Papers by Keyword: Capillary Force

Abstract: In order to study the influence of different initial topography on the molten pool flow under a moving heat source, the finite element analysis method was used to establish a two-dimensional transient model of laser polishing to simulate the evolution of the surface topography of the material during laser polishing. In the simulation process, a moving laser beam was used as the heat source, and the free surface of the actual material was profiled through a three-dimensional profiler. A very similar simulation model surface was constructed, coupled with the flow field and temperature field in the laser polishing process, and the capillary force was considered comprehensively. Combined with thermocapillary force. The results show that under the combined action of capillary force and thermocapillary force, the surface of the polished material has a peak-filling effect, which makes the surface of the material achieve a good polishing effect. The initial shape will affect the polishing effect, the greater the curvature, the faster the flow rate of the molten pool. In molten pools with large spatial curvatures, capillary forces dominate. Keywords: Laser polishing; molten pool; surface topography; numerical analysis; capillary force; thermocapillary force.

Abstract: A two-dimensional nonstationary model of calculation of heat transfer at viscous fluid droplet spreading over the heated substrate is presented. A process of the fixed droplet spreading over a simple geometry substrate has been calculated. A hydrodynamic picture of the process of spreading has been obtained. The influence of the parameters of the model on the nature of spreading has been studied. The temperature profiles at the droplet surface have been obtained. The setting time of the stationary mode has been evaluated.

Abstract: This paper presents a significant finding where a capillary force is observed for a gas hydrate growth under a 24-hours shut-in condition (static fluid) using a newly designed apparatus comprising six units of identical rocking cells within isochoric conditions. The gas hydrate growth (static condition) is compared to a gas hydrate formation under a rocking condition. Crystal growth with a simulated natural gas mixture at various time intervals is noted. The visual observations of nucleation and growth at a wetted surface are described. The obtained visual results suggest that capillary forces provide continuous mass-transfer of water towards gas hydrate growth, even within shut-in conditions.

Abstract: Microfluidic time gates are applied to control accurate flow time of liquids in the autonomous capillary systems, which are critical structures for point-of-care diagnostic and analytical applications. The time gate employs several abruptly changing geometry of the flow path to change the wettability of micro-channels to meet the requirement of delaying flow. However, obtaining desirable flow of liquids in microfluidics is still a limiting factor in the practical implementation. The work demonstrates a novel 2D serial cross-channel time gate and 3D serial cross-channel time gate. They are fabricated in PDMS-based autonomous capillary system. 2D serial cross-channel time gate is comprised of multiple paralleled channels of changeable width with dimensions from 300-800μm. The number of the channels and the width variation of the cross intersections are crucial factors to influence the flow velocity of liquids. Compared with the 2D serial cross-channel time gate, the 3-D structures can eliminate the problem of entrapping air and improve the flow velocity of liquids in the time gate. The controlling time of the flow in 3D serial cross-channel time gate and 2D serial cross-channel time gate are 9~13s and 5s~51s, respectively.

Abstract: The simulation of two-phase oil-water coupling flows in a low permeability reservoir with capillary pressure and start-up pressure gradient was carried out. First of all, the state equations with all the oil pressures at grid nodes were established based on lump-centre finite difference method. Secondly, the recurrence formulae of all the oil pressures and water saturations at grid nodes were built up according to IDPIM and an explicit difference method, respectively. Finally, the simulation of two-phase oil-water coupling flows for a typical five point area water injection as an example was carried out. Simulating results show that capillary pressure has a little effect on moisture rate and oil production, but startup pressure gradients have an outstanding effect on them. Therefore the existence of startup pressure gradients will enhance the difficulty of oil development.

Abstract: Hysteresis effect of contact angle has an important impact on liquid bridges between sphere particles. This effect is not limited to increasing liquid volume of fixed particles. The hysteresis effect of contact angle is expressed by fixed liquid volume while the two sphere particles are in relative movement. The hysteresis effect of contact angle on the liquid bridge is also significant. In this paper, the hysteresis effect of contact angle on capillary forces of liquid bridges is analyzed when the two sphere particles are in relative movement. Results indicate that contact angle hysteresis effects on capillary force are significant.

Abstract: The prediction and the control of the magnitude of the capillary force are essential for the micromanipulation techniques. It is generally considered that the capillary force is an effective and reliable scheme for micromanipulation. In this paper, a very complicated calculation process for the theoretical capillary force is reviewed, and a practical approximate formula for the calculation of the total capillary force in the particle-particle-substrate system is proposed. Comparison is made between the approximation and theoretical results and good agreement is found. It is suggesting that the approximate formula can be applicable for the evaluation of the capillary force in the micromanipulation.

Abstract: In this paper, we describe the development of a needle based dispenser for high-viscosity liquid, and pick & place of micro objects using capillary force. Recently, miniaturization of portable devices and their electronic parts has been remarkable. So we think that there are a lot of needs for micro manipulation for making more complex and smaller devices. There are a lot of possibilities to manipulate complex-shaped micro objects by using liquid because it changes its shape flexibly according to the shape of the contact surface. We have developed a unique surface mounting technology which is based on a movable shaft driven by a piezoelectric linear motor. We can simply apply high-viscosity liquid drops by stamping the wet tip of the shaft on a substrate, and we confirm that the device is able to apply a liquid the viscosity of which is about 1200Pas. We have studied the relation between viscosity and diameters of applied liquid drops via several experiments. We have also conducted interesting experiments in which we pick and place some small and complex-shaped objects using capillary force. We confirmed that if capillary force between the shaft and micro object is larger than that between the substrate and the micro object, we are able to place a chip-capacitor weighing below 1 mg. This simple method is very effective because any shaped object can be mounted. However, fast control and accurate control of the shaft are needed for efficient production and accurate mounting. To realize this, we developed a PID controller for the dispenser with an optical liner encoder with a resolution of 30 nm. We confirm that settling time becomes less than 50 ms when the shaft moves 5 mm with 1 micrometre accuracy.

Abstract: Nanocubes accumulations were built up by meniscus method and developed to achieve a dense structure. For the first attempt, strontium titanate (SrTiO₃, ST) nanocubes were selected for the nanocubes accumulations. The ST nanocubes were prepared by a solvothermal method. For Strontium titanate nanocubes, Sr(OH)₂ and titanium isopropoxide (TP) were used as starting materials and were heated at 240°C for 18h in an autoclave. Size distribution of TP-derived ST nanocubes was narrower than TiO₂-derived ST nanocubes. Moreover ST nanocubes accumulations were prepared by a meniscus method. A dense ST nanocubes accumulation of over 1 μm was prepared at an angle of 50 degrees at 60 °C. The crystal structures were determined by X-ray diffraction (XRD) and the microstructures were observed by scanning electron microscopy (SEM).

Abstract: For developing a unique model in which the rheological performance of fresh concretes from zero-slump to self compacting concrete can be described, it is necessary to define workability in terms of fundamental physical entities. In order to achieve this, the concept of capillary cohesion from science of granular physics has been considered as the first step for investigation. In this paper, focus is on this concept and providing some preliminary achievements of the experimental work. In wet granular material the presence of liquid generates cohesion between particles and affects the mechanical properties of the granular media to a large extent. For the simulation of the behavior of this material by considering pendular state for liquid content, a discrete element method (DEM) is used. The cohesion between a grain-pair is expressed as an explicit function of local geometrical and physical parameters. In this study emphasis is on static and/or quasi-static situations. Since the cohesion dominates over other effects of the liquid, such as viscosity and lubrication, the effect of the size of particles on the cohesion arising from the liquid bridge is investigated explicitly. Based on experimental results, a closed-formula approximation is developed that can be used to calculate the capillary force acting between two glass spheres as a function of the separation distance for a given bridge volume.