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The influence of gravity on the Marangoni flow instability in half zone liquid bridges in the case of liquid metals is investigated by direct 3D and time‐dependent simulation of the problem. The computations are carried out for different heating conditions and environments (zero g conditions and on ground liquid zone heated from above or from below). The case of cylindrical shape (simplified model) and of melt/air interface deformed by the effect of gravity (real conditions) are considered. The comparison among these situations gives insight into the separate (gravity) effects of buoyancy forces and of the free surface deviation with respect to straight configuration. Body‐fitted curvilinear co‐ordinates are adopted to handle the non‐cylindrical problem. The liquid bridge exhibits different behaviours according to the allowed bridge shape. If the shape is forced to be cylindrical, the flow field is stabilized in the case of heating from above and destabilized if gravity is reversed. If the deformation is taken into account, gravity always stabilizes the Marangoni flow regardless of its direction (parallel or antiparallel to the axis) and the 3D flow structure is different according to the heating condition (from above or from below). In the latter case, the critical Marangoni number is larger and the critical wave number is smaller, compared with the opposite condition. In addition, for Pr=0.02 (Gallium), a surprising heretofore unseen behaviour arises. No steady bifurcation occurs and the flow becomes unstable directly to oscillatory disturbances. This phenomenon has never been reported before in the case of low Prandtl number liquids.

This paper aims to derive a reduced-order model for the heat transfer across the interface between a millimetric thermocapillary liquid bridge from silicone oil and the surrounding ambient gas.

Numerical solutions for the two-fluid model are computed covering a wide parametric space, making a total of 2,800 numerical flow simulations. Based on the computed data, a reduced single-fluid model for the liquid phase is devised, in which the heat transfer between the liquid and the gas is modeled by Newton’s heat transfer law, albeit with a space-dependent Biot function Bi(z), instead of a constant Biot number Bi.

An explicit robust fit of Bi(z) is obtained covering the whole range of parameters considered. The single-fluid model together with the Biot function derived yields very accurate results at much lesser computational cost than the corresponding two-phase fully-coupled simulation required for the two-fluid model.

Using this novel Biot function approach instead of a constant Biot number, the critical Reynolds number can be predicted much more accurately within single-phase linear stability solvers.

The Biot function for thermocapillary liquid bridges is derived from the full multiphase problem by a robust multi-stage fit procedure. The derived Biot function reproduces very well the theoretical boundary layer scalings.

The purpose of this paper is to establish a new dynamic coupled discrete-element contact model used for investigating fresh concrete with different grades and different motion states, and demonstrate its correctness and reliability according to the rheological property results of flow fresh concrete in different working states through simulating the slump process and mixing process.

To accurately express the motion and force of flowing fresh concrete in different working states from numerical analysis, a dynamic coupled discrete-element contact model is proposed for fresh concrete of varying strength. The fluid-like fresh concrete is modelled as a two-phase fluid consisting of mortar and aggregate. Depending on the contact forms of the aggregate and mortar, the model is of one of the five types, namely, Hertz–Mindlin, pendular LB contact, funicular mucous contact, capillary LB contact or slurry lift/drag contact.

To verify the accuracy of this contact model, concrete slump and cross-vane rheometer tests are simulated using the traditional LB model and dynamic coupled contact model, for five concrete strengths. Finally, by comparing the simulation results from the two different contact models with experimental data, it is found that those from the proposed contact model are closer to the experimental data.

This contact model could be used to address issues such as (a) the mixing, transportation and pumping of fresh concrete, (b) deeper research and discussion on the influence of fresh concrete on the dynamic performance of agitated-transport vehicles, (c) the behaviour of fresh concrete in mixing tanks and (d) the abrasion of concrete pumping pipes.

To accurately express the motion and force of flowing fresh concrete in different working states from numerical analysis, a dynamic coupled discrete-element contact model is proposed for fresh concrete of varying strength.

In the “dry” state, pigment particles are held together by attraction forces of various physical chemical natures including the van der Waals force and the “liquid bridge” force. These attraction forces must be overcome in order to disperse pigment particles into liquid media. Dispersion machinery is designed to generate energy required to overcome, to various extents, such attraction forces. On the other hand, the efficiency of dispersion operation is significantly dependent upon the effectiveness of the transfer of energy from the dispersion tools/dispersion charges to the oversized pigment particles, as a result of the presence of the adhesion and cohesion within the dispersion system. This paper explores the nature and the significance of various forces between pigment particles and of the adhesion and cohesion phenomena associated with pigment dispersion, from a practical point of view. Principles relevant to improving the efficiency of pigment dispersion via minimisation of the adhesion between pigment particles and via maximisation of the adhesion and cohesion within the dispersion system are also discussed.

The influence of buoyancy forces on oscillatory Marangoni flow in liquid bridges of different aspect ratio is investigated by three‐dimensional, time‐dependent numerical solutions and by laboratory experiments using a microscale apparatus and a thermographic visualisation system. Liquid bridges heated from above and from below are investigated. The numerical and experimental results show that for each aspect ratio and for both the heating conditions the onset of the Marangoni oscillatory flow is characterized by the appearance of a standing wave regime; after a certain time, a second transition to a travelling wave regime occurs. The three‐dimensional flow organization at the onset of instability is different according to whether the bridge is heated from above or from below. When the liquid bridge is heated from below, the critical Marangoni number is larger, the critical wave number (m) is smaller and the standing wave regime is more stable, compared with the case of the bridge heated from above. For the critical azimuthal wave number, two correlation laws are found as a function of the geometrical aspect ratio A.

A linear stability analysis has been employed to investigate the thermocapillary instability occurring in a nonisothermal liquid bridge. The steady, axisymmetric basic state was solved numerically using a finite difference method. A mixed finite difference‐spectral method, combining the advantages of both methods, was then used to reduce the linear disturbance equations to an eigenvalue problem. The critical Marangoni numbers for axisymmetric disturbances are predicted for small Prandtl numbers and various aspect ratios. The effect of surface heat transfer is also investigated. The present results are compared with energy‐theory results and with the results of other experiments.

This paper aims to determine the optimum set of temperatures through correlation study to attain the most effective capillary flow of underfill in a multi-stack ball grid array (BGA) chip device.

Finite volume method is implemented in the simulation. A three-layer multi-stack BGA is modeled to simulate the underfill flow. The simulated models were well validated with the previous experimental work on underfill process.

The completion filling time shows high regression R-squared value of up to 0.9918, which indicates a substantial acceleration on the underfill process because of incorporation of thermal delta. An introduction of 11 °C thermal delta to the multi-stacks BGA managed to reduce the filling time by up to 16.4%.

Temperature-induced capillary flow is a relatively new type of driven underfill designed specifically for package on package BGA components. Its simple implementation can further improve the productivity of existing underfill process in the industry that is desirable in reducing the process lead time.

The effect of temperature-induced capillary flow in underfill encapsulation on multi-stacks BGA by means of statistical correlation study is a relatively new topic, which has never been reported in any other research according to the authors’ knowledge.

A numerical study on the stretching of a Newtonian fluid filament is analysed. Stretching is performed between two retracting plates, moving under constant extension rate. A semi‐implicit Taylor‐Galerkin/pressure‐correction finite element formulation is employed on variable‐structure triangular meshes. Stability and accuracy of the scheme is maintained up to large Hencky‐strain levels. A non‐uniform radius profile, minimum at the filament mid‐plane, is observed along the filament‐length at all times. We have found maintenance of a suitable mesh aspect‐ratio around the mid‐plane region (maximum stretch zone) to restrict early filament break‐up and consequently solution divergence. As such, true transient flow evolution is traced and the numerical results bear close agreement with the literature.

The purpose of this paper is to numerically investigate the effect of various parameters such as density ratio, surface wettabilities and Weber number on the droplet dripping and detachment process.

By using algebraic volume of fluid method, the governing equations are solved using a collocated finite volume approach in two-dimensions.

The results indicate that, for small densities of droplet, it adheres to the surface except when the surface is hydrophobic, while an increase in Weber number or presence of an additional droplet in the vicinity led to detachment.

The paper explores various characteristics of a droplet when two competing forces, namely, gravity and surface tension, act simultaneously. The detachment is observed for a given initial droplet size, as it becomes denser in an uniform gravitational field. The effect of droplet affinity for two droplets is also presented using the simulations.

This work aimed at studying the use of capillary forces as a gripping principle in the handling of sub‐millimetric sized components. The goal was to present the results as design rules of so‐called capillary grippers.

Each parameter (surrounding environment, materials, volume of liquid, separation distance, gripper geometry and gripper size, relative orientation of the gripper with respect to the component) has been quantified, either numerically or experimentally. In some validation cases, both means have been used.

The capillary forces can be modified between a maximum F_max and a minimum F_min so that a component with any mass m between F_min/g and F_max/g can be picked up and released.

By comparison with some existing capillary grippers prototypes, this work is only a theoretical and experimental study. Nevertheless, its originality lies in the exhaustive study and quantification of all parameters so that most of the capillary grippers of the literature can be explained or improved with these results.

The main implication of the capillary gripping is that it provides an alternative to existing gripping principles (vacuum grippers, tweezers). This principle is strong enough (a few mN) and well adapted to pick up components with only one free accessible surface. The scaling laws are the most favorable (F∼L). It provides a “soft” picking, avoiding high contact forces.

The originality lies in the exhaustive quantification of the role of each parameter. These results can be used by researchers and designers.