Papers by Keyword: Coalescence

Abstract: This study reports the unique phenomenon of the coalescence of oil droplets floating over the water surface. For the first time, the coalescence has been initiated through the creation of externally generated low-amplitude surface waves. We used a simple and cost-effective method to manifest the surface waves over the free surface of water to study the merging dynamics. The time-lapse images depict the entire stage of parent droplets merging. The study reveals that the coalescence time required for the complete transformation of parent droplets into the resultant droplet increases as the number of parent droplets over the free surface of water increases. We studied the time-dependent variation in the velocity of two non-identical parent droplets. The experiment reveals that the smaller droplet propagates faster than the larger droplet over a free surface of water. The peak velocities of the two droplets are 2.0 cm/s and 1.07 cm/s, respectively. The point of deposition of droplets does not influence the coalescence phenomenon; whether the droplets are deposited at the center of the petri dish or the wall, they still show coalescence. However, the droplets that are deposited near the center of the petridish propagate faster compared to those deposited near the wall due to the higher intensity of vibration at the center.

Abstract: A mode I, centre crack, in ductile steel plate of finite dimensions is modeled in ANSYS software. Non-linear stress-strain data of steel are used. Plane strain case is adopted. A suitable value of far field tensile stress (pressure) is chosen such that EPFM condition prevails at the crack tip. Process and plastic zones are obtained at the crack tip. Desired values are noted. Areas of high stress and high strain are identified. Validation of void nucleation taking place ahead of crack tip and not exactly at the crack tip and coalescence of voids happening at the crack tip are confirmed from the results. Plots between the distance of desired location from the crack tip and load line stresses and strains are drawn. The plots are in accordance with the expectations.

Abstract: A self-assembled ZnO tail-like cluster (TC) had been successfully synthesized by a simple chemical vapor deposition method. Scanning electron microscopy observations show that ZnO TC is composed of bushy ZnO microwires with flower-shaped cross sections. Long and narrow furrows can be clearly observed on the surface of the ZnO TC. A possible growth model is proposed to discuss the formation mechanism. The analytical result indicates that the flower-shaped ZnO microwires are formed by the lateral coalescence of ZnO wires at high temperature. The room temperature PL spectrum shows a prominent UV emission band around 380 nm, and no green emission is found, implying that the unique flower-shaped ZnO microwires have high optical quality. This controlled growth of ZnO TC may have implication for potential applications in novel optoelectronic micro/nanodevices in the near future.

Abstract: An experimental investigation has been carried out to study the effect of surfactant dosage on micro explosion phenomenon. Three water in diesel emulsion with 20% water by volume was prepared using mechanical stirring at 17000rpm for 100s.The emulsions were stabilised by a were stabilized by a single surfactant with three different doses. Water in diesel emulsion droplet was suspended on a thermocouple and the evolution of micro explosion was recorded with a high speed camera synchronized with temperature data logger. Secondary atomization of emulsion droplet was observed under Leiden frost regime using a hot plate as the heat source. The results show that the occurrences of micro explosion are affected by the volume of added surfactant by influencing the exploding temperature and waiting time. Physical properties like density, viscosity and surface tension were also found to be influenced by the amount of surfactant used.

Abstract: An oil/water separator with inlet component, perforated plates and coalesence internals was designed in this paper. The influence of the perforated plates on the flow field and the structures of coalesence component on the oil/water separation were simulated by commercial software FLUENT. The results show that the perforated plates can prevent turbulence and eliminate back-mixing flow effectively. And the flow field uniformity was the best,when the distance between the two plates was 140mm.The separator with inclined plates had the highest separation efficiency of the three structures.

Abstract: Cu precipitation in steel has been investigated numerous times. Still, a consistent simulation of the nucleation, growth and coarsening kinetics of Cu precipitates is lacking. Major reason for this is the fact that Cu precipitation involves complex physical interactions and mechanisms, which go beyond the classical precipitation models based on evaporation and absorption of precipitate-forming monomers (atoms). In the present work, we attempt a comprehensive modeling approach, incorporating coalescence results from Monte Carlo simulation, prediction of the nucleus composition based on the minimum energy barrier concept, diffusion enhancement from quenched-in vacancies, dislocation pipe diffusion, as well as the transformation sequence of Cu-precipitates from bcc-9R-fcc. Our simulations of number density, radius and phase fraction coincide well with experimental values. The results are consistent over a large temperature range, which is demonstrated in a TTP-plot.

Abstract: This paper briefly reviews the literature on the general crack formation mechanisms and the typical occurrence of crack coalescence in natural rocks, but with no particular reference to specific locations or geologic settings. The field occurrences of tensile wing cracks, horsetail cracks, anticracks and shear cracks, as well as their coalescence are described. In contrast to the tensile wing cracks which develop in the tensile quadrant, anticracks develop from the pre-existing discontinuities in the compressive quadrant. The discussion will be illustrated with plenty of field examples, supplemented by a review of commonly used terminologies.

Abstract: Lagrangian and Eulerian modelling approaches are compared for simulating turbulent dispersion and coalescence of droplets within a spray. Both models predict similar droplet dispersion rates and shifts in droplet size distribution due to coalescence within the spray, over a wide range of droplet and gas flows, and for sprays with different droplet size distributions at the nozzle exit. The computer time required for simulating coalescence within a steady axisymmetric spray is of a similar order of magnitude regardless of which formulation, Eulerian or Lagrangian, is adopted. However, the Lagrangian formulation is more practical in terms of the range of applicability and ease of implementation.

Abstract: The fatigue and fracture mechanism of C/C composites material was investigated in notched and smooth specimen. Also, the initiation and growth behaviors of cracks were continuously observed. Specially, the phenomenon of fracture constraint in notched specimen was discussed. This phenomenon was related to the crack growth behavior and shear damage in the matrix. In the present study, fatigue limit was defined by the critical stress level that the specimen was not broken even after applied 1x10⁶ stress cycles. When the fatigue life was longer than 1x10⁶ stress cycles, the initiated crack was stopped to growth after reaching some critical length. Also, the density of crack initiation was low. When the fatigue life became shorter than that, the cracks extended rapidly and coalescences of cracks were observed. The crack growth behavior was strongly related to the fatigue limit and unstable fracture conditions. Also it is found that the compliance or elastic modulus of the specimen was related to residual fatigue life. Now, an observation of crack in C/C composites was performed effectively in the present study.

Abstract: Several experiments undertaken on cement and mortar samples with internal cracks of different shapes and sizes demonstrated that 3-D cracks growth in compression was qualitatively different from the 2-D cases. This paper employs pre-existing cracks in frozen PMMA（polymethylmethacrylate plastic） which are produced by the mechanical method to analyze the evolution of the boundary effect of PMMA and to study the mechanisms of cracks growth and coalescence. In the experiments, 3-D cracks are tested under uniaxial compression and finally draw two conclusions about failure mechanisms of PMMA and brittle materials.