach to estimating flame radiation in combustion chambers containing suspended-particles

Thermal radiation often plays a key role in heat transfer between flames and the surrounding environment. Therefore, reliable measurement of flame radiation is indispensable in the study of combustion. While the measurement of radiative flux from flames is straightforward in an open environment, it is challenging to do so in a confined chamber, due to the influence of the walls. Radiation emitted by the walls and the reflection of flame radiation off the walls can interfere with measurements of flame radiation. For wall surfaces that are at high temperature or highly reflective, the error in the flame radiation measurement can be significant.In this paper, a theoretical analysis was carried out to study the contribution of wall emission and wall reflection to the incident radiation measured by radiometers. The results reveal that for a typical lab-scale air-fired flame, the contribution of wall emission and wall reflection to the measured incident radiation can be as high as 55% for a refractory-lined wall and 40% for a water-cooled wall. A convenient approach is proposed to distinguish flame radiation from the measured incident radiation. The approach is based on measurements of surface incident radiation and net radiative heat flux through the wall. The approach can be applied to optically thin systems (most lab-scale and some pilot-scale atmospheric pressure combustion systems) and optically dense systems (typically pressurized large-scale combustion systems). CFD simulations were also performed for two coal-fired combustors, one which represents optically thin and the other optically thick systems, to validate the theoretical model and the approach to estimating flame radiation. Good agreement was observed between CFD results and the theoretical model results, and the proposed approach to estimation of flame radiation was found to have reasonable accuracy.

Evaluation of the global MODIS 30 arc-second spatially and temporally complete snow-free land surface albedo and reflectance anisotropy dataset

Land surface albedo is an essential variable for surface energy and climate modeling as it describes the proportion of incident solar radiant flux that is reflected from the Earth’s surface. To capture the temporal variability and spatial heterogeneity of the land surface, satellite remote sensing must be used to monitor albedo accurately at a global scale. However, large data gaps caused by cloud or ephemeral snow have slowed the adoption of satellite albedo products by the climate modeling community. To address the needs of this community, we used a number of temporal and spatial gap-filling strategies to improve the spatial and temporal coverage of the global land surface MODIS BRDF, albedo and NBAR products. A rigorous evaluation of the gap-filled values shows good agreement with original high quality data (RMSE=0.027 for the NIR band albedo, 0.020 for the red band albedo). This global snow-free and cloud-free MODIS BRDF and albedo dataset (established from 2001 to 2015) offers unique opportunities to monitor and assess the impact of the changes on the Earth’s land surface.

Thermal and exergy optimization of a nanofluid-based direct absorption solar collector

An experimental study on a nanofluid-based direct absorption solar collector (DASC) was carried out to analyze the effect of its operating conditions on the thermal performance of the collector. Graphite, magnetite and silver nanoparticles dispersed in de-ionized water were used as the heat transfer fluids. Experiments were conducted for various nanoparticle volume fractions of (5<fv<40 ppm); volumetric flow rates (5<Q<10 ml/min) and incident radiation fluxes (600<GT<1000 W/m2) based on Box-Behnken experimental design feature. The acquired data were analyzed according to response surface methodology (RSM) and the relation between the input parameters and responses (thermal and exergy efficiencies) for each nanofluid was expressed by response surface functions. The results show that among nanofluids, magnetite dispersions gained the highest thermal and exergy efficiencies; followed by graphite and silver nanofluids, respectively. Also, optimum operating conditions for each nanofluid revealed that in the given design range, the maximum thermal and exergy efficiencies occurred at fv = 40 ppm, Q = 10 ml/min and GT = 884 W/m2 for magnetite; fv = 40 ppm, Q = 10 ml/min and GT = 884 W/m2 for graphite and fv = 38.6, Q = 10 ml/min and GT = 826 W/m2 for silver nanofluids.

Implementation of street trees within the solar radiative exchange parameterization of TEB in SURFEX v8.0

Abstract. The Town Energy Balance (TEB) model has been refined and improved in order to explicitly represent street trees and their impacts on radiative transfer: a new vegetated stratum on the vertical plane, which can shade the road, the walls, and the low vegetation has been added. This modification led to more complex radiative calculations, but has been done with a concern to preserve a certain level of simplicity and to limit the number of new input parameters for TEB to the cover fraction of trees, the mean height of trunks and trees, their specific leaf area index, and albedo. Indeed, the model is designed to be run over whole cities, for which it can simulate the local climatic variability related to urban landscape heterogeneity at the neighborhood scale. This means that computing times must be acceptable, and that input urban data must be available or easy to define. This simplified characterization of high vegetation necessarily induces some uncertainties in terms of the solar radiative exchanges, as quantified by comparison of TEB with a high-spatial-resolution solar enlightenment model (SOLENE). On the basis of an idealized geometry of an urban canyon with various vegetation layouts, TEB is evaluated regarding the total shortwave radiation flux absorbed by the elements that compose the canyon. TEB simulations in summer gathered best scores for all configurations and surfaces considered, which is precisely the most relevant season to assess the cooling effect of deciduous trees under temperate climate. Mean absolute differences and biases of 6.03 and +3.50 W m−2 for road, respectively, and of 3.38 and +2.80 W m−2 for walls have been recorded in vegetationless canyons. In view of the important incident radiation flux, exceeding 1000 W m−2 at solar noon, the mean absolute percentage differences of 3 % for both surfaces remain moderate. Concerning the vegetated canyons, we noted a high variability of statistical scores depending on the vegetation layout. The greater uncertainties are found for the solar radiation fluxes received and absorbed by the high vegetation. The mean absolute differences averaged over the vegetation configurations during summertime are 21.12 ± 13.39 W m−2 or 20.92 ± 10.87 % of mean absolute percentage differences for the total shortwave absorption, but these scores are associated with acceptable biases: −15.96 ± 15.93 W m−2.

Characterizing Vegetation Canopy Structure Using Airborne Remote Sensing Data

Vegetation canopy structure plays an important role in the partitioning of incident solar radiation, photosynthesis, transpiration, and other scalar fluxes. The vertical foliage distribution of the plant canopy is represented by leaf area density (LAD), which is defined as the one-sided leaf area per unit volume. Airborne light detection and ranging (LiDAR) offers the possibility to characterize the 3-D variation of LAD over space, which still remains a challenge to estimate. Moreover, the low density of point cloud data generally offered by airborne LiDAR may be insufficient for accurate LAD estimation in dense overlapping forest canopies. We develop a method for the estimation of the LAD profile using a combination of airborne LiDAR and hyperspectral data using a feature-based data fusion approach. After identifying vegetation species using hyperspectral data, point cloud LiDAR data is used in a “tree-shaped” voxel approach to characterize the LAD of trees in a riparian forest setting. We also propose a set of relationships on simple geometry of overlap for the construction of tree shaped voxels. In a forest setting with overlapping canopies, the results indicate that the tree-shaped voxels are better able to attribute the LAD to the upper and middle parts of the overall canopy as well as individual tall and short trees compared with traditional cylindrical voxels.

A Multipurpose CMOS Platform for Nanosensing.

This paper presents a customizable sensing system based on functionalized nanowires (NWs) assembled onto complementary metal oxide semiconductor (CMOS) technology. The Micro-for-Nano (M4N) chip integrates on top of the electronics an array of aluminum microelectrodes covered with gold by means of a customized electroless plating process. The NW assembly process is driven by an array of on-chip dielectrophoresis (DEP) generators, enabling a custom layout of different nanosensors on the same microelectrode array. The electrical properties of each assembled NW are singularly sensed through an in situ CMOS read-out circuit (ROC) that guarantees a low noise and reliable measurement. The M4N chip is directly connected to an external microcontroller for configuration and data processing. The processed data are then redirected to a workstation for real-time data visualization and storage during sensing experiments. As proof of concept, ZnO nanowires have been integrated onto the M4N chip to validate the approach that enables different kind of sensing experiments. The device has been then irradiated by an external UV source with adjustable power to measure the ZnO sensitivity to UV-light exposure. A maximum variation of about 80% of the ZnO-NW resistance has been detected by the M4N system when the assembled 5 m × 500 nm single ZnO-NW is exposed to an estimated incident radiant UV-light flux in the range of 1 nW–229 nW. The performed experiments prove the efficiency of the platform conceived for exploiting any kind of material that can change its capacitance and/or resistance due to an external stimulus.

Can reducing the incoming energy flux over the Southern Ocean in a CGCM improve its simulation of tropical climate?

AbstractAtmosphere‐ocean general circulation models (CGCMs) show important systematic errors. Simulated precipitation in the tropics is generally overestimated over the oceans south of the equator, and stratocumulus (SCu) clouds are underestimated above too warm sea surface temperatures (SSTs). In the extratropics, SSTs are also too warm over the Southern Ocean. We argue that ameliorating these extratropical errors in a CGCM can result in an improved model's performance in the tropics depending upon the success in simulating the sensitivity of SCu to underlying SST. Our arguments are supported by the very different response obtained with two CGCMs to an idealized reduction of solar radiation flux incident at the top of the atmosphere over the Southern Ocean. It is shown that local perturbation impacts are very similar in the two models but that SST reductions in the SCu regions of the southern subtropics are stronger in the model with the stronger SCu‐SST feedbacks.