To see the other types of publications on this topic, follow the link: Radiative Heat Transfer Rate.
Dissertations / Theses on the topic 'Radiative Heat Transfer Rate'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Radiative Heat Transfer Rate.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Wangdhamkoom, Panitan. "Characteristics of multimode heat transfer in a differentially-heated horizontal rectangular duct." Thesis, Curtin University, 2007. http://hdl.handle.net/20.500.11937/1007.
Full textAbstract:
This study presents the numerical analysis of steady laminar flow heat transfer in a horizontal rectangular duct with differential heating on the vertical walls. Three heating configurations: one uniform wall temperature (CS1) and two linearly varying wall temperature cases (CS2 and CS3) are analysed. The study considers the combined effects of natural convection, forced convection and radiation heat transfer on the overall heat transfer characteristics. Air, which is assumed to be a non-participating medium, is chosen as the working fluid. A computational fluid dynamics solver is used to solve a set of governing equations for a range of parameters.For chosen duct aspect ratios, the numerical model simulates the flow and heat transfer for two main effects: buoyancy and radiation heat transfer. Buoyancy effect is represented by Grashof number, which is varied from 2,000 to 1,000,000. The effect of radiation heat transfer is examined by choosing different wall surface emissivity values. The weak and strong radiation effect is represented by the emissivity values of 0.05 and 0.85 respectively. Three duct aspect ratios are considered - 0.5, 1 and 2. The heat transfer characteristics of all the above heating configurations - CS1, CS2, and CS3 are analysed and compared. The numerical results show that, for all heating configurations and duct aspect ratios, the overall heat transfer rate is enhanced when the buoyancy effect increases. Since buoyancy effect induces natural circulation, this circulation is therefore the main mechanism that enhances heat transfer. Radiation heat transfer is found to significantly influence convection heat transfer in high Grashof numbers.
2
Wangdhamkoom, Panitan. "Characteristics of multimode heat transfer in a differentially-heated horizontal rectangular duct." Curtin University of Technology, Department of Mechanical Engineering, 2007. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=17353.
Full textAbstract:
This study presents the numerical analysis of steady laminar flow heat transfer in a horizontal rectangular duct with differential heating on the vertical walls. Three heating configurations: one uniform wall temperature (CS1) and two linearly varying wall temperature cases (CS2 and CS3) are analysed. The study considers the combined effects of natural convection, forced convection and radiation heat transfer on the overall heat transfer characteristics. Air, which is assumed to be a non-participating medium, is chosen as the working fluid. A computational fluid dynamics solver is used to solve a set of governing equations for a range of parameters.For chosen duct aspect ratios, the numerical model simulates the flow and heat transfer for two main effects: buoyancy and radiation heat transfer. Buoyancy effect is represented by Grashof number, which is varied from 2,000 to 1,000,000. The effect of radiation heat transfer is examined by choosing different wall surface emissivity values. The weak and strong radiation effect is represented by the emissivity values of 0.05 and 0.85 respectively. Three duct aspect ratios are considered - 0.5, 1 and 2. The heat transfer characteristics of all the above heating configurations - CS1, CS2, and CS3 are analysed and compared. The numerical results show that, for all heating configurations and duct aspect ratios, the overall heat transfer rate is enhanced when the buoyancy effect increases. Since buoyancy effect induces natural circulation, this circulation is therefore the main mechanism that enhances heat transfer. Radiation heat transfer is found to significantly influence convection heat transfer in high Grashof numbers.
3
Maheria, Mehulkumar. "Thermal Analysis of Natural Convectiona and Radiation in Porous Fins." Cleveland State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=csu1281982835.
Full text
4
Colomer, Rey Guillem. "Numerical methods for radiative heat transfer." Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6691.
Full textAbstract:
L'objectiu principal d'aquesta tesi es l'estudi de la transferència d'energia per radiació. Per aquest motiu, s'ha estudiat la fenomenologia bàsica de la transferencia de calor per radiació. Tenint en compte el tipus d'equació que descriu aquesta transferència d'energia, aquesta tesi esta encarada als metodes numèrics que ens permetran incorporar la radiació en els nostres càlculs. Donat que aquest és el primer treball d'aquestes característiques en el grup de recerca CTTC ("Centre Tecnològic de Transferència de Calor"), està limitat a geometries senzilles, cartesianes i cilíndriques. En el capítol 1 s'exposa una breu introducció a la transferència d'energia per radiació, i una explicació de les equacions que la governen. Es tracta de l'equació del transport radiatiu, formulada en termes dels coeficients d'absorció i de dispersió, i l'equació de l'energia. També s'indica quan cal tenir en compte aquest fenòmen, i a més a més, es defineixen totes les magnituds i conceptes que s'han utilitzat en aquesta tesi. També es dóna una breu descripció d'algunes simplificacions que es poden fer a les equacions governants.
El mètode de les radiositats s'explica en el capítol 2. També s'hi descriu un procediment numèric que permet calcular els factors de vista en geometries amb simetria cilíndrica, i es presenten resultats obtinguts amb el mètode descrit. Tot i que aquest capítol està una mica deslligat de la resta de la tesi, l'algoritme ideat per tractar geometries tridimensionals amb un temps computacional molt proper al de geometries bidimensionals, sense un increment de memòria apreciable, dóna uns resultats prou bons com per formar part de la tesi.
El mètode de les ordenades discretes (DOM) es detalla en el capítol 3. L'aspecte més important d'aquest mètode es l'elecció del conjunt d'ordenades per integrar l'equació del transport radiatiu. S'enumeren quines propietats han d'acomplir aquests conjunts. S'hi explica amb detall la discretització de la equació del transport radiatiu, tant en coordenades cartesianes com en cilíndriques. Es presenten també alguns resultats ilustratius obtinguts amb aquest mètode.
En el moment en que es vol resoldre un problema real, cal tenir present que el coeficients d'absorció pot dependre bruscament de la longitud d'ona de la radiació. En aquesta tesi s'ha considerat aquesta dependència amb especial interés, en el capítol 4. Aquest interès ha motivat una recerca bibliogràfica sobre la modelització aquesta forta dependència espectral del coeficient d'absorció. Aquesta recerca s'ha dirigit també a l'estudi dels diferents models numèrics existents capaços d'abordar-la, i de resoldre la equació del transport radiatiu en aquestes condicions. Es descriuen diversos mètodes, i, d'aquests, se n'han implementat dos: el mètode de la suma ponderada de gasos grisos (WSGG), i el mètode de la suma de gasos grisos ponderada per línies espectrals (SLW). S'hi presenten també resultats ilustratius.
S'han realitzat multitud de proves en el codi numèric resultant de l'elaboració d'aquesta tesi. Tenint en compte els resultats obtinguts, es pot dir que els objectius proposats a l'inici de la tesi s'han acomplert. Com a demostració de la utilitat del codi resultant, aquest ha estat integrat en un codi de proposit general (DPC), resultat del treball de molts investigadors en els darrers anys.
Aquesta esmentada integració permet la resolució de problemes combinats de transferència de calor, analitzats en els capítols 5 i 6, on la radiació s'acobla amb la transferència de calor per convecció. La influència de la radiació en la transferència total de calor s'estudia en el capítol 5, publicat a la International Journal of Heat and Mass Transfer, volum 47 (núm. 2), pàg. 257-269, 2004. En el capítol 6, s'analitza l'efecte d'alguns paràmetres del mètode SLW en un problema combinat de transferència de calor. Aquest capítol s'ha enviat a la revista Journal of Quantitative Spectroscopy and Radiative Transfer, per què en consideri la publicació.
The main objective of the present thesis is to study the energy transfer by means of radiation. Therefore, the basic phenomenology of radiative heat transfer has been studied. However, considering the nature of the equation that describes such energy transfer, this work is focussed on the numerical methods which will allow us to take radiation into account, for both transparent and participating media. Being this the first effort within the CTTC ("Centre Tecnològic de Transferència de Calor") research group on this subject, it is limited to simple cartesian and cylindrical geometries.
For this purpose, chapter 1 contains an introduction to radiative energy transfer and the basic equations that govern radiative transfer are discussed. These are the radiative transfer equation, formulated in terms of the absorption and scattering coefficients, and the energy equation. It is also given a discussion on when this mode of energy transfer should be considered. In this chapter are also defined all of the magnitudes and concepts used throughout this work. It ends with a brief description of some approximate methods to take radiation into account.
The Radiosity Irradiosity Method is introduced in chapter 2. In this chapter it is also described a numerical method to calculate the view factors for axial symmetric geometries. The main results obtained in such geometries are also presented. Although a little disconnected from the rest of the present thesis, the algorithm used to handle "de facto"' three dimensional geometries with computation time just a little longer than two dimensional cases, with no additional memory consumption, is considered worthy enough to be included in this work.
In chapter 3, the Discrete Ordinates Method (DOM) is detailed. The fundamental aspect of this method is the choice of an ordinate set to integrate the radiative transfer equation. The characterization of such valuable ordinate sets is laid out properly. The discretization of the radiative transfer equation is explained in etail. The direct solution procedure is also outlined. Finally, illustrative results obtained with the DOM under several conditions are presented.
In the moment we wish to solve real problems, we face the fact that the absorption and scattering coefficients depend strongly on radiation wavelength. In the present thesis, special emphasis has been placed on studying the radiative properties of real gases in chapter 4. This interest resulted on a bibliographical research on how the wavenumber dependence of the absorption coefficient is modeled and estimated. Furthermore, this bibliographical research was focussed also on numerical models able to handle such wavenumber dependence. Several methods are discussed, and two of them, namely the Weighted Sum of Gray Gases (WSGG) and the Spectral Line Weighted sum of gray gases (SLW), have been implemented to perform non gray calculations. Some significant results are shown.
Plenty of tests have been performed to the numerical code that resulted from the elaboration of this thesis. According to the results obtained, the objectives proposed in this thesis have been satisfied. As a demonstration of the usefulness of the implemented code, it has been succesfully integrated to a general purpose computational fluid dynamics code (DPC), fruit of the effort of many researchers during many years.
Results of the above integration lead to the resolution of combined heat transfer problems, that are analyzed in chapters 5 and 6, where radiative heat transfer is coupled to convection heat transfer. The effect of radiation on the total heat transfer is studied in chapter 5, which has been published as International Journal of Heat and Mass Transfer, volume 47 (issue 2), pages 257--269, year 2004. In chapter 6, the impact of some parameters of the SLW model on a combined heat transfer problem is analyzed. This chapter has been submitted for publication at the Journal of Quantitative Spectroscopy and Radiative Transfer.
5
Ramamoorthy, Babila. "Numerical simulation of radiative heat transfer." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2009r/ramamoorthy.pdf.
Full text
6
Quintero, de la Garza Rodrigo Javier 1974. "Spheroidization of iron powders by radiative heat transfer." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85328.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (leaves 45-46).
by Rodrigo Javier Quintero de la Garza.
S.M.
7
Dai, Jin. "Near-Field Radiative Heat Transfer between Plasmonic Nanostructures." Doctoral thesis, KTH, Optik och Fotonik, OFO, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-195653.
Full textAbstract:
Radiative heat transfer (RHT) due to coupled electromagnetic near field scan significantly exceed that dictated by Planck’s law. Understanding such phenomenon is not only of fundamental scientific interest, but also relevant to a broad range of applications especially connected to nanotechnologies.This dissertation elaborates, through a scattering approach based on the rigorous coupled wave analysis method, how plasmonic nanostructures can tame the near-field RHT between two bodies. The transmission-factor spectra are corroborated by photonic band diagrams computed using a finite element method. The main work begins by showing that the phenomenon of spoofsurface plasmon polariton (SSPP) guided on grooved metal surfaces can play a similar role as surface phonon polariton in enhancing the RHT between two closely placed plates. Since dispersions of SSPPs especially their resonance frequencies can be engineered through geometrical surface profiling,one has great freedom in tailoring spectral properties of near-field RHT. Further enhancement of RHT can be achieved through techniques like filling of dielectrics in grooves or deploying supercells. A thorough study of RHT betweentwo 1D or 2D grooved metal plates confirms super-Planckian RHT at near-field limit, with 2D grooved metal plates exhibiting a superior frequency selectivity. We also present RHT with a more exotic type of plasmonic nanostructures consisting of profile-patterned hyperbolic metamaterial arrays, and show that with such plasmonic nanostructures one can achieve an ultrabroadband super-Planckian RHT.QC 20161111
8
Luo, Gang. "A cloud fraction and radiative transfer model." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/25753.
Full text
9
Safdari, Mohammad Saeed. "Characterization of Pyrolysis Products from Fast Pyrolysis of Live and Dead Vegetation." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/8807.
Full textAbstract:
Wildland fire, which includes both planned (prescribed fire) and unplanned (wildfire) fires, is an important component of many ecosystems. Prescribed burning (controlled burning) is used as an effective tool in managing a variety of ecosystems in the United States to reduce accumulation of hazardous fuels, manage wildlife habitats, mimic natural fire occurrence, manage traditional native foods, and provide other ecological and societal benefits. During wildland fires, both live and dead (biomass) plants undergo a two-step thermal degradation process (pyrolysis and combustion) when exposed to high temperatures. Pyrolysis is the thermal decomposition of organic material, which does not require the presence of oxygen. Pyrolysis products may later react with oxygen at high temperatures, and form flames in the presence of an ignition source. In order to improve prescribed fire application, accomplish desired fire effects, and limit potential runaway fires, an improved understanding of the fundamental processes related to the pyrolysis and ignition of heterogeneous fuel beds of live and dead plants is needed.In this research, fast pyrolysis of 14 plant species native to the forests of the southern United States has been studied using a flat-flame burner (FFB) apparatus. The results of fast pyrolysis experiments were then compared to the results of slow pyrolysis experiments. The plant species were selected, which represent a range of common plants in the region where the prescribed burning has been performed. The fast pyrolysis experiments were performed on both live and dead (biomass) plants using three heating modes: (1) convection-only, where the FFB apparatus was operated at a high heating rate of 180 °C s-1 (convective heat flux of 100 kW m-2) and a maximum fuel surface temperature of 750 °C; (2) radiation-only, where the plants were pyrolyzed under a moderate heating rate of 4 °C s-1 (radiative heat flux of 50 kW m-2), and (3) a combination of radiation and convection, where the plants were exposed to both convective and radiative heat transfer mechanisms. During the experiments, pyrolysis products were collected and analyzed using a gas chromatograph equipped with a mass spectrometer (GC-MS) for the analysis of tars and a gas chromatograph equipped with a thermal conductivity detector (GC-TCD) for the analysis of light gases.The results showed that pyrolysis temperature, heating rate, and fuel type, have significant impacts on the yields and the compositions of pyrolysis products. These experiments were part of a large project to determine heat release rates and model reactions that occur during slow and fast pyrolysis of live and dead vegetation. Understanding the reactions that occur during pyrolysis then can be used to develop more accurate models, improve the prediction of the conditions of prescribed burning, and improve the prediction of fire propagation.
10
End, Thomas [Verfasser]. "Optimal Control of Nonlocal Radiative Heat Transfer / Thomas End." München : Verlag Dr. Hut, 2012. http://d-nb.info/1021072893/34.
Full text
11
Bakeer, Muna. "Radiative heat transfer in gallium arsenide lec crystal pullers." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29916.
Full textAbstract:
A numerical analysis of radiative heat transfer in a liquid encapsulant Czochralski gallium arsenide crystal puller is developed. The heat transfer and equivilent ambient temperature
of each surface element are calculated using the Gebhart radiative model. The effective ambient temperature, to which each surface element is radiating, is found to vary indicating that assuming a constant ambient temperature for all surfaces (simplified radiative model) is incorrect.
The importance of including the middle and top cylinders of the growth chamber in numerical analysis of radiative heat transfer in the system is evaluated in the study. The upper section could be replaced by one isothermal surface without significant change of the effective ambient temperature distribution.
Fluid flow and heat transfer in the GaAs melt, crystal and encapsulant are calculated
using a three dimensional axisymmetric finite difference code which includes the detailed radiative model. The mathematical modelling of the fluid and heat flow describes
steady state transport phenomena in a three dimensional solution domain with latent heat release at the liquid/solid interface.
The predicted flow and temperature fields using the detailed radiative model differ considerably from the predicted fields using the simplified model. The simplified model shows high axial and low radial temperature gradients in the crystal near the encapsulant region; the axial gradient decreases and the radial gradient increases with increasing distance from the encapsulant top. The detailed model shows a high radial temperature gradient in the crystal near the crystal-encapsulant-ambient junction and nearly flat isotherms in the top half of the crystal.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
12
Luan, Wenqi. "Radiative and total heat transfer in circulating fluidized beds." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25101.pdf.
Full text
13
Torpey, Mark R. "A study of radiative heat transfer through foam insulation." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14661.
Full text
14
Mbiock, Aristide. "Radiative heat transfer in furnaces : elliptic boundary value problem." Rouen, 1997. http://www.theses.fr/1997ROUEA002.
Full text
15
Zhang, Yufang. "Coupled convective heat transfer and radiative energy transfer in turbulent boundary layers." Phd thesis, Ecole Centrale Paris, 2013. http://tel.archives-ouvertes.fr/tel-00969159.
Full textAbstract:
If radiation plays an important role in many engineering applications, especially in those including combustion systems, influence of radiation on turbulent flows, particularly on the turbulent boundary layers, is still not well known. The objective is here to perform a detailed study of radiation effect on turbulent flows. An optimized emission-based reciprocal (OERM) approach of the Monte-Carlo method is proposed for radiation simulation using the CK model for radiative gas properties. OERM allows the uncertainty of results to be locally controlled while it overcomes the drawback of the original emission-based reciprocity approach by introducing a new frequency distribution function that is based on the maximum temperature of the domain. Direct Numerical Simulation (DNS) has been performed for turbulent channel flows under different pressure, wall temperatures and wall emissivity conditions. Flow field DNS simulations are fully coupled with radiation simulation using the OERM approach. The role of radiation on the mean temperature field and fluctuation field are analyzed in details. Modification of the mean temperature profile leads to changes in wall conductive heat fluxes and new wall laws for temperature when radiation is accounted for. The influence on temperature fluctuations and the turbulent heat flux is investigated through their respective transport equations whose balance is modified by radiation. A new wall-scaling based on the energy balance is proposed to improve collapsing of wall-normal turbulent flux profiles among different channel flows with/without considering radiation transfer. This scaling enables a new turbulent Prandtl number model to be introduced to take into account the effects of radiation. In order to consider the influence of radiation in the near-wall region and predict the modified wall law, a one-dimensional wall model for Large Eddy Simulation (LES) is proposed. The 1D turbulent equilibrium boundary layer equations are solved on an embedded grid in the inner layer. The obtained wall friction stress and wall conductive flux are then fed back to the LES solver. The radiative power term in the energy equation of the 1D wall model is computed from an analytical model. The proposed wall model is validated by a comparison with the former DNS/Monte-Carlo results. Finally, two criteria are proposed and validated. The first one is aimed to predict the importance of wall radiative heat flux while the other one predicts whether a wall model accounting for radiation in the near wall region is necessary. A parametric study is then performed where a k-ǫ model and a turbulent Prandtl number model are applied to simulate the velocity and temperature field of different channel flows under various flow conditions. The obtained criteria values are analyzed and compared.
16
Glockling, James L. D. "Heat and mass transfer in specific aerosol systems." Thesis, London South Bank University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303937.
Full text
17
Basu, Soumyadipta. "Near-field radiative energy transfer at nanometer distances." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31777.
Full textAbstract:
Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Zhang, Zhuomin; Committee Member: Citrin, David; Committee Member: Hesketh, Peter; Committee Member: Joshi, Yogendra; Committee Member: Peterson, Andrew. Part of the SMARTech Electronic Thesis and Dissertation Collection.
18
Nouri, Nima. "Radiative Conductivity Analysis Of Low-Density Fibrous Materials." UKnowledge, 2015. https://uknowledge.uky.edu/me_etds/66.
Full textAbstract:
The effective radiative conductivity of fibrous material is an important part of the evaluation of the thermal performance of fibrous insulators. To better evaluate this material property, a three-dimensional direct simulation model which calculates the effective radiative conductivity of fibrous material is proposed. Two different geometries are used in this analysis.
The simplified model assumes that the fibers are in a cylindrical shape and does not require identically-sized fibers or a symmetric configuration. Using a geometry with properties resembling those of a fibrous insulator, a numerical calculation of the geometric configuration factor is carried out. The results show the dependency of thermal conductivity on temperature as well as the orientation of the fibers. The calculated conductivity values are also used in the continuum heat equation, and the results are compared to the ones obtained using the direct simulation approach, showing a good agreement.
In continue, the simulated model is replaced by a realistic geometry obtained from X-ray micro-tomography. To study the radiative heat transfer mechanism of fibrous carbon, three-dimensional direct simulation modeling is performed. A polygonal mesh computed from tomography is used to study the effect of pore geometry on the overall radiative heat transfer performance of fibrous insulators. An robust procedure is presented for numerical calculation of the geometric configuration factor to study energy-exchange processes among small surface areas of the polygonal mesh.
The methodology presented here can be applied to obtain accurate values of the effective conductivity, thereby increasing the fidelity in heat transfer analysis.
19
Khan, Yasir Urfat. "Modelling of spectral effects in radiative heat transfer in furnaces." Thesis, Coventry University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337097.
Full text
20
Tong, Jonathan Kien-Kwok. "Photonic engineering of near- and far-field radiative heat transfer." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104127.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 181-195).
Radiative heat transfer is the process by which two objects exchange thermal energy through the emission and absorption of electromagnetic waves. It is one of nature's key fundamental processes and is ubiquitous in all facets of daily life from the light we receive from the Sun to the heat we feel when we place our hands near a fire. Fundamentally, radiative heat transfer is governed by the photonic dispersion, which describes all the electromagnetic states that can exist within a system. It can be modified by the material, the shape, and the environment. In this thesis, morphological effects are used to modify the photonic dispersion in order to explore alternative methods to spectrally shape, tune, and enhance radiative heat transfer from the near-field to the far-field regimes. We start by investigating the application of thin-film morphologies to different types of materials in the near-field regime using a rigorous fluctuational electrodynamics formalism. For thin-film semiconductors, trapped waveguide modes are formed, which simultaneously enhance radiative transfer at high frequencies where these modes are resonant and suppress radiative transfer at low frequencies where no modes are supported. This spectrally selective behavior is applied to a theoretical thermophotovoltaics (TPV) system where it is predicted the energy conversion efficiency can be improved. In contrast, thin-films of metals supporting surface plasmon polariton (SPP) modes will exhibit the opposite effect where the hybridization of SPP modes on both sides of the film will lead to a spectrally broadened resonant mode that can enhance near-field radiative transfer by over an order of magnitude across the infrared wavelength range. In order to observe these morphological spectral effects, suitable experimental techniques are needed that are capable of characterizing the spectral properties of near-field radiative heat transfer. To this end, we developed an experimental technique that consists of using a high index prism in an inverse Otto configuration to bridge the momentum mismatch between evanescent near-field radiative modes and propagation in free space in conjunction with a Fourier transform infrared (FTIR) spectrometer. Preliminary experimental results indicate that this method can be used to measure quantitative, gap-dependent near-field radiative heat transfer spectrally. While utilizing near-field radiative transfer remains a technologically challenging regime for practical application, morphological effects can still be used to modify the optical properties of materials in the far-field regime. As an example, we use polyethylene fibers to design an infrared transparent, visibly opaque fabric (ITVOF), which can provide personal cooling by allowing thermal radiation emitted by the human body to directly transmit to the surrounding environments while remaining visible opaque to the human eye.
by Jonathan Kien-Kwok Tong.
Ph. D.
21
Vujičić, Mile R. "Finite element modelling and experimental validation in radiative heat transfer." Thesis, Swansea University, 2006. https://cronfa.swan.ac.uk/Record/cronfa42640.
Full textAbstract:
The work presented in this thesis can be divided into two parts: numerical modelling and experimental validation. The first part considers a finite element computer code called Pharo which has been developed to simulates heat transfer exchanged in an enclosure via thermal radiation and conduction. This finite element heat transfer code has been written for the Defence, Science and Technology Laboratory (DSTL). Face to face (zonal) thermal radiation which operates with diffuse surface properties of materials without a participating media is analyzed and included in Pharo. To analyze the net heat exchanged within an enclosure several methods for view factor calculation, such as the Monte Carlo and Hemi-cube methods were included in Pharo. During heat transfer simulations a better accuracy of results has been demonstrated using a new approach called the Multiple Reflection of View Factors 'MRV' method. Transient heat flow is solved using both finite difference and finite element time stepping. Also, an analysis of transient heat flow using different solvers (direct and iterative) to find the most appropriate one was carried out. The second part of the work considers experimental validation of numerical results obtained using Pharo. Special attention was given to the analysis of the relationship between view factors and measured heat transfer. To make the experimental data complete the measurements of surface properties including emissivity, reflectivity for different wavelengths as well as roughness of materials is presented. These experimental results can be used as experimental benchmark data for model users and developers.
22
Coyle, Carolyn Patricia. "Advancing radiative heat transfer modeling in high-temperature liquid-salts." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129113.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, September, 2020Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 125-133).
Nuclear and solar-thermal communities are investigating the use of high Prandtl number liquid-salts in energy generation systems, including fluoride salt-cooled high-temperature reactors (FHRs), molten salt reactors (MSRs), fusion devices, and concentrated solar power plants. The temperature distribution in the coolant salts can be affected by participating media radiative heat transfer, due to the high temperature operation and their semitransparent nature. Computational fluid dynamics (CFD) becomes a valuable tool to model the complex 3-dimensional nature of the heat transfer, especially in regions where temperature-dependent material corrosion drives the need for accurate local temperature predictions. Correctly modeling radiative heat transfer in CFD requires well-characterized liquid-salt optical properties, which are not yet known. Additionally, current CFD approaches can become computationally too expensive for practical use when spectral effects need to be resolved.
A lower cost approach, capable of still resolving the coupled convective-radiative heat transfer is therefore needed. In this thesis, an experimental apparatus for measuring the spectral absorption coefficients of 46.5%LiF:11.5%NaF:42%KF (FLiNaK) and 50%NaCl:50%KCl is designed and validated to have high-measurement accuracy in the transmissive and multiphonon absorption regions where radiative emissions peak. A high-fidelity CFD methodology is then developed to model participating media radiative heat transfer. The approach defines a consistent, spectral banding procedure that captures non-gray absorption behavior at reasonable computational cost. The methodology is applied to CFD simulations of a twisted elliptical tube heat exchanger geometry, where local, 3-dimensional effects are especially significant.
A matrix of simulation results comparing FLiNaK and 66.6%LiF:33.4%BeF2 (FLiBe) coolants provides a quantitative assessment of the thermal radiation contributions to the overall heat transfer. Laminar flows, expected in accident scenarios, experience the strongest effect, where lower average wall temperatures and enhanced temperature uniformity result in an effective Nusselt number increase of up to 11%. Turbulent flows see a reduction in maximum local wall temperatures up to 25'C, which could have a notable impact on reducing corrosion effects. The observed trends demonstrate the larger impact of radiation effects in FLiBe simulations due to larger absorption in BeF2. This suggests thermal radiation may be more dominant in MSRs, where dissolved fuel and impurities increase absorption.
The method proposed to include the effects of thermal radiation in CFD analysis can support a more effective and accurate design of high temperature systems and components, providing increased safety margins for operation.
by Carolyn Patricia Coyle.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering
23
Goncalves, Dos santos Rogério. "Large Eddy simulations of turbulent combustion including radiative heat transfer." Châtenay-Malabry, Ecole centrale de Paris, 2008. http://www.theses.fr/2008ECAP1052.
Full textAbstract:
La combustion est actuellement l’un des principaux moyens de convertir l’énergie. Elle reste cependant un phénomène complexe, où des écoulements turbulents, des réactions chimiques, la présence de plusieurs phases et différentes formes de transfert de chaleur peuvent interagir. Mieux comprendre ces interactions est essentiel pour l’amélioration des systèmes actuels de combustion et dans le développement de leurs successeurs. Le but de cette thèse est d’étudier l’interaction entre la combustion turbulente et le rayonnement thermique à l’aide de la simulation numérique en trois dimensions. Pour cela nous utilisons un outil informatique appelé CORBA pour faire communiquer un code dédié à la simulation aux grandes échelles (ou LES, pour Large Eddy Simulation en anglais) de la combustion avec un autre code qui calcule le rayonnement thermique. Cette technique permet l’échange de données entre les codes sans modifier les caractéristiques et la structure de chacun de ces codes. De plus il possible de profiter des temps caractéristiques différents de chaque phénomène physique pour optimiser les calculs sur des calculateurs à architecture massivement parallèle. Dans un premier temps, des simulations bidimensionnelles d’une flamme turbulente prémélangée propane/air stabilisée en aval d’un dièdre ont été réalisées. Après le changement du code de rayonnement pour un code tridimensionnel, la même configuration, du dièdre, a été simulée en 3D. Un maillage avec plus de 4. 7 millions de cellules pour le code de combustion (AVBP) et un autre avec plus de 3. 3 millions de cellules pour le code de rayonnement (DOMASIUM) ont été utilisés. Les résultats montre un changement dans les champsThe combustion is one of the principal ways to produced energy used nowadays, it is also a complex phenomenon, where the turbulent flow, chemical reactions, different phases and different heat transfer phenomena can interact. Better understanding of these interactions is essential to improve the actual combustion system and to developed the new ones. The goal of this thesis is to study the interaction of the turbulent combustion with the thermal radiation by the use of three-dimensional numerical simulation. For that, using a computational tool named CORBA, a code for the combustion Large Eddy Simulation (LES) was coupled with a radiative heat transfer code. This technique allows the exchange of information between the two codes without big changes in their structure, then it is possible to take advantages of the different characteristic time from each phenomenon in a high performance parallel computational environment. In a first time, two-dimensional simulation of a turbulent propane/air premixed flame stabilized downstream a triangular flame holder has been realised. After the changing of the twodimensional radiation code for another three-dimensional one, the same configuration was simulated in 3D. A mesh with more than 4. 7 millions cells for the combustion code (AVBP) and more than 3. 3 millions cells for the radiation code (DOMASIUM) are used. Results show a changing in the temperature and species fields, as well as in the flame dynamics when the thermal radiation was taken into account, with a minor intensity in the three-dimensional simulations. This method, also, shows that it is possible to perform 3D complex simulations in a industrial acceptable time
24
Lussange, Johann A. "The Casimir energy and radiative heat transfer between nanostructured surfaces." Paris 6, 2012. http://www.theses.fr/2012PA066244.
Full textAbstract:
Le sujet de cette thèse porte sur les calculs numériques de deux observables quantiques influents à l'échelle submicrométrique: le premier étant la force de Casimir et le second étant le transfert thermique radiatif. En champ proche, ces deux grandeurs physiques sont à l'origine de nombreuses applications potentielles dans le domaine de la nano-ingénierie. Elles sont théoriquement et expérimentalement bien évaluées dans le cas de géométries simples, comme des cavités de Fabry-Pérot formées par deux miroirs plans parallèles. Mais dans le cas des géométries complexes invariablement rencontrées dans les applications nanotechnologiques réelles, les modes électromagnétiques sur lesquels elles sont construites sont assujettis à des processus de diffractions, rendant leur évaluation considérablement plus complexe. Ceci est le cas par exemple des NEMS ou MEMS, dont l'architecture est souvent non-triviale et hautement dépendante de la force de Casimir et du flux thermique, avec par exemple le problème de mal fonctionnement courant dû à l'adhérence des sous-composants de ces systèmes venant de ces forces ou flux. Dans cette thèse, je m'intéresse principalement à des profils périodiques de forme corrigée qui posent d'importantes contraintes sur la simplicité de calcul de ces observables, et présente les résultats des estimations numériques de ces grandeurs pour des profils variés
25
Morales, Rebellon Juan Carlos. "Radiation exchange within enclosures of diffuse gray surfaces : the inverse problem /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Full text
26
Ströhle, Jochen [Verfasser]. "Spectral Modelling of Radiative Heat Transfer in Industrial Furnaces / Jochen Ströhle." Aachen : Shaker, 2004. http://d-nb.info/1172612382/34.
Full text
27
Ip, Samuel Chun Hung. "Study of radiative heat transfer in porous media for sintering applications /." View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?MECH%202002%20IP.
Full textAbstract:
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002.Includes bibliographical references (leaves 82-85). Also available in electronic version. Access restricted to campus users.
28
Clements, Alastair Greenman. "Modelling mercury oxidation and radiative heat transfer in oxy-coal environments." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/12594/.
Full textAbstract:
There is a growing need for secure, flexible and inexpensive energy across the world, however there is also a need to simultaneously curb emissions of greenhouse gasses and toxic pollutants. Fossil fuel combustion is expected to meet a significant portion the world's growing energy demand, however CO2 emissions need to be mitigated to avoid potentially catastrophic effects caused by global warming. Carbon capture and storage (CCS) technologies have been developed to permit the use of fossil fuel combustion in a future with strict controls over greenhouse gas emissions. CCS technologies are still yet to be deployed at large industrial scales, and it is necessary to reduce the efficiency overheads associated with CCS before the technology is economically feasible. Computational modelling can play a significant role in designing and optimising CCS technologies for power generation due to its flexibility and comparatively low costs. The work in this thesis develops and validates models for predicting mercury oxidation and thermal radiation under oxyfuel combustion conditions, which is a promising CCS technology that is competitively placed for large-scale implementation. The oxidation of mercury is a key chemical process in mitigating emissions of the toxic metal, and predicting the principal oxidation pathways will improve the design of control technologies. Thermal radiation, which is the most significant mode of heat transfer at combustion temperatures, is a very important physical mechanism for predicting many properties of combustion, such as gas temperatures, chemical reaction rates and heat fluxes, and thermal radiation models must accurately account for changes in the combustion environment. The models developed and validated in this thesis provide new approaches to predict mercury oxidation and thermal radiation under oxyfuel conditions. The results and conclusions from this work offer clear guidance on methods to model thermal radiation in oxyfuel conditions, and provide new insight on the mercury oxidation mechanism.
29
Cui, Xiaoming. "Discontinuous finite/boundary element method for radiative heat transfer with application in laser cancer therapy." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Fall2005/x%5Fcui%5F121805.pdf.
Full text
30
Liu, Yan. "Modelling of radiation in laminar flames." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319826.
Full text
31
Fu, Ceji. "Radiative Properties of Emerging Materials and Radiation Heat Transfer at the Nanoscale." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4941.
Full textAbstract:
A negative index material (NIM), which possesses simultaneously negative permittivity and permeability, is an emerging material that has caught many researchers attention after it was first demonstrated in 2001. It has been shown that electromagnetic waves propagating in NIMs have some remarkable properties such as negative phase velocities and negative refraction and hold enormous promise for applications in imaging and optical communications. This dissertation is centered on investigating the unique aspects of the radiative properties of NIMs. Photon tunneling, which relies on evanescent waves to transfer radiative energy, has important applications in thin-film structures, microscale thermophotovoltaic devices, and scanning thermal microscopes. With multilayer thin-film structures, photon tunneling is shown to be greatly enhanced using NIM layers. The enhancement is attributed to the excitation of surface or bulk polaritons, and depends on the thicknesses of the NIM layers according to the phase matching condition. A new coherent thermal emission source is proposed by pairing a negative permittivity (but positive permeability) layer with a negative permeability (but positive permittivity) layer. The merits of such a coherent thermal emission source are that coherent thermal emission occurs for both s- and p-polarizations, without use of grating structures. Zero power reflectance from an NIM for both polarizations indicates the existence of the Brewster angles for both polarizations under certain conditions. The criteria for the Brewster angle are determined analytically and presented in a regime map. The findings on the unique radiative properties of NIMs may help develop advanced energy conversion devices. Motivated by the recent advancement in scanning probe microscopy, the last part of this dissertation focuses on prediction of the radiation heat transfer between two closely spaced semi-infinite media. The objective is to investigate the dopant concentration of silicon on the near-field radiation heat transfer. It is found that the radiative energy flux can be significantly augmented by using heavily doped silicon for the two media separated at nanometric distances. Large enhancement of radiation heat transfer at the nanoscale may have an impact on the development of near-field thermal probing and nanomanufacturing techniques.
32
Singer, Farah. "Influence of the nonlocal effects on the near-field radiative heat transfer." Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2338.
Full textAbstract:
Dans ce mémoire de thèse, nous étudions la validité de quelques modèles non locaux de la permittivité diélectrique (PD) dans le calcul du coefficient de transfert de chaleur par rayonnement (CTCR) entre deux matériaux diélectriques, semi- infinies, plans et parallèles, et séparés par un espace vide de largeur d.Dans les études théoriques antérieures, il a été montré que lorsque l'on considère un modèle local de la PD, le transfert de chaleur par rayonnement en champ proche (TCRCP) suit une loi 1/d² quand d devient de l'ordre ou inférieure à quelques centaines de nanomètres. Cette divergence non physique constitue la faille majeure du modèle local. Plusieurs efforts ont été fournis afin de développer un nouveau modèle de la PD qui tient compte des effets nonlocaux. Aucune correction non locale pour le TCRCP n’a été abordée dans le passé dans le cas des diélectriques. Cependant dans le cas des métaux, un travail complet a été effectué en utilisant le modèle non local de Lindhard-Mermin de la PD.Nos travaux portent sur l'étude de quatre modèles différents de la PD nonlocale. Nous exploitons ces modèles pour le calcul du CTCR entre deux plans de 6H-SiC. Nous montrons que le CTCR sature quand d tend vers zéro. La distance du début de saturation dépend grandement des paramètres clés de chaque modèleIn this thesis, we study the validity of few nonlocal models of the dielectric permittivity in the calculation of the radiative heat transfer coefficient (RHTC) between two semi-infinite parallel dielectric planes separated by a vacuum gap of width d.In past theoretical studies, it has been shown that upon considering a local model of the dielectric permittivity, near field radiative heat transfer (NFRHT) between two dielectric materials follows a 1/d2 law when d is of the order or less than few hundreds of nanometers. This nonphysical diverging increase has been the bottleneck of the local model. Overwhelming efforts have been deployed in order to come up with a new model in which the nonlocal effects of the dielectric permittivity are taken into account. To the best of our knowledge, no nonlocal correction to the NFRHT has been addressed in the past in the case of dielectrics. In the case of metals however, an important and complete work has been performed using the Lindhard-Mermin nonlocal dielectric permittivity model.Our work focuses on studying four different nonlocal models of the dielectric permittivity and on using them in the calculation of the RHTC between two solid semi-infinite parallel planes of 6H-SiC. We show that the RHTC saturates as the separation distance d tend to zero. The distance at which saturation starts to take place depends on key parameters involved in each model
33
English, Justin. "HEAT TRANSFER CHARACTERISTICS IN WILDLAND FUELBEDS." UKnowledge, 2014. http://uknowledge.uky.edu/me_etds/52.
Full textAbstract:
The fundamental physics governing wildland fire spread are still largely misunderstood. This thesis was motivated by the need to better understand the role of radiative and convective heat transfer in the ignition and spread of wildland fires. The focus of this work incorporated the use of infrared thermographic imaging techniques to investigate fuel particle response from three different heating sources: convective dominated heating from an air torch, radiative dominated heating from a crib fire, and an advancing flame front in a laboratory wind tunnel test. The series of experiments demonstrated the uniqueness and valuable characteristics of infrared thermography to reveal the hidden nature of heat transfer and combustion aspects which are taking place in the condensed phase of wildland fuelbeds. In addition, infrared thermal image-based temperature history and ignition behavior of engineered cardboard fuel elements subjected to convective and radiative heating supported experimental findings that millimeter diameter pine needles cannot be ignited by radiation alone even under long duration fire generated radiant heating. Finally, fuel characterization using infrared thermography provided a better understanding of the condensed phase fuel pyrolysis and heat transfer mechanisms governing the response of wildland fuel particles to an advancing flame front.
34
Ko, Min Seok. "Numerical simulation of three-dimensional combined convective radiative heat transfer in rectangular channels." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-2542.
Full text
35
Erfurth, Jens [Verfasser]. "Radiative Heat Transfer in Coal-Fired Furnaces and Oxycoal Retrofit Considerations / Jens Erfurth." Aachen : Shaker, 2012. http://d-nb.info/1069048372/34.
Full text
36
Rehfeldt, Sebastian [Verfasser], and Günter [Akademischer Betreuer] Scheffnecht. "Radiative heat transfer in oxy-fuel steam generators / Sebastian Rehfeldt ; Betreuer: Günter Scheffnecht." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2016. http://d-nb.info/1118507487/34.
Full text
37
Henson, Jonathan Charles. "Numerical simulation of spark ignition engines with special emphasis on radiative heat transfer." Thesis, Loughborough University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297589.
Full text
38
Shapiro, Michael Jay. "An experimental investigation of the thermal conductivity of thin-wall hollow ceramic spheres." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/8667.
Full text
39
Lan, Chao-ho. "Radiative combined-mode heat transfer in a multi-dimensional participating medium using spectral methods /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004312.
Full text
40
Maag, Gilles. "Monte Carlo radiative heat transfer analysis of a CH₄ flow laden with carbon particles." Zürich : ETH, Eidgenössische Technische Hochschule Zürich, Institute of Energy Technology, 2006. http://e-collection.ethbib.ethz.ch/show?type=dipl&nr=283.
Full text
41
Warude, Anand. "Analysis of glass mold to enhance rate of heat transfer." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000618.
Full text
42
Savur, Mehmet Koray. "A numerical study of combined convective and radiative heat transfer in a rocket engine combustion chamber." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FSavur.pdf.
Full text
43
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.
Full textAbstract:
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.
44
Okyay, Gizem. "Impact of the morphology of soot aggregates on their radiative properties and the subsequent radiative heat transfer through sooty gaseous mixtures." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC031/document.
Full textAbstract:
Les suies et leur caractérisation constituent des sujets de recherche très actuels dans divers domaines tels que le diagnostic de la combustion, la combustion numérique, l’optique atmosphérique, l'environnement et les applications de santé. Notre étude se concentre sur les propriétés radiatives des agrégats de suie issus de flammes de combustion ; notre objectif est de déterminer l’effet de la présence de suies sur le transfert de chaleur par rayonnement pour la simulation d'applications industrielles à haute température impliquant la combustion de gaz. Les études actuelles de modélisation du transfert de chaleur par rayonnement à travers les mélanges gazeux chargés de suies ne considèrent que l'absorption comme phénomène d'interaction rayonnement-matière. Des corrélations généralisées sont utilisées pour déterminer les propriétés radiatives des suies, soit sur la base de morphologies générées numériquement, soit plus simplement à partir de la taille moyenne des suies, de leur dimension fractale et de leur fraction volumique. Cependant, lorsque la taille de l'objet atteint l'ordre de grandeur des longueurs d'onde du rayonnement incident, l'interaction matière-rayonnement est susceptible d’être plus complexe du fait du phénomène de diffusion au niveau de l’agrégation qui ne peut plus être ignoré.Dans notre travail, nous établissons une méthodologie complète assortie d’une chaîne de calcul allant de la définition d'une morphologie de suie réaliste jusqu'au calcul du transfert de chaleur par rayonnement. À cette fin, des observations de suies émises par des flammes propane / air, méthane / air et méthane / oxygène sont effectuées par Microscopie Electronique à Balayage (MEB). La tomographie MEB est appliquée pour la première fois sur une suie issue d’une flamme propane / air, en combinaison avec la Microscopie Electronique en Transmission (MET) pour les observations. Des techniques d'analyse fractale 2D et 3D sont utilisées pour étudier les propriétés fractales d’agrégats de suie virtuels (générés numériquement) et de l'objet obtenu par la tomographie. Les propriétés radiatives des suies sont ensuite calculées en utilisant notre propre code d’Approximation Dipolaire Discrète (ADD – Discrete Dipole Approximation, ou DDA, en anglais). Une attention particulière est accordée à la modélisation ADD des suies en raison de l’indice optique complexe élevé de leur matériau constitutif, et aux méthodes numériques d’intégration directionnelle car les moyennes directionnelles des propriétés radiatives sont nécessaires pour les simulations ultérieures de transfert radiatif. La morphologie et les propriétés radiatives de l’agrégat de suie réaliste (tomographié) sont comparées à celles d'agrégats de suie numériques représentatifs, générés par un algorithme d’agrégation amas-amas limitée par la diffusion (Diffusion Limited Cluster-Cluster Aggregation, ou DLCCA, en anglais). Les compatibilités et les écarts entre les propriétés radiatives sont examinés, et les différences entre agrégats numériques représentatifs d’une part et agrégat réaliste d’autre part en termes de propriétés radiatives sont soulignées. Enfin, l'effet de la présence et de la morphologie des suies sur le transfert de chaleur par rayonnement est étudié par la résolution de l'équation du transfert radiatif en utilisant la méthode des ordonnées discrètes (Discrete Ordinates Method, ou DOM, en anglais) dans un mélange gazeux chargé de suies et dans une configuration académique 1D de plaques parallèles isothermesSoot and its characterization are of interest to researchers from various domains such as combustion diagnostics, numerical combustion, atmospheric optics, environmental and health applications. In this study, the main interest is on the radiative properties of soot aggregates issued directly from combustion flames in order to determine the effect of the presence of soot on the radiative heat transfer in the simulation of high temperature industrial applications involving gas combustion. Current studies modeling the radiative heat transfer through sooty gaseous media consider only the absorption as the main phenomenon of material-radiation interaction. Generalized correlations are used to determine the radiative properties of soot: these radiative properties are either computed over numerically generated aggregate morphologies or simply as a function of the soot average size, the fractal dimension and the volume fraction. However, the material-radiation interaction is susceptible to be more complex and morphology dependent at the aggregate level because of multiple scattering when the size of the object reaches the order of magnitude of the incident radiation wavelengths.In our work, we investigate the possibility to establish a computational methodology and workflow, starting from the definition of a realistic soot morphology up to the computation of the radiative heat transfer. To that end, observations of soot issued from propane/air, methane/air and methane/oxygen flames are performed using Scanning Electron Microscopy (SEM). SEM tomography is applied for the first time on soot issued from a propane/air flame, combined with Transmission Electron Microscopy (TEM) observations. 2D and 3D fractal analysis techniques are used to investigate the fractal properties of virtual (numerically generated) soot clusters and also of the tomography reconstructed objects. The radiative properties of soot are then computed using our in-house developed DDA (Discrete Dipole Approximation) code. Special attention is paid to the DDA modeling of soot because of the high complex extinction index of the material, and to the directional integration numerical methods because direction-averaged radiative properties are required for the subsequent radiative heat transfer simulations. The morphology and the radiative properties of the realistic morphology are compared to the ones of representative soot aggregates numerically generated by a DLCCA (Diffusion Limited Cluster-Cluster Aggregation) algorithm. The similarities and discrepancies on the radiative properties are investigated, and the differences between representative virtual aggregates on the one hand and the tomography reconstructed object on the other hand in terms of radiative properties are highlighted. Finally the effect of the presence and of the morphology of soot on the radiative heat transfer within a sooty gaseous mixture in a 1D isothermal parallel plate configuration is investigated by the resolution of the radiative transfer equation using DOM (Discrete Ordinates Method)
45
Zhang, Chang. "Radiative Heat Transfer in Free-Standing Silicon Nitridemembranes in the Application of Thermal Radiation Sensing." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41409.
Full textAbstract:
Thin-film silicon nitride (SiN) membranes mechanical resonators have been widely used for many fundamental opto-mechanical studies and sensing technologies due to their extremely low mechanical dissipation (high mechanical Q-factor). In this work, we experimentally demonstrate an opto-mechanical approach to perform thermal radiation sensing, using a SiN
membrane resonator. An important aspect of this work is to develop a closed-form analytical heat transfer model for assessing the thermal coupling conditionbetween free-standing membranes and their environment. We also derive analytical expressions for other important intrinsic thermal quantities of the membrane, such as thethermal conductance, the heat capacity and the thermal time constant. Experimental results show good agreement with our theoretical prediction. Of central importance, we show that membranes of realistic dimensions can be coupled to their environment more strongly via radiation than by solid-state conduction. For example, membranes with 100nm thickness (frequently encountered size) are predicted to be radiation dominated when their side length exceeds 6 mm. Having radiation dominated thermal coupling is a key ingredient for reaching the fundamental detectivity limit of thermal detectors. Hence, our work proves that SiN membranes are attractive candidates for reaching the fundamental limit. We also experimentally exhibit the high temperature responsivity of the SiN membranes resonance, in which we shift a 88.7 KHz resonance by over 1 KHz when temperature increment on the membrane is approximately 2 K.
46
Johnson, Dennis R. "Analysis and synthesis of radiative heat transfer in longitudinal fins in free space and non-free space." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA236942.
Full textAbstract:
Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, June 1990.Thesis Advisor(s): Kraus, Allan D. Second Reader: Brown, Sue. "June 1990." Description based on signature page. DTIC Identifier(s): Radiators (heating and cooling), radiative transfer, heat transfer (radiation). Author(s) subject terms: Radiative heat transfer, longitudinal fins, free space and non-free space. Includes bibliographical references (p. 147-148). Also available online.
47
Avila, Matías. "Nonlinear subgrid finite element models for low Mach number flows coupled with radiative heat transfer." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285809.
Full textAbstract:
The general description of a fluid flow involves the solution of the compressible Navier-Stokes equations, a very complex problem whose mathematical structure is not well understood. It is widely accepted that these equations provide an accurate description of any problem in fluid mechanics which may present many different nonlinear physical mechanisms. Depending on the physics of the problem under consideration, different simplified models neglecting some physical mechanisms can be derived from asymptotic analysis. On the other hand, radiative heat transfer can strongly interact with convection in high temperature flows, and neglecting its effects may have significant consequences in the overall predictions. Problems as fire scenarios emphasized the need for an evaluation of the effect of radiative heat transfer. This work is directed to strongly thermally coupled low Mach number flows with radiative heat transfer.
The complexity of these mathematical problem makes their numerical solution very difficult. Despite the important difference in the treatment of the incompressibility, the low Mach number equations present the same mathematical structure as the incompressible Navier-Stokes equations, in the sense that the mechanical pressure is determined from the mass conservation constraint. Consequently the same type of numerical instabilities can be found, namely, the problem of compatibility conditions between the velocity and pressure finite element spaces, and the instabilities due to convection dominated flows. These instabilities can be avoided by the use of stabilization techniques. Many stabilization techniques used nowadays are based on the variational multiscale method, in which a decomposition of the approximating space into a coarse scale resolvable part and a fine scale subgrid part is performed. The modeling of the subgrid scale and its influence leads to a modified coarse scale problem providing stability. The quality of the final approximation (accuracy, efficiency) depends on the particular model.
The extension of these techniques to nonlinear and coupled problems is presented. The distinctive features of our approach are to consider the subscales as transient and to keep the scale splitting in all the nonlinear terms appearing in the finite element equations and in the subgrid scale model. The first ingredient permits to obtain an improved time discretization scheme(higher accuracy, better stability). The second ingredient permits to prove global conservation properties, being also responsible of the higher accuracy of the method. This ingredient is intimately related to the problem of thermal turbulence modeling from a strictly numerical point of view. The capability for the simulation of turbulent flows is a measure of the ability of modeling the effect of the subgrid flow structures over the coarser ones. The performance of the model in predicting the behavior of turbulent flows is demonstrated.
The radiation transport equation has been also approximated within the variational multiscale framework, the design and analysis of stabilized finite element methods is presented.La descripción general del movimiento de un flujo implica la solución de las ecuaciones de Navier-Stokes compresibles, un problema de muy compleja estructura matemática. Estas ecuaciones proporcinan una descripción detallada de cualquier problema en mecánica de fluidos, que puede presentar distintos mecanismos no lineales que interactúan entre si. En función de la física del problema que se esté considerando, pueden derivarse modelos simplificados de las ecuaciones de Navier-Stokes mediante analisis dimensional, que ignoran algunos fenómenos físicos. Por otro lado, la transferencia de calor por radiación puede interactuar con el movimiento de un fluido, e ignorar sus efectos puede tener consecuencias importantes en las predicciones del flujo. Problemas donde hay fuego implican la evaluacion del efecto del calor por radiación. El presente trabajo está dirigido a flujos a bajo número de Mach térmicamente acoplados, donde el calor por radiación afecta al flujo. Debido a la complejidad del problema matemático, la solución numérica es muy complicada. A pesar de las diferencia en el tratamiento de la incompresibilidad, las ecuaciones de flujo a bajo número de Mach poseen una estructura matemática similar a la de flujo incompresible, en el sentido que la presión mecánica se determina a partir de la ecuación de conservación de la masa. En consecuencia poseen el mismo tipo de inestabilidades numéricas, que son el problema de condiciones de compatibilidad entre los espacios de elementos finitos de velocidad y presión, y las inestabilidades debidas a flujos con convección dominante. Estas inestabilidades pueden evitarse mediante técnicas de estabilización numérica. Muchos métodos de estabilización utilizados hoy día se basan en el método de multiscalas variacionales, donde el espacio funcional de la solucion se divide en un espacio discreto y resolubre y un espacio infinito de subscalas. El modelado de las subescalas y su influencia modifican el problema discreto proporcionando estabilidad. La calidad de la aproximación numérica final (precisión, eficiencia) depende del modelo particular de subescalas. En este trabajo se extienden estas técnicas de estabilización a problemas no lineales y acoplados. Las características que distinguen a nuestra aproximación son considerar las subsecalas como transitorias y mantener la división de escalas en todos los términos no lineales que aparecen en las ecuaciones de elementros finitos y en las del modelo de subescalas. La primera característica permite obtener mayor precisión y mejor estabilidad en la solución, la segunda característica permite obtener esquemas donde las propiedades se conservan globalmente, y mayor precisión del método. El hecho de mantener la división de escalas en todos los términos no lineales está intimamemte relacionado con el modelado de turbulencia en flujos térmicamente acoplados desde un punto de vista estrictamente numérico. La capacidad de simulación de flujo turbulento es una medida de la habilidad de modelar el efecto de las estructuras de escala fina sobre las estructuras de escala gruesa. Se muestra en esta tesis el desempeño del método para de predecir flujo turbulento. La ecuación de transporte de radiación también se aproxima numéricamente en el marco de multiscala variacional. El diseño y análisis de este método se presenta en detalle en esta tesis
48
Coetsee, Theresa. "Non-isothermal reaction of iron ore-coal mixtures." Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-07092008-142912/.
Full text
49
Paul, Sreebash Chandra. "Large eddy simulation of a fuel-rich turbulent non-premixed reacting flow with radiative heat transfer." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/203/.
Full textAbstract:
The aims of this thesis are to apply the Large Eddy Simulation (LES) and beta Probability Density Function (β- PDF) for the simulation of turbulent non-premixed reacting flow, in particularly for the predictions of soot and NO production, and to investigate the radiative heat transfer during combustion process applying Discrete Ordinates Method (DOM). LES seeks the solution by separating the flow field into large-scale eddies, which carry the majority of the energy and are resolved directly, and small-scale eddies, which have been modelled via Smagorinsky model with constant Cs (Smagorinsky model constant) as well as its dynamic calibration. This separation has been made by applying a filtering approach to the governing equations describing the turbulent reacting flow. Firstly, LES technique is applied to investigate the turbulent flow, temperature and species concentrations during the combustion process within an axi-symmetric model cylindrical combustion chamber. Gaseous propane (C3H8) and preheated air of 773K are injected into this cylindrical combustion chamber. The non-premixed combustion process is modelled through the conserved scalar approach with the laminar flamelet model. A detailed chemical mechanism is taken into account to generate the flamelet. The turbulent combustion inside the chamber takes place under a fuel-rich condition for which the overall equivalence ratio of 1.6 is used, the same condition was used by Nishida and Mukohara [1] in their experiment. Secondly, the soot formation in the same flame is investigated by using the LES technique. In this thesis, the soot formation is included through the balance equations for soot mass fraction and soot particle number density with finite rate kinetic source terms to account for soot inception/nucleation, surface growth, agglomeration and oxidation. Thirdly, the NO formation in the flame is studied by applying the LES. The formation of NO is modelled via the extended Zeldovich (thermal) reaction mechanism. A transport equation for NO mass fraction is coupled with the flow and composition fields. Finaly, the radiative heat transfer in the flame is investigated. Both the luminous and non-luminous radiations are modelled through the Radiative Transfer Equation (RTE). The RTE is solved using the Discrete Ordinates Method (DOM/Sn) combining with the LES of the flow, temperature, combustion species and soot formation. The computed results are compared with the available experimental results and the level of agreement between measurements and computations is quite good.
50
Hua, Yulong. "Modelling and simulation of circulating fluidized bed combustors : solid segregation, radiative heat transfer and coal combustion." Perpignan, 2004. http://www.theses.fr/2004PERP0570.
Full textAbstract:
This dissertation aims to develop an overall mathematical model of circulating fluidized bed (CFB) combustors on up-to-date theories and experimental data of previous research work. Since solid exhibits a wide particle size distribution in a CFB boiler, a hydrodynamic model based on the semi-empirical approach is developed to approximate the local particle size distribution in CFB. The core/annulus flow structure is applied to this model and the particles in the bed are discretized into several size groups. The model accounts for the disintegration and shrinking of coal particles during the combustion process of each group of particles. It shows that coarser particles are gathered near the walls and the average particle diameter decreases along the boiler height, and this trend is more significant in the splash region. A three-dimensional model is developed to predict the bed-to-wall radiative heat transfer coefficient in the upper dilute zone of CFB combustors. The radiative transfer equation is solved by the discrete ordinates method. The Mie scattering theory is applied to calculate the absorption and scattering efficiency factors of particles existing in CFB combustors. The model considers the influences of the particle properties (including particle size distribution, particle optical constants and solid composition) on the radiative heat transfer coefficient. Simulation results show that the particle properties have significant influences on the bed-to-wall radiative heat transfer coefficient in CFB combustors. A coal combustion model is developed combined to the hydrodynamic model and heat transfer modelL'objectif de ce travail est de développer un modèle mathématique global d'une chaudière à lit fluidisé circulant (LFC) à partir des théories les plus récentes et des résultats expérimentaux issus de la bibliographie. Un modèle hydrodynamique basé sur une approche semi-empirique est développé pour estimer localement la distribution de taille de particules dans le LFC. Une structure de flux solide de type cœur/anneau est appliquée dans le modèle, et la population de particules est discrétisée en plusieurs groupes de différentes tailles. Il montre que les particules les plus grosses se regroupent près des parois et que le diamètre moyen décroît avec la hauteur dans la chaudière, et cette tendance est encore plus forte dans la zone de projections. Un modèle à trois dimensions est développé pour calculer le coefficient de transfert de chaleur par rayonnement dans la zone diluée supérieure des chaudières à LFC. L'équation de transfert radiatif est résolue par la méthode des ordonnées discrètes. La théorie de Mie est appliquée pour calculer les efficacités d'absorption et de diffusion des particules présentes dans le LFC. Le modèle traite de l'influence des propriétés des particules (distribution de taille, propriétés optiques, composition des la phase solide) sur le coefficient de transfert de chaleur par rayonnement. Les résultats de la simulation montrent que les propriétés des particules ont une influence importante sur les échanges radiatifs dans les chaudières à LFC. Un modèle de combustion de charbon combiné au modèle hydrodynamique est développé