Defect and Diffusion Forum Vols. 283-286

Abstract: The present work describes the mass transfer process between a moving fluid and a slightly soluble flat surface buried in a packed bed of small inert particles with uniform voidage, by both advection and diffusion. Numerical solutions of the differential equation describing solute mass conservation were undertaken to obtain the concentration profiles, for each concentration level, the width and downstream length of the corresponding contour surface and the mass transfer flux was integrated to give the Sherwood number as a function of Peclet number. A mathematical expression that relates the dependence with the Peclet number is proposed to describe the approximate size of the diffusion wake downstream of the reactive solid mass.

Abstract: Cold-set gels of whey protein isolate (WPI) were produced. The cold gelation was induced through the addition of magnesium chloride whose cation is an alternative to the most common cations used in this kind of gelation. A phase diagram for denatured WPI in magnesium was determined by varying protein and salt concentrations. In this diagram the protein and cation concentrations varied from 0.3 to 8.0 wt % and 1 to 75 mM, respectively. The viscoelastic behaviour of the WPI was analysed, whereas gels elastic properties were measured by means of texture tests. Mathematical manipulation of the experimental data relative to the puncture tests was made in order to obtain the Young’s modulus for each cold-set gel.

Abstract: A series of biodegradable superabsorbent polymers (SAP) based on starch grafted with acrylic acid (AA) and crosslinked with N,N’-methylenebisacrylamide (MBIS) were obtained. The parameters that define SAPs properties, such as starch type, amount of initiator, acrylic acid and crosslinker concentrations, and degree of neutralization were varied according to an experimental design. The swelling rate, the degree of swelling, the water sorption isotherms and the texture profile of the new materials were determined. A new method was used to measure the swelling rate. The water sorption results were correlated using various isothermal models as the BET (Brunauer-Emmett-Teller) and GAB (Guggenheim-Andersson-DeBoer) models. Hydrogels obtained from regular cornstarch presented better absorption capacities than those from waxy cornstarch. Maximum swelling was observed for 70% neutralization of carboxylic acid groups. More rigid SAPs presented lower swelling rates, but not necessarily lower swelling degrees.

Abstract: Cold-set gels of whey protein isolate (WPI) and of WPI plus polysaccharide were produced. The cold gelation was induced through the addition of magnesium chloride whose cation is an alternative to the most common cations used in this kind of gelation. The polysaccharide used was tara gum (TG) which is a galactomannan with many applications in the food industry. The viscoelastic behaviour of the WPI, TG and WPI+TG samples was analysed: Newtonian behaviour was observed for WPI while TG and WPI+TG displayed typical rheological behaviours of thickened fluids that can be described through the Cross and Carreau models, for which the parameters are presented.

Abstract: In this paper, current-voltage (i-Vg) results from different kinds of n-type InP Schottky diodes are reported. The diodes were fabricated on an unintentionally doped n-type (100) indium phosphide substrate, and the i-Vg characteristics were measured in the temperature range 100 300 K. For the ideality factor, n always exhibited a small (1) but continuous increase with the voltage. At higher forward voltage, slightly higher values of n were due to series resistance effect; in other words, the interface state density always remained small. However, it was possible to obtain some information in the case of discrete interface traps. It was shown that i-Vg measurements can be used as a fast method to determine the densities of the interface states when they equilibrate with the semiconductor.

Abstract: In this work, the effective diffusion coefficient of the gas contained in closed cell polyethylene foams under static loading is measured. To do this, compressive creep experiments were performed on low density polyethylene foams produced under a gas diffusion process. Density dependence of this coefficient has been analysed as well as the variation of pressure with time inside the cells. Finally, immediately after compressive creep, the recovery behaviour of the foams was also characterised. Different abilities for recovering were observed depending on the density of the foam and the absolute recovery resulted independent of the initial stress applied.

Abstract: Salinity currently has the highest priority of all environmental issues nowadays. The only means of preventing the development of soil salinity was combining leaching and artificial drainage. Recently a new method of capturing and removing salt from the soil surface called a dry drainage method [1-4] has been studied (fig.1) to help arid soils prevention against such threat. This work is a numerical simulation of the simultaneous water, solute and heat transfer in an unsaturated porous media during the simultaneous evaporation and drainage of saline dry land soils. A detailed mathematical model was formulated to describe the non-isothermal transport of water in the unsaturated porous media [5]. The model consists of the coupled conservative equations of mass for liquid phase, gas phase, water vapour, species and the energy. The boundary conditions at the soil–atmosphere interface include dynamical mass flux and energy flux. Comparison of numerical simulations with analytical results demonstrated that the present model is able to describe water and energy transport dynamics.

Abstract: Intense research on development of ozone and global warming protection heat pump machine technology is observed, because of the international environment protection. In arid areas, electricity network is not often available or it is at high price while the sun is shining and the cooling demand is important during almost the year. Absorption refrigeration has been intensively investigated over the world, during the last twenty years. This report is concerned by the solar energy conversion and use in an absorption cooling process where a specific porous medium is used to improve the efficiency. This process is the best appropriate solution to refrigeration and air conditioning problems in the desert areas and other remote countries where electricity power network is not available. The simulation of absorbing/desorbing chemical reaction in a solar cooling system, working according to absorption principle has given some results allowing to confirm the efficiency improve, the economical and technical feasibility and to avoid difficulties.

Abstract: Many researches have performed some studies about pressure gradient in the one phase flow, particle-liquid two-phase flow and porous media. However, there is no any report about interaction among them. In this study, this interaction idea is developed by using the same particle size for particle-liquid two-phase flow and porous media. For the experimental study, an apparatus is designed, and at the first step one phase water pressure gradient is investigated, next in the further steps, little by little spherical particles are added to the cycle till accumulation of the particles did not allow any movement to the particles (i.e. porous media occur), and after that well pack porous media is investigated. The results confirm the relation between pressure gradient over mass flow rate in the one phase flow, particle-liquid two-phase flow and porous media obeys as a parabolic curve.

Abstract: Grape stalk constitutes a by-product of wineries with low economic value. The extraction of compounds with antioxidant capacity may be considered as an alternative to increasing its value. Prior to extraction there must be a drying process, which may affect not only the product structure but also the antioxidant activity of extracts. The aim of this work was to address the influence of grape stalk drying conditions on the subsequent extraction of antioxidant compounds. Prior to the extraction experiments, grape stalk was dried under different conditions: freeze dried and hot air dried at different temperatures (40, 70 and 100 °C). The extraction experiments were carried out at 60 °C using ethanol-water (80 % v/v) as solvent. Extracts were taken after 5, 10, 15, 30, 60, 120, 180, 240 and 1380 min. Antioxidant concentration in the solvent was evaluated by measuring the total antioxidant activity using the FRAP method. Extraction kinetic was modelled from the evolution of antioxidant concentration in the solvent using a diffusion model. Extracts obtained from freeze dried samples presented the highest antioxidant concentration, almost double that from hot air dried samples. Among these, the highest antioxidant concentration was found for samples dried at 100 and 40 °C. The freeze dried samples also showed the highest kinetic parameters: effective antioxidant diffusivity and mass transfer coefficient.