Explore the vast range of titles available.

Friction stir welding (FSW) joints are inevitably accompanied with the change in shape of the abutting surfaces due to the tool movement. Further, the formation of brittle intermetallics (during dissimilar welding) is also unavoidable. Therefore, the current work is focused to study the role of the shape of the new interface in properties of the joints and to control the morphology of intermetallics subsequently. FSW experiments were carried out between aluminum AA2024 and pure copper for different tool offset positions (on either side of the interface), plate positions (copper in advancing or retreating side), and tool geometry (plain and threaded). The microstructure observation showed noticeable changes in the shape of the new interface with respect to the selected parameters. Tensile tests highlighted that the weld which has continuous and smooth new interface gave better properties than the welds which had an irregular discontinuous interface. Also, this kind of interfaces had formed with a continuous thin intermetallic layer, and it was a desirable morphology of the intermetallics. The weld with this thin intermetallic layer (metallurgical bonding) alone has the maximum strength, whereas the welds that also had fine steps at the interface (mechanical bonding from interlocking effect) have maximum ductility. The mechanism behind this was explained in detail with the help of material flow behavior study for the selected conditions. This concluded that to achieve better properties, the shape of the new interface and the bonding along this interface are mainly important to be considered.

Gas–liquid flow in a pipeline is a very common. Slug two-phase flow is dominated in the case of slightly upward flow (+0.25°) and considered to be the comprehensive flow configuration, and can be in close contact with all the other flow patterns. The models of different flow patterns can be unified. Precise prediction of the slug flow is crucial for proper design and operation. In this paper, we develop hydrodynamics unified modeling for gas–liquid two-phase slug flow, and the bubble and droplet entrainment is optimized. For the important parameters (wall and interfacial friction factors, slug translational velocity and average slug length), the correlations of these parameters are optimized. Furthermore, the related parameters for liquid droplet and gas bubble entrainment are given. Accounting for the gas–liquid interface shape, hydrodynamics models, i.e., the flat interface model (FIM) and the double interface model (DIM), of liquid film in the slug body are applied and compared with the experimental data. The calculated results show that the predictions for the liquid holdup and pressure gradient of the DIM agree with experimental data better than those of the FIM. A comparison between the available experimental results and Zhang’s model calculations shows that the DIM model correctly describes the slug dynamics in gas–liquid pipe flow.

Dynamics of a multiphase flow phenomenon involving water (at top), molten metal (at bottom), and vapor (between them), was numerically studied using volume of fluid method. Multiphase flow systems like this are present in a wide range of industrial applications and natural phenomena and are extensively investigated because of their potential to produce energy. This work pays special attention to the interface shape because of its influence on heat transfer rate. An approach, new for systems larger than drop scale, which consists in the construction of an interface shape diagram based on Reynolds (Re) and Bond (Bo) dimensionless numbers is proposed. The presented model demonstrated good capability to discern the governing forces such as viscous, inertial, and surface tension. The most favorable interface shapes for efficient premixing of phases involved were identified. The premixing significance lies in its determining role in steam explosion generation. Moreover, the effect of density ratio and triggering pressure is examined. In addition, Kelvin-Helmholtz and Rayleigh-Taylor fragmentation mechanisms were observed, and their preponderance was analyzed. The results obtained were validated with previous experimental data available in the literature finding good agreement. This proposal aims to provide useful information to enhance our understanding of this phenomenon from a fundamental perspective, applicable to further numerical and experimental studies in different research areas.

A metallic wire mesh screen, wire diameter of approximately 50 μm, is folded into ~80 “accordion-shaped” mini-channels and placed inside the evaporator package of a novel passive thermal management device for cooling overhead light-emitting diodes (LEDs) used in factory floors and high-bay facilities. The thermal power dissipated via these devices ranges between 75 W and 171 W. The channel walls (screen) wick liquid water from the porous wick (located centrally above the screen) and facilitate its evaporation. The closed-loop tests on this device confirm that the two-phase mixture quality exiting the evaporator is approximately 0.2. This paper presents a steady-state numerical model of this separated liquid–vapor flow in a single mini-rectangular channel (900 μm × 2000 μm, 4 cm long) with wire mesh-screen walls. The primary objective of the model is to estimate the pressure drops occurring in this two-phase flow. The model initially assumes a flat liquid–vapor interface along the channel and uses an iterative approach to estimate its final meniscus shape (curvature). In addition to the temperature distribution along the screen walls, this paper also discusses the velocity and pressure distributions in both liquid and vapor regions. It also helps understand the liquid–vapor interfacial shear in this flow configuration and proposes a flow-limiting condition for the device by predicting flow reversal in the channel.

Tb3Sc1.95Lu0.05Al3O12 (TSLAG) crystals are novel and high-quality magneto-optical materials with the most promising application as the core component of Faraday devices. Cracking is an obstacle to TSLAG crystal growth and is closely influenced by crystal thermal stress distribution. In this work, the evolution of thermal stress during TSLAG crystal growth in the initial Czochralski (Cz) furnace is numerically studied. The reasons for high thermal stress in TSLAG crystal are explained based on the results about the melt flow, the temperature distribution in the furnace, and the crystal/melt interface shape. A large crucible with a shallow melt is proposed to address the problem of significant variations in melt depth during TSLAG crystal growth. Based on the numerical results, the proposed design can stabilize the melt flow structure, suppressing changes in the crystal/melt interface shape and effectively improving thermal stress in the TSLAG crystal growth process, which contributes to precisely regulating the preparation of large-sized high-quality TSLAG crystals.

We investigated the optimal surface structure of an n -type Si substrate for Si-Al bonding (which prevents high-energy barrier formation) using simulation by the phase field method. The surface structure of the substrate contained a groove to suppress regrowth layer formation at the bottom of the groove. We determined the appropriate width and depth of the groove to effectively suppress the regrowth layer. The features of the regrowth layer suppression mechanism were clarified as the following: narrowing the groove caused the Al concentration to increase inside the groove and, in turn, decreased the degree of supercooling of the Si-Al liquid. However, when the groove was too narrow, the radius of curvature at the bottom of the groove decreased, and the equilibrium melting point of the Si-Al liquid rose due to the Gibbs–Thomson effect. On the other hand, the narrow groove increased the Al concentration, leading to decrease of the equilibrium melting point of the Si-Al liquid. This implies that there is always an optimum value for the width and the depth of the groove by which the regrowth layer is effectively suppressed through forming the groove in the Si surface for the Si-Al bonding process. Any groove morphology with the growth ratio (the ratio of the regrowth layer at the bottom to that at the top of the groove) less than 0.3 is appropriate to achieve good ohmic contact; however, it is considered that the groove with periodic length of 9.4 μm and aspect ratio around 0.2 is the best because of the ease of manufacturing.

Slippery hydrodynamics in grooved hydrophobic microchannels is known to be primarily dictated by the area of the gas–liquid contact surface. Here, we augment this classical notion by bringing out the critical role played by the channel dimensions on the underlying slip mechanisms and the consequent drag reduction. Our analysis, towards this, reveals the non-trivial implication of gas–liquid interface topology and its position inside the groove towards dictating the underlying frictional characteristics, which in turn is largely dependent on the confluence of the channel hydraulic diameter and the groove width. These results may turn out to be of immense consequence towards arriving at preferred frictional drag characteristics of hydrophobic microchannels and nanochannels by judicious choices of the pertinent geometric parameters.

Modern microfabrication techniques have led to a growing interest in micropillars and pillar–pore structures. Therefore, in this paper a study of the liquid entry pressure of a hydrophobic pillar–pore structure and the corresponding liquid–gas interface shape for the pressurized liquid is presented. We theoretically analysed the constant mean curvature problem for the rotationally symmetric case and determined an analytical expression for the liquid entry pressure of a hydrophobic pillar–pore structure. Furthermore, the shape of the liquid–gas interface as well as a formula for the location of the minimum were derived. The results are useful for designing geometries with specific properties, such as preventing or facilitating liquid intrusion into rough structures. We compared these results to multiphase lattice Boltzmann simulations where equilibrium contact angles in the range of 157∘ to 102∘ were tested. In our further analysis, we compared theoretical findings from previous works to our lattice Boltzmann simulations. The presented cases can serve as a benchmark for the development and validation of numerical multiphase models.

Calibration or parameter identification is used with computational mechanics models related to observed data of the modeled process to find model parameters such that good similarity between model prediction and observation is achieved. We present a Bayesian calibration approach for surface coupled problems in computational mechanics based on measured deformation of an interface when no displacement data of material points is available. The interpretation of such a calibration problem as a statistical inference problem, in contrast to deterministic model calibration, is computationally more robust and allows the analyst to find a posterior distribution over possible solutions rather than a single point estimate. The proposed framework also enables the consideration of unavoidable uncertainties that are present in every experiment and are expected to play an important role in the model calibration process. To mitigate the computational costs of expensive forward model evaluations, we propose to learn the log-likelihood function from a controllable amount of parallel simulation runs using Gaussian process regression. We introduce and specifically study the effect of three different discrepancy measures for deformed interfaces between reference data and simulation. We show that a statistically based discrepancy measure results in the most expressive posterior distribution. We further apply the approach to numerical examples in higher model parameter dimensions and interpret the resulting posterior under uncertainty. In the examples, we investigate coupled multi-physics models of fluid–structure interaction effects in biofilms and find that the model parameters affect the results in a coupled manner.

We have carried out the numerical simulation for DS system for growing multi-crystalline silicon (mc-Si) ingot with different size additional insulation blocks. Thermal Stress, melt-crystal interface shape and dislocation density are the main factors that can determine the efficiency of solar cells. Thermal stress and dislocation density can be controlled by controlling the heat dissipation from the crucible. The simulation results revealed that the effective controll of melt-crystal interface shape has been obtained by the suitable additional insulation block in DS system. At particular size of insulation block (3 cm) the optimal melt-crystal interface shape, von Mises stress, Maximum shear stress and maximum principal stress have been established during the solidification process which can enhace the mc-Si ingot quality, for photovoltaic application.