Incident Flux Research Articles

Plasma facing components with capillary porous system and liquid metal coolant flow

Liquid metal can create a renewable protective surface on plasma facing components (PFC), with an additional advantage of deuterium pumping and the prospect of tritium extraction if liquid lithium (LL) is used and maintained below 450 °C, the temperature above which LL vapor pressure begins to contaminate the plasma. LM can also be utilized as an efficient coolant, driven by the Lorentz force created with the help of the magnetic field in fusion devices. Capillary porous systems can serve as a conduit of LM and simultaneously provide stabilization of the LM flow, protecting against spills into the plasma. Recently, a combination of a fast-flowing LM cooling system with a porous plasma facing wall (CPSF) was investigated [A. Khodak and R. Maingi, Nucl. Mater. Energy 26, 100935 (2021)]. The system takes an advantage of a magnetohydrodynamics velocity profile as well as attractive LM properties to promote efficient heat transfer from the plasma to the LL at low pumping energy cost, relative to the incident heat flux on the PFC. In the case of a disruption leading to excessive heat flux from the plasma to the LM PFCs, LL evaporation can stabilize the PFC surface temperature, due to high evaporation heat and apparent vapor shielding. The proposed CPSF was optimized analytically for the conditions of a fusion nuclear science facility [Kessel et al., Fusion Sci. Technol. 75, 886 (2019)]: 10 T toroidal field and 10 MW/m2 peak incident heat flux. Computational fluid dynamics analysis confirmed that a CPSF system with 2.5 mm square channels can pump enough LL so that no additional coolant is needed.

The influence of snow deposits on thermal efficiency of vacuum tube collectors

Global warming promotes the acceleration forces all countries to reduce fossil energy sources and increase renewable energy sources with the development of environmentally friendly resource-saving technologies. The vast territory of Russia is permafrost or has seasonally frozen soils. The use of renewable energy sources, especially solar energy sources, is especially important for such territories.The article presents the experimental results of the operating modes of a pilot industrial solar hot water supply system with two vacuum tube collectors after snow pollution or icing of pipe surfaces. This technique is used to measure the hourly values of thermal energy from the conversion of solar radiation by collectors with polluted and cleaned collector surfaces on a sunny day after snowfall or icing. The average hourly value of solar insolation (with contaminated surfaces and after their cleaning) is obtained by integrating the meter recordings on the incident heat flux from the sun (by 600 values each) at an interval of 6 seconds. It is found that when the collector pipe surface is iced, the decrease in the thermal energy supply is maximum and amounts to 36.96 %. In other cases it varies from 8.51 to 13.47 %.

The Equations and Optical Parameters of Antireflective Multilayers: A Literature Review

In this paper, the study is focused on the anti-reflection coatings on silicon solar cells and monocrystalline solar cells. The impact of optical parameters such as refractive index on the reflectivity as well as the impact of the as well as the impact of the diffusion length of the carriers was studied. The calculations performed according to the transfer matrices on the stacking of layers through the diopters have allowed establishing simulations for antireflective multilayer coatings. In our study, the reference wavelength was chosen equal to l= 700 nm, which gives us an optimal refractive index of silicon (n = 3.7838) corresponding to a reflectivity at the surface of 33%. To reduce this high reflectivity, the coating of the surface is a technique used to improve the transmission of the incident luminous flux in the active material and light flux in the active material which is silicon.

A parametric logistic equation with light flux and medium concentration for cultivation planning of microalgae.

Microalgae are considered to be promising producers of bioactive chemicals, feeds and fuels from carbon dioxide by photosynthesis. Thus, the prediction of microalgal growth profiles is important for the planning of cost-effective and sustainable cultivation–harvest cycles. This paper proposes a mathematical model capable of predicting the effect of light flux into culture and medium concentration on the growth profiles of microalgae by incorporating these growth-limiting factors into a logistic equation. The specific form of the equation is derived based on the experimentally measured growth profiles of Monoraphidium sp., a microalgal strain isolated by the authors, under 16 conditions consisting of combinations of incident light fluxes into culture and initial medium concentrations. Using a cross-validation method, it is shown that the proposed model has the ability to predict necessary incident light flux into culture and initial medium concentration for harvesting target biomass at a target time. Finally, model-guided cultivation planning is performed and is evaluated by comparing the result with experimental data.

The Outer Edge of the Venus Zone around Main-sequence Stars

A key item of interest for planetary scientists and astronomers is the habitable zone: the distance from a host star where a terrestrial planet can maintain necessary temperatures in order to retain liquid water on its surface. However, when observing a system’s habitable zone, it is possible that one may instead observe a Venus-like planet. We define “Venus-like” as greenhouse-gas-dominated atmosphere occurring when incoming solar radiation exceeds infrared radiation emitted from the planet at the top of the atmosphere, resulting in a runaway greenhouse. Our definition of Venus-like includes both incipient and post-runaway greenhouse states. Both the possibility of observing a Venus-like world and the possibility that Venus could represent an end state of evolution for habitable worlds require an improved understanding of the Venus-like planet, specifically the distances where these planets can exist. Understanding this helps us define a “Venus zone”—the region in which Venus-like planets could exist—and assess the overlap with the aforementioned “habitable zone.” In this study, we use a 1D radiative−convective climate model to determine the outer edge of the Venus zone for F0V, G2V, K5V, and M3V and M5V stellar spectral types. Our results show that the outer edge of the Venus zone resides at 3.01, 1.36, 0.68, 0.23, and 0.1 au, respectively. These correspond to incident stellar fluxes of 0.8, 0.55, 0.38, 0.32, and 0.3 S ⊙, respectively, where stellar flux is relative to Earth (1.0). These results indicate that there may be considerable overlap between the habitable zone and the Venus zone.

A novel external reflecting raceway pond design for improved biomass productivity

Outdoor raceway ponds for microalgae cultivation suffer from low biomass productivity due in part to the low photosynthetic photon flux received by the microalgae culture in the mornings and evenings and during the winter months at middle and high latitudes. This study explores the use of external mirrors to reflect additional sunlight onto the culture and increase the incident solar flux at critical times of the day and year. Four designs cultivating Chlorella vulgaris were considered: a raceway pond without mirrors (Configuration A), a pond oriented along the north/south axis with dual east/west mirrors (Configuration B), a pond oriented along the east/west axis with a single north mirror (Configuration C), and a solar tracking rotating pond with a single mirror (Configuration D). The biomass productivity was predicted by coupling the simulated radiative field within the culture to a microalgae growth kinetics model accounting for photolimitation and biomass loss due to respiration. Two different locations were considered, namely Los Angeles, CA, USA and Saint-Nazaire, France. The use of mirrors was predicted to increase the daily culture-area-based and volumetric biomass productivity at both locations and all months of the year. Configuration D yielded the highest biomass productivity year-round. Configuration B had a higher biomass productivity than Configuration C in the summer months and vice versa in the winter months. Overall, Configuration C was considered to be the simplest and most cost-effective method to increase raceway productivity. Indeed, this configuration improved the raceway pond volumetric and culture-area-based biomass productivity by as much as 73% in the winter months compared to Configuration A. Additionally, the impact of operational parameters (initial biomass concentration and culture depth) and design parameters (pond length-to-width ratio and mirror height) were assessed to provide practical recommendations for maximizing biomass productivity.

A Thin-Film Thermal Meta-Device With Dual Function of Thermal Shield and Generation Based on an Artificially Tilted Structure

A thin-film thermal meta-device with a dual-function of thermal shield and generation is proposed and fabricated in this work. The tilted layered structure composed of thermoelectric materials with low thermal conductivity and metal materials with high thermal conductivity is designed to realize the orientation of the incident heat flux and the utilization of heat energy based on the Seebeck effect of the materials. The constructed transverse thin-film thermoelectric device with a Bi2Te3/Cu-layered structure can achieve a maximum output voltage of 20.4 mV and a maximum output power of 7.39 μW at a temperature difference of 80 K. On this basis, the dual-functional film meta-device based on transformation thermodynamics is capable of realizing a heat flux shielding in the central area and generating a transverse output voltage. The experimental results also indicate that there exists a well linear relationship between the output voltage of the meta-device and the temperature difference, which can be extended to accurately monitor the temperature of the central area. This work provides a certain reference for the development of a new class of thermoelectric devices with thermal protection and temperature detection capability.

Оценка токсичности не распространяющих горение сигнальных кабелей при пожаре в производственных помещениях

Currently, flame retardant materials made from polymers with flame retardant additives are widely used. However, the thermal effects of the fire on these materials from the point of view of the release of toxic gases are not sufficiently studied. The purpose of the article is an experimental assessment of the toxicity of the gaseous environment of a room during thermal decomposition of flame retardant signal cables used in the industrial premises and in the buildings with a massive presence of people. Experimental method is used for studying the process of formation of the hydrogen cyanide and carbon monoxide during thermal decomposition of the cable product samples in a small-scale pilot plant. The analysis of the obtained results was carried out. Density of the radiant heat flux incident on the cable surface, which is characteristic of a fire in a room, is modeled. Dependences are obtained concerning the partial densities of hydrogen cyanide and carbon monoxide, as well as the specific emission coefficients of these gases on the duration of experiments in the case of thermal decomposition of a modern flame retardant signal cable of the ng LS FR HF E1180 brand, the insulation of which is made of polymers with flame retardant additives. It is found that this cable under real fire conditions can release toxic compounds (carbon monoxide and hydrogen cyanide) in the concentrations exceeding their maximum allowable values during the evacuation of people from the premises. The obtained values of the specific mass coefficients of formation of CO and HCN, as well as the specific mass coefficient of O2 absorption, can be used in the mathematical models of the dynamics of fire hazards when calculating the time of blocking escape routes in the industrial premises, as well as in the buildings with a mass stay of people, where flame retardant signal cables are located.

Effect of porosity on ignition and burning behavior of cellulose materials

Porosity is one of the important factors to determine the fuel efficiency and the risk of forest combustible fire. In this work, we explore the porosity effect on the ignition phenomena, autoignition limit, and extinction of flaming combustion. The ignition experiment of pine needle and wood powder fuel bed with various porosity was conducted under external radiation at a constant heat flux of 5 ∼ 60 kW/m2. Several ignition phenomena including the cone-piloted flaming ignition, smouldering, smouldering to flaming transition, and no ignition can be obtained. And the pine needle could be burnt out in the flaming state, but the wood powder was easily ignited and presented a short flaming period, such as only 10% mass loss in flaming combustion and 70 ∼ 80% mass loss in smouldering combustion for an 84.67% porosity fuel under the radiant heat flux of 35 kW/m2. The ignition of a larger porosity fuel bed is more difficult, requiring a higher critical heat flux. The measurements suggested that the porosity was important to determine smouldering to flaming transition, but weak affected the smouldering ignition with the critical surface temperature 350 °C to pine needle and 280 °C to wood powder. The porosity has a slight influence on the ignition time and critical mass flux, with an order of magnitude lower than incident heat flux. The fuel with low porosity is more likely to be self-extinguished due to limited oxygen supply, and responds to a higher critical mass flux of flaming self-extinguishing. The proposed heat-transfer analysis explains and well predicted the ignition limit and delay time. This research helps understand the development of biomass burners and forest fire, and the interaction between flaming and smouldering fires.

Thermo-mechanical optimization of thermoelectric generators using deep learning artificial intelligence algorithms fed with verified finite element simulation data

The rising levels of global warming in the environment owing to emissions from fossil-fuel-based engines has increased the search for efficient clean energy systems. Thermoelectric generators (TEGs) standout as a promising energy conversion device which can directly convert heat to electricity. Several optimization studies have been carried out on these devices to improve their power generation rate and efficiencies while guaranteeing long lifespan. However, the limitations of finite element methods (FEMs) in easily providing optimization guidelines at a fast rate has hindered the manufacture of TEGs with high thermo-mechanical performance.This is why this paper presents the first ever artificial intelligence enabled optimization of a TEG conducted via deep neural networks (DNNs). Previous research on this topic completely neglected the mechanical performance and consequently, the service lifetime of the TEG when exposed to thermal operating conditions. To fill this gap, the effects of strategic parameters on the power output, efficiency and thermal stress performances of the TEG are investigated. These parameters are the hot and cold junction temperatures/heat transfer coefficients, incident heat flux, external load resistance, TE leg height, area, and area ratio. The DNN is fed with verified three-dimensional FEM simulations carried out on the ANSYS Workbench platform. The FEM results exhibit almost perfect correlation with experimental data which establishes the precision of the model.Results are that the DNN model is able to provide the necessary optimization guidelines for maximum thermo-mechanical performance in just 8 seconds compared to the 8 hours required by the FEM. The TEGs that were modelled using the DNN optimization guidelines improved the power, efficiency and mechanical performance of the unoptimized TEG by 11.94%, 14.17%, and 91%, respectively. These results are sufficient to provide useful guidelines at a fast rate for the fabrication of high-efficiency TEGs that will operate for a long time.

TOI-1759 b: A transiting sub-Neptune around a low mass star characterized with SPIRou and TESS

We report the detection and characterization of the transiting sub-Neptune TOI-1759 b, using photometric time series from the Transiting Exoplanet Survey Satellite (TESS) and near-infrared spectropolarimetric data from the Spectro-Polarimètre Infra Rouge (SPIRou) on the Canada-France-Hawaii Telescope. TOI-1759 b orbits a moderately active M0V star with an orbital period of 18.849975 ± 0.000006 days, and we measured a planetary radius and mass of 3.06 ± 0.22 R⊕ and 6.8 ± 2.0 M⊕. Radial velocities were extracted from the SPIRou spectra using both the cross-correlation function and the line-by-line methods, optimizing the velocity measurements in the near-infrared domain. We analyzed the broadband spectral energy distribution of the star and the high-resolution SPIRou spectra to constrain the stellar parameters and thus improve the accuracy of the derived planet parameters. A least squares deconvolution analysis of the SPIRou Stokes V polarized spectra detects Zeeman signatures in TOI-1759. We modeled the rotational modulation of the magnetic stellar activity using a Gaussian process regression with a quasi-periodic covariance function and find a rotation period of 35.65−0.15+0.17 days. We reconstructed the large-scale surface magnetic field of the star using Zeeman-Doppler imaging, which gives a predominantly poloidal field with a mean strength of 18 ± 4 G. Finally, we performed a joint Bayesian Markov chain Monte Carlo analysis of the TESS photometry and SPIRou radial velocities to optimally constrain the system parameters. At 0.1176 ± 0.0013 au from the star, the planet receives 6.4 times the bolometric flux incident on Earth, and its equilibrium temperature is estimated at 433 ± 14 K. TOI-1759 b is a likely gas-dominated sub-Neptune with an expected high rate of photoevaporation. Therefore, it is an interesting target to search for neutral hydrogen escape, which may provide important constraints on the planetary formation mechanisms responsible for the observed sub-Neptune radius desert.

Fire behaviour of hemp, clay and gypsum-based light biobased concretes and renders

Greenhouse gas emissions from cement manufacturing account for about 8 to 10 percent of total CO2 emissions worldwide. To reduce these emissions, researchers are developing new concrete manufacturing techniques and processes to reduce high energy consumption and environmental impacts. Biobased concretes are eco-friendly insulating materials for building industry that can respond to this problem. However, there is a lack of knowledge regarding how these plant-based fillers ignite and contribute to heat release in case of fire. In this work, the fire behaviour of a series of hemp-based earth and/or gypsum concretes covering a large range of densities (180–1500 kg/m3) is investigated using the cone calorimeter at an incident heat flux of 50 kW/m2. The fire performances are mainly monitored by the thermal inertia of the materials. Only the lightest concretes ignite with a density threshold for ignition occurrence around 500 kg/m3. For a density of 261 kg/m3, the critical heat flux of an earth-hemp concrete was found to be close to 27 kW/m2. The flaming period remains very short in all cases.

Impact of multi-busbar front grid patterns on the performance of industrial type c-Si solar cell

Solar cell performance is highly dependent upon the front contact grid design for minimizing the power losses due to shading (optical loss) and for proper collection of the photo-generated charge carriers (electrical loss). In this paper, theoretical calculations (optimization) have been carried out for the total power losses (viz. optical and electrical) due to different front grid multi-busbar patterns similar to the ones currently used in industrial production. Busbar width and finger spacing, the two important design parameters of solar cell with standard busbar structure, are optimized for multi busbar systems. Role of interlinks between the fingers to reduce the power loss has also been studied. The effect of each optimized grid design on the component in the levelized cost of electricity (LCOE) due to Silver (Ag) requirement has been estimated for a 10 MW power system with a 25 years lifespan. The study of EM field distribution due to incident photon flux shows that increasing the number of busbars can generate carriers within the shaded areas under the busbars.

Thermo-physical evaluation of firefighter outer garment in high flux environments

Thermal protective performance tests have been conducted and improved over the years to assess the safety provided by firefighters’ outer thermal garments. Existing evaluation criteria based on empirical relations require an iterative process to estimate skin burn injuries. In this work, the concept of critical time – maximum exposure time before physical failure, is proposed, and utilized to abate this iterative process. The critical time relation to the fabric performance is investigated at an incident heat flux of 41, 84 and 126 kW/m2. Furthermore, parametric studies are performed to characterize the fabric thermo-physical behavior and associated burn degree. The tested specimens consist of an outer shell, a moisture barrier and a thermal liner. The methodology of visual assessment as per ISO 6942 is implemented to approximate the critical time. The critical time relation to increasing incident heat flux displayed a nonlinear performance reduction in the garment. An increase in the second degree burn time was observed for a vertically oriented bench-scale test. The firefighter’s current outer garment failed at a high flux of 126 kW/m2. The concept of relating the critical time to cumulative incident flux will aid the education of firefighters on fluctuating fire environments. This research opens a new domain to analyse the protective garments utilising the critical time.

Optimized Permeability of Microporous Foam for Transpiration Cooling in Hypersonic Leading Edge

Motivated by knowledge gaps within the topics of wicking dry-out and graded porosity, we present a computational method to determine the optimum micropore distribution for maximum cooling in response to an incident heat flux on the leading edge (LE) of hypersonic aircraft. The investigated geometry is a 5° half-angle wedge with a semicircular nose tip of 1 mm radius of curvature. The aerodynamic heat flux along the LE is estimated for Mach 5–8. The complex method of optimization is a gradient-free method that is used to maximize the cooling effectiveness in the porous LE with stratified permeability. We show that porosity optimization leads to a modest 6% increase in cooling effectiveness near the stagnation point. The results are then used to analyze the LE’s ability to pump the liquid coolant passively from capillary action during acceleration. We determine that a porous LE having an average pore diameter of with strong wettability performs far better than a pore diameter of with poor wettability.

In vitro corrosion response of CoCrMo and Ti-6Al-4V orthopedic implants with Zr columnar thin films

This study focuses on the functionalized modification of Ti-6Al-4V and CoCrMo alloys substrates widely used by the biomedical domain as total joint replacements (TJRs) of the hip and knee. To improve the corrosion resistance of these devices, nanostructured columnar zirconium (Zr) thin films were produced by oblique angle deposition (OAD) using DC magnetron sputtering to model the particular design of the joint. The influence of the angular distribution of the incoming particle flux on the resulting film morphology (column tilt angle, porosity) and electrochemical behavior was studied by varying the substrates inclination angle θ from 15 to 90°. The experimental deposition process was reproduced by kinetic Monte Carlo (kMC) models. With the increase of the flux incidence angle α from 0 to 70°, the film thickness and the column tilt angle β vary in agreement with the theoretical models. Additionally, the corrosion behavior of uncoated and Zr-coated alloys (CoCrMo and Ti-6Al-4V) was compared through open circuit potential chronopotentiometry and electrochemical polarization test in NaCl 0.9% solution at 37 °C. It was found that the corrosion protection was successfully improved by the presence of the films. The variation of the corrosion behavior with the flux incidence angle is explained by the changes in the film density.

Sampling molecular gas in the Helix planetary nebula: Variation in HNC/HCN with UV flux

Context. Observations of molecular clouds, prestellar cores, and protoplanetary disks have established that the HNC/HCN ratio may be a potent diagnostic of molecular gas physical conditions. The processes that govern the relative abundances of these molecules nevertheless remain poorly understood. Aims. We seek to exploit the wide range of UV irradiation strengths within the ∼pc diameter Helix planetary nebula to explore the potential role of UV radiation in driving HNC/HCN. Methods. We performed IRAM 30 m and APEX 12 m radio line observations across six positions within the Helix Nebula, making use of radiative transfer and photodissociation modeling codes to interpret the results for line intensities and line ratios in terms of the molecular gas properties. Results. We have obtained the first detections of the plasma-embedded Helix molecular knots (globules) in HCN, HNC, HCO+, and other trace molecules. Analysis of the HNC/HCN integrated line intensity ratio reveals an increase with radial distance from the Helix central star. In the context of molecular line ratios of other planetary nebulae from the literature, the HNC/HCN ratio appears to be anticorrelated with UV emission over four orders of magnitude in incident flux. Models of the photodissociation regions within the Helix using the RADEX and Meudon codes reveal strong constraints on the column density (1.5–2.5 × 1012 cm−2) of the molecular gas, as well as pressure and temperature. Analysis of the molecular ion HCO+ across the Helix indicates that X-ray irradiation is likely driving HCO+ production in the outer regions of planetary nebulae, where photodissociation is limited but cold gas and ionized molecules are abundant. Conclusions. Although the observational results clearly indicate that UV irradiation is important in determining the HNC/HCN ratio, our photodissociation region modeling indicates that the UV flux gradient alone cannot reproduce the observed variation in HNC/HCN across the Helix Nebula. Instead, HNC/HCN appears to be dependent on both UV irradiation and gas pressure and density.

Thermal management of solar photovoltaic panels using a fibre Bragg grating sensor-based temperature monitoring

Solar photovoltaic (PV) performance is affected by increased panel temperature. Maintaining an optimal PV panel temperature is essential for sustaining performance and maximizing the productive life of solar PV panels. Current temperature sensors possess a long response time and low resolution and accuracy. Advanced fibre-optic sensors offer distinct advantages of greater accuracy, a more comprehensive range, and a very high sampling rate. The present experimental work focuses on fibre Bragg grating sensor-based solar PV panel temperature monitoring. The unique capabilities of fibre-optic sensors are demonstrated by studying the rapid perturbations in panel temperature over time for indoor and outdoor conditions. The effects of incident radiation flux and the inclination angle on panel temperature are analyzed. Temperature sensitivity of 6 pm/°C is obtained. The results are helpful in dynamic monitoring of panel temperature, understanding the thermal interactions at the microscale level, and streamlining the measured temperature of multiple panels on solar farms. Thus, the proposed advanced method of FBG-based temperature monitoring of solar panels could be helpful to operate an integrated cooling system to improve the performance of solar panels.

Characterization of 128 × 128 MM-PAD-2.1 ASIC: a fast framing hard x-ray detector with high dynamic range

We characterize a new x-ray Mixed-Mode Pixel Array Detector (MM-PAD-2.1) Application Specific Integrated Circuit (ASIC). Using an integrating pixel front-end with dynamic charge removal architecture, the MM-PAD-2.1 ASIC extends the maximum measurable x-ray signal (in 20 keV photon units) to > 107 x-rays/pixel/frame while maintaining a low read noise across the full dynamic range, all while imaging continuously at a frame rate of up to 10 kHz. The in-pixel dynamic charge removal mechanism prevents saturation of the input amplifier and proceeds in parallel with signal integration to achieve deadtime-less measurements with incident x-ray rates of > 1010 x-rays/pixel/s. The ASIC format consists of 128 × 128 square pixels each 150 μm on a side and is designed to be 3-side buttable so large arrays can be effectively tiled. Here we use both laboratory x-ray sources and the Cornell High Energy Synchrotron Source (CHESS) to characterize two single ASIC prototype detectors for both low (single x-ray) and high incident flux detection. In the first detector the ASIC was solder bump-bonded to a 500 μm thick Si sensor for efficient detection of x-rays below 20 keV, whereas the second detector used a 750 μm thick CdTe sensor for x-rays above ∼ 20 keV.

Prediction of Incident Heat Flux of Facade Considering Opening Jet Plume

In this study, a combustion experiment was performed by setting fire source conditions to generate an opening fire plume and flame for various opening shapes using a large-scale compartment model. It was confirmed that the opening temperature and incident heat flux increased with increasing fire source condition. Regression analysis was performed using the relationship between the dimensionless numbe QD*-2/3z* and the incident heat flux q’’. Comparison of the derived formula with the experimental value confirmed the validity of the results.