Papers by Keyword: Thermal Diffusion

Abstract: Air lime coating mortars with mussel shells exhibit useful hygrothermal properties related to humidity and temperature regulation. Introducing mussel shell sand produces a significant increase in pore volume, changing mortar’s microstructure and reducing density. This is attributed to the flaky and irregular shape of the shell particles that present also traces of organic matter. In this work, the natural aggregate is replaced by mussel shell sand in increasing percentages of 25%, 50% and 75%. Additionally, a mortar with 0% of sand replacement is used as baseline of reference. These mortars are tested focusing in two main parameters, in first term, thermal conductivity. And also absorption and desorption cycles, at 80 and 50% relative humidity. The results are very positive for mussel shells specimens, it can be concluded that the use of mussel shell aggregates can improve the hygrothermal properties of air lime coating mortars. Another interesting result is a subjective property such as the aesthetic quality of the finishing, the results is pleasing and, combined with the promising hygrothermal properties opens a good opportunity for mussel shell mortars.

Abstract: The investigation is undertaken to study the thermal diffusion and radiation effects on unsteady MHD heat and mass transfer flow past a semi-infinite inclined porous plate embedded in a porous medium in a slip flow regime with variable suction in the presence of first order chemically reaction. The analytical solutions for velocity, temperature and concentration fields are obtained by reducing the governing nonlinear coupled partial differential equations in dimensionless form into a system of ordinary differential equations, using perturbation method. The effect of pertinent flow parameters on velocity, temperature, concentration, the skin friction, the rate of heat transfer and the rate of mass transfer are studied graphically.

Abstract: The work formulates a particular problem on redistribution of an active element from brazing alloy into brazed materials with due account for thermodiffusion effect. The analysis of the solution has demonstrated that thermodiffusion can facilitate the acceleration of mass transfer from brazing alloy into brazed materials and cause the accumulation of components in the vicinity of contact boundaries.

Abstract: Learning by the actual experience of fabrication and evaluation of a p-n junction is a very effective way for students to obtain a deep meaningful understanding of the fundamentals of semiconductor physics. To achieve this requirement at a real-world classroom situation, a simplified fabrication process for making the silicon p-n junction as the educational application was studied. The process without using the lithography process, and in use of simple thermal diffusion furnace under the air environment for the impurity thermal diffusion process by using phosphorous silicate glass (PSG) thin film prepared by the Sol-Gel material as the phosphorus (P) diffusion source was proposed and tested. As the results, it was obtained that the impurity concentration and diffusion depth were controlled well by this method, and good rectification phenomenon of the p-n junction was successfully observed. The typical diode factor n of the p-n junction was approximately 2.3. The p-n junction also performed well as a solar cell. The FF is approximately 0.7. These results show that it is possible to use the p-n junction prepared by this simplified process as the educational device to help students’ understanding of the theory of the p-n junction.

Abstract: Cr25Ni35Nb and Cr35Ni45Nb austenitic steels, used as furnace tube material in the ethylene pyrolysis furnace, generally suffer from coking during the long operation period. In the present paper, for coked Cr25Ni35Nb and Cr35Ni45Nb austenitic steel, using the finite element ABAQUS code, a sequentially coupled thermal stress procedure was developed to calculate distribution of the temperature and thermal stress field. The results show that thermal diffusion property of Cr25Ni35Nb and Cr35Ni45Nb steel deteriorates obviously with coking layer increasing. Radial bulge and rupture at local field would generate due to excess temperature for applied subsequent measurement. Maximum stress distribute along the cross-section of coking layer and metal matrix. Finally, the critical depth of coking layer of Cr25Ni35Nb and Cr35Ni45Nb austenitic steel are predicted when decoking measurement must be executed.

Abstract: The present study investigates the thermal diffusion and radiation effects on magneto hydro dynamic mixed convection flow of a micro polar fluid past an infinite, steadily moving porous plate with variable suction and constant viscosity. The equations of continuity, linear momentum, angular momentum, energy and diffusion, which govern the flow field, are solved by using a regular perturbation method. The behavior of the velocity, micro rotation, temperature, concentration, skin-friction, Nusselt number, and Sherwood number has been discussed for variations in the physical parameters with the help of the graphs.

Abstract: The problem has been analyzed on alloying elements redistribution between the coating (containing Cr and N) and the substrate (Si) in condition of surface heating. The model takes into account the effect of thermal diffusion on the redistribution of elements. The analytical solution of the particular linearized problem about redistribution of elements in the substrate coating is presented. It is shown that the thermal diffusion significantly affects the impurity distribution, resulting in the appearance of supersaturated or depleted regions.

Abstract: It is found that the samples usually melt and even gasify in the magnetic driven high-speed flying plate experiments, which phenomenon goes against the investigation on materials’ equation of state (EOS). To understand this phenomenon, the whole process of magnetic driven flying plate experiment is simulated by the magnetohydrodynamic code MDSC. The ablation mechanism of magnetic driven flying plate is analyzed through the control of thermal conduction coefficient, and resistivity coefficient which is related to the magnetic diffusion velocity, in the energy conversing equation. Inside the flying plate the velocity of stress wave is much higher than that of magnetic diffusion, and hence the current goes into the inside of sample no early than the stress wave, so the magnetic diffusion doesn’t play an important role in the first stage of flyer free surface velocity history. The thermal conduction doesn’t influence the whole free surface velocity history of the flying plate much, while the Ohmic heating has a big effect on it, without which more than 20% error will be produced. The energy transportation in the flying plate medium is mainly caused by the Ohmic heating from magnetic diffusion. Besides, the relationship between the magnetic diffusion and temperature of flying plate is also analyzed.

Abstract: The number of gas molecules and the volume of the vessel are used as independent arguments in the equation of state. It allows one to use this description in difficult conditions when variability in the number of moles of the structural elements and in the molar volume plays an appreciable role. Application of the kinetic model of the processes in multicomponent mixtures allowed one to determine the area of macroparameters, where mesoscopic properties of large clusters appear in thermal diffusion: thermal diffusion coefficient for them corresponds to liquids.

Abstract: Thermal diffussion (TD) is a method of coating steels to improve the service life of materials and tools. With this process, high hardness of vanadium carbide coating is formed on the surface of materialsso that its wear, bite, corrosion resistance can be greatly improved. Since thereare still several problems remaining to be solved, this technology is still not widely used in our country and that limit the popularity of the salt bath technology. In this paper, these problems and their causes are discussed based on experiments, and several solutions are presented to hopefully provide suggestions for industrial production.