<p> In very high resolution galaxy simulations, the supercomputers of today offer the possibility of enough resolution to capture the bubble of a supernova, though not the originating star itself. Modeling the energy released as originating from a single SPH particle initially arranged amongst a grid of particles requires the introduction of an artificial thermal conductivity term that allows the SPH method to resolve the thermal energy discontinuity inherently present in such a scenario. Such an artificial thermal conductivity is implemented in the SPH code GASOLINE. Resolution tests show that the method is insensitive to resolution changes when determining the radius of the Sedov-Taylor blast wave, and that the numerical solution agrees with the analytic prediction R = βE^1/5ρ0^-1/5t^2/5. The peak density at the shock is lower than the actual value of four times the ambient density, though it is found to scale with resolution. The density of the interior of the shock, near the center of the supernova remnant is found to be elevated compared to the value expected from the Sedov-Taylor solution, but this too is resolution dependent, and with increased resolution the central density converges towards the expected value of zero. The fluid quantities pressure and velocity are also found to be in good agreement with the profiles predicted by the analytic solution.</p> / Thesis / Master of Science (MSc)

no / The coupling between natural convection and conduction within rectangular enclosure was investigated numerically. Three separate heat sources were flush mounted on a vertical wall and an isoflux condition was applied at the back of heat sources. The governing equations were solved using control volume formulation. A modified Rayleigh number and a substrate/fluid thermal conductivity ratio were used in the range 10^4 −10^7 and 10−10^3 respectively. The investigation was extended to examine high thermal conductivity ratio values. The results illustrated that, when Rayleigh number increased the dimensionless heat flux and local Nusselt number increased and the boundary layers along hot, cold and horizontal walls were reduced significantly. An opposite behaviour for the thermal spreading in the substrate and the dimensionless temperature, were decreased for higher Rayleigh number. Moreover, the thermal spreading in the substrate increased for higher substrate conductivity, which affected the temperature level. However the effect of the substrate is negligible when the thermal conductivity ratio higher than 1,500. / The full text of book chapters are not available for self deposit under the Publisher's copyright restrictions.

Yes / In this study, the thermal performance analysis of porous fin with temperature-dependent thermal conductivity and internal heat generation is carried out using Haar wavelet collocation method. The effects of various parameters on the thermal characteristics of the porous fin are investigated. It is found that as the porosity increases, the rate of heat transfer from the fin increases and the thermal performance of the porous fin increases. The numerical solutions by the Haar wavelet collocation method are in good agreement with the standard numerical solutions.

Yes / In this paper, the Chebychev spectral collocation method is applied for the thermal analysis of convective-radiative straight fins with the temperature-dependent thermal conductivity. The developed heat transfer model was used to analyse the thermal performance, establish the optimum thermal design parameters, and also, investigate the effects of thermo-geometric parameters and thermal conductivity (nonlinear) parameters on the thermal performance of the fin. The results of this study reveal that the rate of heat transfer from the fin increases as the convective, radioactive, and magnetic parameters increase. This study establishes good agreement between the obtained results using Chebychev spectral collocation method and the results obtained using Runge-Kutta method along with shooting, homotopy perturbation, and adomian decomposition methods.

Yes / This study aims to evaluate the impacts of using thermally enhanced concrete on the thermal performance of geoenergy structures and interaction between the thermo-active-structures and adjacent dry and partly saturated soils. Experiments using a fully instrumented testing rig were carried out on prototypes of energy pile and diaphragm wall made from normal concrete and thermally enhanced concrete by the addition of graphTHERM powder. Results illustrated that adding 36% of graphTHERM powder to the concrete by weight of cement was found to double the thermal conductivity of concrete and improve the stiffness by 15% without detrimental effects on the compressive strength. The heat transfer efficiency of energy pile and energy diaphragm wall made from thermally enhanced concrete was significantly improved by 50% and 66% respectively, in comparison with the efficiency of the same type of energy structure that was made from a typical normal concrete.

Nanotechnology has made it possible to create materials with unique properties. This development offers new opportunities and overcomes challenges for many thermal transport applications. Yet, it requires a more fundamental scientific understanding of nanoscale transport. This thesis emphasizes how simulation, mathematical, and numerical methods can lead to more grounded studies of nanoscale thermal transport for biological and physical applications. For instance, magnetic fluid hyperthermia (MFH), an emerging cancer treatment, is a noninvasive method to selectively destroy a tumor by heating a ferrofluid-impregnated malignant tissue with minimal damage to the surrounding healthy tissue. We model the problem by considering an idealized spherical tumor that is surrounded by healthy tissue. The dispersed magnetic nanoparticles in the tumor are excited by an AC magnetic field to generate heat. The temperature distribution during MFH is investigated through a bioheat transfer relation which indicates that the P\'eclet, Joule, and Fourier numbers are the more influential parameters that determine the heating during such a thermotherapy. Thus, we show that a fundamental parametric investigation of the heating of soft materials can provide pathways for optimal MFH design. Since ferrofluid materials themselves play a key role in heating, we examine six materials that are being considered as candidates for MFH use. These are simulated to investigate the heating of ferrofluid-loaded tumors. We show that iron-platinum, magnetite, and maghemite are viable MFH candidates since they are able to provide the desired heating of a tumor which will destroy it while keeping the surrounding healthy tissues at a relatively safe temperature. Recent advances in the synthesis and nanofabrication of electron devices have lead to diminishing feature sizes. This has in turn increased the power dissipation per unit area that is required to cool the devices, leading to a serious thermal management challenge. The phonon thermal conductivity is an important material property because of its role in thermal energy transport in semiconductors. A higher thermal conductivity material is capable of removing more heat since higher frequency phonons are able to travel through it. In this thesis, the effects of surface stress on the lattice thermal conductivity are presented for a silicon nanowire. Based on a continuum approach, a phonon dispersion relation is derived for a nanowire that is under surface stress and the phonon relaxation time is employed to subsequently determine its thermal conductivity. The surface stress is found to significantly influence the phonon dispersion and thus the Debye temperature. Consequently, the phonon thermal conductivity decreases with increasing surface stress. Different magnitudes of surface stress could arise from various material coatings and through different nanofabrication processes, effects of which are generally unclear and not considered. Our results show how such variations in surface stress can be gainfully used in phonon engineering and to manipulate the thermal conductivity of a nanomaterial. The thermal transport during thermoelectric cooling is also an important property since thermoelectric devices are compact, reliable, easy to control, use no refrigerants and require lower maintenance than do more traditional refrigeration devices. We focus on the Thomson effect that occurs when there is a current flow in the presence of a temperature gradient in the material, and investigate its influence on an intrinsic silicon nanowire cooler. The temperature dependence of the Thomson effect has a significant influence on the cooling temperature. We also consider thermal nonequilibrium between electrons and phonons over the carrier cooling length in the nanowire. The results show that a strong energy exchange between electrons and phonons lowers the cooling performance, suggesting useful strategies for thermoelectric device design. / Ph. D.

All interfaces offer resistance to heat transport. As the size of a device or structure approaches nanometer lengthscales, the contribution of the interface thermal resistance often becomes comparable to the intrinsic thermal resistance offered by the device or structure itself. In many microelectronic devices, heat has to transfer across a metal-nonmetal interface, and a better understanding about the origins of this interface thermal conductance (inverse of the interface thermal resistance) is critical in improving the performance of these devices. In this dissertation, heat transport across different metal-nonmetal interfaces are investigated with the primary goal of gaining qualitative and quantitative insight into the heat transport mechanisms across such interfaces. A time-domain thermoreflectance (TDTR) system is used to measure the thermal properties at the nanoscale. TDTR is an optical pump-probe technique, and it is capable of measuring thermal conductivity, k, and interface thermal conductance, G, simultaneously. The first study examines k and G for amorphous and crystalline Zr47Cu31Al13Ni9 metallic alloys that are in contact with poly-crystalline Y2O3. The motivation behind this study is to determine the relative importance of energy coupling mechanisms such as electron-phonon or phonon-phonon coupling across the interface by changing the material structure (from amorphous to crystalline), but not the composition. From the TDTR measurements k=4.5 W m-1 K-1 for the amorphous metallic glass of Zr47Cu31Al13Ni9, and k=5.0 W m-1 K-1 for the crystalline Zr47Cu31Al13Ni9. TDTR also gives G=23 MW m-2 K-1 for the metallic glass/Y2O3 interface and G=26 MW m-2 K-1 for the interface between the crystalline Zr47Cu31Al13Ni9 and Y2O3. The thermal conductivity of the poly-crystalline Y2O3 layer is found to be k=5.0 W m-1 K-1. Despite the small difference between k and G for the two alloys, the results are repeatable and they indicate that the structure of the alloy plays a role in the electron-phonon coupling and interface conductance. The second experimental study examines the effect of nickel nanoparticle size on the thermal transport in multilayer nanocomposites. These nanocomposites consist of five alternating layers of nickel nanoparticles and yttria stabilized zirconia (YSZ) spacer layers that are grown with pulsed laser deposition. Using TDTR, thermal conductivities of k=1.8, 2.4, 2.3, and 3.0 W m-1 K-1 are found for nanocomposites with nickel nanoparticle diameters of 7, 21, 24, and 38 nm, respectively, and k=2.5 W m-1 K-1 for a single 80 nm thick layer of YSZ. The results indicate that the overall thermal conductivity of these nanocomposites is strongly influenced by the Ni nanoparticle size and the interface thermal conductance between the Ni particles and the YSZ matrix. An effective medium theory is used to estimate the lower limits for the interface thermal conductance between the nickel nanoparticles and the YSZ matrix (G>170 MW m-2 K-1), and the nickel nanoparticle thermal conductivity. / Ph. D.

The objective of this study was to determine the photothermal and photochemical tissue response to carbon nanotube inclusion in laser therapy using experimental and computational methods. In this study, we specifically considered varying types and concentrations (0.01-1 mg/ml) of carbon nanotubes (CNTs), e.g., multi-walled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs), and single-walled carbon nanohorns (SWNHs). In order to determine the photothermal effect of CNT inclusion, the thermal conductivity and optical properties of tissue representative phantoms with CNT inclusion were measured. Thermal conductivity of tissue phantoms containing CNTs was measured using the hot wire probe method. For identical CNT concentrations, phantoms containing MWNTs had the highest thermal conductivity. Optical properties (absorption and reduced scattering coefficients) of solutions and tissue phantoms containing carbon nanotubes were measured with spectrophotometry and determined by the inverse adding doubling (IAD) method. Inclusion of CNTs in phantoms increased light absorption with minimal effect on scattering and anisotropy. Light absorption of MWNTs was found to be higher than SWNTs and SWNHs. The photochemical response to laser irradiation (wavelength 1064 nm) of CNTs was measured with spin-trap electron paramagnetic resonance (EPR) spectroscopy. Only SWNHs appeared to produce significant levels of ROS production in response to laser excitation in the presence of NADH. We detected the predominant presence of trapped hydroxyl radical (•OH) with a trace of the trapped super oxide (O2•-) radical. These free radicals are highly reactive and could be utilized to cause targeted toxicity to cancer cells. The distribution of CNTs at the cellular level, in phantoms, and in kidney tumors was measured using transmission electron microscopy (TEM) imaging. Samples were imaged following various time periods (2-48h) of incubation and CNTs were observed inside the cell cytoplasm, nucleus, vacuole, and outside cells for the above mentioned time periods. CNTs in phantoms and tumor tissue were randomly and uniformly distributed in the entire volume. Computational model geometries were developed based on CNTs distribution in cells, tissue phantoms, and kidney tumor tissue. In the computational part of this research the temperature response to laser irradiation alone or with CNT inclusion was determined using Penne's bioheat equation which was solved by finite element methods. Experimentally measured thermal conductivity and absorption and reduced scattering coefficients were used as input parameters in Penne's bioheat equation. The accuracy of the model predicted temperature distribution was determined by comparing it to experimentally measured temperature in tissue phantoms and kidney tumors following CNT inclusion and laser therapy. The model determined temperature distribution was in close correspondence with the experimentally measured temperature. Our computational model can predict the effectiveness of laser cancer therapy by predicting the transient temperature distribution. / Ph. D.

The use of electrospun polystyrene (PS) fibers to create continuous long range ordered multi-scale porous structures in titanium diboride (TiB2) is investigated in this work. The introduction of electrospun PS fibers as a sacrificial filler into a colloidal suspension of TiB2 allows for easy control over the pore size, porosity, and long range ordering of the porous structures of the sintered ceramic. Green bodies were formed by vacuum infiltrating an electrospun-fiber-filled mold with the colloidal TiB2 suspension. The size, volume, distribution, and dispersion of the pores were optimized by carefully selecting the sacrificial polymer, the fiber diameter, the solvent, and the solid content of TiB2. The green bodies were partially sintered at 2000 C in argon to form a multiscale porous structure via the removal of the PS fibers. Aligned continuous cylindrical pores were derived from the PS fibers in a range of ~5 - 20 μm and random porosity was revealed between the ceramic particles with the size of ~0.3 - 1 μm. TiB2 near-net-shaped parts with the multi-scale porosities (~50 to 70%) were successfully cast and sintered. The multi-scale porous structure produced from electrospun fibers was characterized both thermally and mechanically, at room temperature. The conductivity ranged from 12-31 W m^(-1) K^(-1) at room temperature and the compressive strength ranged from 2-30 MPa at room temperature. Analytical thermal and mechanical models were employed to understand and verify he processing-structure-properties relationship. Finally, a method was devised for estimating the effective thermal conductivity of candidate materials for UHTC applications at relevant temperatures using a finite difference model and a controlled sample environment. This low-cost processing technique facilitates the production of thermally and mechanically anisotropic structures into near-net shape parts, for extreme environment applications, such as ultra high temperature insulation and active cooling components. / MS / Society is on the cusp of hypersonic flight which will revolutionize defense, space and transport technologies. Hypersonic flight is associated with conditions like that of atmospheric re-entry, high heat and force or specific locations of a space craft. The realization of hypersonic flight relies on innovative materials to survive the harsh conditions for repeated flight. We have created a new material with tiny holes that can help prevent heat flow from the harsh atmosphere from damaging the hypersonic craft. Thesis tiny holes are made from placing a polymer fiber in an advanced ceramic (which withstand high temperatures) and removing the fiber to leave holes. The tiny hole’s effect on strength and heat flow have been studied, to understand how the tiny holes can be made better. It is difficult to test materials in the harsh atmosphere associated with hypersonic flight, so a program has been written to estimate thermal properties of candidate materials for hypersonic flight.

<p dir="ltr">This Thesis is divided into four parts. Its main themes are the thermal transport characteristics of Surface Phonon-Polaritons (SPhPs) and Surface Plasmon Polaritons (SPPs).</p><p dir="ltr">Chapter 1 introduces the main problem at issue in this Thesis: the decline in thermal conductivity with decreasing thicknesses in electronic devices and the feasibility of optimizing polar semiconductors and metals to produce polaritons that augment heat dissipation at these length scales.</p><p dir="ltr">Chapter 2 discusses Surface Phonon-Polariton (SPhP)-mediated thermal conductivity, or radiation conduction, in polar semiconductors. It considers the propagation of SPhPs in the case of two semi-infinite planes consisting of air and a polar semiconductor with a dielectric function described by its transverse- and longitudinal-optical (TOLO) phonon energies. It characterizes twenty different polar semiconductors in terms of radiation conduction via SPhPs and proposes a Figure of Merit (FoM) that describes the effectiveness of polariton conductance using easily-measured TO and LO phonon energies and linewidths.</p><p dir="ltr">Chapter 3 considers the propagation of SPPs in the case of two semi-infinite planes consisting of air and a metal with a dielectric function described by the Lorentz-Drude (LD) model. This chapter characterizes the effectiveness of eleven different metals as radiation conductors via SPPs and relates polariton conductance to electrical resistivity. It proposes a FoM analogous to the Wiedemann-Franz law that relates the effectiveness of polariton conductance and thermal conductance to the material’s electron scattering or linewidth.</p><p dir="ltr">Chapter 4 chapter compares the relative effectiveness of SPhP- and SPP-mediated radiation conduction. It describes why SPPs demonstrate far higher polariton conductance values than SPhPs by highlighting the underlying mechanisms at work in both—that is, available modes of energy transmission and their respective mean free path lengths.</p>