Thermal Profile Measurements Research Articles

Measurement of autoclave thermal profiles during high pressure steam de-waxing of investment shells Part 2 - Wax body profiles

Investment casting research is being carried out by the University of Birmingham, sponsored by EPSRC and a consortium of industrial companies. The programme is aimed at developing a fundamental understanding of the process, with a view to routinely producing sound, net shape castings. A key stage within the investment process is that involving the removal of wax from the unfired ceramic shell. This important process is carried out within the confines of a sealed pressure vessel, more commonly referred to as a Boilerclave*, with external pressure gauges as the only indication of what is actually happening inside the cavity. The de-wax stage is a key stage in the process as wax needs to be removed from a weak ceramic shell system without cracking or dimensional alterations, which would be reflected in out of tolerance casting scrap. Due to the nature of the process, wax removal is probably the least understood or controlled aspect of the whole investment sequence. The following paper is the second of two which contain results obtained at The University of Birmingham using a specially instrumented stream autoclave which allows visual data capture, thermal and steam pressure profiles within the chamber, and thermal instrumentation of waxes and shells to be obtained. Results of thermal and pressure profiles within individual wax components are presented and implications of these results upon the mechanism of wax removal and the effect upon ceramic shells are discussed.

Measurement of gas-phase temperatures in flames with a point-diffraction interferometer

Experiments were performed to evaluate the performance of a point-diffraction interferometry (PDI) system to measure gas-phase temperatures in flames. PDI is an interferometric technique that creates the reference beam after the laser beam passes through the test section and directly provides the index of refraction in two dimensions. PDI-based temperature measurements were compared with thermocouple measurements of two-dimensional and axisymmetric thermal boundary layers, as well as two-dimensional and axisymmetric diffusion flames. The PDI system provided excellent agreement in the measurement of thermal profiles in the boundary layers and was within the uncertainties that are due to the radiation corrections for the thermocouple-based flame temperature measurements.

Combustion of Binary and Ternary Silicon/Oxidant Pyrotechnic Systems, Part IV: Kinetic Aspects

Abstract Abstract–Kinetic parameters for the processes occurring during controlled heating and during combustion of the binary silicon-fuelled pyrotechnic systems. Si/Fe2O3, Si/SnO2. Si/Sb203 and SilKN03 have been estimated,where possible, from the results of both thermal analysis and temperature profile measurements. The values obtained from the two very different techniques are compared and discussed, and the role of the oxidant, in a series of binary combinations of silicon as the common fuel with different oxidants, is discussed in terms of the detailed results reported in this and the immediately preceding three papers.

Experimental Study of the Horizontal Ohno Continuous Casting System

Pure tin rod of 8.5 mm diamétér has been cast using the horizontal Ohno continuous casting (OCC) system. Thermal profile measurements have been made during casting in order to obtain an understanding of the phenomena which occur within the OCC mould. The influence of interactive casting variables on the temperature gradient in the liquid ahead of the solid-liquid interface, the superheat within the mould, and the solid-liquid interface position have been investigated. It was found that the superheat of the melt within the mould increased linearly with decreasing casting speed and decreasing mould-eooler distance. It was also found that the temperature gradient is sensitive to the mould exit temperature whereas it remains independent of the casting speed within the range investigated. Heat transfer coefficients have been evaluated and conditions established for the production of single crystals. Résumé Une tige d'étain pure de 8.5 mm de diamètre a été coulée au moyen du systéme de Coulée Continue Horizontale Ohno (OCC). Des mesures de profil thermique ont été enregistrées durant la coulée afin de comprendre les phénomènes qui interviennent à l'intérieur du moule OCC. L'influence des variables interactives de coulée sur le gradient thermique dans le liquide en avant de l'interface liquide-solide, sur la surchauffe dans lemoule ainsi que sur la position de l'interface, a été étudiee. Il apparait que la surchauffe du liquide a l'interieur du moule augmente linéairement avec une diminution de la vitesse de coulee et de la distance moule-refroidisseur. Le gradient thermique est également sensible à la température de sortie du moule bien qu'il soit indépendant de la vitesse de coulée pour l'intervalle de température étudié. Ces coefficients d'échange de chaleur ont été évalués et des conditions de production de monocristaux ont été établies.

Eddy current measurement of crystal axial thermal profiles during Czochralski silicon crystal growth

The axial thermal profiles of silicon crystals during the Czochralski crystal growth process were measured experimentally by using an eddy current technology. The intrinsic conductivity changes in the crystal resulting from cooling were measured in terms of the eddy current amplitude and phase responses, and the axial thermal profiles of the growing crystal were subsequently derived from the results. The experimental setup consisted of a resistance-heated Czochralski puller with a 203 mm (8 inch) hot-zone, a multifrequency encircling eddy current sensor and a commercially available eddy current system interfaced with an IBM PC. The silicon crystals, 70 mm in diameter and up to 406 mm (16 inches) in length, were grown from 5 kg melts. The eddy current sensor was initially positioned 100 mm above the melt, and then the measurements were made as it was lowered to 25 mm above the melt at a constant speed of 25 mm/min. The experimental results indicate that the axial thermal profile in the region is nearly linear and quite transient during the initial phase of body growth. As the crystal gets longer, the increasing heat loss by radiation from the crystal surface causes the overall profile to shift downward. When the crystal reaches 200–250 mm in length, a steady state condition is achieved, and the overall axial thermal profile stays nearly invariant for the remainder of the growth. The steady state axial thermal gradient in the region is estimated to be about 4–6°C/mm.

In situ and laboratory geotechnical tests of the Pierre Shale near Hayes, South Dakota—A characterization of engineering behavior

A geotechnical investigation of the Pierre Shale near Hayes, South Dakota, was conducted by the U.S. Geological Survey as a basis for evaluating problems in deep excavations into that formation. The physical and mechanical properties of the shale were determined through use of core holes drilled to a maximum depth of 184 m. In situ borehole determinations included a gravimeter survey, pressuremeter testing, thermal profile measurements, and borehole velocity measurements. Onsite and offsite laboratory measurements included rebound measurements, sonic velocity measurements of shear and primary waves, X-ray mineralogy and major element determinations, size analyses, fracture analyses, fabric analyses, and determination of thermal properties.Below 15–22 m, the shale is an unweathered, saturated, overconsolidated, underpressured clay shale with a clay-mineral content ranging between 50 and 100%, dominantly composed of mixed-layer illitic smectites. The physical and mechanical properties vary widely. The variation is related to the clay mineral content (especially in bentonite zones), a large transverse mechanical anisotropy, and zones of fractures and microfractures, which may result from rebound caused by erosion. These may contribute to slope instability over large areas. The thermal and mechanical properties change markedly if the shale is permitted to dry out. The state of stress and overconsolidation appear to be functions of the depositional and erosional history of the deposit. Both are markedly affected by the large fracture zones. The properties of the clay shale indicate problems that may be encountered in excavation and use of deep underground facilities. Key words: anisotropy, characterization, clay shale, consolidation state, physical properties, rebound, relaxation, stress state, thermal properties.