Radiative Model Research Articles

Influence of vortex generator on performance of concentrated solar photovoltaic module in existence of heat sink

New configuration of concentrated photovoltaic thermal (CPVT) with the implementation of parabolic concentrator and heat sink combined with the vortex generator (VG) were presented in current work. The testing fluid is water and temperature-dependent features were utilized. The regime of water flow in absence and presence of VG are laminar and turbulent, respectively. Numerical simulations were done for different values of angle of VG (θ = 30°, and 60°), pitch ratio (S = 0.025, 0.0375, and 0.05), and volumetric flow rate (Q = 0.5, to 2 Lit/min). Four values for width of reflector have been applied and radiation model was utilized to derive the absorbed heat flux. The accuracy of modeling has been examined for three cases and good accommodations have been reported. The maximum values of thermal (ηth) and electrical (ηel) performance are 63.75 % and 13.96 % which happens when θ = 30°, S = 0.025, Q = 2 Lit/min. Installing VG leads to increments of ηth and ηel about 1.42 % and 2.74 %. Increase of S and θ cause performance to decrease while this function increases with rise of Q. Increase of Q causes ηth and ηel to increase about 1.17 % and 2.55 % for the best case.

Optimized design and simulation study of liquid-cooled heat sink model for IGBT module based on TPMS structure

Abstract In this paper, we propose a liquid-cooled heat sink model utilizing a TPMS (triple periodic minimal surface) structure for IGBT modules. Using parametric modeling software nTopology, we establish three TPMS structures: Schwarz P, Gyroid, and Diamond. Thermal simulation analysis is conducted on the radiator model using ANSYS Fluent. The optimal structural parameters are determined to ensure effective heat dissipation while preventing excessive pump power consumption due to inappropriate inlet flow rates. Simulation results demonstrate that the liquid-cooled radiator with TPMS structure outperforms conventional radiators in heat transfer efficiency, albeit with higher inlet and outlet pressure drops. Among the TPMS-structured radiators, the Schwarz P configuration exhibits the lowest pressure drop, approximately 20% less than the remaining two, offering superior thermal management advantages.

A new-proposed triangular- prism flame radiation model of large-scale spilling fire to subsurface convection flow area

The usage of liquid fuel is commonly subjected to a spilling fire due to the accidental leakage. The flame radiation is the primary heat transfer mode in supporting the advancement of large-scale spilling fire. In this work, spilling fires are carried out based on a 6 m × 0.8 m × 0.1 m tray, and the spilling fire performance and flame radiation are examined. The instantaneous flame height and mass burning rate versus fire spread distance are examined. The radiation heat flux of large-scale spilling fire to subsurface flow area is obtained by dividing the flame configuration into a triangular-prism flame and a cuboid flame. The multi-cuboid flame equivalent-division method is proposed to estimate the radiation heat flux of leading triangular-prism flame, finding that the maximal 70 equivalent divisions are sufficiently accurate. The proportion of triangular-prism flame radiation to total heat flux reduces from 100 % to 50 % during spilling fire propagation. The triangular-prism flame radiation plays a dominant role in heat transfer to the subsurface flow area while the cuboid flame radiation plays a secondary role. The current research is of great significance for revealing heat transfer mechanism and predicting rate of spilling fire.

Computational modeling of thermal radiation and activation energy effects in Casson nanofluid flow with bioconvection and microorganisms over a disk

Ensuring sustained thermal propagation is a crucial role in many industrial and thermal systems since it facilitates the improvement of the efficiency of thermal engineering engines and machinery. Therefore, the usage of magnetized nanoparticles in a heat-carrying non-Newtonian fluid is a promising development for the enhancement of thermal power energy. This paper uniquely contributes by comprehensively analyzing heat and mass transfer characteristics in a Casson nanofluid subjected to bioconvection over a disk. The study also explores in detail the interaction of gyrotactic microorganisms, and activation energy in the system. Similarity transformations have been used to make the governing partial differential equations (PDEs) dimensionless, which has then transformed them into ordinary differential equations. The solution method has utilized the Shooting technique combined with the Bvp4c solver in MATLAB. Graphs have been drawn to explain the different parameters of the flow; also, other engineering quantities, like motile microbes density and Sherwood numbers, have been calculated and are represented graphically. Furthermore, the interplay of mixed convection, buoyancy ratio, bioconvection Rayleigh constant, and resistivity due to magnetization significantly influences the distribution of velocity in the Casson nanofluid. Remarkably, parameters that characterize the motile microorganism profile significantly attenuate said profile; therefore, they play a very important role in shaping the system dynamics. The application of bioconvection phenomena spans diverse fields, ranging from healthcare and environmental monitoring to agriculture and renewable energy, offering innovative solutions to address complex challenges.

Investigation into the thermal noise propagation mechanism within composite materials for gravitational wave detection systems

The thermal transmission properties of polymer-based composites, commonly used in satellites, are crucial for high-precision thermal management applications. The study constructed the structures of polyimide polymers and polyimide/graphene interfaces based on molecular dynamics and fluctuation dissipation theorem. Optical parameters were determined through first-principles calculations, and the thermal transport from a microthermal source was simulated using Reverse Non-Equilibrium Molecular Dynamics (RNEMD) and the modified four-dimensional transfer matrix method (M4D-TMM). Simulations of polymers, interface structures, and interfacial thermal radiation models investigated the transmission dynamics of microthermal sources during heat transport. Findings showed that the differences in the temperature fields formed within the polymer from microthermal heat sources were less than 20 K for heat source inputs ranging from 0.002 W/m² to 20 GW/m². With a microthermal source, the heat diffusion was extensive, the heat transport was continuous, and the temperature field remained stable. At the level of the heat source up to the intermolecular energy level, the temperature field distribution showed significant instability, leading to nonlinear effects. Within the interface structure, the continuity of heat diffusion increased as the heat source intensified. The interface structure demonstrated enhanced temperature sensitivity and improved stability, with minimal fluctuations of only 0.59 %. The increase in heat flux perpendicular to the interface structure was ascribed to near-field radiative heat transfer. As the temperature difference decreased to less than 0.1 K, the influence of evanescent waves on radiative heat flux nearly disappeared. Phonon polaritons maintained temperature stability during thermal transport through micro- and nanoscale gaps. Integrating thermal conduction principles in polyimide polymers and interface structures with near-field thermal radiation provides a theoretical framework for high-precision thermal management in gravitational wave detection.

Utilization of vortex flow pattern in the design of an efficient solar air heater

In this work, numerical and experimental analyses of a new model of circular solar air heater are carried out to examine the effect of employing vortex flow inside the air vessel of collector for convection enhancement. In three-dimensional numerical CFD-based analysis, the COMSOL Multi-physics is used to solve the flow equations for the turbulent forced convection airflow and conduction equation for the solid parts of the solar heater at different air mass flow rates in the range of 0.003 to 0.012 kg/s. In the calculation of turbulent stresses and heat fluxes, the RNG κ-∊ turbulence model is employed. The surface to surfaces (S2S) radiation model is used to consider the radiations emitted by the hot surfaces in collaboration with the energy equation. For validation, the theoretical findings are evaluated against the experiment. For the studied test cases with different values of solar irradiation and air mass flow rate, thermal efficiencies of up to 80 % are found. In comparison to the conventional rectangular-shaped solar air heaters with smooth ducts, more than 100 % increase in the value of thermal efficiency is delineated from the theoretical and experimental findings. This gain is attributed to the unique flow pattern in the developed solar collector.

Synergistic approach of frozen hydrometeor retrievals: considerations on radiative transfer and model uncertainties in a simulated framework

Abstract. In cloudy situations, infrared (IR) and microwave (MW) observations are complementary, with infrared observations being sensitive to small cloud droplets and ice particles and with microwave observations being sensitive to precipitation. This complementarity can lead to fruitful synergies in precipitation science (e.g., Kidd and Levizzani, 2022). However, several sources of errors do exist in the treatment of infrared and microwave data that could prevent such synergy. This paper studies several of these sources to estimate their impact on retrievals. To do so, simulations from the radiative transfer (RT) for TIROS Operational Vertical Sounder (RTTOV v13) are used to build simulated observations. Indeed, we make use of a fully simulated framework to explain the impacts of the identified errors. A combination of infrared and microwave frequencies is built within a Bayesian inversion framework. Synergy is studied using different experiments: (i) with several sources of errors eliminated, (ii) with only one source of errors considered at a time and (iii) with all sources of errors together. The derived retrievals of frozen hydrometeors for each experiment are examined in a statistical study of 15 d in summer and 15 d in winter over the Atlantic Ocean. One of the main outcomes of the study is that the combination of infrared and microwave frequencies takes advantage of the strengths of both spectral ranges, leading to more accurate retrievals. Each source of error has more or less impact depending on the type of hydrometeor. Another outcome of the study is that, in all cases explored, even though the radiative transfer and numerical modeling errors may decrease the magnitude of benefits generated by the combination of infrared and microwave frequencies, the compromise remains positive.

Estimation of canopy photon recollision probability from airborne laser scanning

The past two decades have witnessed the widespread application of the spectral invariant theory (p-theory) in modeling the shortwave radiation absorbed or scattered by vegetation. The basic principle of this theory is that the canopy reflectance is solely determined by the optical properties of leaves and the photon recollision probability p. As one of the spectral invariants, p serves as a critical bond between the spectral characteristics of the canopy at any wavelength and the reflectance, transmittance, or absorptance of the vegetation canopy, and is intimately associated with the solution of the radiative transfer equation. Currently, estimation of p-value is predominantly accomplished through canopy structural parameters, such as the spherically averaged silhouette to total area ratio (STAR¯) or Leaf Area Index (LAI). In this work, we provide an approach to estimate canopy photon recollision probability directly from Airborne Laser Scanning (ALS) data. We showed that the recollision probability can be interpreted as the interceptions of virtual rays emitted from sampling points within tree crowns described with turbid media, which avoided detailed reconstruction of leaf structures. The approach was evaluated with both virtual experiments as well as field measurements. The virtual experiments employed the Large-scalE remote Sensing data and image Simulation model (LESS) to simulate virtual ALS scanning data based on three RAdiation transfer Model Intercomparison (RAMI) actual canopies, with each divided into 25 segments, for which the p-values could be obtained through LESS. Our findings showed that p-values can be accurately estimated from ALS point clouds. Specifically, it exhibited great consistency with RMSE% less than 5% for broadleaved forest scenes, 25% for mixed forest scenes, and less than 10% for coniferous forest scenes in virtual experiments, respectively, and less than 25% compared to field measurements. This study displays the potential of ALS as a promising tool for forest structure characterization and short-wave radiation modeling in forest ecosystems.

Numerical investigation of optical characterization of polycarbonate panels

Polycarbonate panels (PC panels) are state-of-the-art transparent insulating materials widely used in the construction industry due to their cavity structure, which provides exceptional thermal insulation and optimal optical performance. However, the inherent anisotropy of the three-dimensional cavity structure complicates radiative transfer and requires consideration of both azimuth and zenith angles in optical performance evaluation. This aspect has received limited attention in existing research. This study aims to accurately characterize the optical performance of PC panels through numerical simulations. A three-dimensional radiative transfer model based on the discrete ordinate radiation model is developed to solve the radiation transfer equation. The model's independency regarding mesh division, angular discretization, and accuracy is validated. The effects of incidence angle, geometric parameters, and optical properties of PC panels on optical performance are analyzed. The findings reveal a strong correlation between transmittance and absorption with variations in incident zenith and azimuth angles. The transmittance exhibits a consistent monotonic variation expressible as a rational bifunction. Notably, absorption peaks occur within specific solid angle ranges, with increased structural complexity resulting in heightened absorption and greater uncertainty. For conventional PC materials, maximum transmittance ranges from 46.9 % to 73 %, while maximum absorption ranges from 2.3 % to 13.5 %. Increasing absorption coefficients, refractive index, and surface scattering coefficients nonlinearly decrease transmittance while increasing absorption. Additionally, deviations in transmittance and absorption with azimuth angle amplify with an increase in non-horizontal structures. Sensitivity analysis indicates a significant influence of zenith angle on transmittance, and absorption coefficient predominantly affects absorption.

Experimental investigation on thermal radiation of compartment fire under fuel-controlled condition

Due to the serious adverse thermal impact on adjacent rooms and buildings, compartment fire is one of the very important topics in fire research. While for the thermal radiation of compartment fire, there are few related studies with a lack of thermal radiation models. This article experimentally studied the evolutions of radiation heat flux of compartment fire under fuel-controlled condition. Experiments were carried out employing a reduced-scale compartment with a wall opening whose size can be adjusted. The radiant heat flux (RHF) from compartment fire received by target object was measured and analyzed for various opening sizes, fuel supply rates, horizontal distances and vertical heights, and a total of 180 test data were considered. Results showed that with the increasing horizontal distance between the target object and the compartment opening, the RHF decreased rapidly at first and then decreased gradually. The view factor of the opening toward the target object was analyzed, which was related to the opening size, the horizontal distance and vertical height. The view factor exhibited an evolution pattern of the first rapidly decreasing and then slowly decreasing with horizontal distance, which was similar to the RHF received by the target object. Then, based on the view factor, the radiation model related to the opening dimension and temperature inside compartment was proposed to calculate RHF received by target object, which was proved to be in good consistency with experimental data.

Comparative simulation of transpiration and cooling impacts by porous canopies of shrubs and trees

Vegetation cooling effects can effectively improve the outdoor microclimate. To explore the potential of vegetation transpiration cooling, we validated the feasibility of a new coupled porous medium and solar radiation model to simulate the interactions between vegetation transpiration and other physical processes in CFD. To emphasize the spatial extent of vegetation's influence, we compared and quantified the flow-adjustment distances(LFA) for wind speed, the temperature difference between simulated temperature and background temperature(ΔT(°C)), and water vapor mass fraction(ΔMw(g/kg)) between shrub(100m) and tree(200m) canopies: 1)For both vegetations, the LFA required for ΔT and ΔMw exceeds that of wind speed achieve fully-developed, indicating the momentum adjustment occurs more rapidly than energy and mass transport processes. 2)Vegetation drag effect depends on both leaf area density and vegetation canopy's height and width.3)Vegetation exhibits a significantly higher transpiration cooling effect under ambient relative humidity(RH)=0% than RH=60%(the mean value of ΔT, ΔTfd), for the tree(z=1.5m): ΔT fd is -5.4°C (-1.4∼-1.5°C) at RH=0%/60%. 4)At RH=60%, both shrubs and trees exhibit a notable warming phenomenon near the vegetation canopies tops(ΔTMax=1.3°C/0.9°C for shrubs/trees). This study provides and confirms a reliable numerical method for simulating the interactions of vegetation transpiration and other physical processes in urban or rural areas.

Influence of meteoric smoke particles on the incoherent scatter measured with EISCAT VHF

Abstract. Meteoric ablation in the Earth's atmosphere produces particles of nanometer size and larger. These particles can become charged and influence the charge balance in the D region (60–90 km) and the incoherent scatter observed with radar from there. Radar studies have shown that, if enough dust particles are charged, they can influence the received radar spectrum below 100 km, provided the electron density is sufficiently high (>109 m3). Here, we study an observation made with the EISCAT VHF radar on 9 January 2014 during strong particle precipitation so that incoherent scatter was observed down to almost 60 km altitude. We found that the measured spectra were too narrow in comparison to the calculated spectra. Adjusting the collision frequency provided a better fit in the frequency range of ± 10–30 Hz. However, this did not lead to the best fit in all cases, especially not for the central part of the spectra in the narrow frequency range of ±10 Hz. By including a negatively charged dust component, we obtained a better fit for spectra observed at altitudes of 75–85 km, indicating that dust influences the incoherent-scatter spectrum at D-region altitudes. The observations at lower altitudes were limited by the small number of free electrons, and observations at higher altitudes were limited by the height resolution of the observations. Inferred dust number densities range from a few particles up to 104 cm−3, and average sizes range from approximately 0.6 to 1 nm. We find an acceptable agreement with the dust profiles calculated with the WACCM-CARMA (Whole Atmosphere Community Climate Model-Community Aerosol Radiation Model for Atmospheres) model. However, these do not include charging, which is also based on models.

Effects of ballistic transport on the thermal resistance and temperature profile in nanowires

Effects of ballistic transport on the temperature profiles and thermal resistance in nanowires are studied. Computer simulations of nanowires between a heat source and a heat sink have shown that in the middle of such wires the temperature gradient is reduced compared to Fourier’s law with steep gradients close to the heat source and sink. In this work, results from molecular dynamics and phonon Monte Carlo simulations of the heat transport in nanowires are compared to a radiator model which predicts a reduced gradient with discrete jumps at the wire ends. The comparison shows that for wires longer than the typical mean free path of phonons the radiator model is able to account for ballistic transport effects. The steep gradients at the wire ends are then continuous manifestations of the discrete jumps in the model.Graphical abstract

Impacts of topographic shadows cast by surrounding terrain on the solar irradiance on glaciers' surface in High Mountain Asia (HMA)

High Mountain Asia (HMA) hosts a large number of mountain glaciers, where the terrains are complex and mountain shadows prevail. Solar radiation is an important factor influencing the surface energy balance of glacier and hence glaciers mass balance, as mountain shadows will inevitably decrease the direct solar irradiance on glaciers' surface. Although shadows caused by slope self-shading (SS) have been widely considered in previous research, the influence of topographic shadows (TS) cast by surrounding terrains on solar irradiance on glaciers' surface in HMA still remains unknown. In this study, a topographic solar radiation model was developed, and mountain shadows (including SS and TS) were simulated and validated against manually interpreted and automatically extracted shadows on the basis of Landsat images. Then the influence of TS on solar irradiance on glaciers' surface were evaluated. Results show that, the calculated mountain shadows have a good precision, with a mean mapping accuracy of 0.76, a mean user accuracy of 0.9, and a mean Tanimoto coefficient of 0.74. In HMA, the mean shadow duration over all glaciers is about 1385.5 h per year, accounting for about 30.5% of the daylight time, and exceeding 1900 h for many glaciers, even reaching 3000 h for some glaciers. The average TS shading time over all glaciers is about 719.6 h per year. In Karakoram and Western Tien Shan, the TS shading time is higher than 1000 h per year for many glaciers. For most glaciers, the TS shading time accounts for about one half of the total shading time. The reduction in annual solar irradiance caused by TS exceeds 5.0 W/m2 (3.5% of the annual mean) over 40%, and 7.9 W/m2 (5.7% of the annual mean) over 20% of the glaciers in HMA. On average, the mean ratio of shaded incoming direct solar irradiance caused by TS to the total caused by both TS and SS is about 49.4% over all glaciers. Overall, the solar irradiance reduction is minimal in the interior of the Qinghai-Tibet Plateau, followed by the Himalayas and the Transverse Range, and with the Western Tien Shan and Karakoram being the strongest. In a word, the solar irradiance reduction caused by TS is remarkable, ignoring it could pose a significant impact on the calculation of glacier mass balance in HMA.

Theoretical interpretation of W soft X-ray spectra collected by the pulse height analysis system on Wendelstein 7-X stellarator

In many fusion devices, such as tokamaks or stellarators like Wendelstein 7-X (W7-X), soft x-ray pulse height analysis (PHA) system diagnostics are routinely used during the experiments. The PHA system is dedicated to providing information about the impurity content, and average along line-of-sight electron temperature in the plasma conditions. Moreover, it is also able to estimate impurity density and an average effective charge from the comparison of experimental spectra with the modeled ones. However, the experimental x-ray spectra can be interpreted in terms of interesting plasma parameters only when the theoretical radiation models first identify and then take into account all the relevant factors that affect the spectrum. Therefore, for this purpose, a theoretical model has been applied. Flexible Atomic Code, which allows for calculation of various atomic properties such as energy levels, cross sections for excitation and ionization by electron impact, transition probabilities for radiative transitions and autoionization, and any others as needed in the collisional–radiative approximation. The chosen spectra collected during the W7-X campaign (OP1.2b) were examined, trying to obtain an agreement between the observed and simulated spectra. The analysis carried out allowed for a reliable interpretation of experimental x-ray spectra, estimation of the electron temperature, and obtaining information on the content of tungsten impurities.

Evaluation of the simulation performance of WRF-Solar for a summer month in China using ground observation network data

Solar energy is a pivotal clean energy source in the transition to carbon neutrality from fossil fuels. However, the intermittent and stochastic characteristics of solar radiation pose challenges for accurate simulation and prediction. Accurately simulating and predicting solar radiation and its variability are crucial for optimizing solar energy utilization. This study conducted simulation experiments using the WRF-Solar model from 25 June to 25 July 2022, to evaluate the accuracy and performance of the simulated solar radiation across China. The simulations covered the whole country with a grid spacing of 27 km and were compared with ground observation network data from the Chinese Ecosystem Research Network. The results indicated that WRF-Solar can accurately capture the spatiotemporal patterns of global horizontal irradiance over China, but there is still an overestimation of solar radiation, and the model underestimates the total cloud cover. The root-mean-square error ranged from 92.83 to 188.13 Wm−2 and the mean bias (MB) ranged from 21.05 to 56.22 Wm−2. The simulation showed the smallest MB at Lhasa on the Qinghai–Tibet Plateau, while the largest MB was observed in Southeast China. To enhance the accuracy of solar radiation simulation, the authors compared the Fast All-sky Radiation Model for Solar with the Rapid Radiative Transfer Model for General Circulation Models and found that the former provides better simulation.摘要准确模拟和预测太阳辐射及其变化对于优化太阳能利用至关重要. 本研究使用WRF-Solar模式对中国2022 年 6 月 25 日至 7 月 25 日的太阳辐射情况进行了深入模拟, 模式网格水平分辨率为27 km, 通过与中国生态系统研究网络 (CERN) 的地面观测网络数据的37个观测站点进行对比, 以评估模式性能. 结果表明: WRF-Solar模式能较好地捕捉到中国上空的辐照度GHI (Global Horizontal Irradiance) 的时空分布特征, 但存在高估太阳辐射量, 以及低估总云量的情况. 全国的总辐射模拟均方根误差范围为92.83–188.13 W m−2, 平均偏差范围为21.05–56.22 W m−2. 青藏高原拉萨站的偏差最小, 在中国东南部的偏差最大. 为了进一步提升太阳辐射模拟的精确度, 本研究还对比了FARMS与RRTMG辐射方案, 发现FARMS方案的模拟精度更高.

Relationship Between NM Data and Radiation Dose at Aviation Altitudes During GLE Events

AbstractGround‐level enhancements (GLEs) are sporadic events that signal the arrival of high fluxes of solar energetic particles (SEPs) that have been produced by solar eruptions. Ground‐level enhancement events are characterized by a significant increase in the count rate of ground‐based neutron monitors (NMs). The arrival of high‐energy SEPs in the atmosphere leads to an enhancement of the radiation environment, with the enhancement at aviation altitudes being particularly hazardous to human health as pilots, crew, and airline passengers can be subjected to dangerous levels of radiation during a GLE. Through the use of a currently expanding library of analyzed GLEs and the application of a newly developed atmospheric radiation model, both of which have been created in‐house, we found a strong statistically significant relationship between real‐time NM data during GLE events and the radiation doses at aviation altitudes. This result provides a strong scientific basis for the use of real‐time NM data as a proxy for radiation dose estimates during GLE events and aids in the development of future nowcasting models to help mitigate the dangerous impacts of future GLEs.

Simulation-Based Decision Support for Agrivoltaic Systems

In this study, a framework to compare the performances of different agrivoltaic systems, or agriphotovoltaic systems, in a range of environments was developed and tested. A set of key performance indicators derived from simulations was combined in a multi criteria decision analysis approach. The agriphotovoltaic systems were then ranked based on their similarity to the optimal solution for a specific environment. Main key performance indicators were crop ratio, energy conversion per hectare, specific energy yield, water use efficiency, and initial capital expenditure. Four agriphotovoltaics, namely vertical, interspace mono-axial, overhead mono-axial, and an overhead bi-axial, with five pitch width for each agriphotovoltaic and cultivated with processing tomato, were modelled across five sites (from the North to the South of Italy) during a ten-year period. The different scenarios were simulated in Scilab, in which a radiation model and GECROS crop model were coded. Global irradiation distribution beneath modules, and thus crop yield, were more homogeneous in vertical and overhead mono-axial than in the other agriphotovoltaic. Processing tomato demonstrated high adaptability to shading and yield was marginally affected in most of the agriphotovoltaic system alternatives. Vertical and overhead mono-axial accounted for the least yield reduction when the same pitch is compared. Overall, overhead mono-axial APV with 6 m pitch ranked first in each site when a 0.7 crop ratio threshold was considered. This framework could serve as a valuable tool for assessing the performance of different solution of agriphotovoltaics systems and their compliance with national regulation, and economic and technical targets.

Influence of radiation modelling in under-resolved FDS free-burn simulations

Focusing on the impact of radiation modelling in under-resolved fire simulations, the paper presents LES of free-burn scenarios. The work aims to evaluate the performance of the current fire modelling capabilities of the Fire Dynamics Simulator (FDS) code and to identify the best practices for FDS practitioners in terms of simulating radiative heat transfer. To this purpose, both optically thin and optically thick approaches are considered and their predictive capabilities over different grid sizes is evaluated. The impact of various radiation modelling parameters with the optically thick approach (i.e., path length, number of solid angles) is also considered. Comparisons of the predicted centreline flame temperatures and axial velocities as well as of the predicted radiative heat fluxes at different locations are presented. Overall, there were obvious differences between the two approaches with the optically thin being more accurate when compared to both experimental data and empirical correlations available in the literature.

Broadband near-infrared emission in silicon waveguides

Silicon photonic integrated circuit foundries enable wafer-level fabrication of entire electro-optic systems-on-a-chip for applications ranging from datacommunication to lidar to chemical sensing. However, silicon’s indirect bandgap has so far prevented its use as an on-chip optical source for these systems. Here, we describe a fullyintegrated broadband silicon waveguide light source fabricated in a state-of-the-art 300-mm foundry. A reverse-biased p-i-n diode in a silicon waveguide emits broadband near-infrared optical radiation directly into the waveguide mode, resulting in nanowatts of guided optical power from a few milliamps of electrical current. We develop a one-dimensional Planck radiation model for intraband emission from hot carriers to theoretically describe the emission. The brightness of this radiation is demonstrated by using it for broadband characterization of photonic components including Mach-Zehnder interferometers and lattice filters, and for waveguide infrared absorption spectroscopy of liquid-phase analytes. This broadband silicon-based source can be directly integrated with waveguides and photodetectors with no change to existing foundry processes and is expected to find immediate application in optical systems-on-a-chip for metrology, spectroscopy, and sensing.