Papers by Keyword: Transport Phenomena

Abstract: The publication deals with the comparison of mathematic models that simulate heat transfer by radiation and of models of spectral characteristics of the burnt gases. The heat transfer in the combustion chamber with the shape of rectangular cross-section of 200 x 288 mm and 1,000 mm high has been numerically analysed by means of the individual models. A low pressure burner of the ejection type and of the power output from 20 to 40 kWs is located in the lower part of the combustion chamber. As the heating gas, methane is used. The interest is especially focused on the evaluation of the radiation intensity in the combustion chamber and on the heat fluxes to the walls that are predicted by the models. Results of the P1 and Discrete Transfer models and results of the Gray and MultiGray models of spectral characteristics of the burnt gases have been compared. A part of the research is also the recommendation dealing with the individual models usability.

Abstract: Bio-drying is an important method to reduce the excess sludge which use the inner biomass of sludge itself to generate heat for a water discharging has a broad prospects in sludge treatment. However, our research in this field is still very limited. In order to better mastering and promoting sludge bio-drying technology, this paper summarized the advantages of bio-drying, initially described the microbial mechanism of spontaneous heat generation and the heat and mass transfer phenomena in a bio-drying process, then build a macro heat conservation formula based on material conservation.

Abstract: La1-x(Sr, Ca)xMnO3 manganites present a special interest due their high Curie and metal-insulator transition temperatures and the possibility to obtain magnetoresistive sensors able to work near room temperature. We have synthesized two rows of manganites, with La0.54Ho0.11Sr0.35-xKxMnO3 and La0.54Ho0.11Ca0.35-xNaxMnO3 chemical compositions. XRD analysis, performed with a Huber diffractometer at room temperature, indicated that the manganites contain perovskite phases, with Pnma structure. The atomic positions, lattice parameters and some microstructure parameters, as average size of coherent blocks and microstrains, were obtained by using GSAS program. The dependence of the resistivity with temperature and the applied magnetic field was determined by means of four probes method, between 77 and 300 K. The influence of K/Na concentration on the disorder degree (at atomic and crystallite level) and on the transport mechanisms was discussed.

Abstract: In the present work, a three dimensional model examining the fluid flow along with the fundamental transport phenomena occurring in a typical polymer electrolyte fuel cell (PEMFC), i.e. heat transfer, mass transport and charge transfer, has been developed. The flow field was simulated according to the well known Navier-Stokes equations, while the heat transfer was described by the typical conduction/convection equation and the mass transport by the convection/diffusion one. Furthermore, reaction kinetics were studied by the Butler-Volmer equation for the heterogeneous reactions occurring at the porous electrodes. The developed model was numerically solved by using the commercially available CFD package CFD-RC©, which is based on the multi-step finite volume method. The fuel cell performance in terms of velocity, temperature, mass fractions of active compounds and electric field has been investigated as well.

Abstract: This paper introduces a general numerical scheme for solving convective-diffusive problems that appear in the solution of microscopic and macroscopic transport phenomena in continuous castings and the heat treatment of aluminium alloys. The numerical scheme is based on spatial discretisation that involves pointisation only. The solution is based on diffuse collocation with multi-quadric radial basis functions. The application of the method is demonstrated in a simplified model of a billet DC casting and verified by a comparison with the classical finite volume method.