Defect and Diffusion Forum Vol. 391

Abstract: We discuss the heat and mass transport in unsaturated-saturated porous mediaincluding heat exchange between inltrated water and matrix. We include the thermal inuenceon hydraulic permeability and on the water expansion which changes the water saturation.This consequently inuences the hydraulic permeability.Numerical modelling includes the direct and inverse solution of the problem, where model parametersare determined. Numerical experiments require only simple input/output measurementsof suitable ow characteristics in laboratory conditions with 3D cylindrical samples.The ow model is based on Richard's strongly non-linear parabolic equation based on empiricalvan Genuchten's capillary-pressure model. The transport includes longitudinal and transversaldispersion.

Abstract: This paper presents a quick calculation procedure to solve the heat transfer problem in some specific experimental arrangements. A brief overview of our previous efforts related to this topic is found in [1][2]. The goal of our effort is to quantify the thermal properties of insulation coatings applied to concrete material. We mostly deal with the computational aspects of thermal properties’ determination process. The proposed calculation approach is based on restricting the calculation to the first four members of the Fourier decomposition of the heat transfer partial differential equation’s solution. The reason for such a level of restrictions is given. The approach to the problem of deciding on the sufficient number of Fourier series’ members is indicated [3]. The effecting speedup is of three order of magnitude. Simplified formulas allowing the quick calculation of estimated values of material parameters are derived. The outline of an even quicker calculation procedure is described in a simplified manner.

Abstract: Currently available diffusion constant and Sieverts constant experimental results are based on time dependent permeation experiments. The common principle is an analysis which is expecting that the permeating hydrogen is “transported” from the retentate chamber to the permeate chamber through the connecting membrane, with a vanishing hydrogen partial pressure on the permeate side. But reality shows a different behaviour caused by the fact that a nonzero hydrogen partial pressure in the permeate chamber is necessary for detection purposes. This nonzero pressure is mostly not considered by analysis. This issue is solved (approximatively) numerically by the procedure as described in this paper. This work is rooted in the field of fusion research, where so called purge gas with low partial pressure of tritium is contacting the structural materials (300-550°C) of the fusion reactor (blanket) and of process equipment, where the tritium losses are of interest. The developed algorithms are intended for the evaluation of an experiment termed “Q-PETE” (Q for any hydrogen isotope, PEermeation Transport Experiment), which abstracts the hydrogen transport conditions of the fusion blanket, and where the effect of nonzero hydrogen concentration on the permeate side is relevant. The algorithms are useful for all experiments, where the ratio of hydrogen pressures between retentate and peremeate side are far from infinite.

Abstract: Resin transfer molding (RTM) is one technique that has been used to produce polymer composites, which consists in injecting a thermoset pre-catalysed resin into a closed mold containing a dry fiber preform. In this sense, this study aims to investigate the effect of the calcium carbonate content (CaCO₃) in the polyester resin during the RTM process. Several experiments were conducted using glass fiber mat molded in a RTM system with cavity dimensions 320 x 150 x 3.6 mm, at room temperature, and different injection pressure (0.75 bar) and CaCO₃content (0, 10, 20, 30 and 40%). Results of the physical parameters such as viscosity, permeability, and mobility, and flow front position of the resin into the mold along the RTM process are presented and analyzed. From the results was concluded that the higher the injection pressure and lower CaCO₃content into the resin, the lower filling time.

Abstract: This work presents a theoretical and experimental study of drying of sisal fibers. The fibers were submitted to drying in oven with forced air circulation at temperatures ranging from 50°C up to 90°C. Drying and heating lumped models were proposed and fitted to the experimental data. Non-linear regression analyzes were performed to verify the consistency of the models to predict the experimental data. It was verified that the curves of moisture loss and temperature of the sisal fibers were influenced by the drying-air temperature, showing a gradual variation with the drying time, being more accentuated in the higher temperatures of the drying-air. The fitted models presented good agreement with the experimental data.

Abstract: This work presents a theoretical and experimental study of banana drying. Whole banana were peeled, sliced manually and dried in an oven at constant drying condition (40 and 70°C). Drying, heating and shrinkage lumped models were proposed and fitted to experimental data. Non-linear regression analyses were done to verify the consistence of the models to predict the experimental data. Results revealed which air temperature affect significantly moisture removal, heating and shrinkage of banana slices. Drying, heating and dimensions variations were increased when higher temperature and area/volume relationship are used. The fitted results presented good agreement with experimental data.

Abstract: The drying process can be defined how unit operation for removing water of one moist solid to an unsaturated gaseous phase due to heat transfer. Numerical simulation emerges like a tool that allows the reproduction of drying experiments using computers and suitable softwares. In this sense, this works aims to predict drying process of an industrial hollow ceramic brick inside the kiln using computational fluid dynamics analysis. For one drying temperature of 60°C, results of the drying and heating kinetics, and moisture content, velocity and temperature distributions are shown and analyzed. A comparison between predicted and experimental data of the moisture content and temperature of the brick along the process was done and a good agreement was obtained.

Abstract: This work aims to develop a transient three-dimensional mathematical model to predict the temperature distribution in a fixed-bed elliptical cylindrical reactor to different geometric aspect ratio (L₂/L₁=1.5, 2.0 and 3.0). The model considers variable thermo-physical properties, a flat temperature profile at the fluid inlet, as well as a variable porosity model. The governing equation is solved using the finite volume method, coupled with WUDS interpolation scheme and fully implicit method. Results of the temperature profile along the reactor are presented and discussed at different times. As results, it was found that the maximum rate of heat transfer within the reactor occurs near the minor half-axis region of the ellipse (cross-section area of the reactor) and it intensifies over time and that the dimensionless temperature profile is practically unchanged with the aspect ratio.

Abstract: Catalytic hydrogenation of CO₂ into fuels and chemicals is regarded as one of the most promising alternatives to reduce the concentration of CO₂ in the atmosphere. In this study, double-promoted Cu/ZnO catalysts were prepared on Al₂O₃ and CNTs supports via impregnation method. The physicochemical properties of the catalysts were characterized by XPS, TEM, N₂ adsorption, H₂-TPR and CO₂-TPD analyses. Introduction of Nb and Zr promoters into the Cu-based catalysts on CNTs support resulted in smaller Cu nanoparticles and improved reducibility compared to those of the Al₂O₃-supported catalyst. The catalyst activity was evaluated in a fixed-bed stainless steel reactor operated at 22.5 bar and 523K. Conversion of CO₂ higher than 20% was achieved and product distribution was influenced by the type of catalyst supports.