Browsing by Subject "Thermal diffusivity"
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Item Characterization of Thermal Properties of Depleted Uranium Metal Microspheres(2012-07-16) Humrickhouse, Carissa JoyNuclear fuel comes in many forms; oxide fuel is the most commonly used in current reactor systems while metal fuel is a promising fuel type for future reactors due to neutronic performance and increased thermal conductivity. As a key heat transfer parameter, thermal conductivity describes the heat transport properties of a material based upon the density, specific heat, and thermal diffusivity. A material?s ability to transport thermal energy through its structure is a measurable property known as thermal diffusivity; the units for thermal diffusivity are given in area per unit time (e.g., m2/s). Current measurement methods for thermal diffusivity include LASER (or light) Flash Analysis and the hot-wire method. This study examines an approach that combines these previous two methods to characterize the diffusivity of a packed bed of microspheres of depleted uranium (DU) metal, which have a nominal diameter of 250 micrometers. The new apparatus is designated as the Crucible Heater Test Assembly (CHTA), and it induces a radial transient across a packed sample of microspheres then monitors the temperature profile using an array of thermocouples located at different distances from the source of the thermal transient. From the thermocouple data and an accurate time log, the thermal diffusivity of the sample may be calculated. Results indicate that DU microspheres have very low thermal conductivity, relative to solid uranium metal, and rapidly form an oxidation layer. At 500?C, the thermal conductivity of the DU microspheres was 0.431 ? 13% W/m-K compared to approximately 32 W/m-K for solid uranium metal. Characterization of the developed apparatus revealed a method that may be useful for measuring the thermal diffusivity of powders and liquids.Item Enhancement of two-phase thermosyphon heat transfer(Texas Tech University, 1990-05) Al-Baluski, Khamis Rajab NasserEnhancement of the two-phase flow thermosyphon heat transfer was experimentally investigated in terms of geometry, orientation and the cooling plate temperature. The thermosyphon consists of a heated wall and a parallel cooled wall with a gap of a certain width in between. Vapor phase is generated through boiling on the heated wall, and is condensed by the cooled wall. Characteristics regarding the enhanced heat transfer coefficient and critical heat flux are discussed. The results have a potential to be applied in electronic devices, turbines and solar systems.Item Separation of the isotopes of neon by thermal diffusion(Texas Tech University, 1966-05) LeMaster, Edwin WilliamThe possibility of thermal diffusion in gases appeared for the first time as a theoretical prediction in a paper by Enskog (1) in 1911, Enskog's paper was concerned with the extension of the kinetic theory of gases to the ease of gases in non-equilibrium states. A particular term in an equation indicated that if there existed a temperature gradient across a mixture of gases, a concentration gradient of the eonponent gases would appear. Chapman (2), working independently on the same problem, predicted the same phenomenon in his results published in 1912. The approach which Chapman used was completely different from that of Enskog. The theory was verified experimentally by Chapman and Dootson (3) in 1917, The effect agreed in sign and magnitude with the predictions of the theory.Item Transport properties of polystyrene above and below the glass transition temperature(Texas Tech University, 1983-12) Fike, Lawrence RobertIn the production of expandable polystyrene (EPS) foam, it is desirable to be able to predict the density of the final product by some means other than empirical estimates. Therefore, a mathematical model was developed to predict the density of EPS during a prepuffing expansion process. Use of the mathematical model requires some knowledge of the fundamental properties of viscosity, shear modulus, and mass diffusion coefficients for water and n-pentane through polystyrene. Since expansion is induced by thermal stimulus, these properties must be known as a function of temperature. The theoretical and experimental development in measuring these parameters constitute the bulk of the text in this thesis. A very simplistic Maxwell model for viscoelastic behavior was used as the basis for the theoretical development in the determination of the viscosity and shear modulus of polystyrene. Mass diffusion coefficients for water and n-pentane in polystyrene were determined by a solution to Fick's second law with appropriate initial and boundary conditions. Once the parameters had been determined, they were fit to an Arrhenius type model in order to determine temperature dependence. The transport properties were observed to be strongly affected by the polymer's glass transition. Finally, a computer program was developed and used to predict the density of EPS as a function of time during the expansion process.