Advanced Deterministic Phonon Transport Techniques for Predicting Spectral Thermal Conductivity in Homogeneous and Heterogeneous Media

We present a deterministic spectral method to predict equilibrium temperature distributions, heat flux, and thermal conductivity in homogeneous and heterogeneous media. We solve the Boltzmann transport equation in a second order spatial, self-adjoint angular flux formulation. We implemented this method into the radiation transport code Rattlesnake, built using the MOOSE (Multiphysics Object Oriented Simulation Environment) framework. The spatial variable is discretized using the continuous finite element method with unstructured meshes, and the angular variable is discretized with the discrete ordinates method. We implemented the diffuse mismatch model in a general geometry to simulate phonon interfacial resistance, using the grey approximation of the Boltzmann transport equation. Using material properties generated by density functional theory and molecular dynamics methods, we were able to elucidate properties of xenon (Xe) at temperatures and pressures experienced in irradiated nuclear fuel. We found Xe to undergo phase change from liquid to solid, and were able to compute coefficients of phonon transmission and reflection at the Xe-UO$_{2}$ interface. We found $\kappa$ to decrease by about a factor of 4 with increasing temperature, agreeing with other trends and research in the open literature. We developed a new method for simulating deterministic, spectral phonon transport to predict heat flux, thermal conductivity, and equilibrium temperature distributions in homogeneous and heterogeneous materials. All the spectral phonon groups are coupled through a local average material temperature, and a new term, $\beta$, is derived and is used as a closure term in the phonon transport equation. $\beta$ acts to redistribute the fraction of total energy which is exchanged between the transport system and equilibrium distribution of phonons. This method predicts thermal conductivity trends in materials spanning geometric domain sizes from nanometers to micrometers, and exhibits the correct asymptotic heat flux behavior as domain size increases. We observed $\beta$ to be the most influential at smaller domain sizes, where equilibrium is difficult to establish due to the proximity of the boundary phonon sources; as domain size increased, $\beta$ diminished in size, and nearly vanished at the maximum domain size of 10 $\mu$m. This further makes the case to perform BTE simulations for nanometer to micrometer heat transfer, as Fourier's law will not accurately capture the heat transfer in such small domain sizes, e.g., thermoelectric devices, heat transfer around defects and heterogeneities in reactor fuel. Additionally, we developed a novel material property discretization scheme which is consistent with the discretization of the angular variable in the transport equation. We performed convergence studies to test the efficiency of the spectral method, which used a modified source iteration (MSI) to solve the linear system of equations. We compare the performance of traditional source iteration (SI) of the uncoupled self-adjoin angular flux method we previously implemented to the new method and comment on the iterative performance of each. We capture ballistic and diffusive phonon scattering, and are able to make comparisons between the accuracy and efficiency of both methods. We find that MSI outperforms SI in most cases, especially as the spatial domain becomes acoustically thick

Heat Transfer

Over the past few decades there has been a prolific increase in research and development in area of heat transfer, heat exchangers and their associated technologies. This book is a collection of current research in the above mentioned areas and describes modelling, numerical methods, simulation and information technology with modern ideas and methods to analyse and enhance heat transfer for single and multiphase systems. The topics considered include various basic concepts of heat transfer, the fundamental modes of heat transfer (namely conduction, convection and radiation), thermophysical properties, computational methodologies, control, stabilization and optimization problems, condensation, boiling and freezing, with many real-world problems and important modern applications. The book is divided in four sections : "Inverse, Stabilization and Optimization Problems", "Numerical Methods and Calculations", "Heat Transfer in Mini/Micro Systems", "Energy Transfer and Solid Materials", and each section discusses various issues, methods and applications in accordance with the subjects. The combination of fundamental approach with many important practical applications of current interest will make this book of interest to researchers, scientists, engineers and graduate students in many disciplines, who make use of mathematical modelling, inverse problems, implementation of recently developed numerical methods in this multidisciplinary field as well as to experimental and theoretical researchers in the field of heat and mass transfer

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis

NASA thesaurus. Volume 1: Hierarchical Listing

There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions

Third International Conference on Inverse Design Concepts and Optimization in Engineering Sciences (ICIDES-3)

Papers from the Third International Conference on Inverse Design Concepts and Optimization in Engineering Sciences (ICIDES) are presented. The papers discuss current research in the general field of inverse, semi-inverse, and direct design and optimization in engineering sciences. The rapid growth of this relatively new field is due to the availability of faster and larger computing machines