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Stream temperature is widely considered the master variable in stream ecosystems. One of the key drivers of diel and seasonal stream temperature variability is the solar radiation received at the stream surface, which can be influenced by shading associated with both larger scale topographic features and riparian vegetation. In this study, a stream shade model was developed that uses LiDAR point cloud data to model shading by riparian vegetation, including canopy overhang, and conventional elevation data to model stream shading by topography. The model was applied to a dominantly north–south oriented river flowing in a floodplain within a mountain valley. When compared with shade interpreted from PlanetScope visual imagery, the model predicted stream shade at the point scale with 92% agreement. Sources of error were attributed to pixel and azimuth band size, which can be refined within the model arguments, although at the cost of increased processing time. The shade model was re‐run after virtually rotating the reach by 90° and 270° clockwise to evaluate the effect of valley orientation. Peak reach‐wide sunlight exposure occurred approximately 2 h later in the day when the stream reach was rotated 90°, and produced greater shading from mid‐morning to mid‐afternoon. Further work should test the model on smaller streams using ground‐based oblique or drone‐based photography to provide ground‐truthing, particularly to assess the accuracy of predicted shade below over‐hanging vegetation. [ABSTRACT FROM AUTHOR]

Copyright of Ingenius, Revista Ciencia y Tecnología is the property of Universidad Politecnica Salesiana and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, an approximate analytical solution (AS) is presented to evaluate the radiative thermal exchange through a gaseous participating medium composed of H2O, CO2, and CO, which is valid for the product values of pressure path‐length (PL) from 0.06 to 20 atm m and temperatures (T) from 300 K to 2100 K. The Spence root weighting method is used to approximate the exact solutions. For each set of PL;T $\mathrm{PL}{\rm{;}}T$, the value of exact spectral emissivity and absorptivity ελ ${\varepsilon }_{\lambda }$ and aλ ${a}_{\lambda }$ for the gas mixture is calculated using the AS, the Hottel graphical method (HGM) and the proposed approximate solution. The weaker adjustment was achieved in the modeling of the HGM, with a mean deviation obtained of ±15% and ±20% for 43.8% and 56.3% of the data evaluated, respectively, while the best indices were obtained in the estimation of the proposed method, with a mean deviation obtained of ±10% and ±15% for 81.3% and 98.1% of the available data, respectively. In all cases, the agreement of the proposed model with the available experimental data is good enough to be considered satisfactory for practical design. [ABSTRACT FROM AUTHOR]

According to the provisions on fire separation distance between industrial and civil buildings in the latest 'General Code for Fire Protection of Buildings and Constructions' (GB 55037-2022). Radiant heat intensity is one of the main factors in calculating the fire separation distance between buildings. Therefore, the design process involves a lot of calculation of radiant heat intensity. This paper mainly studies the prediction model of radiant heat flux. Three different view factor calculation models, Mudan, Mudan-Sparrow, and Rai-Kalelkar, are used to evaluate the influence of key factors such as the diameter of the pool and the distance between the target and the center point of the liquid pool on the calculation results of radiant heat flux. The results show that when it came to estimating the radiant heat flux, the Mudan and Mudan-Sparrow models yielded comparable results. The calculation of the Rai-Kalelkar model shows that the radiant heat flux is about half of the heat flux in the first two models. When calculating the minimum fire separation distance for combustible liquid storage tanks with a fire dike, the results show that all three models can provide a larger safety margin than the point source model.

Tailoring the properties of hot-stamped components offers the potential to enhance crash performance while simultaneously improving downstream joining processes. In recent years, an innovative technology suited for achieving tailored properties involving the utilization of a specialized furnace chamber, known as the TemperBox®, has been introduced. Within this chamber, a cooled aluminum mask shields specific areas of the blank from incoming heat radiation and concurrently absorbs the blank's own radiation. The duration of the heat radiation exchange can influence the diffusion-dependent phase transformation and, consequently, the resulting mechanical properties. Hence, the intermediate cooling duration assumes a pivotal role as a parameter, as is investigated in this study. To examine the effects, specimens of the steel 22MnB5 AS150 are subjected to intermediate cooling of varying durations, followed by forming and partial quenching. The temperature profile of the blank during intermediate cooling prior to forming and quenching is analyzed. Subsequently, the tailored hot-stamped components are assessed for hardness, strength, ductility, and thickness strain. The study reveals that with increasing duration of partial intermediate cooling and targeted radiation exchange, a homogeneous ferritic–pearlitic structure is formed from an austenitic structure. This uniform structure of ferrite and pearlite is reflected in lower hardness and strength values, along with improved ductility. Additionally, this paper introduces a simulation methodology designed to calculate the dynamics of thermal radiation and the kinetics of phase transformation. [ABSTRACT FROM AUTHOR]

The calculation of the view factor is an important consideration in radiative heat transfer analysis. Thermal engineering requires the view factor calculations between complex geometries containing parallel and inclined surfaces. There is currently no analytic formula available for this, so the summation rule (SR) must be used. However, when complex geometries are analyzed, processing SR becomes a very intensive task. Therefore, the present study aims to exploit vector calculus to develop a formula for calculating the view factors for radiative heat transfer from any two rectangular oblique or parallel surfaces. The exact solution obtained by means of the contour integration was compared with the numerical integration of the quadruple integral using the multiple Simpson's rule 1/3 with five intervals (MSR) and the summation rule via the Hamilton–Morgan solution (HMS). The lack of similar precedents in the literature reinforces the scientific and practical nature of the proposed method. [ABSTRACT FROM AUTHOR]

The photovoltaic (PV) module energy rating standard series IEC 61853 does not cover bifacial PV modules. However, the market share of bifacial PV modules has dramatically increased in recent years and is projected to grow. This work demonstrates how Parts 3 and 4 of the IEC 61853 standard could be extended to bifacial modules. First, we develop an irradiance model that uses the data already given in the standard IEC 61853‐4 to calculate the irradiance on the rear side of the module. Second, we propose a way to extend the energy yield calculation algorithm IEC 61853‐3 to include bifacial modules and make it available to the PV community. This rear irradiance and bifacial energy yield calculation procedure is tested using real outdoor measurements for a nine‐month period with a root mean square difference between measured and simulated energy yield of 4.65%. To conclude, we investigate the impact of different climates and normalization on the bifacial module energy rating results. [ABSTRACT FROM AUTHOR]

Radiant systems are an energy-efficient method for providing cooling to building occupants through active surfaces. To assess the impact of the radiant environment on occupants in space, we develop a ray-tracing simulation, which accounts for longwave radiation. Thermal radiation shares many characteristics with visible light, and thus is highly dependent on surface geometry. Much research effort has been dedicated to characterizing the behavior of visible light in the built environment and its impact on the human experience of space. However, longwave infrared radiation's effect on the human perception of heat is still not well characterized or understood within the design community. In order to make the embodied effect of radiant surfaces' geometry and configuration legible, we have developed a Mean Radiant Temperature (MRT) simulation method, which is based on a ray-tracing technique. It accounts for the detailed geometry of the human body and its surrounding environment. We use a case study of a pavilion built with an envelope consisting of active cooling panels in Singapore. Using measured data for the surrounding surface temperatures in the pavilion, we explore the impact of both the active panels and the surrounding passive elements and thermal environment on a person's radiant heat exchange in different postures. The reflectivity and emissivity values of different surfaces are taken into account, and the ray-tracing process allows for multiple-bounce simulation. The model accounts for both longwave and shortwave radiation, and the simulation results are compared with field measurements for validation. The results are expressed both numerically and as spatial radiant-heat-maps. These show a variation of up to 11°C in MRT across the space studied. Furthermore, a digital manikin is used to assess the impact of the radiant cooling panels across the human body. The results show a 10°C variation in radiant temperature perceived by different regions of the body in one position. The findings reveal a significant heterogeneity of radiant heat transfer that current analysis methods typically overlook for both architectural space and the geometry of the human body. [ABSTRACT FROM AUTHOR]

The heat receiver is an essential part of the Concentrating Solar Power plant, directly affecting its operation and safety. In this paper, the Monte Carlo ray-tracing algorithm was introduced to evaluate a 50 MW (e) external cylindrical receiver's thermal performance. The radiation heat flux concentrated from the heliostats field and the view factors between grids divided from the tubes were both calculated using Monte Carlo ray-tracing algorithm. Besides, an in-house code was developed and verified, including three modules of the view-factor calculation, thermal performance calculation, and thermal stress calculation. It was also employed to investigate the 50 MW (e) receiver, and the detailed 3D profiles of temperature and thermal stress in the receiver were analyzed. It was found that the molten salt was heated from 298°C to 565°C and the tube at the 50 MW (e) receiver's outlet had a high temperature, while the high thermal stress came out at the receiver's entrance. Finally, the over-temperature of the receiver was discussed, and an optimization algorithm was introduced. The tube wall temperature and film temperature at the overheated area matched the safety criteria, and the outlet molten salt temperature still reached 563°C after the optimization process, with only 2°C dropped. [ABSTRACT FROM AUTHOR]

Fuel ignition potential is one of the primary drivers influencing the extent of damage in wildland and wildland–urban interface fires and it is a decisive factor in planning prescribed fires. Determining the susceptibility of fuels, which vary spatially and temporally, to fire will help to recognize necessary defensive actions, reduce damages, and help to configure prescribed fire plans. In this paper, the development of a new computational model, Complex-environment Temperature and Moisture Predictor (CeTMP), is presented. CeTMP predicts the diurnal temperature and moisture content variations, and thus vulnerability to ignition, of objects/fuels with complex shapes, settings, or topography and materials under variable environmental conditions. The model is applicable to complex scenarios (e.g., interface or intermix communities) composed of natural and manmade random-shaped items in open atmosphere under the influence of local weather and diurnal solar radiation. The vulnerability of fuels to ignition is determined by predicting the transient temperature and dryness of fuel in connection with the surroundings, topography, and local environment, as well as flame heat if any exists. In this regard, a detailed surface energy balance analysis, coupled with a water budget analysis, is performed in high spatiotemporal resolution. The model performance was validated against several existing analytical and measured data. The discrete, high-resolution surface temperature and moisture content information obtained from the model can also provide unsteady boundary conditions for computational fluid dynamics simulations when coupled physics is desired. [ABSTRACT FROM AUTHOR]

Li-ion batteries play a key role in energy storage and conversion in engineering systems such as electric vehicles and grid energy storage, with critical impact on electrification and storage of renewable energy. A key unresolved technological challenge in Li-ion batteries pertains to thermal runaway initiation and propagation in a battery pack, which can lead to subsequent fire and explosion. Despite significant past work, there remains a critical need to understand how thermal runaway propagates in a pack. This work presents a comprehensive investigation of the effect of radiative heat transfer on thermal runaway propagation. Radiation can be important when a battery is exposed to adjacent heat and fire sources, as well as in thermal runaway propagation from one hot cell to another. A theoretical radiative heat transfer model based on view factor theory is developed. Calculations based on this model for a simple 2D cylinder-to-cylinder geometry are found to be in very good agreement with analytical expressions. Radiation-induced thermal runaway propagation between two cylindrical 18650 batteries is evaluated. It is shown that radiation may play a key role in thermal runaway propagation, depending strongly on the triggering temperature. It is found that radiative effects in thermal runaway propagation exhibit both nonlinear and non-monotonic characteristics. At high temperatures, thermal runaway is triggered rapidly in the region close to the battery surface, where the chemical reactions are strongly coupled, and radiation plays a dominant role. In contrast, at lower temperatures, thermal runaway is triggered much more slowly and towards the core of the cell, where some chemical reactions may be decoupled, and pre-runaway chemical heat release plays an increasingly important role. The results presented here suggest that radiation can either facilitate or mitigate thermal runaway. The net radiation heat flux has a cross-over instant, beyond which radiation starts to retard thermal runaway. Additionally, the blocking effect in radiative heat transfer between cells arranged in equal-spacing homogenous or orthogonal arrangements in a battery pack is investigated, along with the effect of the hot spot size. Results from this work help understand the role of radiation in thermal runaway propagation and provide useful insights into the thermal runaway control and design of safe Li-ion battery packs. [ABSTRACT FROM AUTHOR]

According to accident databases, severe accidents, usually leading to catastrophic events, have originated from 50% of registered jet fires. This "domino effect" is usually caused by the high heat fluxes emitted from jet flames, and the flame impingement. This study analyses the thermal radiation emitted from partially premixed methane–air jet flames, obtained with volumetric fuel flows of 7 L/min, 8 L/min, and 9 L/min. The main geometrical features of the flames (lift-off distance, radiant flame length, and flame area) were obtained by analysing over 500 images, then used to calculate the parameters involved in the solid flame radiation model to determine the heat flux emitted. The view factor was calculated for finite areas, while emissivity was obtained by correlating the average flame diameter of each flame with a soot particle constant. The results obtained from the experiments clearly identify three general regions for the flame temperature and heat flux profiles, as a function of the flame's axial position. The maximum flame temperature and heat flux are reached in the second region, at approximately 73% of the flame's axial position. The geometric considerations used throughout the present work allowed for more accurate thermal radiation values in regard to other known techniques. [ABSTRACT FROM AUTHOR]

Copyright of Ingenius, Revista Ciencia y Tecnología is the property of Universidad Politecnica Salesiana and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Thermal interactions through longwave radiation exchange between buildings, especially in a dense urban environment, can strongly influence a building’s energy use and environmental impact. However, these interactions are either neglected or oversimplified in urban building energy modeling. We developed a new feature in EnergyPlus to explicitly consider this term in the surface heat balance calculations and developed an algorithm to batch calculating the surrounding surfaces’ view factors using a ray-tracing technique. We conducted a case study with a district in the Chicago downtown area to evaluate the longwave radiant heat exchange effects between urban buildings. Results show that the impact of the longwave radiant effects on annual energy use ranges from 0.1% to 3.3% increase for cooling and 0.3% to 3.6% decrease for heating, varying among individual buildings. At the district level, the total energy demand increases by 1.39% for cooling and decreases 0.45% for heating. We also observe the longwave radiation can increase the exterior surface temperature by up to 10 ◦C for certain exterior surfaces. These findings justify a detailed and accurate way to consider the thermal interactions between buildings in an urban context to inform urban planning and design.

The irradiance model is significant for accurately modelling the electrical and thermal performance of bifacial photovoltaic (bPV) modules, but existing irradiance models fail to be employed for bPV modules in a simple but reliable way. Therefore, this paper presented a concise and anisotropic irradiance model to predict the irradiance received by bPV modules, in which an improved view factor-based model was adopted to calculate the ground-reflected irradiance. In addition to its computational simplicity, the proposed model can satisfy the assumption of an anisotropic irradiance at both sides of the horizontal, tilted, and vertical bPV modules. Outdoor experiments were conducted to validate the proposed model under different conditions. Results show that the proposed model can well predict the irradiance of bPV modules placed above a concrete ground. The prediction errors of the front/rear/total irradiance are 7.1%/12.5%/6.1% and 11.9%/16.5%/8.7% for tilted and vertical bPV modules, respectively. In addition, the prediction performance decreases when a high-reflective ground made of aluminum foil is used. It is found that the albedo of the high-reflective ground will vary significantly on sunny days, mainly due to the incident-angle dependence of the ground reflection. Grounds with more diffuse reflections can improve the accuracy of the model's predictions. [ABSTRACT FROM AUTHOR]

In radiation heat transfer calculations, the view factor between surfaces is an element of vital importance. Currently, the available technical literature does not have an analytical expression that allows the view factor to be directly computed for combinations of triangular surfaces. An analytical view factor solution requires the addition of multiple integrals, given the changes in the integration contours, which makes it a complex task to obtain solutions for various configurations. This work aims to analytically develop the view factor expression for radiative heat transfer of 30 triangular geometries with common edge and included angle θ . To establish comparisons, twelve examples with several aspect ratios were calculated for each geometry, using the analytical solution (AS), the numerical solution of the quadruple integral using multiple Simpson's 1/3 rule with five intervals (MSR), the graphical solution given by Sauer (GS) and the view factors calculated using Bretzhtsov cross-roots. From the eight basic geometries, the view factor for another 22 triangular geometries is obtained, by means of the Summation Rule. In all cases, identical fit values of MSR and GS were obtained with respect to AS, while Bretzhtsov cross-root showed the best fit in all cases examined. Given the practical nature of the contribution and the reasonable values of adjustments obtained, the proposal is a suitable tool for application in thermal engineering and related practices that require thermal radiation calculations. [ABSTRACT FROM AUTHOR]

In a baking oven, radiation heat transfer is the most prevalent mode of heat exchange. In the present investigation, a new baking oven was designed with two hemi cylindrical domes (called reflectors) attached to the heating coils at the top and bottom of the baking oven. Firstly, view factors were computed by finite element and analytical methods with different bread dimensions, as well as with and without the reflectors. The network representative method and S2S method were employed to analyze the radiation energy transfer in the oven at different baking temperatures using the same bread sizes. The results obtained from numerical and analytical methods were fairly similar. The radiative heat energy absorbed by bread surface was higher with the reflector than without the reflector in the oven. As the number of obstructions increased, the radiative heat flux was reduced. The inclusion of reflector shield in oven affect the heat lux on the bread. The radiative heat flux received by bread was found to have increased on increasing the oven temperatures. Moreover, quality parameter such as the color of the bread with and without the reflectors were also examined. The oven reflector had a noticeable effect on the color of the bread (p < 0.05). Practical applications: In recent years, reducing energy consumption has become more important in the design of ovens. Although domestic electric ovens are a convenient way to bake quality goods, they have a very significant energy loss. Prior research has focused on CFD modeling for commercial ovens to assess the thermal behavior of the system and overall energy efficiency of baking. Baking ovens operate at higher temperatures, hence, heat transfer by radiation is highly essential. In reality, one or more surfaces in oven are obstructing the surfaces. To calculate view factors and achieve accurate radiative heat transfer in such cases, the shadow effect must be taken into account. To solve them precisely in this situation, numerical techniques are highly beneficial. [ABSTRACT FROM AUTHOR]

• Local view factor (VF) distributions were simulated across various building sizes using the S2S model. • A comprehensive VF formula applicable to 16 body segments was derived. • A novel and rapid VF calculation method has been validated against existing research results. • A VF calculation tool was developed with the potential to evaluate scenarios involving windows and radiant panels. In non-uniform environments, such as spaces with radiant ceilings or floors, or with hot or cold windows, view factors (VFs) of a person towards these surfaces are needed for calculating the heat exchanges between the person and the surroundings. Multi-body segmented human models can simulate the heat exchanges of individual body parts with the environment. Simulating heat transfer at the local body parts is important for assessing comfort in non-uniform environments. These models require VFs for each individual body part. Accurately determining these VFs is time-consuming, often requiring methods such as ray-tracing techniques. A fast calculation method to accurately determine the view factor (VF) for each segment has yet to be investigated. This study employed a 16-segment human model into various architectural radiation scenarios. The surface-to-surface model in computational fluid dynamics was utilized to simulate VFs for the 16 body segments in relation to radiant surfaces at different locations. Through a series of simulations, comprehensive formulas for VFs were derived for each individual at various positions within a room, encompassing 16 body segments and computing parameters for 24 building surfaces. The accuracy of these general formulas was validated by comparing the whole-body VF with results from several available studies. Additionally, this study developed a visualization tool for calculating VF and mean radiant temperatures with different room space dimension and embedded radiant surfaces. The users can use this online tool to easily calculate VFs and mean radiant temperatures for each body parts, and for the whole-body. The tool offers valuable insights for predicting thermal comfort in asymmetric radiant environments and facilitating control over building environments. [ABSTRACT FROM AUTHOR]

A view factor is a fundamental parameter for evaluating radiative heat transfer between two surfaces. View factors for various geometries have been investigated in the past studies. However, the view factors of a spheroid and an ellipse are known only for limited configurations. In this study, the analytical view factor expressions of an ellipse and a spheroid from a plate element are derived. The spheroid view factor solution applies to a plate element with any position and orientation, and the ellipse solution is valid when the plate element is on the perpendicular axis through the ellipse center. The derived analytical solutions are validated against the numerical results for various configurations, showing deviations of less than 0.0001 for all cases. • Spheroid and ellipse view factors from a plate element are derived analytically. • The derived analytical solutions are validated against the numerical results. • Besides the general solution, simple formulas are given for specific configurations. [ABSTRACT FROM AUTHOR]

Tailoring the properties of hot-stamped components offers the potential to enhance crash performance while simultaneously improving downstream joining processes. In recent years, an innovative technology suited for achieving tailored properties involving the utilization of a specialized furnace chamber, known as the TemperBox®, has been introduced. Within this chamber, a cooled aluminum mask shields specific areas of the blank from incoming heat radiation and concurrently absorbs the blank’s own radiation. The duration of the heat radiation exchange can influence the diffusion-dependent phase transformation and, consequently, the resulting mechanical properties. Hence, the intermediate cooling duration assumes a pivotal role as a parameter, as is investigated in this study. To examine the effects, specimens of the steel 22MnB5 AS150 are subjected to intermediate cooling of varying durations, followed by forming and partial quenching. The temperature profile of the blank during intermediate cooling prior to forming and quenching is analyzed. Subsequently, the tailored hot-stamped components are assessed for hardness, strength, ductility, and thickness strain. The study reveals that with increasing duration of partial intermediate cooling and targeted radiation exchange, a homogeneous ferritic–pearlitic structure is formed from an austenitic structure. This uniform structure of ferrite and pearlite is reflected in lower hardness and strength values, along with improved ductility. Additionally, this paper introduces a simulation methodology designed to calculate the dynamics of thermal radiation and the kinetics of phase transformation.

View factor calculation is an element of vital importance in radiation heat transfer. In engineering practice, it is common to find a radiant exchange between more complex configurations of emitting and receiving surfaces, which simultaneously include several configurations of perpendicular and parallel plane surfaces. Currently, the available technical literature does not have an analytical expression that allows the view factor to be directly computed for these combinations of surfaces. In these cases, the use of the summation and reciprocity techniques given by the superposition rule (SR) turns out to be very laborious. Therefore, this work aims to analytically develop the view factor expression for radiative heat transfer of 11 combinations between two arbitrary perpendicular or parallel rectangular surfaces in the 3-D space. The results obtained from the proposed method were compared with those computed by the Simpson's rule on Hottel's solution and the result of the quadruple integral using multiple Simpson's 1/3 rule with five intervals. Given the inexistence of similar antecedents in the literature, the proposed analytical solutions reinforce their scientific and practical value. [ABSTRACT FROM AUTHOR]

• The incidence angle effect (IAE) of bifacial PV modules considers both front-side beam radiation and rear-side reflection. • A mathematical model related to the rear-side incidence angle effect of bifacial PV modules was derived theoretically. • The effects of different installation conditions on the IAE of bifacial PV modules was simulated based on view-factor method. Improving the accuracy of performance evaluation of bifacial photovoltaic (PV) devices is critical to the development of bifacial PV technology. The incidence angle effect (IAE) is one of the characteristics related to the power generation of PV modules. Due to the ability of bifacial PV modules to collect light from double sides, the IAE evaluation should involve the effects of both the front and rear sides of PV simultaneously. This work aims to investigate the IAE of bifacial PV modules considering both front-side beam irradiation and rear-side reflection. The rear-side reflection makes the IAE of bifacial PV modules more complicated than that of monofacial PV modules. The rear-side IAE of bifacial PV modules was defined, and a corresponding mathematical model was derived theoretically in this work. A simulation model based on the view-factor method was developed to investigate the performance of bifacial PV modules under various incidence angles, whose validity was verified by indoor measurements. Furthermore, the results show that rear-side IAE is more suitable to be investigated with the simulation, and it is sensitive to the surrounding and installation conditions. The proposed method is applicable in evaluating and predicting the performance of bifacial PV modules related to IAE under different installation conditions. [ABSTRACT FROM AUTHOR]

Li-ion batteries play a key role in energy storage and conversion in engineering systems such as electric vehicles and grid energy storage, with critical impact on electrification and storage of renewable energy. A key unresolved technological challenge in Li-ion batteries pertains to thermal runaway initiation and propagation in a battery pack, which can lead to subsequent fire and explosion. Despite significant past work, there remains a critical need to understand how thermal runaway propagates in a pack. This work presents a comprehensive investigation of the effect of radiative heat transfer on thermal runaway propagation. Radiation can be important when a battery is exposed to adjacent heat and fire sources, as well as in thermal runaway propagation from one hot cell to another. A theoretical radiative heat transfer model based on view factor theory is developed. Calculations based on this model for a simple 2D cylinder-to-cylinder geometry are found to be in very good agreement with analytical expressions. Radiation-induced thermal runaway propagation between two cylindrical 18650 batteries is evaluated. It is shown that radiation may play a key role in thermal runaway propagation, depending strongly on the triggering temperature. It is found that radiative effects in thermal runaway propagation exhibit both nonlinear and non-monotonic characteristics. At high temperatures, thermal runaway is triggered rapidly in the region close to the battery surface, where the chemical reactions are strongly coupled, and radiation plays a dominant role. In contrast, at lower temperatures, thermal runaway is triggered much more slowly and towards the core of the cell, where some chemical reactions may be decoupled, and pre-runaway chemical heat release plays an increasingly important role. The results presented here suggest that radiation can either facilitate or mitigate thermal runaway. The net radiation heat flux has a cross-over instant, beyond which radiation starts to retard thermal runaway. Additionally, the blocking effect in radiative heat transfer between cells arranged in equal-spacing homogenous or orthogonal arrangements in a battery pack is investigated, along with the effect of the hot spot size. Results from this work help understand the role of radiation in thermal runaway propagation and provide useful insights into the thermal runaway control and design of safe Li-ion battery packs.

Studying the interplay between heat transfer mechanisms in a burning wildland fuel layer enables to better understand wildfire behavior. This works aims to assess the effect of air flowing through wildland fuels on the radiative properties of a small-scale flame produced with such fuels. Well-controlled flames are produced with Eucalyptus globulus leaves of reduced size imposing three increasing air flows in a small-scale configuration. Mass loss measurements are experimentally obtained and modeled to determine the mass loss rate of the fuel sample. The view factor between the flame and a radiometer is estimated with a contour technique, while color pyrometry is employed to retrieve soot temperature. View factor decreases with time at a larger rate than flame height. Radiation emitted by the flame decreases with time, while radiant fraction first reaches a peak and further decreases until extinction. View factor, thermal radiation and radiant fraction first decrease with air flow, then these variations are slight. The relation between normalized radiant fraction and flame height is independent of air flow. Soot temperature first increases with air flow, then remains almost unchanged. Therefore, smaller air flows through wildland fuels affect the radiant properties of a flame produced with these fuels, but larger flows might not exert this influence. [ABSTRACT FROM AUTHOR]

• Flame radiation heat transfer and heat flux of vehicle fires beneath a tunnel arced ceiling are studied. • The transverse flame extension length of an arched ceiling is less than that of a horizontal ceiling. • The flame extension length beneath the arced ceiling decreases as the burner aspect ratio increases. • A correlation is developed to characterize the flame extension length beneath an arced ceiling. • A cuboid-arc plate flame model is proposed to predict near-field radiative heat flux upon below surface of rectangular fires. As a major form of heat transfer, flame thermal radiation has an important effect on the ignition of adjacent energy, fire spread and environmental damage. Forecasting the flame radiation heat flux can provide theoretical basis for fire hazard assessment, fire extinguishing and salvation. Meanwhile, the distinctive structure of the arc tunnel can result in significant variations in the local heat and mass transfer processes during tunnel fires compared to those in rectangular tunnels, leading to different fire characteristics parameters. In this study, experiments and theoretical analyses were conducted to investigate the flame length scale and near-field radiation heat flux on the lower surface of an arc-shaped ceiling induced by vehicle fires in a tunnel. The findings reveal that the flame length scale in the transverse direction beneath the arc-shaped ceiling decreases with an increasing burner aspect ratio and increases with the increasing heat release rate. A dimensionless model of the flame length scale under the arced ceiling with various burner aspect ratios was proposed based on the amount of remaining unburned fuel after flame impingement and the buoyancy component along the arc-shaped ceiling. Simultaneously, radiative heat fluxes on the lower surface also increase with rising heat release rate. The flame geometry beneath the arc-shaped ceiling is assumed to be a combination of a cuboid and an arc plate model based on the actual flame length scale. Subsequently, the view factor, radiative fraction, and flame surface area are analyzed to predict the radiative heat fluxes on the lower surface. The predictions of the cuboid and arc plate flame model show good agreement with the current experimental data. This work presents a dimensionless correlation of the flame length scale and calculates the view factor between the target and the arc plate to predict the near-field radiative heat flux more accurately. This approach also facilitates the understanding of flame spreading behavior and thermal hazards impacted by arced ceiling. [Display omitted] [ABSTRACT FROM AUTHOR]

The concept behind agrivoltaics, the use of photovoltaics (PV) with agriculture to simultaneously produce electric power and food, was first introduced by Goetzberger and Zastrow (1982) (GZ), who developed models for shading effects of fixed, opaque, monofacial PV panels on beam and diffuse solar radiation reaching the ground. This article has been cited by many since 2000. However, since then nearly all authors of related papers that cited GZ have not adopted the GZ models. Instead, ray-tracing and other methods have been used in custom computer codes. The reasons might be rooted in limitations of GZ assumptions or the need for algorithms to accommodate individual experiments and systems. Another may be lack of a complete expression for a key angle in the shadowing problem and an integral expression for diffuse solar fraction that produces suspicious results in GZ. In this work we provide a simpler, complete, and validated model for the diffuse solar fraction, add insight into the interactions between a panel and its neighbors, and the number of PV panels needed through shadowing to reach an asymptotic value. By normalizing the problem, plots of diffuse and beam solar fractions are enabled that form the basis of simple tools useful for first-order estimates in design. A design case study is presented against which results of the current work are favorably compared. [Display omitted] • Diffuse & beam solar fractions for stationary photovoltaic (PV) array considered • A complete and validated model for diffuse solar fraction at ground presented • Interactions with PV panel and neighbors show 20 neighboring PVs needed in model • Diffuse solar fraction is practically independent of PV panel support height • Polynomials of diffuse solar fraction depends only on panel height/spacing and panel slope • Normalization enables simple design tool plots for diffuse and beam solar fractions [ABSTRACT FROM AUTHOR]

Mean radiant temperature (MRT) is an indispensable physical parameter of indoor thermal environments. Especially in indoor environments controlled by radiant systems, MRT plays an important role in thermal comfort. In order to determine MRT of indoor environments controlled by radiant cooling systems quickly and inexpensively, a numerical program is developed in this study. Based on the finite element method (FEM), view factors and radiant temperature fields are numerically calculated. The singular solution problem generated by FEM is corrected using the Monte Carlo method. The numerical program is validated against the results of an experiment performed in a radiant cooling laboratory and the reported data from previous studies. Then radiant temperature fields of different shaped surfaces in a radiant cooling indoor environment are predicted, and thermal comfort level is preliminarily evaluated. [ABSTRACT FROM AUTHOR]

In solar PV fields, solar photovoltaic panels are typically arranged in parallel rows one after the other. This arrangement introduces variations in the distribution of solar irradiance over the entire field, compared to measurements recorded at meteorological weather stations and data obtained from climatic database platforms. This is due to the difference in the view factors between the rows of the solar PV field and a single surface, as well as the presence of shade on rear sides and in the space separating the rows. These phenomena combined will reduce the intensity of solar irradiance incident on the PV solar field; consequently will reduce the energy yields. Accurate estimation of solar radiation on solar fields requires knowledge of the sky, ground, and rear side of the preceding row view factors, and an estimation of the time and space occupied by the row’s shadow. Prior literature has addressed this issue using two-dimensional (2-D) techniques such as the crossed-strings method (CSM). This study developed a novel three-dimensional (3-D) analysis in addition to numerical analysis to determine the view factors associated with solar fields. The study uses both isotropic and anisotropic transposition analyses to determine solar irradiance incident on the solar field with varying tilt angles of solar panels and distance separating the rows (distance aspect ratio) for several latitudes. The present research also tested the validity of the CSM for wide ranges of distance separating rows and length aspect ratios, the obtained results show that the CSM shows good agreements in both sky and ground view factor in the range of length aspect ratio greater than one. But the CSM fails in rear-side view factor in the design ranges of PV solar fields, where the error rate was found about 11%, this result is important in the case of bifacial PV solar systems. Also, the present work compared the solar irradiance calculated for a single surface with that incident on a PV solar field for wide range of sky conditions and latitudes. The obtained results ensure the accuracy of using the solar irradiance incident on a single surface data for low latitudes and for most sky conditions for PV rooftop solar systems as well as PV solar fields. While it has remarked a large error in the case of cloudy skies, where the error rate exceeded 17% in the case of aspect ratio equals to 1.5 and about 15.5% in the aspect ratio of 2.0.

The extent of fire spread by radiation is delimited by separation distances, required to prevent external fire spread due to excessive radiation heat or falling burning brands. The simplified calculation method uses a series of precalculated tabulated values. Alternatively, a more precise analytical calculation approach can be used. The resolution of the method can determine the required separation distances significantly. This paper evaluates analytical calculation methods and CFD simulations to determine their accuracy of separation distances prediction. The most appropriate are standard analytical calculation methods with sufficient number of evaluation points along the radiating surface.

In a laser-induced breakdown spectroscopy (LIBS) system that performs elemental analysis of a target by acquiring the emission of plasma generated on the material surface by a focused laser, the plasma signal may be affected by the flow of the surrounding gas. A flow of gas may be present when LIBS measurements are performed in a special environment where an inert gas is normally applied. In such an environment, the flow of gas may affect the intensity of emission generated in plasma. The LIBS spectral intensity in the gas flow field changes according to the direction of the gas flow and the signal detector of the LIBS. In this case, the correlation between the flow rate and intensity of the spectral line can be confirmed both theoretically and experimentally. In this study, changes in the signal according to the flow rate were theoretically evaluated using the view factor and wave equation. In addition, LIBS signals were examined based on the flow of Ar, N2, and He gases in the experiment. The experimental results confirmed the range of effective gas flow rates over which the correlation between the flow rate and intensity of the LIBS spectral line could be inferred. These results could be used for calibration to achieve accurate measurement of LIBS signals in gas flow fields. In addition, this analysis has the potential to shed light on the properties of flowing gases that affect plasma by reversibly tracking changes in the signal of LIBS in a confined environment. [ABSTRACT FROM AUTHOR]

It's an unsolved problem to calculate the thermal radiation view factors among fuel pebbles as accurately and quickly as possible in the simulation of the temperature fields within the pebble-bed. In this study, a series of fully connected neural networks (FCNs) has been developed to realize the fast calculation of view factors. In order to verify the accuracy and effects of the networks, the neural networks are compared with the Monte Carlo (MC) algorithm. The results show that, in most cases, the relative errors of the FCN method can be controlled within 1.0%, and the prediction accurate probability is up to 99%. In comparisons of specific examples, the temperature errors of the FCN method and the MC method are less than 1 K within the range neural networks have covered. In addition, the time of neural networks for a single calculation is about 2-20 µs, which is even less than 10-4 of the time taken by the MC algorithm. In conclusion, neural networks can greatly improve computational efficiency while keeping the same accuracy as the MC algorithm, which makes real-time simulation of the temperature fields possible. [ABSTRACT FROM AUTHOR]

The ability to calculate the radiation view factor from a tubular microalgae photobioreactor plant to the sky is needed to accurately predict the broth temperature in it, because the calculation of diffuse solar radiation in a heat transfer model for determining the broth temperature requires the view factor. A calculus-based method has been proposed previously for calculating the view factor that consists of multiple horizontal tubes arranged in multiple equally spaced vertical walls. In this paper, a new method for calculating the view factor is developed. Compared with the previous method, the new method requires elementary mathematical operations only, and both equally spaced and nonequally spaced cases are considered. The effects of six main design parameters (number of photobioreactors, number of tubes in a wall, outer radius of tubes, distance between two photobioreactors, distance between two walls of a single photobioreactor, and outer distance between two neighboring tubes within a wall) on the view factor are then assessed, and some suggestions are made on how to select these parameters when designing an outdoor tubular microalgae photobioreactor plant. [Display omitted] • Calculating the view factor from tubular microalgae photobioreactor plants to the sky. • A new calculation method based on elementary mathematics is developed. • Both the arrangement of equally and nonequally spaced vertical walls are considered. • Only about 20% of diffuse solar radiation strikes the surface of the photobioreactor plants. [ABSTRACT FROM AUTHOR]

East/West (E/W) vertical bifacial photovoltaic (PV) modules can achieve higher profits than the conventional North/South (N/S) tilted configuration depending on the design choices and external conditions. In this study a model based on 2D view factor concept is developed to estimate the power generated by a large-scale bifacial PV farm, considering the non-uniformity of the incident irradiance and the spectral impact. A validation using measured data is performed, focusing on the non-uniformity of the rear irradiance. This model is used to compare the profitability between E/W vertical and N/S tilted PV farm configurations, considering higher prices during noon with respect to morning/evening periods. The results identify the ratio between these two price values as the key variable that influences the comparison between the PV farm configurations. Specifically, a sufficiently high price ratio ensures the higher profitability of E/W vertical modules, however, the exact value is dependent on the location and the design variables. In general, higher row-to-row distance and lower diffuse fraction enhance the profitability of the E/W vertical over the N/S tilted configuration. On the other hand, elevation of the modules, curtailment strategies and hybrid solutions have a minor influence. • The model simulates the performance of bifacial photovoltaic farms. • The profitability of vertical bifacial modules depends on the design parameters. • The electricity market conditions influence the profitability of vertical modules. • Large daily price differences are favourable for vertical modules. • Vertical modules are favourable in locations characterized by low diffuse fraction. [ABSTRACT FROM AUTHOR]

Radiative heat transfer is the most effective mechanism of energy transport inside buildings. One of the methods capable of computing the radiative heat transport is based on the system of algebraic equations. The algebraic method has been initially developed by mechanical engineers for wide range of thermal engineering problems. The first part of the present serial paper describes the basic features of the algebraic model and illustrates its applicability in the field of building physics. The computations of radiative heat transfer both in building enclosures and also in open building envelopes are discussed and their differences explained. The present paper serves as a preparation stage for the development of a more general model evaluating heat losses of buildings. The general model comprises both the radiative and convective heat transfers and is presented in the second part of this serial contribution.

In this paper, a precise method for calculating albedo and IR heat flux applied to a satellite is presented. For obtaining albedo heat flux applied to a satellite, a point on the earth’s surface that sun flux reflected at that point and reach to the satellite is obtained, hence albedo heat flux reaches to a satellite is obtained as a function of longitude, attitude and longitude. IR heat flux is integration of emitting heat flux for points on the earth surface that in satellite’s view. Atmospheric transparency for calculating albedo and IR heat is considered for sun light and IR spectrum using MODTRAN algorithm using PcModWin software. For a generic LEO satellite, IR and albedo heat fluxes are calculated at a time period and compare with reference values. Obtained heat fluxes are used to obtain temperature variation of satellite’s components during its mission.

This paper recounts an historical record of the origins of bifacial PV modelling in the years between 1983 and 1989. Associated to the first industrial production of bifacial PV modules, that took place in 1984, PV modelling was developed by completing the three stages of an engineering modelling path: model development, experimental validation and application in practical designs. This took place over two distinguishable stages. In the first stage, the mathematical foundations, based on the "view factor" concept and an application procedure, based on calculating the so-called albedo and sky maps were established and applied to the PV generators with only a ground reflector surface. In the second stage, an additional mathematical twist lead to solving the problem of multiple reflector surfaces, and different practical configurations were analyzed. As PV modules were expensive at that time, it was economically sensible to consider PV arrays made up of rows of modules with a module-to-module separation between the modules of the same row. That led to the development of 3D models. Experimental values of rear irradiance were compared with modeled ones, using the global horizontal irradiance and direct irradiance values given by a pyranometer and a pyrheliometer respectively as input. The theoretical ratio between the daily front and rear irradiations was within 3% of the determined experimental value. This is the same as the accuracy in standard tilted surface irradiation predictions. [ABSTRACT FROM AUTHOR]

This paper develops an incident energy-based model for fixed multi-row bifacial PV systems considering ground albedo and different configuration parameters, including the inclination (tilt) and orientation angles, the height off the ground, and the horizontal distance between PV rows. The various view factors (VFs) involved in the study, sky model, and the angular position of the sun are included in the model. The proposed analytical model is capable of evaluating the solar irradiance reaching each side of a bifacial PV array at any time and location. The impacts of the configuration parameters on the total energy achievable on the front and back surfaces are studied in detail. Finally, simulations are performed on the IEEE 69-bus test network to show how bifacial PVs can help tackle the Duck curve issue caused by conventional mono-facial PVs. [ABSTRACT FROM AUTHOR]

One of the prerequisites for a reliable energy yield prediction of bifacial photovoltaic (PV) systems is the capability of modeling the backside irradiance of those systems with high accuracy. Currently, the most important optical models used to quantify the reflected irradiance on the backside of a bifacial solar panel are view factor and ray tracing. The MoBiDiG simulation tool has been developed at ISC Konstanz uses the view factor (VF) concept to model the rear irradiance. In addition to the VF concept, ray tracing (RT) has been adopted to determine the backside irradiance of bifacial modules by using the open‐source tool bifacial_radiance that has been developed by the National Renewable Energy Laboratory (NREL). A customized monocrystalline silicon solar panel has been built in order to evaluate the accuracy of the existing optical models by locally resolved rear irradiance measurement. The performance of rear irradiance has been investigated along the rows of the customized PV module during sunny and cloudy days with typical back irradiance values of ≈ 50 and ≈150W/m2. The comparison of measured and modeled data has been carried out on hourly, daily, and monthly basis, and the results show lower deviations for solar cells located in the center of the PV module than on the edge. Moreover, the concept of decisive solar cells has been introduced and applied to both measured and modeled data, solar cells located in the center rows were found to act as the most decisive solar cells. Finally, considering the installation configuration studied here, ie, bifacial mounting with low clearance height (below 0.2 m), both hourly RT and VF approaches are able to model long‐term cumulative irradiance received by decisive solar cells with a very high accuracy ranging from ± 0.5% to ± 2%. [ABSTRACT FROM AUTHOR]

• A complete radiation heat transfer model s developed for receiver tube. • Contour integration technique and analytical methods are used to obtain View factor. • Gebhart factor is used for modeling all modes of radiation heat transfer. • RMSE of View factor algebra is obtained as 5.5394e-5. • Efficiencey and heat loss estimation have RMSE of 0.6035 and 4.5996 W/m2. • Proposed model is the best among all the four models compared. Solar Parabolic Trough Collectors (PTC) are alternative clean solution for the thermal power plants to generate electricity and thermal energy. It can be configured to support small, medium and high temperature applications. In PTC, solar radiation is concentrated to a pipe coated selectively and enclosed in a glass tube with vacuum maintained in the annulus, through which a heat transfer fluid is circulated. Heat transfer analysis of PTC is important to determine the operating characteristics as well as for optimization of the parameters under different operating conditions. In this paper a heat transfer model is developed for receiver tube with the focus on a complete radiation heat transfer model for the annulus. For the analysis the receiver tube is divided into severe elements where the governing energy equations are discretized using Finite Volume Method. Gerhart factor is used for modelling the radiation heat transfer. View factors are computed using contour integration technique and analytical solutions. Heat transfer results are then validated with the test results obtained from Sandia National Laboratory. The results obtained show close agreement with the test results. Also the result is compared with other four published models. Based on the RMSE analysis, it is proven that our model is the best among all the four models compared. [ABSTRACT FROM AUTHOR]