Defect and Diffusion Forum Vol. 390

Abstract: We present results of numerical experiments performed to evaluate the effects of the material interface supporting wire grid on the Richtmyer-Meshkov instability (RMI). An air-SF6 interface initially perturbed sinusoidally supported on a number of solid circular cylinders. These cylinders are introduced along the interface to mimic the presence of the grid thin wires. The resulted mixing and growth rate of the perturbation in the presence and absence of the supporting grid were analyzed and validated with experimental measurements. The small scales perturbation imposed by the cylinders are around two orders of magnitude smaller than the interface sinusoidal perturbation wavelength requiring the adaptive mesh refinement (AMR) to adequately resolve small scale features. Furthermore, an embedded boundary technique is used to handle the complex geometry stemming from the presence of these multiple. A multi-fluid formulation is utilized to form a multi-gas species interface and compute the gas mixture properties.

Abstract: Underwater exercise programs are among the nursing programs for which positive effects have been reported with regard to the promotion of good health in diverse subjects, such as patients suffering arthritis, as well as elderly people and middle-aged women. Through many previously conducted studies, subjects participating in underwater exercises have been reported to continuously experience reduced pain, and improvement in muscle strength, flexibility, sense of balance, and muscular endurance. However, few studies have delved into the fundamental phenomena of positive effects of underwater exercises on the human body. In this study, a model of the upper limbs of the human body was used in a simulation of underwater exercises to analyse the resulting pressure fluctuation on the skin of the hands and arms of the model through the methods of computational fluid dynamics. During the simulation of underwater exercises, pressure fluctuation of diverse frequencies, arising from the vortex flow around the articulations of the fingers and hands of the model, were identified and were seen to create varied cutaneous stimulations and massage effects. Such cutaneous stimulations seem to continuously excite capillary vessels situated between hands and finger joints, creating positive effects in blood circulation around pain sites of patients suffering from arthritis.

Abstract: The purpose of this analysis is to evaluate the structural integrity of the jet pump assembly of a BWR during the performance of its operational and safety functions. The natural frequencies and vibration modes of the jet pump assembly immersed in water were determined. It was observed that the fourth mode shape was torsional, and its associated resonance frequency was 41.82 Hz. Also, the vibration induced by the flow in the leakage of the slip joint was analyzed with an axisymmetric model. The gap of the slip joint was varied from 0.2 mm until 0.65bmm. A gap between 0.6 and 0.64, would cause flow-induced vibration because this excitation frequency matches with the fourth natural frequency of the jet pump assembly. The above was carried out using computational fluid dynamics, as well as the finite element method, with ANSYS Structural and ANSYS Fluent codes.

Abstract: The purpose of this work is to study the effect of heat treatments on the microstructure of the nickel-based superalloy Inconel 713C. Three different conditions were studied and the results compared: (1) as cast; (2) solution treatment (1,179°C/2h) and (3) stabilizing treatment (1,179°C/2h plus 926°C/16h). Inconel 713C is normally used in the as-cast condition, an improvement in the 980°C stress-rupture life is often obtained by a solution heat treatment. However, the material in this condition tested under high stress at 730°C shows a marked decreased in rupture life and ductility [1]. The mechanical resistance in creep increases in Inconel 713C by precipitation hardening phase, such γ’ (Ni₃Al) formed during the heat treatments [2]. The characterization techniques used was: chemical analysis, hardness test, X-ray diffraction, optical microscope and scanning electron microscopy (SEM), EDS analyzes and thermocalculation. The heat treatments modified the dendritic structure, reducing the acicularity. The SEM and EDS analysis illustrated the γ, γ’ and carbides. The matrix phase (γ), has in its constitution the precipitation of the γ’ phase, in a cubic form, and in some regions, veins of carbides were modified with the heat treatments.

Abstract: Thermal characteristic of insulation concretes is one of the key components in materials selection especially in civil constructions. In this article, non–tabulated material parameters of some innovative highly-insulating non-structural concretes are presented. The specific volumetric heat capacity, specific heat capacity, parameter of temperature diffusivity and thermal mass parameter of the innovative highly-insulating cementitious composites were determined. The experiments were conducted using a prototype automated calorimetric chamber. The measurement results are compared with those obtained by using a commercial multifunctional instrument (Isomet 2114) and are accompanied by the measurement of other significant thermal parameters of the cementitious composites under investigation. The results indicated that there is potential of using the newly created types of concrete for insulation purposes.

Abstract: Several important key problems and issues remain to be addressed about the numerical analysis of friction stir welding. The main feature of the thermal numerical approach is to accurately compute the thermal distribution produced by the friction between the plate and the tool. It is well known that the downward force applied from the tool creates a distributed pressure between the shoulder and the workpiece. Based on this, a new expression to represent the heat generation in FSW is proposed. Results of thermal cycles, thermal histories, and shapes of the weld and HAZ obtained with the proposed expression in SAE-AISI 1524 carbon steel are presented. Results demonstrate that the energy input is strongly dependent on the tool advance speed, rotational speed, and the axial pressure necessary to produce yielding. For instance, at a constant increase in axial pressure, lower peak temperature increments are produced when higher tool advance speeds are chosen. The mathematical modeling has been investigated with a view to generate numerical data to provide values for further assessment and experimental comparison.

Abstract: A study is presented which implies the knowledge of rare earth magnetic anisotropy, nanotechnologies with the advancement of electromagnetic (EM) waves to induce alteration on oil-nanofluid interfacial tension (IFT) and nanofluid viscosity. The study had been done by doping of Samarium rare earth into Yttrium Iron Garnet (YIG) nanoparticles to improve the magnetic properties of the YIG nanoparticles. The doping process has been done by sol-gel method at 1000oC and at the pH of 7. Samarium rare earth was doped into YIG nanoparticles at different composition (x = 0.00, 0.25, 0.50, 0.75, 1.00). The results show that a Samarium doping composition at x =1.00 at pH 7 resulted in the highest nanofluid wettability, highest magnetic saturation, highest reduction in oil-water interfacial tension (IFT), and the highest alteration in viscosity. Moreover, overall of the experiment proved that when EM wave applied to the Samarium doped YIG nanofluid it had resulted in the increment of viscosity, more reduction in oil-water IFT. The experiment proved that Samarium doping into YIG nanoparticles/nanofluid (Sm-YIG) under the presence of electromagnetic waves are theoretically correct to alter oil-nanofluid IFT and nanofluid viscosity. This can be seen from the ability of Sm-YIG under the presence of EM waves effect on oil-water IFT reduction, nanofluid viscosity increment, reduction in oil-water mobility ratio and nanoparticles magnetic saturation increment.

Abstract: In this study, nine vertical flat plates of pin fin arrays were fabricated by selective laser melting to investigate the possible enhancements of external condensation. These specimens are cylindrical pin fins of the same fin diameter of 300 μm but are of different fin heights (l) and fin pitches (p) from 300 μm to 900 μm. Experiments were conducted in a condensation chamber with near quiescent vapor to simulate free-convection condensation. The aim is to investigate the effects of fin pitch and fin height on the condensation heat transfer performance of the surfaces. The results of this study show that the increase in fin height and the decrease in fin pitch lead to a systematic increase in the condensation heat flux (q''). At the same fin pitch, the increase in fin height from 600 μm to 900 μm resulted in a more significant increase in q'' as compared to the increase in fin height from 300 μm to 600 μm. On the other hand, at the same fin height, a larger increase in q'' is observed when the fin pitch is reduced from 900 μm to 600 μm as compared to the reduction in fin pitch from 600 μm to 300 μm. It can be deduced that increasing the fin height enables the fins to protrude out of the thick condensate film and increases the effective heat transfer area of the surfaces. However, when the fin density is large, it impedes the condensate drainage path and limits the enhancement in q''. The enhancement factor (η), which is the ratio of the average condensation heat flux of a pin fin surface to that of a plain surface, was computed for each specimen. The highest η value of 1.72 was achieved with the specimen of 900 μm fin height and 300 μm fin pitch. Finally, a relationship between η and the dimensionless fin pitch-to-height ratio (p/l) is proposed.

Abstract: In this paper MHD flow of Casson hybrid nanofluids are investigated with Caputo time-fractional derivative. Alumina (Al) and copper (Cu) are used as nanoparticles in this study with heat, mass transfer and MHD flow over a vertical channel in a porous medium. The problem is modeled using Caputo fractional derivatives and thermophysical properties of hybrid nanoparticles. The influence of concerned parameters is investigated physically and graphically on the heat, concentration and flow. The effect of volume fraction on thermal conductivity of hybrid nanofluids is observed.