This research is concerned with the self-adaptive numerical solution of the neutral particle radiation transport problem. Radiation transport is an extremely challenging computational problem since the governing equation is seven-dimensional (3 in space, 2 in direction, 1 in energy, and 1 in time) with a high degree of coupling between these variables. If not careful, this relatively large number of independent variables when discretized can potentially lead to sets of linear equations of intractable size. Though parallel computing has allowed the solution of very large problems, available computational resources will always be finite due to the fact that ever more sophisticated multiphysics models are being demanded by industry. There is thus the pressing requirement to optimize the discretizations so as to minimize the effort and maximize the accuracy. One way to achieve this goal is through adaptive phase-space refinement. Unfortunately, the quality of discretization (and its solution) is, in general, not known a priori; accurate error estimates can only be attained via the a posteriori error analysis. In particular, in the context of the finite element method, the a posteriori error analysis provides a rigorous error bound. The main difficulty in applying a well-established a posteriori error analysis and subsequent adaptive refinement in the context of radiation transport is the strong coupling between spatial and angular variables. This research attempts to address this issue within the context of the second-order, even-parity form of the transport equation discretized with the finite-element spherical harmonics method. The objective of this thesis is to develop a posteriori error analysis in a coupled space-angle framework and an efficient adaptive algorithm. Moreover, the mesh refinement strategy which is tuned for minimizing the error in the target engineering output has been developed by employing the dual argument of the problem. This numerical framework has been implemented in the general-purpose neutral particle code EVENT for assessment.

The first part of the thesis assesses the aerosol direct radiative effect (ADRE) with a focus on ground-based AERONET and satellite MODIS measurements. The AERONET aerosol climatology is used, in conjunction with surface albedo and cloud products from MODIS, to calculate the ADRE and its normalized form (NADRE) for distinct aerosol regimes. The NADRE is defined as the ADRE normalized by optical depth at 550 nm and is mainly determined by internal aerosol optical properties and geographical parameters. These terms are evaluated for cloud-free and cloudy conditions and for all-mode and fine-mode aerosols. We find that the NADRE of fine-mode aerosol is larger at the TOA but smaller at the surface in comparison to that of all-mode aerosol. Cloudy-sky TOA ADRE with clouds is sensitive to the relative location of aerosols and cloud layer. The high-resolution MODIS land surface albedo is also applied to study the clear-sky ADRE over North Africa and the Arabian Peninsula for summer 2001. TOA ADRE shows the high spatial variability with close similarity to that of surface albedo. The second part of the thesis is to develop a 2-D conceptual model for a climatological convective boundary layer over land as a persistent and distinct component in climate models, where the convective-scale motion is explicitly described by fluid dynamics and thermodynamics while the smaller scale effect is parameterized for a neutral stratification. Our conceptual model reasonably reproduces essential statistics of a convective boundary layer in comparison to large eddy simulations. The major difference is that our model produces a better organized and more constrained spatial distribution with coherent convective cells. The simulations for a climatological convective boundary layer are conducted for a prescribed constant and homogenous surface heat flux and a specified cooling term representing the background large scale thermal balance. The results show the 2-D coherent structures of convective cells with characteristic scales comparable with PBL height; downward maximum velocities being 70-80% of the accompanying upward maxima; vertical profiles of a constant potential temperature and linear decreasing heat fluxes; a square-root increase in the velocity magnitude with increasing surface heat flux.

Simultaneous solution of the conservation equations for energy and chemical species in conjunction with radiative transfer equation was carried out by coupling a previously developed and tested system model of fluidized bed combustion (FBC) to an existing radiation model. The predictive accuracy of the coupled code was assessed by applying it to 0.3 MWt METU Atmospheric Bubbling Fluidized Bed Combustor (ABFBC) Test Rig burning lignite in its own ash and comparing its predictions with the measured temperatures and concentrations of gaseous species along the combustor and radiative heat fluxes incident on the refractory-lined freeboard walls on two combustion tests, with and without recycle. The predictions of the coupled code were found to be in good agreement with the measurements. For the investigation of the significance of coupling of the radiation model to the system model, temperature predictions of the coupled code were compared with those obtained by the original system model. It was found that the effect of incorporating a radiation model into the system model on the predictions was not significant because the high temperatures of refractory-lined freeboard walls and high surface to volume ratio of the test rig under consideration cause the incident radiative heat fluxes to be dominated by walls rather than the particle laden gas emissions. However, in industrial boilers, freeboard is surrounded by water-cooled membrane walls and boilers have much lower surface to volume ratio. In order to examine the effects of both on radiation in industrial boilers, an investigation was carried out on 16 MWt Stationary Fluidized Bed Boiler (SFBB) by applying radiation model, in isolation from the system model, to the freeboard of the boiler. It was found that in the boiler, incident radiative heat fluxes were dominated by particle laden gas emissions. In brief, the coupled code proposed in this study proves to be a useful tool in qualitatively and quantitatively simulating the processes taking place in an atmospheric fluidized bed boilers.

Finned heat sink use for electronics cooling via natural convection is numerically investigated. An experimental study from the literature that is for vertical surfaces is taken as the base case and the experimental setup is numerically modeled using commercial CFD software. The flow and temperature fields are resolved. A scale analysis is applied to produce an order-of-magnitude estimate for maximum convection heat transfer corresponding to the optimum fin spacing. By showing a good agreement of the results with the experimental data, the model is verified. Then the model is used for heat transfer from inclined surfaces. After a large number of simulations for various forward and backward angles between 0-90 degrees, the dependence of heat transfer to the angle and Rayleigh number is investigated. It is observed that the contributions of radiation and natural convection changes with the angle considerably. Results are also verified by comparing them with experimental results available in literature.

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission provides unique measurements of vertical profiles of aerosols and clouds and their properties during day and night-time over all types of surfaces. This information has the potential to significantly improve our understanding of the properties and effects of aerosol and clouds. This dissertation presents the results of a comprehensive analysis of CALIPSO lidar (version 2 and version 3.01) data in conjunction with A-Train satellite and ground-based observations aimed at characterizing mineral aerosol in East Asia and other major dust sources. The specific objectives were to characterize the spatial distribution and properties of atmospheric dust in the dust source regions using new CALIOP (version 3.01) data in conjunction with satellite MODIS, OMI, and CloudSat data and ground-based meteorological and lidar data; investigate changes in the vertical distribution and properties of dust during mid- and long-range transport; perform a modeling of the optical properties of nonspherical dust particles, and assess the radiative forcing and heating/cooling rates of atmospheric dust by performing radiative transfer modeling constrained by satellite data in major dust source regions.

The spectral and directional control of radiative properties by utilizing engineered micro/nanostructures has enormous applications in photonics, microelectronics, and energy conversion systems. The present dissertation aims at: (1) design and analysis of micro/nanostructures based on wave interference and magnetic resonance effects to achieve tunable coherent thermal emission or enhanced optical transmission; (2) microfabrication of the designed structures; and (3) development of a high-temperature emissometer to experimental demonstrate coherent thermal emission from fabricated samples at temperatures from 300 K to 800 K. Asymmetric Fabry-Perot resonant cavities were studied as a potential coherent emission source. The reflectance was measured at room temperature using a Fourier-transform infrared spectrometer, and the emittance can be indirectly obtained from Kirchhoff's law. A high-temperature emissometer was built to measure the thermal emission of fabricated samples, and the temperature effect on the emission peaks was discussed. The direct and indirect approaches were unified and a generalized Kirchhoff's law was deduced to calculate thermal emission from layered structures with nonuniform temperatures. Magnetic polaritons were identified as a mechanism for achieving extraordinary optical transmission/absorption, through the comparison between equivalent capacitor-inductor models and the rigorous coupled-wave analysis. With carefully tuned geometric parameters, the resonance frequencies can be tailored for specific applications. A coherent emission source was designed with grating structures by excitation of magnetic polaritons, and is well suitable for thermophotovoltaic applications, thanks to the spectral selectivity and directional insensitivity of magnetic polaritons. Test samples were fabricated, and coherent thermal emission was experimentally observed at room temperatures up to 800 K. The results obtained in this dissertation will facilitate the design and application of micro/nanostructures in energy-harvesting systems.

Arrays of nanotubes/rods made of appropriate materials can yield unique radiative properties, such as large absorption and optical anisotropy, with broad applications from high-efficiency emitters and absorbers for energy conversion to the polarization conversion via anisotropic responses. The objective of this dissertation is to investigate the radiative properties of arrays formed by aligned carbon nanotubes (CNTs) and silver nanorods (AgNRs). The CNT arrays used in the present study consist of multi-walled CNTs synthesized vertically on silicon substrates using thermal chemical vapor deposition. Their close-to-unity absorptance is demonstrated by measuring the directional-hemispherical reflectance in the visible and near-infrared spectral ranges using an integrating sphere. The bidirectional reflectance distribution function and angle-resolved reflectance were measured at the 635-nm wavelength. The results demonstrate that high-absorptance CNT arrays may be diffusely or specularly reflecting and have important applications in radiometry. Theoretical modeling based on the effective medium theory (EMT) and reflectivity of an anisotropic medium are developed to explain the high absorption and polarization dependence. The effective optical constants of the CNT array for both ordinary and extraordinary polarizations are quantitatively determined by fitting the angle-resolved reflectance. The AgNR arrays used in the present study were fabricated using oblique angle deposition, which results in inclined Ag nanorods that can be modeled as an effective homogenous and optically anisotropic thin film. The spectral and directional radiative properties of AgNRs grown on different substrates, including a glass slab with a silver film, and compact disc gratings, were characterized at the 635-nm and 977-nm wavelengths for different polarizations. The results are analyzed based on the EMT, rigorous coupled-wave analysis, and anisotropic thin-film optics. The results of this dissertation help gain a better understanding of radiative properties of anisotropic nanostructures for potential applications in high-efficiency energy conversion, radiometric devices, and optical systems.

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Das Afterglow tritt am Übergang vom Plasma zur Gasphase auf. Die dominierende aktive Spezies im Afterglow sind metastabil angeregte Neutralteilchen. Der Abbau der Metastabilen erfolgt in drei verschiedenen Prozessen: dem radiativen Zerfall, den Quenching-Stößen sowie der Relaxation in Stößen mit Oberflächen. Potentielle Anwendungsmöglichkeiten des Afterglows für Schichtabscheidung und Oberflächenmodifizierung werden diskutiert. Zur theoretischen Beschreibung des strömenden Afterglows wurde ein Collisional Radiative Modell entwickelt, welches die Reflexion angeregter Spezies an Oberflächen berücksichtigt. Als Diagnostikmethoden wurden die optische Emissionsspektroskopie (OES), die Chemolumineszenz sowie die Langmuir-Sondenmessungen eingesetzt, um die Konzentration metastabil angeregter Spezies zu bestimmen. Es wurde der Einfluß von konstruktiven und äußeren Paramentern auf die Konzentration metastabil angeregter Spezies im Afterglow untersucht. Es zeigt sich, daß unter den gegebenen Bedingungen die Quenching-Stöße der dominierende Verlustprozeß im Afterglow sind. Die Parameter Druck, Strömungsgeschwindigkeit und Länge des Afterglows können zu einem Skalierungsparameter zusammengefaßt werden, der zur online-Prozeßregulierung verwendet werden kann. Es werden

Part I of this thesis is a theoretical background to parts II and III. Part II treats the phenomenon of decreased visibility through a glazing due to external water condensation, dew, on the external surface. Some simulations are presented where it is shown that under certain circumstances condensation can be expected. A combination of coatings on the external surface is suggested to overcome the problem of external condesation. It consists of both a coating which decreases the emissivity of the surface and a hydrophilic coating which reduces the detrimental effects to the view through the window. Fresnel calculations of the optical properties are used to discuss the feasibility of using different coatings. A new test box was used to verify that the proposed window coatings perform as expected. Part III is a study on the angular dependence of solar absorptance in windows. Optical properties vary with the angle of incidence of the incoming light. The variation is different from one window pane to another. A model is proposed to approximate the angular variation of the solar absorptance in window panes. The model is semi-empirical and involves dividing the wide range of windows into nine groups. To which group a window belongs, depends on how many panes it has and on the features of the outer pane. The strength of the model is that it can be used without knowing the exact optical properties of each pane of the window. This makes it useful in the many cases when these data are not given by the manufacturer and Fresnel calculations to get the optical properties of the window are not feasible. The model is simple and can be added as an appendix to existing standards for measuring optical properties of windows.