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Artykuły w czasopismach na temat "Radiative Heat Flux Rate"
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Cheung, C. S., C. W. Leung i T. P. Leung. "Modelling Spatial Radiative Heat Flux Distribution in a Direct Injection Diesel Engine". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 208, nr 4 (listopad 1994): 275–83. http://dx.doi.org/10.1243/pime_proc_1994_208_048_02.
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In this paper, the spatial distribution of radiative heat flux from a luminous flame to various positions on the cylinder head of a direct injection diesel engine is modelled and the results compared with some published experimental investigations. The model is primarily based on measured pressure data, which are converted into fuel-burned rate data through a single-zone heat-release rate analysis. Coupled with appropriate soot formation and oxidation models, the fuel-burned rate data are converted into the soot contents in the cylinder. By separating the combustion chamber into a burned zone and an unburned zone, the radiation temperature, the absorption coefficient and the spatial distribution of radiative heat flux to the cylinder walls are calculated.
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Zhang, Chong, Zhongnong Zhang i Chun Lou. "Thermodynamic Irreversibility Analysis of Thermal Radiation in Coal-Fired Furnace: Effect of Coal Ash Deposits". Materials 16, nr 2 (13.01.2023): 799. http://dx.doi.org/10.3390/ma16020799.
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In this paper, a three-dimensional (3-D) high-temperature furnace filled with a gas-solid medium was investigated, and the radiative transfer equation and the radiative entropy transfer equation in the chamber were applied in order to analyze the effect of coal deposits on thermal radiation. The heat flux on the walls of the furnace and the entropy generation rate were determined due to the irreversibility of the radiative heat transfer process in the furnace. Furthermore, the effect of ash deposits on the wall surface on the irreversibility of the radiation heat transfer process was investigated. The numerical results show that when burning bituminous and sub-bituminous coal, ash deposits in the furnace led to a 48.2% and 63.2% decrease in wall radiative heat flux and a 9.1% and 12.4% decrease in the radiative entropy rate, respectively. The ash deposits also led to an increase in the entropy generation number and a decrease in the thermodynamic efficiency of the radiative heat transfer process in the furnace.
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Budaev, Bair V., i David B. Bogy. "The role of EM wave polarization on radiative heat transfer across a nanoscale gap". Journal of Applied Physics 132, nr 5 (7.08.2022): 054903. http://dx.doi.org/10.1063/5.0094382.
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This work presents a novel study of radiative heat transfer between closely separated plates based on an extension of Planck’s spectrum of thermal radiations to systems with a steady heat flux. This extension together with electromagnetic wave theory is chosen specifically to avoid the commonly used so-called fluctuation dissipation theory, which is also limited to equilibrium systems. The spectrum of thermal radiation with a heat flux is described by the introduction of an analog of a chemical potential, which creates a bias toward the direction of heat transfer. This is the first comprehensive study of radiative heat transfer based on the generalization of Planck’s spectrum for systems with a heat flux, which eliminates contradictions arising when a heat flux is described in terms of the laws limited to equilibrium systems. The total heat flux is split into fluxes carried by waves with different frequencies, directions of propagation, and polarizations. This simplifies the analysis because due to the stochastic independence, the energy fluxes of such waves are additive, and this also reveals that the heat carrying capacity of radiation with the parallel polarization is significantly higher than that of the perpendicularly polarized radiation. This suggests that the rate of radiative heat transfer may be noticeably increased by the control of the polarization of thermal radiation.
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Liu, L. H., i S. X. Chu. "On the Entropy Generation Formula of Radiation Heat Transfer Processes". Journal of Heat Transfer 128, nr 5 (21.10.2005): 504–6. http://dx.doi.org/10.1115/1.2190695.
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Because thermal radiation is a long-range phenomenon, the local radiative heat flux is dependent on the temperature distribution of the entire enclosure under consideration and is not determined by the local temperature gradient. In the community of heat transfer, traditionally, the conduction-type formula of entropy generation rate is used to calculate the entropy generation rate of radiation heat transfer. In the present study, three counterexamples are considered. The discrete ordinates method is employed to solve the radiative transfer equation and then solve the radiative entropy generation rate. The results show that the traditional formulas of entropy generation rate for heat transfer generally cannot be used to calculate the local entropy generation rate of radiation heat transfer. Only in optically extremely thick situations, the traditional formula of entropy generation rate for heat transfer can be approximately used to calculate the local entropy generation rate of radiation heat transfer.
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Liu, Cheng, Evgeni Fedorovich, Jianping Huang, Xiao-Ming Hu, Yongwei Wang i Xuhui Lee. "Impact of Aerosol Shortwave Radiative Heating on Entrainment in the Atmospheric Convective Boundary Layer: A Large-Eddy Simulation Study". Journal of the Atmospheric Sciences 76, nr 3 (1.03.2019): 785–99. http://dx.doi.org/10.1175/jas-d-18-0107.1.
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AbstractEntrainment is critical to the development of the atmospheric convective boundary layer (CBL), but little is known about how entrainment is impacted by the aerosol radiative effect. An aerosol radiation transfer model is used in conjunction with large-eddy simulation (LES) to quantify the impact of aerosol shortwave radiative heating on entrainment and thermodynamics of an idealized dry CBL under aerosol-loading conditions. An entrainment equation is derived within the framework of a zero-order model (ZOM) with the aerosol radiative heating effect included; the equation is then examined against the LES outputs for varying aerosol optical depths (AODs) and free-atmosphere stratification scenarios. The results show that the heat flux profiles become more nonlinear in shape as compared to the case of the clean (no aerosol pollution) CBL, with the degree of nonlinearity being highly dependent on the AOD of the layer for the given type of radiation-absorbing aerosols. As AOD increases, less solar radiation reaches the surface and thus the surface heat flux becomes smaller, and both actual (LES) and ZOM-derived entrainment flux ratios decrease. This trend is opposite to the clean CBL where the LES-predicted flux ratios show an increasing trend with diminishing surface heat flux, while the ZOM-calculated flux ratio remains constant. The modified dimensionless entrainment rate closely follows the −1 power law with a modified Richardson number. The study suggests that including the aerosol radiative effect may improve numerical air quality predictions for heavy-air-pollution events.
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Hayat, T., M. Waleed Ahmed Khan, M. Ijaz Khan i A. Alsaedi. "Nonlinear radiative heat flux and heat source/sink on entropy generation minimization rate". Physica B: Condensed Matter 538 (czerwiec 2018): 95–103. http://dx.doi.org/10.1016/j.physb.2018.01.054.
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GODBOLE, RV, i RR KELKAR. "Net Terrestrial Radiative Heat Fluxes over India during Monsoon". MAUSAM 20, nr 1 (30.04.2022): 1–10. http://dx.doi.org/10.54302/mausam.v20i1.5421.
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Infrared radiative heat flux and instantaneous rate of temperature change have been computed for Indian, subcontinent for monsoon season by making use of the numerical method developed for the purpose. The effects of water Vapour alone have been considered. It is found that the radiative beat loss near the surface is minimum over the Western Ghats. Over northeast and northwest India, the radiative heat loss is relatively high. Also, the radiative cooling integrated from the surface upto 300 mb indicates a large cooling over northeast and northwest India (>loC per day) and relatively small cooling over the southern Peninsula ( <0.25°C per day). Analysis of the day to day values of net flux and temperature suggest no cause-and-effect relationship. However, a good correspondence has been noticed between net flux, temperature and total moisture content as far as surface level is concerned. The day to day values of net flux at higher levels follow very closely to those at the surface.
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Palesskiy, F. S. "Numerical Study of Combustion Regimes and Heat Radiation of Cylindrical Porous Burner". Key Engineering Materials 685 (luty 2016): 94–98. http://dx.doi.org/10.4028/www.scientific.net/kem.685.94.
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Temperature and radiative characteristics of different regimes of premixed gas combustion in porous cylindrical burner are investigated numerically. Two-temperature thermal diffusion model with radiative heat transfer and external radiative heat losses described in the framework of Eddington model is applied. It is found that two different combustion regimes can be realized under the same mixture equivalence ratio and flow rate depends on ignition conditions. It is shown that total radiative heat flux from the external surface of the burner and burner’s radiative efficiency strongly depend on the combustion regime.
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Narahari, Marneni, i Noorhana Yahya. "Effects of Time Dependent Temperature and Thermal Radiation on Free Convection Flow in Unsteady Couette Motion". Applied Mechanics and Materials 249-250 (grudzień 2012): 15–21. http://dx.doi.org/10.4028/www.scientific.net/amm.249-250.15.
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The effect of thermal radiation on free convection flow in unsteady Couette motion between vertical parallel plates has been investigated subject to a time dependent temperature boundary condition at the moving plate. Rosseland diffusion approximation is used to describe the radiative heat flux in the energy equation. Analytical solutions of the dimensionless governing equations are derived using the Laplace transform technique. The velocity and temperature profiles are shown on graphs, the variation of skin-friction, Nusselt number, volume flow rate and vertical heat flux are presented in tabular form. The effects of system parameters such as Grashof number, radiation parameter and time on the flow fields have been discussed in detail.
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Dupuy, J. L., i J. Maréchal. "Slope effect on laboratory fire spread: contribution of radiation and convection to fuel bed preheating". International Journal of Wildland Fire 20, nr 2 (2011): 289. http://dx.doi.org/10.1071/wf09076.
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Two series of 16 and 18 laboratory fire experiments were conducted to explore the respective roles of radiation and convection heat transfer in slope effect on fire spread. The first series attempts to measure fuel temperature and gas temperature simultaneously and at the same location using an infrared camera and thermocouples respectively. The second series measures the incident radiant heat flux as would be received by a small fuel bed volume ahead of the fire line. These measurements are used to compute a fuel bed heat balance for each slope angle (0°, 10°, 20° and 30°). Overall, radiative heating is found to be the heat transfer mechanism that dominates in the slope effect between 0° and 20°, but close to the fire line (<10 cm), the flux due to convective heating is also significant, reaching one-third of the net heat flux at a 20° slope angle. When the slope angle increases from 20° to 30°, the rate of spread rises by a factor of 2.5 due to a marked increase in convective heating, while radiative heating no longer increases. Far from the fire line, cooling by convection is found to be substantial except at the 30° slope angle.
Rozprawy doktorskie na temat "Radiative Heat Flux Rate"
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Liu, Xianglei. "Tailoring thermal radiative properties and enhancing near-field radiative heat flux with electromagnetic metamaterials". Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54960.
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All substances above zero kelvin temperature emit fluctuating electromagnetic waves due to the random motions of charge carriers. Controlling the spectral and directional radiative properties of surfaces has wide applications in energy harvesting and thermal management. Artificial metamaterials have attracted much attention in the last decade due to their unprecedented optical and thermal properties beyond those existing in nature. This dissertation aims at tailoring radiative properties at infrared regime and enhancing the near-field radiative heat transfer by employing metamaterials. A comprehensive study is performed to investigate the extraordinary transmission, negative refraction, and tunable perfect absorption of infrared light. A polarizer is designed with an extremely high extinction ratio based on the extraordinary transmission through perforated metallic films. The extraordinary transmission of metallic gratings can be enhanced and tuned if a single layer of graphene is covered on top. Metallic metamaterials are not the unique candidate supporting exotic optical properties. Thin films of doped silicon nanowires can support negative refraction of infrared light due to the presence of hyperbolic dispersion. Long doped-silicon nanowires are found to exhibit broadband tunable perfect absorption. Besides the unique far-field properties, near-field radiative heat transfer can be mediated by metamaterials. Bringing objects with different temperatures close can enhance the radiative heat flux by orders of magnitude beyond the limit set by the Stefan-Boltzmann law. Metamaterials provide ways to make the energy transport more efficient. Very high radiative heat fluxes are shown based on carbon nanotubes, nanowires, and nanoholes using effective medium theory (EMT). The quantitative application condition of EMT is presented for metallodielectric metamaterials. Exact formulations including the scattering theory and Green’s function method are employed to investigate one- and two-dimensional gratings as well as metasurfaces when the period is not sufficiently small. New routes for enhancing near-field radiative energy transport are opened based on proposed hybridization of graphene plasmons with hyperbolic modes, hybridization of graphene plasmons with surface phonon modes, or hyperbolic graphene plasmons with open surface plasmon dispersion relation. Noncontact solid-state refrigeration is theoretically demonstrated to be feasible based on near-field thermal radiation. In addition, the investigation of near-field momentum exchange (Casimir force) between metamaterials is also conducted. Simultaneous enhancement of the near-field energy transport and suppress of the momentum exchange is theoretically achieved. A design based on repulsive Casimir force is proposed to achieve tunable stable levitation. The dissertation helps to understand the fundamental radiative energy transport and momentum exchange of metamaterials, and has significant impacts on practical applications such as design of nanoscale thermal and optical devices, local thermal management, thermal imaging beyond the diffraction limit, and thermophotovoltaic energy harvesting.
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Phillips, Bren Andrew. "Nano-engineering the boiling surface for optimal heat transfer rate and critical heat flux". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/76536.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 130-133).
The effects on pool boiling characteristics such as critical heat flux and the heat transfer coefficient of different surface characteristics such as surface wettability, roughness, morphology, and porosity are not well understood. Layer-by-layer nanoparticle coatings were used to modify the surface of a sapphire heater to control the surface roughness, the layer thickness, and the surface chemistry. The surface was then tested in a water boiling test at atmospheric pressure while imaging the surface with high speed infrared thermography yielding a 2D time dependent temperature profile. The critical heat flux and heat transfer coefficient were enhanced by over 100% by optimizing the surface parameters. It was found that particle size of the nanoparticles in coating, the coating thickness, and the wettability of the surface have a large impact on CHF and the heat transfer coefficient. Surfaces were also patterned with hydrophobic "islands" within a hydrophilic "sea" by coupling the Layer-by-layer nanoparticle coatings with an ultraviolet ozone technique that patterned the wettability of the surface. The patterning was an attempt to increase the nucleation site density with hydrophobic dots while still maintaining a large hydrophilic region to allow for rewetting of the surface during the ebullition cycle and thus maintaining a high critical heat flux. The patterned surfaces exhibited similar critical heat fluxes and heat transfer coefficients to the surfaces that were only modified with layer-by-layer nanoparticle coatings. However, the patterned surfaces also exhibited highly preferential nucleation from the hydrophobic regions demonstrating an ability to control the nucleation site layout of a surface and opening an avenue for further study.
by Bren Andrew Phillips.
S.M.
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Sopkin, Kristin L. "Heat fluxes in Tampa Bay, Florida". [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002398.
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Beaulieu, Patricia. "Flammability Characteristics at Heat Fluxes up to 200 kW/m2 and The Effect of Oxygen on Flame Heat Flux". Digital WPI, 2005. https://digitalcommons.wpi.edu/etd-dissertations/427.
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"This dissertation documents two interrelated studies that were conducted to more fundamentally understand the scalability of flame heat flux. The first study used an applied heat flux in the bench scale horizontal orientation which simulates a large scale flame heat flux. The second study used enhanced ambient oxygen to actually increase the bench scale flame heat flux itself. Understanding the scalability of flame heat flux more fully will allow better ignition and combustion models to be developed as well as improved test methods. The key aspect of the first study was the use of real scale applied heat flux up to 200 kW/m2. An unexpected non-linear trend is observed in the typical plotting methods currently used in fire protection engineering for ignition and mass loss flux data for several materials tested. This non-linearity is a true material response. This study shows that viewing ignition as an inert material process is inaccurate at predicting the surface temperature at higher heat fluxes and suggests that decomposition kinetics at the surface and possibly even in-depth may need to be included in an analysis of the process of ignition. This study also shows that viewing burning strictly as a surface process where the decomposition kinetics is lumped into the heat of gasification may be inaccurate and the energy balance is too simplified to represent the physics occurring. The key aspect of the second study was direct experimental measurements of flame heat flux back to the burning surface for 20.9 to 40 % ambient oxygen concentrations. The total flame heat flux in enhanced ambient oxygen does not simulate large scale flame heat flux in the horizontal orientation. The vertical orientation shows that enhanced ambient oxygen increases the flame heat flux more significantly and also increases the measured flame spread velocity."
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Burchfield, Nicole Ashley. "Narrow Angle Radiometer for Oxy-Coal Combustion". BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8423.
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A new method of power production, called pressurized oxy-fuel combustion, burns coal with CO2 and oxygen, rather than air, bringing us closer to the end goal of developing zero emission coal-fired utility boilers. However, high-pressure, high-temperature systems such as these are under-studied, and their behavior is difficult to measure. An accurate model for previously untested conditions requires data for validation. The heat release profile of flames and their radiative intensity is one of the key data sets required for model validation of an oxy-coal combustion system. A radiometer can be used to obtain the necessary radiative heat flux data. However, several studies show significant measurement errors of past radiometer designs. This work focuses on developing a narrow angle radiometer that can be used to describe radiative heat transfer from a pressurized oxy-coal flame. The sensitivity of the instrument to outside environmental influences is thoroughly examined, making it possible to obtain the axial radiative heat flux profile of the flame in a 100kW pressurized facility by accurately converting the measured quantities into radiative heat flux. Design aspects of the radiometer are chosen to improve the accuracy of radiative heat flux measurements as well as conform to the physical constraints of the 100kW pressurized facility. The radiometer is built with a 0.079-inch aperture, an 8.63-inch probe internally coated with high emissivity coating, four baffles spaced evenly down the length of the probe, no optic lens, a thermopile as the sensor, argon purge gas, and a water-cooled jacket. The radiometer has a viewing angle of 1.33 degrees. The instrument is calibrated with a black body radiator, and these calibration data are used in combination with radiation models to convert the radiometer signal in mV to radiative heat flux in kW/m2. Environmental factors affecting accuracy are studied. The results of the calibration data show that the radiometer measurements will produce a calculated heat flux that is accurate to within 5.98E-04 kW/m2.
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Baud, Germain. "Conception de récepteurs solaires à lit fluidisé sous flux radiatif concentré". Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0106/document.
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L'objectif de ce travail est d’évaluer le positionnement et le potentiel des récepteurs à lit fluidisé à changement de section par rapport aux autres méthodes de chauffage de gaz à haute température par voie solaire. A cette fin, une connaissance approfondie des phénomènes thermiques et hydrodynamiques du récepteur est nécessaire. Pour acquérir cette connaissance, nous avons modélisé les transferts thermiques dans le récepteur en portant une attention particulière sur les transferts radiatifs en prenant en compte les diffusions multiples de la lumière dans le milieu particulaire, les effets de parois sur les transferts radiatifs et la directionnalité du rayonnement solaire concentré. La détermination précise de la distribution de particules dans le ciel du lit fluidisé s'est avérée un paramètre critique pour le calcul des transferts thermiques. Ces modèles, plus tard affinés par une confrontation avec des références expérimentales, nous ont permis d'explorer l'effet de la géométrie sur les transferts thermiques dans le récepteur. Il ont permis entre autres de mettre en évidence l'intérêt d'utiliser une colonne de fluidisation à changement de section et l'importance de l'optimisation du couple concentrateur solaire / récepteur afin d'éviter d'éventuelles surchauffes au niveau des parois du récepteur. De même, il semble que l'homogénéisation de la température dans le lit fluidisé contenu dans le récepteur soit favorable à son rendementThe aim of this work is to evaluate the position and the potential of solar fluidized bed receivers compared to other methods for the solar heating of gases at high temperature. To this end, a thorough knowledge of the heat transfer and hydrodynamic of the receiver is necessary. To acquire this knowledge, we modeled the heat transfer in the receiver with a focus on the radiative transfer by taking into account the multiple scattering of light in the particle medium, the effect of walls on radiative heat transfer and the directionality of the concentrated solar radiation. The accurate determination of the distribution of particles within the fluidized bed has been a critical parameter for the calculation of heat transfer. With these models, later refined by a confrontation with experimental references, we have studied the effect of geometry on heat transfer in the receiver. This study highlighted the necessity to use a switching section fluidization column and the importance to optimize the pair : solar concentrator / receiver to avoid any overheating at the walls of the receiver. Moreover, it appears that the homogenization of the temperature in the fluidized bed of the receiver increase its performance
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Zhang, Zihao. "Investigating the far- and near-field thermal radiation in carbon-based nanomaterials". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54433.
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Two classes of carbon nanomaterials—carbon nanotubes and graphene—have promoted the advancement of nanoelectronics, quantum computing, chemical sensing and storage, thermal management, and optoelectronic components. Studies of the thermal radiative properties of carbon nanotube thin film arrays and simple graphene hybrid structures reveal some of the most exciting characteristic electromagnetic interactions of an unusual sort of material, called hyperbolic metamaterials. The features and results on these materials in the context of both far-field and near-field radiation are presented in this dissertation.
Due to the optically dark nature of pyrolytic carbon in the wavelength range from visible to infrared, it has been suggested vertically aligned carbon nanotube (VACNT) coatings may serve as effective radiative absorbers. The spectral optical constants of VACNT are modeled using the effective medium theory (EMT), which is based on the anisotropic permittivity components of graphite. The effects of other EMT parameters such as volume filling ratio and local filament alignment factor are explored. Low reflectance and high absorptance are observed up to the far-infrared and wide range of oblique incidence angles. The radiative properties of tilt-aligned carbon nanotube (TACNT) thin films are illustrated. Energy streamlines by tracing the Poynting vectors are used to show a self-collimation effect within the TACNT thin films, meaning infrared light can be transmitted along the axes of CNT filaments.
Graphene, a single layer sheet of carbon atoms, produces variable conductance in the terahertz frequency regime by tailoring the applied voltage gating or doping. Periodically embedding between dielectric spacers, the substitution of graphene provides low radiative attenuation compared to traditional metal-dielectric multilayers. The hyperbolic nature, namely negative angle of refraction, is tested on the graphene-dielectric multilayers imposed with varying levels of doping. EMT should be valid for graphene-dielectric multilayers due to the nanometers-thick layers compared to the characteristic wavelength of infrared light. For metal- or semiconductor-dielectric multilayers with thicker or lossier layers, EMT may not hold. The validity of EMT for these multilayers is better understood by comparing against the radiative properties determined by layered medium optics.
When bodies of different temperatures are separated by a nanometers-size vacuum gap, thermal radiation is enhanced several-fold over that of blackbodies. This phenomenon can be used to develop more efficient thermophotovoltaic devices. Due to their hyperbolic nature, VACNT and graphite are demonstrated to further increase evanescent wave tunneling. The heat flux between these materials separated by vacuum gaps smaller than a micron is vastly improved over traditional semiconductor materials. A hybrid structure composed of VACNT substrates covered by doped graphene is analyzed and is shown to further improve the heat flux, due to the surface plasmon polariton coupling between the graphene sheets.
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Fernandes, Cássio Spohr. "Implementação de modelos atualizados de gás cinza no software FDS para predição do fluxo de calor radiativo em incêndios". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/184710.
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Este trabalho tem como objetivo implementar e testar modelos de gás cinza atualizados na rotina de radiação térmica do software Fire Dynamics Simulator (FDS), além da utilização do próprio modelo de gás cinza disponível no software, para a predição do fluxo de calor radiativo. Os modelos de gás cinza estudados foram o modelo padrão do software FDS (aqui denominado como GC1), e os modelos de gás cinza mais atuais: o GC2, no qual o coeficiente de absorção do meio participante é dado por relações polinomiais, e o GC3, sendo este um modelo de gás cinza que baseia o cálculo do coeficiente de absorção no modelo WSGG. Os novos modelos de gás cinza foram implementados no código fonte do software FDS, o qual é um código aberto, e a verificação da implementação foi realizada através da solução numérica do equacionamento utilizando os valores reportados pelo software. Com os novos modelos de gás cinza já corretamente implementados, passou-se então para a simulação computacional dos casos previamente selecionados. Para todos os modelos de gás cinza, foram simulados incêndios em poças, para diferentes combustíveis (etanol, n-heptano e metanol) em diferentes cenários de incêndio, considerando ou não a presença de fuligem no sistema. Os cenários de incêndio eram: (i) totalmente fechado, (ii) totalmente aberto e (iii) com uma condição intermediária, fechado, porém com uma abertura para o meio externo. Um estudo de análise de malha e de diferentes parâmetros, como o estudo da quantidade necessária de ângulos sólidos discretos, foram realizados para correta padronização dos parâmetros. As simulações computacionais foram validadas para o modelo de gás cinza padrão do FDS através da comparação de resultados com aqueles reportados na literatura específica de cada caso. Com os modelos já validados simulou-se novamente cada cenário de incêndio com os diferentes modelos de gás cinza anteriormente implementados. A partir da análise dos resultados obtiveram-se boas concordâncias para os campos de temperatura, frações molares tanto de CO2 quanto de H2O e para as frações volumétricas de fuligem. Os fluxos de calor radiativos foram corretamente preditos para todos os modelos de gás cinza implementados. O modelo GC2 apresentou resultados com desvios médios na faixa de 15%, o modelo de gás cinza baseado no WSGG (GC3) apresentou os melhores resultados, com erros médios inferiores a 10%, enquanto que o modelo padrão do software, GC1, apresentou resultados intermediários.This work aims to implement and test updated gray gas models in the thermal radiation routine of the Fire Dynamics Simulator (FDS) software, as well as the use of the gray gas model available in the software to the prediction of radiative heat flux. The gray gas models studied were the default model of the FDS software (determined GC1), and the most current gray gas models: the GC2, in which the absorption coefficient of the participant medium is given by a polynomial relations, and the GC3, which is a gray gas model that was based on the calculation of the absorption coefficient in the WSGG model. The most recently gray gas models were implemented in the source code, which is an open source, and the verification of the implementation was performed by the numerical solution of the equations from the reported values of the software. With the new gray gas models already implemented, the next step was the computational simulation of the previously selected cases. For all the gray gas models, pool fires were simulated different scenarios of fire for different fuels (ethanol, nheptane and methanol), with and without considering soot presence in the system. The fire scenarios were: (i) fully closed, (ii) fully open and (iii) with an intermediate condition, closed but with an opening to the external environment. A study of a mesh analysis and different parameters, such as the study of the required amount of discrete solid angles, were performed to correct the standard parameters. The computational simulations were verified for the default gray gas model of the FDS by comparing the simulations results with those reported in the specific literature of each case. With the models already verified, each fire scenario was simulated with the different gray gas models previously implemented. From the analysis of the results, good agreements were obtained for the fields of temperature, molar fraction of CO2 and H2O and soot volume fraction. The radiative heat fluxes were correctly predicted for all gray gas models early implemented. The GC2 model present results with average deviation in the range of 15%, the gray gas model based on WSGG (GC3) presented the best results, with average deviation lower than 10%, while the default software model (GC1) presented intermediate results.
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Alanazi, Mohammed Awwad. "Non-invasive Method to Measure Energy Flow Rate in a Pipe". Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/103179.
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Current methods for measuring energy flow rate in a pipe use a variety of invasive sensors, including temperature sensors, turbine flow meters, and vortex shedding devices. These systems are costly to buy and install. A new approach that uses non-invasive sensors that are easy to install and less expensive has been developed. A thermal interrogation method using heat flux and temperature measurements is used. A transient thermal model, lumped capacitance method LCM, before and during activation of an external heater provides estimates of the fluid heat transfer coefficient h and fluid temperature. The major components of the system are a thin-foil thermocouple, a heat flux sensor (PHFS), and a heater. To minimize the thermal contact resistance R" between the thermocouple thickness and the pipe surface, two thermocouples, welded and parallel, were tested together in the same set-up. Values of heat transfer coefficient h, thermal contact resistance R", time constant �[BULLET], and the water temperature �[BULLET][BULLET], were determined by using a parameter estimation code which depends on the minimum root mean square RMS error between the analytical and experimental sensor temperature values. The time for processing data to get the parameter estimation values is from three to four minutes. The experiments were done over a range of flow rates (1.5 gallon/minute to 14.5 gallon/minute). A correlation between the heat transfer coefficient h and the flow rate Q was done for both the parallel and the welded thermocouples. Overall, the parallel thermocouple is better than the welded thermocouple. The parallel thermocouple gives small average thermal contact resistance average R"=0.00001 (m2.�[BULLET][BULLET]/W), and consistence values of water temperature and heat transfer coefficient h, with good repeatability and sensitivity. Consequently, a non-invasive energy flow rate meter or (BTU) meter can be used to estimate the flow rate and the fluid temperature in real life.MS
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Ozler, Emrah Talip. "Modelling Of Dropwise Condensation On A Cylindrical Surface Including The Sweeping Effect". Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608440/index.pdf.
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The purpose of this study was to analyze the dropwise condensation on a cylindrical surface including the sweeping effect theoretically. For this purpose, first the problem of the equilibrium shape and departure size of drops on the outer surface of a cylinder was formulated. The equations of the surface of the drop were obtained by minimizing (for a given volume) the total energy of the drop which consists of surface and gravitational energy by using the techniques of variational calculus. The departure size of the droplets on a surface at varies angle of inclinations were also determined experimentally. Drop departure size is observed to decrease up to as the surface inclination was decreased up to 90 degree and then it increased up to 180 degree.
Mean base heat flux, drop departure rate, sweeping frequency, fraction of covered area, sweeping period, local heat flux and average heat flux for the dropwise condensation on a cylindrical surface including the sweeping effect is formulated and the resulting integral equation was solved by using the finite difference techniques.
The results show that drop departure rate and sweeping frequency was strongly affected by the angular position and reached asymptotic value at large angular positions.
Comparing the results of the average heat flux values at different diameters show that at larger diameters the average heat flux becomes larger. This is due to the increased sweeping effect at larger diameters.
Książki na temat "Radiative Heat Flux Rate"
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Beddini, Robert A. Analysis of turbulent convective and radiative heat transfer in high temperature rocket chamber flows. New York: AIAA, 1987.
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Siegel, Robert. Two-flux and Green's function method for transient radiative transfer in a semitransparent layer. [Washington, D.C: National Aeronautics and Space Administration, 1995.
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Siegel, Robert. Two-flux and Green's function method for transient radiative transfer in a semitransparent layer. [Washington, D.C: National Aeronautics and Space Administration, 1995.
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Siegel, Robert. Two-flux and Green's function method for transient radiative transfer in a semitransparent layer. [Washington, D.C: National Aeronautics and Space Administration, 1995.
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S, Wichman I., i United States. National Aeronautics and Space Administration., red. An experimental and theoretical study of radiative extinction of diffusion flames: Final technical report ... period covered: duration of contract, 1991-1994; grant number: NAG3-1271. [Washington, DC: National Aeronautics and Space Administration, 1994.
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Siegel, Robert. Two-flux Green's function analysis for transient spectral radiation in a composite. Reston, VA: American Institute of Aeronautics and Astronautics, 1996.
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Siegel, Robert. Two-flux Green's function analysis for transient spectral radiation in a composite. Reston, VA: American Institute of Aeronautics and Astronautics, 1996.
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Siegel, Robert. Two-flux Green's function analysis for transient spectral radiation in a composite. Reston, VA: American Institute of Aeronautics and Astronautics, 1996.
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United States. National Aeronautics and Space Administration., red. Two-flux Green's function analysis for transient spectral radiation in a composite. Reston, VA: American Institute of Aeronautics and Astronautics, 1996.
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1954-, Padron Victor, red. Classification of radial solutions arising in the study of thermal structures with thermal equilibrium or no flux at the boundary. Providence, R.I: American Mathematical Society, 2010.
Znajdź pełny tekst źródłaCzęści książek na temat "Radiative Heat Flux Rate"
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Li, Changying, Shuqi Meng, Tianming Ruan i Yalun Yan. "Research of Corrosion Products Migration Behavior in PWR Primary Circuit Under Extended Low Power Operation Mode". W Springer Proceedings in Physics, 45–52. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-1023-6_5.
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AbstractIn order to improve the flexibility of response to power grid demand, both newly built and in-service nuclear power units need to demonstrate the feasibility of ELPO (Extended Low Power Operation) and design schemes. During ELPO, the change of local thermal hydraulic conditions caused by the change of core power will have a great impact on the migration behavior of corrosion products in the primary circuit of PWR (Pressurized Water Reactor). Corrosion products deposited in the core will affect the heat transfer of fuel cladding, axial power distribution and critical heat flux. Corrosion products deposited outside the reactor, such as the main tubes, will affect the dose rate of personnel and pose challenges to radiation protection. A model for simulating the migration of corrosion products in the primary circuit of a PWR was established. The variation trends of the total amount of fuel CRUD (Chalk Rivers Unidentified Deposit), the total amount of fouling outside the reactor, the removal amount of corrosion products, the coolant source term and the main tubes deposition source term of a PWR before and after ELPO were compared. The results show that ELPO mode can inhibit the deposition of corrosion products in the core, and make more corrosion products deposit outside the core or be removed by CVCS (Chemical and Volume Control System). Because ELPO mode accelerates the migration of activated corrosion products to other regions, the coolant source term increases slightly. For the source term of main tubes sediment, ELPO model can reduce its total activity, thus reducing the personnel dose rate.
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Su, Ching-Hua. "Vapor Transport Rate (Mass Flux) Measurements and Heat Treatments". W Vapor Crystal Growth and Characterization, 39–73. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-39655-8_3.
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Mogstad, Torkil S. "DSMC Computation of Radiative Heat Flux During Huygens Entry into the Titan Atmosphere". W Shock Waves @ Marseille II, 347–54. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-78832-1_57.
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Ferdows, M., i Sakawat Hossain. "Local Non-similar Solution of Induced Magnetic Boundary Layer Flow with Radiative Heat Flux". W Flow and Transport in Subsurface Environment, 343–65. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-10-8773-8_12.
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Porat, H., R. G. Morgan i T. J. McIntyre. "Radiative Heat flux Measurements for Titan Atmospheric Entry Condition in a Superorbital Expansion Tunnel". W 30th International Symposium on Shock Waves 1, 139–43. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-46213-4_22.
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Venkata Rao, Ch, i Ch RamReddy. "Natural Convective Flow of a Radiative Nanofluid Past an Inclined Plate in a Non-Darcy Porous Medium with Lateral Mass Flux". W Numerical Heat Transfer and Fluid Flow, 93–102. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-1903-7_12.
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Karpov, Alexander, Artem Shaklein, Mikhail Korepanov i Artem Galat. "Numerical Study of the Radiative and Turbulent Heat Flux Behavior of Upward Flame Spread Over PMMA". W Fire Science and Technology 2015, 841–48. Singapore: Springer Singapore, 2016. http://dx.doi.org/10.1007/978-981-10-0376-9_86.
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Park, S., C. Ryu, T. Y. Chae, W. Yang, Y. Kim, S. Lee i S. Seo. "Effect of Combustion Characteristics on Wall Radiative Heat Flux in a 100 MWe Oxy-Coal Combustion Plant". W Cleaner Combustion and Sustainable World, 1275–82. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-30445-3_169.
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Wickramasinghe, Amila, Nazmul Khan, Alexander Filkov i Khalid Moinuddin. "Physics-Based Modelling for Mapping Firebrand Flux and Heat Load on Structures in the Wildland-Urban Interface’". W Advances in Forest Fire Research 2022, 746–50. Imprensa da Universidade de Coimbra, 2022. http://dx.doi.org/10.14195/978-989-26-2298-9_114.
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The mechanisms of structure ignition by wildfires are classified into direct flame contact, radiant heat, firebrand attack and a combination of two or all of them. Arguably, airborne firebrands play a vital role as the main cause for structure ignition and fire propagation by forming spot fires far from the fire front. Firebrand flux and the heat load are important parameters to calculate the wildfire risk on structures. Australian Building Standard AS3959 is developed based on radiation heat flux and it does not quantify the effects of firebrand landing flux on structures to assess the wildfire risk completely. To improve the assessment of the Bushfire Attack Level (BAL) in AS3959, there is a need for firebrand flux quantification at different scales of wildfires. Lacking information about firebrand generation from various vegetation species at different environmental conditions creates a gap to estimate the firebrand flux accurately. In this study, we aim to use a physics-based model to quantify the firebrand generation rate of Eucalyptus dominant forest vegetation at different severities of wildfires expressed by the Fire danger indices (FDI) of 100, 80, 50. The wind speed is adjusted while keeping the temperature, relative humidity, and drought factor as constants to obtain the focused FDIs. A 40 m height Eucalyptus forest is modelled with 25 t/ha understorey and 10 t/ha canopy fuel loads as per AS3959 forest vegetation classification. The forest fires are prescribed with the intensities of 53.4, 43.1, and 27 MW/m with 100 m length to replicate the fire events explained by FDIs. The depth of the fireline is approximated according to the fire residence time and the spread rate. The firebrand size, shape, and quantity are taken from our previous firebrand generation study (Wickramasinghe et al. 2022) and the particles are injected randomly through the forest volume which is engulfed by the fire. The distances between the modelled structure that follows an Australian standard house design and the vegetation are maintained according to the BALs. We obtained the radiative heat flux on the houses close to the algorithm provided in AS3959 for each BAL. In this study, both firebrand and heat flux are quantified at strategic locations of the house. We find a logarithmic relationship exists between firebrand flux and radiative heat flux in the range of R2 0.96 to 0.99. Hence, for a certain BAL, the firebrand flux increases with the FDI similar to radiative heat flux. Results from this study can be used to quantify the firebrand flux on houses from different vegetation fires, which may improve the design standards and construction requirements of buildings to mitigate the vulnerability of wildfires at the wildland-urban interface (WUI).
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Gutschick, Vincent P., i Keirith A. Snyder. "Water and Energy Balances within the Jornada Basin". W Structure and Function of a Chihuahuan Desert Ecosystem. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780195117769.003.0012.
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This chapter describes general characteristics and components of the energy and water balances in arid regions, with specific examples from the Jornada Basin. Various research efforts to characterize the energy and water balances and resultant carbon dioxide fluxes in the Jornada Basin are detailed. We provide a brief overview of how plant physiology interacts with energy and water balances in this region, and characterize general abiotic conditions and some physiological traits of plants in this arid region. The surface of a landscape may be considered as a layer with some amount of vegetation. More general descriptions divide the vegetation, like the soil, into layers, but the concern here is energy balance at the interface with the atmosphere. The net energy balance of the land surface is determined by inputs (radiant energy), outputs (reflection [i.e., albedo], emission of longwave radiation, convective heat transfer to the atmosphere [i.e., sensible heat flux], evapotranspiration of water [i.e., latent heat flux], and conduction of heat into soil), and changes in heat storage. The balance of these terms is adjusted as the surface temperature comes into steady state or nearly so. Increased solar input will drive surface temperatures higher until longwave emission and other losses come into a new balance. The net energy input, as inputs minus outputs, may be stated formally as an energy-balance equation . . . Rate of heat storage = S = Q+sw + Q+TIR − Q+TIR _ Q_E Q_H − Q_S, (8-1) . . . where the superscript + indicates an input, and − indicates an output or loss, and all terms are expressed as flux density in units of W/m2. Q+SW is the energy added to the surface layer by solar radiation from above. Q+TIR is the thermal infrared radiation emitted by gases in the atmosphere, principally water vapor and CO2, whereas Q_TIR is the thermal infrared radiation emitted from components of the Earth’s surface and lost back to the atmosphere. Q_E is the latent heat flux from the heat of vaporization of water vapors resulting from soil evaporation (E) and plant transpiration, generally measured as the composite evapotranspiration flux (ET).
Streszczenia konferencji na temat "Radiative Heat Flux Rate"
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Chang, S. S., H. H. Chiu i T. S. Lee. "Droplet Combustion With Radiative Heat Transfer". W ASME 1997 Turbo Asia Conference. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-aa-144.
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Combustion of a droplet, either in stationary or convective motion under the effect of radiative heat transfer is studied. The closed form expression of gasification laws and the radiative flux distribution surrounding a stationary droplet are calculated using Potential Theory of Radiation in conjunction with the canonical theory of droplet recently developed. Various mechanisms contributing to gasification rate of a combusting droplet under radiative condition are determined by the Canonical Integral Method to assess their importance. It is found that radiation effect plays an important role when the droplet considered is of large size and under high environmental temperature. It is seen from the present study that for a typical application in turbine combustor, the enhancement of droplet combustion rate due to radiation ranges from 5 percents to 15 percents depending on the droplet size and the environmental conditions.
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Martins, Nelson, Maria da Graça Carvalho, Naim Afgan i Alexander Ivanovich Leontiev. "Radiation and Convection Heat Flux Sensor for High Temperature Gas Environment". W ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-224.
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The heat flux measurement is one of the essential parameter for the diagnostic of thermal systems. In the high temperature environment there are difficulties in differentiating between the convective and radiation component of heat flux on the heat transfer surface. A new method for heat flux measurement is being developed using a porous sensing element. The gas stream flowing through the porous element is used to measure the heat received by the sensor surface exposed to the hot gas environment and to control whether or not the sensing element receives the convection component of the total heat flux. It is possible to define a critical mass flow rate corresponding to the destruction of the boundary layer over the sensing element. With subcritical mass flow rate the porous sensing element will receive both the convective and radiative heat fluxes. A supercritical mass flow rate will eliminate the convective component of the total heat flux. Two consecutive measurements considering respectively a critical and a sub-critical mass flow rate can be used to determine separately the convection and radiation heat fluxes. A numerical model of sensor with appropriate boundary condition has been developed in order to perform analysis of possible options in the design of the sensor. The analysis includes: geometry of element, physical parameters of gas and solid and gas flow rate through the porous element. For the optimal selection of the relevant parameters an experimental set-up was designed, including the sensor element with corresponding cooling and monitoring system and high temperature radiation source. Applying the respective measuring procedure the calibration curve of the sensor was obtained. The linear dependency of the heat flux and respective temperature difference of the gas was verified. The accuracy analysis of the sensor reading has proved high linearity of the calibration curve and accuracy of ± 5%.
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Seytier, Charline, i Mohammad H. Naraghi. "Combined Convective-Radiative Thermal Analysis of Inclined Roof Top Solar Chimney". W ASME 2011 5th International Conference on Energy Sustainability. ASMEDC, 2011. http://dx.doi.org/10.1115/es2011-54043.
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A model for the combined spectral radiative and convective heat transfer analysis of solar chimneys is developed. The radiation part of this model is based on the spectral distribution of the solar heat flux and spectral radiative properties solar chimney components. Two methods are used for the convective part of this model, empirical correlations and a CFD analysis. The empirical correlations consist of stack effect correlation for air flow motion and convective heat transfer correlation for heat transfer coefficient calculations. The empirical correlations were used to obtain an initial estimation of surface temperatures which were then used in a CFD model to determine an improved estimation of the heat transfer coefficients and flow rates. By iterating between the spectral radiative and CFD models a converged value for the solar chimney flow rate and its thermal characteristics is obtained. The model is used to predict the volume flow rate of air moved for various configurations of solar chimneys (slopes and air gap distance).
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Naka, Genya. "Numerical Model of Radiative and Convective Heat Flux for Fuel Regression Rate of Wax-based Hybrid Rocket". W AIAA Scitech 2021 Forum. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2021. http://dx.doi.org/10.2514/6.2021-2040.
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Fu, Ceji, i Zhuomin M. Zhang. "Prediction of Nanoscale Radiative Heat Transfer Between Silicon and Silicon or Another Material". W ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56332.
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This work investigates the near-field radiative heat transfer between two semi-finite media separated by a vacuum gap. The fluctuational electrodynamics is used to calculate the net heat flux between a high-temperature medium, which is assumed to be silicon at 1000 K, and a room-temperature (300 K) medium, which is taken as either silicon or a different material, such as silicon carbide and aluminum. The dielectric function of silicon is modeled with a Drude model, considering the effects of temperature and doping level on the carrier concentrations and scattering rates. The calculated results show that the net radiative energy flux can be greatly enhanced in the near field. In the case of energy exchange between silicon and silicon, the net heat flux approaches to a constant value as the distance between the media is reduced to below 100 nm. Furthermore, increasing the doping level of the high-temperature medium causes a slight decrease in the near-field energy flux. On the contrary, in the case of energy exchange between silicon and a different material (silicon carbide or aluminum), the net heat flux continue to increase as the distance is reduced even below 1 nm. Increasing the doping level of silicon can significantly enhance the net energy flux, especially when the distance is shorter than 20 nm.
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Lam, Cecilia S., Alexander L. Brown, Elizabeth J. Weckman i Walter Gill. "Measurement of Heat Flux From Fires". W ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56896.
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Heat flux is an important parameter for characterization of the thermal impact of a fire on its surroundings. However, heat flux cannot be measured directly because it represents the rate of heat transfer to a unit area of surface. Therefore, most heat flux measurements are based on the measurement of temperature changes at or near the surface of interest [1,2]. Some instruments, such as the Gardon gauge [3] and the thermopile [2], measure the temperature difference between a surface and a heat sink. In radiation-dominated environments, this difference in temperature is often assumed to be linearly related to the incident heat flux. Other sensors measure a surface and/or interior temperature and inverse heat conduction methods frequently must be employed to calculate the corresponding heat flux [1,4]. Typical assumptions include one-dimensional conduction heat transfer and negligible heat loss from the surface. The thermal properties of the gauge materials must be known and, since these properties are functions of temperature, the problem often becomes non-linear.
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Gomez-Ramirez, David, Srinath V. Ekkad, Brian Y. Lattimer, Hee-Koo Moon, Yong Kim i Ram Srinivasan. "Separation of Radiative and Convective Wall Heat Fluxes Using Thermal Infrared Measurements Applied to Flame Impingement". W ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-52322.
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Flame impingement is critical for the processing and energy industries. The high heat transfer rates obtained with impinging flames are relevant in metal flame cutting, welding, and brazing; in fire research to understand the effects of flames on the structures of buildings; and in the design of high temperature combustion systems. Most of the studies on flame impingement are limited to surfaces perpendicular to the flame, and measurements are often performed using heat flux sensors (such as Schmidt-Boelter heat flux transducers) at discrete locations along the target surface. The use of in-situ probes provides high accuracy but heavily limits the spatial resolution of the measurement. Moreover, flame radiation effects are often neglected, due to the small contribution in non-luminous flames, and the entire heat flux to the target is assumed to be due to convection. Depending on the character of the flame and the impingement surface, local radiative heat transfer can be significant, and the contribution of radiation effects has not been fully quantified. This study presents a novel non-intrusive method with high spatial resolution to simultaneously determine the convective and radiative heat fluxes at a wall interacting with a flame or other high temperature environment. Two initial proof of concept experiments were conducted to evaluate the viability of the technique: one consisting of a flame impinging normal to a target and another with a flame parallel to the target surface. Application of the methodology to the former case yielded a stagnation convective heat flux in the order of 106kWm−2 that decreased radially away from the stagnation point. The radiation field for the direct impingement case accounted on average for 4.4% of the overall mean heat flux. The latter experiment exemplified a case with low convective heat fluxes, which was correctly predicted by the measurement. The radiative heat fluxes were consistent between the parallel and perpendicular cases.
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Lille, Simon, Wlodzimierz Blasiak, Magnus Mo¨rtberg, Tomasz Dobski i Weihong Yang. "Heat Flux Evaluation in a Test Furnace Equipped With High Temperature Air Combustion (HTAC) Technique". W 2002 International Joint Power Generation Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/ijpgc2002-26031.
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High Temperature Air Combustion has already been applied in various industrial furnaces. Steel producers use most of the revamped furnaces. These are: • Batch and continuous heating furnaces in which HRS burners with open flames were used, • Batch and continuous heat treatment furnaces in which HRS burners with radiant tubes were used. Apart from steel industry the HTAC systems were applied to melt aluminium or to incinerate odour, vapour gases for example in pulp and paper industry. In all these applications very high fuel savings (sometimes as high as 60%), reduction of NOx and production increase (by 20–50%) was achieved. Progress in applications of the HTAC increased also needs of more information and data required by furnace and process designers. For this reason study in larger scale where at least one set of regenerative burner systems is installed are very much needed. Aim of such studies is not only to verify furnace performance with respect to the known general advantages of HTAC but are focused on specific problems related to furnace and high-cycle regenerative burners operation, process and product properties or type of fuels used. Parallel to the semi-industrial tests numerical models of furnaces have to be developed and verified. In this work, mainly results of heat flux measurements as well as results of numerical modeling of heat transfer in the HTAC test furnace are presented. Results were obtained for propane combustion at firing rate equal to 200 kW. The general code, STAR-CD, was employed in this work to analyse the HTAC test furnace numerically. HTAC test furnace at Royal Institute of Technology (KTH) with capacity of 200 kW was used in this work. The furnace is equipped with two different high-cycle regenerative systems (HRS). In both systems the “honeycomb” regenerator is used. The two-burner system is made of two pairs (four burners) of high cycle-regenerative burners with switching time between 10 and 40 seconds. HTAC test furnace is equipped with four air-cooled tubes to take away heat from the furnace. The total radiative heat flux measured in the HTAC furnace shows very uniform distribution over the whole combustion chamber. For total radiative heat flux, the values are in the range of 110–130 kW/m2 as measured by means of the total radiative heat flow meter at the furnace temperature 1100 C. Average total radiation flux on the top furnace wall is as high as 245.5 kW/m2 as well as total incident radiation flux. Total radiation heat flux on the air-cooled tube surface is very uniform along and around the tubes. Average radiant heat flux taken away by air cool tube is 35.46 kW/m2.
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Christian, Joshua M., i Clifford K. Ho. "CFD Simulation and Heat Loss Analysis of the Solar Two Power Tower Receiver". W ASME 2012 6th International Conference on Energy Sustainability collocated with the ASME 2012 10th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/es2012-91030.
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Solar Two was a demonstration of the viability of molten salt power towers. The power tower was designed to produce enough thermal power to run a 10-MWe conventional Rankine cycle turbine. A critical component of this process was the solar tower receiver. The receiver was designed for an applied average heat flux of 430 kW/m2 with an outlet temperature of 565°C (838.15 K). The mass flow rate could be varied in the system to control the outlet temperature of the heat transfer fluid, which was high temperature molten salt. The heat loss in the actual system was calculated by using the power-on method which compares how much power is absorbed by the molten salt when using half of the heliostat field and then the full heliostat field. However, the total heat loss in the system was lumped into a single value comprised of radiation, convection, and conduction heat transfer losses. In this study, ANSYS FLUENT was used to evaluate and characterize the radiative and convective heat losses from this receiver system assuming two boundary conditions: (1) a uniform heat flux on the receiver and (2) a distributed heat flux generated from the code DELSOL. The results show that the distributed-flux models resulted in radiative heat losses that were ∼14% higher than the uniform-flux models, and convective losses that were ∼5–10% higher due to the resulting non-uniform temperature distributions. Comparing the simulations to known convective heat loss correlations demonstrated that surface roughness should be accounted for in the simulations. This study provides a model which can be used for further receiver design and demonstrates whether current convective correlations are appropriate for analytical evaluation of external solar tower receivers.
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Satoh, Koyu, Naian Liu, Xiaodong Xie i Wei Gao. "CFD Study of a Fire Whirl of Huge Oil Tank: Burning Rate, Flame Length, Distributions of n-Heptane and Oxygen in a Fire Whirl". W ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37276.
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The number of huge oil storage tanks is increasing in the world. If a fire occurs in one of these tanks, it is very difficult to suppress. Additionally, if a fire whirl occurs in an oil tank fire, it is extremely dangerous for firefighters to extinguish the fire. The authors have numerically studied huge fire whirls in a large oil tank depot and predicted the generation of those fire whirls. Here, another study is attempted to clarify the details of huge fire whirl in a large oil tank, using two kinds of fire whirl generation channels in CFD simulations using the software, FDS by NIST. Details of burning rates, velocities of whirling flames, radiative heat flux, heat release rates and whirling cycles are examined, using oil tanks with the diameters of 0.2 to 80 m. In oil tanks with a diameter of 80 m, a tall fire whirl is generated. The height is about 1000 m. In this study of oil tanks fires with small to large diameters, it has been found that fire whirl lengths are about 8 to 11 times of the oil tank diameter. The maximum radiative heat flux due to a fire whirl in 80 m diameter oil tanks exceeds 100 kW/m2. Since the maximum radiation is found at twice the distance of oil tank diameters from the tank centers, adjacent oil tanks may be ignited. This study has also examined a method used to prevent fire whirl generation in huge oil tanks.
Raporty organizacyjne na temat "Radiative Heat Flux Rate"
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Madrzykowski, Daniel. Firefighter Equipment Operational Environment: Evaluation of Thermal Conditions. UL Firefighter Safety Research Institute, sierpień 2017. http://dx.doi.org/10.54206/102376/igfm4492.
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The goal of this study was to review the available literature to develop a quantitative description of the thermal conditions firefighters and their equipment are exposed to in a structural fire environment. The thermal exposure from the modern fire environment was characterized through the review of fire research studies and fire-ground incidents that provided insight and data to develop a range of quantification. This information was compared with existing standards for firefighting protective equipment to generate a sense of the gap between known information and the need for improved understanding. The comparison of fire conditions with the thermal performance requirements of firefighter protective gear and equipment demonstrates that a fire in a compartment can generate conditions that can fail the equipment that a firefighter wears or uses. The review pointed out the following: 1. The accepted pairing of gas temperature ranges with a corresponding range of heat fluxes does not reflect all compartment fire conditions. There are cases in which the heat flux exceeds the hazard level of the surrounding gas temperature. 2. Thermal conditions can change within seconds. Experimental conditions and incidents were identified in which firefighters would be operating in thermal conditions that were safe for operation based on the temperature and heat flux, but then due to a change in the environment the firefighters would be exposed to conditions that could exceed the protective capabilities of their PPE. 3. Gas velocity is not explicitly considered within the thermal performance requirements. Clothing and equipment tested with a hot air circulating (convection) oven are exposed to gas velocities that measure approximately 1.5 m/s (3 mph). In contrast, the convected hot gas flows within a structure fire could range from 2.3 m/s (5 mph) to 7.0 m/s (15 mph). In cases where the firefighter or equipment would be located in the exhaust portion of a flow path, while operating above the level of the fire, the hot gas velocity could be even higher. This increased hot gas velocity would serve to increase the convective heat transfer rate to the equipment and the firefighter, thereby reducing the safe operating time within the structure. 4. Based on the limited data available, it appears currently available protective clothing enables firefighters to routinely operate in conditions above and beyond the "routine" conditions measured in the fire-ground exposure studies conducted during the 1970s. The fire service and fire standards communities could benefit from an improved understanding of: • real world fire-ground conditions, including temperatures, heat flux, pressure, and chemical exposures; • the impact of convection on the thermal resistance capabilities of firefighting PPE and equipment; and • the benefits of balancing the thermal exposures (thermal performance requirements) across different components of firefighter protective clothing and safety equipment. Because it is unlikely due to trade offs in weight, breathe-ability, usability, cost, etc., that fireproof PPE and equipment will ever be a reality, fire officers and fire chiefs need to consider the capabilities of the protection that their firefighters have when determining fire attack strategies and tactics to ensure that the PPE and equipment is kept within its design operating environment, and that the safety buffer it provides is maintained.
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Seginer, Ido, Daniel H. Willits, Michael Raviv i Mary M. Peet. Transpirational Cooling of Greenhouse Crops. United States Department of Agriculture, marzec 2000. http://dx.doi.org/10.32747/2000.7573072.bard.
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Background Transplanting vegetable seedlings to final spacing in the greenhouse is common practice. At the time of transplanting, the transpiring leaf area is a small fraction of the ground area and its cooling effect is rather limited. A preliminary modeling study suggested that if water supply from root to canopy is not limiting, a sparse crop could maintain about the same canopy temperature as a mature crop, at the expense of a considerably higher transpiration flux per leaf (and root) area. The objectives of this project were (1) to test the predictions of the model, (2) to select suitable cooling methods, and (3) to compare the drought resistance of differently prepared seedlings. Procedure Plants were grown in several configurations in high heat load environments, which were moderated by various environmental control methods. The difference between the three experimental locations was mainly in terms of scale, age of plants, and environmental control. Young potted plants were tested for a few days in small growth chambers at Technion and Newe Ya'ar. At NCSU, tomato plants of different ages and planting densities were compared over a whole growing season under conditions similar to commercial greenhouses. Results Effect of spacing: Densely spaced plants transpired less per plant and more per unit ground area than sparsely spaced plants. The canopy temperature of the densely spaced plants was lower. Air temperature was lower and humidity higher in the compartments with the densely spaced plants. The difference between species is mainly in the canopy-to-air Bowen ratio, which is positive for pepper and negative for tomato. Effect of cooling methods: Ventilation and evaporative pad cooling were found to be effective and synergitic. Air mixing turned out to be very ineffective, indicating that the canopy-to-air transfer coefficient is not the limiting factor in the ventilation process. Shading and misting, both affecting the leaf temperature directly, proved to be very effective canopy cooling methods. However, in view of their side effects, they should only be considered as emergency measures. On-line measures of stress: Chlorophyll fluorescence was shown to accurately predict photosynthesis. This is potentially useful as a rapid, non-contact way of assessing canopy heat stress. Normalized canopy temperature and transpiration rate were shown to correlate with water stress. Drought resistance of seedlings: Comparison between normal seedlings and partially defoliated ones, all subjected to prolonged drought, indicated that removing about half of the lowermost leaves prior to transplanting, may facilitate adjustment to the more stressful conditions in the greenhouse. Implications The results of this experimental study may lead to: (1) An improved model for a sparse canopy in a greenhouse. (2) A better ventilation design procedure utilizing improved estimates of the evaporation coefficient for different species and plant configurations. (3) A test for the stress resistance of transplants.