Defect and Diffusion Forum Vol. 399

Abstract: The oscillatory electroosmotic flow (OEOF) under the influence of the Navier slip condition in power law fluids through a microchannel is studied numerically. A time-dependent external electric field (AC) is suddenly imposed at the ends of the microchannel which induces the fluid motion. The continuity and momentum equations in the and direction for the flow field were simplified in the limit of the lubrication approximation theory (LAT), and then solved using a numerical scheme. The solution of the electric potential is based on the Debye-Hückel approximation which suggest that the surface potential is small, say, smaller than 0:025V and for a symmetric () electrolyte. Our results suggest that the velocity profiles across the channel-width are controlled by the following dimensionless parameters: the dimensionless slip length , the Womersley number, , the electrokinetic parameter, , defined as the ratio of the characteristic length scale to the Debye length, the parameter which represents the ratio of the Helmholtz-Smoluchowski velocity to the characteristic length scale and the flow behavior index, . Also, the results reveal that the velocity magnitude gets higher values as increases and become more and more nonuniform across the channel-width as the and are increased, so OEOF can be useful in micro-fluidic devices such as micro-mixers.

Abstract: Flow-induced vibrations occur in some of the internal components of a nuclear reactor. When specific conditions are present, these vibrations may result in excessive deformations or fatigue that can generate mechanical damage. Several boiling water reactor (BWR) of nuclear power plants (NPP) have experienced failures in the jet pump assembly due to flow-induced vibration (FIV) which could be caused by acoustic pulsations derived from recirculation pumps, vibration induced by turbulence and vibration induced by leakage at the slip joint. The purpose of this paper is to establish a viable numerical methodology to evaluate the fluid-structural interaction at the slip joint of a jet pump. In this analysis, the fluid-structural interaction was evaluated with the finite element method and finite volume method with ANSYS^® code in the case of two steel plates with a divergent gap. Results show that a critical velocity could cause fluidelastic instability, if only one flow in a two-way fluid-structural interaction was considered. This is one of the phenomena that could take place at the slip joint of a jet pump assembly.

Abstract: The paper investigates the tunneling currents through the gate terminals of the last MOSFET production and proposes a related structure, noted as p-NOI (planar-Nothing On Insulator) device. In fact, the p-NOI structure can arise as parasitic device in any MOSFET having a gate insulator sub-10nm thickness or can be separately produced to offer a tunneling device. The work principle of a p-NOI structure consists in the Fowler-Nordheim's tunneling of a thin insulator. Its architecture is derived from the Nothing On Insulator (NOI) device, using oxide instead vacuum. Essentially, the p-NOI current follows a metal-insulator-semiconductor trajectory. A critical issue is the field effect of a transistor that must be fulfilled by independent p-NOI device. In this purpose, a diffusion process seems to be the key. A planar p-NOI device with top three terminals is proposed. A diffusion process along to the Si-surface is a key technological step that offers distinct current traces.

Abstract: Multiphase transport processes are encountered in many branches of science and engineering. Bubbles can be used, for example, as to cut off the blood flows that feed sick tissue growth and as potential drug delivery systems. This paper addresses the effect of bubbles on the increase of flow resistance within optimized Y-shaped tubes under different size constraints (volume, surface area). Y-shaped constructs of fluid streams can mimic the anatomy of the vascular system, and the results presented in this paper can be used for facilitating the design and analysis of the flow of bubbles through these systems.

Abstract: The paper is devoted to the study of thermal parameters (specific heat capacity, diffusivity and thermal conductivity) changes after thermally induced aging of BMC Mensolite 3100. Results of several measurements are statistically treated. From obtained results it is visible the greatest correlation in the diffusivity values, i.e. the heat irradiation effect is the smallest on the diffusivity values dispersion, the influence of the heat irradiation on the thermal capacity has approximately the same trend as the thermal conductivity. From the starting point represented by the virgin sample both values decrease and for the sample heated at 300°C it is visible an increase of the above mentioned values under investigation. Results are interpreted by using of the thermogravimetric analysis (TGA). All physical values under this investigation have a dominant decreasing tendency after the thermal treatment described.

Abstract: The purpose of this study is to find the cause of the physical changes on the human body caused by water during aquatic exercise. We extracted the shape of the upper limb using 3D scanner and made chamber and upper limb with Catia to simulate the movement. Finally, in order to analyze the effects on the human body through engineering analysis, this study analyzes the water pressure and vortex on the upper limb according to the angular velocity by fluid flow simulation. The result has shown that the vortex and the pressure applied to the upper limbs moved up and down vary depending on the angular speed of such an upper limb movement. Considering such a result, it is thought that in-depth studies on the effects of vortex generated depending on the moving speed and the water pressure on skin or muscle are required to be conducted later.

Abstract: As it is difficult to confirm mixed shape and mixing ratio which depend on the actual mixer inside the SCR, the present study on mixed shape and mixing ratio has been conducted by producing an SCR system simulator. Total 19 sensors were installed and the system was designed not to allow formation of a negative pressure inside the exhaust pipe. The experiment was conducted setting engine rpm, temperature, mixer shape, and distance as the experiment variables. As a result of the experiment, in the case of non-mixer type, a phenomenon was found where urea became locally packed as the exhaust gas and urea were not mixed and, when an R-type mixer was applied, urea was formed being spread on the whole. It was also confirmed that uniformity index was increased by 8 % in average when an R-type mixer was used in comparison to that of the non-mixer type, and the non-mixer type failed to achieve flow uniformity of 90 % or higher while the case where an R-type mixer was used could achieve it when the distance was 20 cm or bigger. Based on such a result, changes in the uniformity of urea and exhaust gas depending on existence of a mixer, exhaust gas temperature, engine rpm, and distance could be confirmed. It is thought that additional studies are required to be conducted later on the effect of a change in the mixer shape on flow uniformity.

Abstract: This paper investigates the effect of the laser cutting parameters on the heat-affected zone, and on the boundary layer of stainless steel processing. A new analytical resolution based on the boundary layer theory is used to deduce the interaction effects of the cutting parameters on the above zones. The results revealed that, the laminar nitrogen assist gas has a negligible effect on the HAZ depth but it has a remarkable effect on the molten boundary layer. It is also noticed that the pressure gradient remains very small compared to the interface shearing and the conductive heat losses from the cutting zone towards the substrate is dominant compared to the convective heat losses towards the gas.

Abstract: This work presents a non-steady state and three-dimensional mathematical modeling to predict moisture transport (based on the Langmuir-Type Model) inside the vegetable fiber-reinforced composite materials. The numerical solutions of the governing equations have been obtain using the finite-volume method. The model was apply for vegetable fiber-reinforced polymer composites. Emphasis to the geometrical dimension effect of the composite in the water absorption process was given. Results of the average moisture content, free and entrapped water molecules concentration kinetics and free and entrapped water molecules concentration distributions inside the material along the process are shown and analyzed. In the distributions of the analyzed properties, it was observed that the geometric dimensions of the composite has influence in the water absorption process.

Abstract: Drying characteristics of watermelon seeds using infrared (IR) heating combined to non-heated air flow were determined varying the IR source temperature and air velocity. The effects of the process variables on the effective moisture diffusivity (D_eff) and specific energy consumption (SEC) were also evaluated. Experiments in the hybrid dryer were conducted with seeds arranged in a single layer and exposed to three IR temperatures levels (45, 65 and 85 W/m²) and three air velocities levels (0.4, 0.8 and 1.2 m/s) at 25°C. The effective moisture diffusivity was estimated using Fick’s diffusion model assuming negligible shrinkage and surface moisture in equilibrium with the surrounding air. D_eff-values ranged from 0.62 x 10^-10 to 1.83 x 10^-10 m²/s, while SEC-valued varied from 29.91 to 73.16 kWh/g. Statistical analysis carried out on the experimental data indicated that the effective moisture diffusivity and specific energy consumption were significantly influenced only by the IR source temperature, which had a positive linear effect on D_eff and a negative linear effect on SEC. Maximum effective diffusivity and minimum energy consumption values in hybrid drying of watermelon seeds were obtained with the use of the highest IR temperature and lowest air velocity.