Evaluation of novel Ti-doped 3D carbon-carbon composites under transient thermal loads

3D Ti-doped and undoped carbon-carbon composites (CFCs) were exposed to transient thermal loads to simulate plasma disruptions, in the electron beam test facility JUDITH at different power densities and multiple shots in order to study the evolution in the behavior of the material. The thermal shock response of the undoped and Ti-doped materials was compared in order to study the influence of titanium carbide as dopant. The erosion itself is driven during the first shots by macroscopic erosion (brittle destruction), which is a result of thermally induced stresses. With increasing number of shots, no more brittle destruction is observed and the main erosion mechanism is sublimation due to local overheating. This is also confirmed by the decrease of the erosion rate with increasing the number of shots. The pitch fibers are hardly affected by the applied heat loads and they show almost no erosion, especially in the Ti-doped composite.     

Hybrid Numerical Method Applied to Multilayered Hollow Cylinder with Time-Dependent Boundary Conditions

ABSTRACT

This article deals with one-dimensional axisymmetric quasi-static coupled thermoelastic problems with time-dependent boundary conditions. Laplace transform and finite difference methods are used to analyze the problems. Using the Laplace transform with respect to time, the general solutions of the governing equations are obtained in transform domain. The solution is obtained by using the matrix similarity transformation and inverse Laplace transform. We obtain solutions for the temperature and thermal deformation distributions for a transient and steady state. It is demonstrated that the computational procedures established in this article are capable of solving the generalized thermoelasticity problem of a hollow cylinder with nonhomogeneous layers.     

The early design model for prediction of energy and cost performance of building design options

In order to encourage the use of computer modelling in building environmental analysis, it is necessary to provide a model developed from the designer's point of view. Detailed simulation models require a high degree of expertise and familiarity, further, there is also a need for detailed information not available in the early stages of the design process. Simplified models play an important role in the early stages of a design to achieve an integrated design: firstly, they are easy to use and, secondly, they require information easily available at the start of a design. In the Early Design Model (EDM) the solar gain utilisation factor has been determined as a continuous function of thermal mass. The differences between the annual energy predictions of EDM and SERI-RES ranges from 0.1% to 4.6% for time constants ranging from 378 to 2.52 hours. The differences between the two sets of predictions on monthly basis ranges from m 3.6% to m 6.48% (EDM's predictions being larger) during the heating season, and from +2.86% to a maximum of +51% (EDM's predictions being smaller) in the remaining part of the year. In addition to energy predictions, EDM incorporates a facility which gives cost indications.     

Integrated Photoelasticity for Axisymmetric Thermal Stress Measurement Using the Stress Function

By investigating axisymmetric stress fields with integrated photoelasticity, the stress components σ_z and σ_rz can be determined directly from the experimental data. Stress components σ_r and σ_θ are usually determined using the equilibrium and compatibility equations. In this article it is shown that the stress function for an axisymmetric thermoelastic stress field can be determined on the basis of experimental data, obtained with integrated photoelasticity. Knowledge of the stress function permits one to calculate all the stress components as well as the temperature field in the test object.     

Combining continuous catalytic regenerative naphtha reformer with thermally coupled concept for improving the process yield

Advancements in the catalytic naphtha reforming process, as one of the main processes in petrochemical industry, contributed to development of continuous catalytic regenerative naphtha reformer units. Increasing the yield of aromatic and hydrogen as well as saving the energy in this process through the application of thermal coupling technique is a potentially interesting idea. This novel idea has been assessed in this paper. In the proposed configuration, continuous catalyst regeneration naphtha reforming process is coupled with hydrogenation of nitrobenzene in a two co-axial reactor separated by a solid wall, where the generated heat in nitrobenzene hydrogenation reaction transfers to naphtha reforming reaction medium through the surface of the tube. A steady-state, homogeneous, two-dimensional model is used to describe the performance of this configuration and a kinetic model including 32 pseudo-components with 84 reactions is considered for naphtha reforming reaction. After validating the model with the commercial data of a domestic plant, the obtained results of coupled reactor are compared by the conventional one. The obtained results show the superiority of CCR coupled reactor against the conventional one.     

Properties of purified direct steam grown silicon thermal oxides

Thermal silicon oxides are known to very effectively passivate silicon surfaces. Choosing a water vapor ambient instead of a dry oxygen atmosphere increases the oxidation rate by about one order of magnitude and considerably reduces process time and costs. State of the art pyrox systems produce steam by pyrolysis of hydrogen and oxygen gas. A new approach is the purification of vaporized deionized (DI) water. In this work we present a direct comparison of both steam generation systems, which are connected to the same quartz tube of an industrial high quality tube furnace. The higher steam saturation of the direct steam process enhances the growth rate by about 20% compared to a pyrolytic steam based process. On low-resistivity p-type substrates, excellent surface recombination velocities of around 25 cm/s are found for both systems after a forming gas anneal. Detailed characterization shows similar physical properties of the oxide layers grown by either steam from pyrolysis or purified steam. Moreover, thermal oxide rear surface passivated silicon solar cells show similar high efficiencies exceeding 18.0% irrespective of the applied steam generation technology.     

High-temperature thermal and X-ray diffraction studies, and room-temperature spectroscopic investigation of some inorganic pigments

Inorganic Cr- and Mn-containing pigments of different structural types were investigated by high-temperature and spectroscopic methods. The differential scanning calorimetry in the temperature interval 298-1723 K was applied to measure temperatures of phase transition and melting of the studied compounds. High-temperature X-ray diffraction in the range 298-1173 K was used for the determination of the thermal expansion coefficients for the first time. Factor group analysis was used to predict general vibration modes of pigments and determine the activity of these vibrations in Raman and IR spectra, the Assignment of bands in Raman, IR and diffuse reflectance spectra was undertaken.     

Thermomechanical properties of copper–carbon nanofibre composites prepared by spark plasma sintering and hot pressing

Several types of carbon nanofibres (CNF) were coated with a uniform and dense copper layer by electroless copper deposition. The coated fibres were then sintered by two different methods, spark plasma sintering (SPS) and hot pressing (HP). The Cu coating thickness was varied so that different volume fraction of fibres was achieved in the produced composites. In some cases, the CNF were pre-coated with Cr for the improvement the Cu adhesion on CNF. The results show that the dispersion of the CNF into the Cu matrix is independent of the sintering method used. On the contrary, the dispersion is directly related to the efficiency of the Cu coating, which is tightly connected to the CNF type. Overall, strong variations of the thermal conductivity (TC) of the composites were observed (20–200 W/mK) as a function of CNF type, CNF volume fraction and Cr content, while the coefficient of thermal expansion (CTE) in all cases was found to be considerably lower than Cu (9.9–11.3 ppm/K). The results show a good potential for SPS to be used to process this type of materials, since the SPS samples show better properties than HP samples even though they have a higher porosity, in applications where moderate TC and low CTE are required.     

Thermal characterisation of a tungsten magnetoresistive heat switch

A magnetoresistive heat switch has been developed to improve the performance of our flight-worthy cryogen-free ADR. We have characterised the switch’s thermal conductivity in the temperature range 0.3-4 K under an applied magnetic field of 1.8 T for two tungsten samples of different purity. The results are discussed relating to the key aspects of semi-classical magnetoresistance theory. We show that crystal purity has a strong effect on switch performance and magnetoresistive effect. Our findings are verified by comparison to results obtained by other authors. The measured switching ratio for our best sample is 1.75 × 10⁴ at 1.5 K and 1.51 × 10⁴ at 4.26 K. The lattice conductivity remains dominated by the electronic conductivity in the investigated range of temperatures under an applied magnetic field of 1.8 T. In order for the lattice conductivity to dominate a purity of >99.999% would be required.