Analytical determination of the effect of thermal property variations on the performance of a charring ablator

Effects of thermal-property variations on performance of charring ablato

Thermal Property Estimation of Fibrous Insulation: Heat Transfer Modeling and the Continuous Genetic Algorithm

Thermal properties of high-temperature fibrous insulation materials were estimated from transient thermal tests using an inverse heat transfer technique. Transient temperature data from an experimental set up was collected and a simple, one-dimensional numerical model was constructed to replicate the temperatures within the test assembly. The Continuous Genetic Algorithm optimization technique in conjunction with a numerical thermal model and transient test data was used to estimate coefficients of a functional representation of the thermal property. The thermal properties, i.e., thermal conductivity and specific heat, of an alumina insulation felt were estimated over the temperature range of 300 K to 1700 K at various constant static pressures in nitrogen gas and compared with published data. The resulting thermal property estimates were within 10% of published values over the entire temperature range at various pressures. The methodology, application, and results are presented

Streambed Thermal Property Instrument (SPI)

The purpose of this research, the Streambed thermal Property Instrument (SPI) is to determine the applicability of this instrument for in situ thermal (conductivity and diffusivity) and porous flow (magnitude and direction) measurements. Currently, no such thermal instrument exists for such in situ measurements and the reason for developing this unique instrument, the SPI to fill the technology gap in sediment thermal property measurement devices. Prior to testing the instrument under controlled laboratory conditions to determine its functionality through a series of static and flow tests, the instrument was designed and built. A lab-sized version of an actual river called a flow cell with a gravity-driven flow was also built, making it possible for testing the SPI under controlled lab conditions .The instrument was tested in the flow case by fixing the instrument in two orientations in the saturated porous media (glass particles). Results from the static tests indicated that these bulk thermal measurements (diffusivity and conductivity) can be off the expected value by as much as 15% while the porous flow measurements (magnitude and direction) displayed more variability in results for the two orientations of the probe for the flow rate range considered. This variability in flow measurements has been partly attributed to the movement of the offset probes during insertion and rotation and the large size of the center probe of the SPI. The findings from this research has made it possible for more advanced research in this field by using computer simulations to make possible, accurate porous flow measurements using a large scale thermal probe such as the SPI

Ab initio based thermal property predictions at a low cost : an error analysis

Ab initio calculations often do not straightforwardly yield the thermal properties of a material yet. It requires considerable computational efforts, for example, to predict the volumetric thermal expansion coefficient alpha(V) or the melting temperature T-m from first principles. An alternative is to use semiempirical approaches. They relate the experimental values to first-principles predictors via fits or approximative models. Before applying such methods, however, it is of paramount importance to be aware of the expected errors. We therefore quantify these errors at the density-functional theory level using the Perdew-Burke-Ernzerhof functional for several semiempirical approximations of alpha(V) and T-m, and compare them to the errors from fully ab initio methods, which are computationally more intensive. We base our conclusions on a benchmark set of 71 ground-state elemental crystals. For the thermal expansion coefficient, it appears that simple quasiharmonic theory, in combination with different approximations to the Gruneisen parameter, provides a similar overall accuracy as exhaustive first-principles phonon calculations. For the melting temperature, expensive ab initio molecular-dynamics simulations still outperform semiempirical methods

Characterization of surficial units on Mars using Viking orbiter multispectral image and thermal data

Albedo and thermal property correlations of the topography of Mars were conducted with emphases upon the types and origins of materials exposed in the central equatorial region. This area displays a wide variation in color, albedo and thermal properties, and is relatively free of dust and haze. The physical, mineralogical and elemental characteristics of this area are discussed

Physical property measurements of doped cesium iodide crystals

Mechanical and thermal property values are reported for crystalline cesium iodide doped with sodium and thallium. Young's modulus, bulk modulus, shear modulus, and Poisson's ratio were obtained from ultrasonic measurements. Young's modulus and the samples' elastic and plastic behavior were also measured under tension and compression. Thermal expansion and thermal conductivity were the temperature dependent measurements that were made

Temperature at Horizon in de Sitter Spacetime

It is found that there is no period in the imaginary Beltrami-time of the de Sitter spacetime with Beltrami metric and that the `surface-gravity' in view of inertial observers in de Sitter spacetime is zero! They show that the horizon might be at zero temperature in de Sitter spacetime and that the thermal property of the horizon in the de Sitter spacetime with a static metric should be analogous to that of the Rindler horizon in Minkowski spacetime.Comment: 7 pages, 1 figur

A New Kind of Uniformly Accelerated Reference Frames

A new kind of uniformly accelerated reference frames with a line-element different from the M{\o}ller and Rindler ones is presented, in which every observer at $x, y, z=$consts. has the same constant acceleration. The laws of mechanics are checked in the new kind of frames. Its thermal property is studied. The comparison with the M{\o}ller and Rindler uniform accelerated reference frames is also made.Comment: 10 pages, 2 figures. to appear in Int. J. Mod. Phys.

Nonlinear Photothermal Radiometry and its Applications to Pyrometry and Thermal Property Measurements

Accurate temperature and thermal property measurements are critical for the modeling and prediction of heat transfer. In many industries thermal management is a limiting factor of performance, and rely on advanced modeling techniques to develop and design methods to better manage thermal energy. This study expands the thermal property and pyrometry measurement capabilities by developing three new techniques based on thermal emission’s nonlinear dependence on temperature