Coalescence Phenomena Research Articles

A Monte Carlo Approach for Simulating Electrical Conductivity in Highly Porous Ceramic Composites: Impact of Internal Structure.

Porous ceramic composites play an important role in several applications. This is due to their unique properties resulting from a combination of various materials. Determination of the composite properties and structure is crucial for their further development and optimization. However, composite analysis often requires complex, expensive, and time-demanding experimental work. Mathematical modeling represents an effective tool to substitute experimental approach. The present study employs a Monte Carlo 3D equivalent electronic circuit network model developed to analyze a highly porous composite on the basis of minimum easily obtainable input parameters. Solid oxide cell electrodes were used as a model example, and this study focuses primarily on materials with a porosity of 55% and higher, characterized by deviation of behavior from those of lower void fraction share. This task is approached by adding to the original Monte Carlo model an additional parameter defining the void phase coalescence phenomenon. The enhanced model accurately simulates electrical conductivity for experimental samples of up to 75% porosity. Using sample composition, single-phase properties, and experimentally determined conductivity, this model allows us to estimate data of the internal structure of the material. This approach offers a rapid and cost-effective method to study material microstructure, providing insights into properties, such as electrical conductivity and heat conductivity. The present research thus contributes to advancing predictive capabilities in understanding and optimizing the performance of composite materials with potential in various technological applications.

Hydrophobicity of Benzene-Based Surfactants and Its Effect on Bubble Coalescence Inhibition.

Bubble coalescence plays a critical role in optimizing biological and industrial processes, impacting efficiency in areas such as fermentation, wastewater treatment, and foaming control. While the relationship between chemical structure and bubble coalescence has been thoroughly explored for inorganic ions, limited data exist on organic ions and surfactants, despite their widespread use in these industries. This study addresses this gap by investigating the effects of surfactant hydrophobicity and bubble size on coalescence behavior at a flat air-liquid interface and within a bubble column. Surface tension measurements were employed to assess surfactant hydrophobicity, while bubble size and coalescence time were analyzed to determine their respective influences. The results reveal a novel quantitative relationship between surfactant hydrophobicity and the half-coalescence inhibition concentration (HCIC), a new variable introduced in this study. This relationship demonstrates that as hydrophobicity increases, the HCIC also rises, providing a new relationship between surfactant hydrophobicity and bubble coalescence. While it is well-known that more hydrophobic molecules delay coalescence, this is the first time a direct, proportional relationship has been established with HCIC, offering a new parameter for predicting and controlling coalescence phenomena.

Computation of Deformable Interface Two‐Phase Flows: A Semi‐Lagrangian Finite Element Approach

ABSTRACTThis work aims at presenting a new computational approach to study two and three dimensional two‐phase flows and two dimensional coalescence phenomenon using direct numerical simulation. The flows are modeled by the incompressible Navier–Stokes equations, which are approximated by the finite element method. The Galerkin formulation is used to discretize the Navier–Stokes equations in the spatial domain and the semi‐Lagrangian method is used to discretize the material derivative. In order to satisfy the Ladyzhenskaya–Babuška–Brezzi condition, high‐order stable pair of elements are used, with pressure and velocity fields being calculated on different degrees of freedom in the unstructured mesh nodes. The interface is modeled by an unfitted adaptive moving mesh, where interface nodes are tracked in a Lagrangian fashion and moved with the velocity solution of the fluid motion equations. The surface tension is computed using the interface curvature and the gradient of a Heaviside function, and added in the momentum equations as a body force. In order to avoid undesired spurious modes at the interface due to high property ratios, a smooth transition between fluid properties is defined on the interface region. Several benchmark tests have been carried out to validate the proposed approach, and the obtained results have demonstrated agreement with analytical solutions and numerical results reported in the literature. A coalescence model is also proposed based on geometric criteria and results show interesting dynamics.

Process Intensification of Gas–Liquid Separations Using Packed Beds: A Review

The gas–liquid multiphase process plays a crucial role in the chemical industry, and the utilization of packed beds enhances separation efficiency by increasing the contact area and promoting effective gas–liquid interaction during the separation process. This paper primarily reviews the progress from fundamental research to practical application of gas–liquid multiphase processes in packed bed reactors, focusing on advancements in fluid mechanics (flow patterns, liquid holdup, and pressure drop) and the mechanisms governing gas–liquid interactions within these reactors. Firstly, we present an overview of recent developments in understanding gas–liquid flow patterns; subsequently we summarize liquid holdup and pressure drop characteristics within packed beds. Furthermore, we analyze the underlying mechanisms involved in bubble breakup and coalescence phenomena occurring during continuous flow of gas–liquid dispersions, providing insights for reactor design and operation strategies. Finally, we summarize applications of packed bed reactors in carbon dioxide absorption, chemical reactions, and wastewater treatment while offering future perspectives. These findings serve as valuable references for optimizing gas–liquid separation processes.

Drivers and consequences of microbial community coalescence.

Microbial communities are undergoing unprecedented dispersion and amalgamation across diverse ecosystems, thereby exerting profound and pervasive influences on microbial assemblages and ecosystem dynamics. This review delves into the phenomenon of community coalescence, offering an ecological overview that outlines its four-step process and elucidates the intrinsic interconnections in the context of community assembly. We examine pivotal mechanisms driving community coalescence, with a particular emphasis on elucidating the fates of both source and resident microbial communities and the consequential impacts on the ecosystem. Finally, we proffer recommendations to guide researchers in this rapidly evolving domain, facilitating deeper insights into the ecological ramifications of microbial community coalescence.

Two-phase active immersion cooling for vertically mounted electronics with interchip component-assisted bubble departure

To address growing heat dissipation demands in high-performance computing chips, there is a transition from conventional cooling methods to advanced two-phase immersion cooling techniques for electronics thermal management. Here, we present a numerical investigation into the fluid dynamics and heat transfer in two-phase immersion cooling systems with vertically mounted chips on a printed circuit board (PCB) with interchip components such as capacitors, switches, and inductors. Leveraging a combined phase tracking and volume of fluid model, we study how the physical layout and geometries of interchip components affect the flow paths of bubbles, bubble coalescence phenomena, vapor coverage on chip surfaces, and cooling rates of heated chips. In an optimal PCB topology, a maximum heat flux of 18 W/cm2 and a heat transfer coefficient of 9650 W/m2K are observed for dielectric hydrofluoroether (HFE) - 7100 at an excessive wall temperature of 20 K under a constant wall temperature boundary condition. The research offers insights into the electronic system design to achieve efficient cooling for high-performance computing applications, demonstrating the critical role of interchip components in heat transfer.

Influence of purification methods on the extraction of nanocrystals from bio-hydroxyapatite under consideration of the coalescence phenomenon

The coalescence of nanocrystals that occurs during low-temperature thermal treatments during the purification of hydroxyapatite from pigs has not yet been studied in the context of low-temperature environmentally friendly purification. To preserve the nature of hydroxyapatite, two extraction methods were investigated: Route 1 (autoclave and Soxhlet) and Route 2 (calcination at low temperatures with different times). The focus is on observing the effectiveness of removing fats and proteins while maintaining crystallite size and morphology. DSC showed that coalescence of crystallites occurred at 452, 566, 648, and 704 °C. Raw has a higher IR FWHM (phosphate band) due to the organic material; R1 had a lower FWHM (partial removal of lipids and proteins). Increasing the calcination temperature decreases the FWHM, indicating a shift in vibrational states from surface to bulk, leading to an increase in apparent crystallite size due to coalescence. For 20–80 h at quasi-stable temperatures of 400 and 500 °C, no significant changes occur in the IR spectrum. X-ray diffraction indicates the removal of organic material during calcination, as the peaks become clearer with increasing temperature. The crystallite size is not affected and remains in similar ranges. Purification with hydroxide shows an increase in both lattice parameters, in addition to the fluctuations that occur due to the ionic substitutions that naturally occur in biogenic HAp. And the TEM study confirms that the changes in apparent size from 2D to 3D are the result of the phenomenon of interplanar coalescence at low temperatures that occurs in sintering processes.

Enhancing surface chemistry and wetting behavior of laser-modified Ti–6Al–4V surgical titanium alloy surfaces through wet deposition of biogenic hydroxyapatite

This study focuses on enhancing the surface properties of surgical titanium alloys (Ti–6Al–4V) to optimize their suitability for biomedical implant applications. Direct laser writing (DLW) was used to modify the titanium surface and facilitate the deposition of biohydroxyapatite (BHA) particles through wet deposition and the coalescence phenomenon. Four types of etching patterns were tested, resulting in biomimetic bone-like surfaces with microtextured features, exhibiting suitable hydrophilic characteristics for biomedical implants. The resulting surfaces were characterized structurally, morphologically, chemically, and in terms of wettability. X-ray diffraction was performed to validate the titanium alloy composition and determine the crystallite size of BHA particles, both before and after thermal treatment. Optical and electron microscopy results demonstrated that the etching pattern density directly impacts the distribution and anchoring of BHA particles, with denser patterns leading to better particle fixation. Dense etching patterns were found to reduce the wettability of Ti surfaces. However, after coating with BHA particles, the contact angle decreased, resulting in more wettable surfaces. Energy-dispersive X-ray spectroscopy (EDS) mapping revealed variations in elemental distribution across different samples, providing an elemental composition analysis that supports the findings from optical and electron microscopy. The effectiveness of BHA deposition is closely tied to the density and pattern of the surface texturization. Overall, this study presents a straightforward yet effective methodology to optimize the surface properties of titanium alloys, potentially enhancing their compatibility with biological tissues.

Effect of droplet spacing on micro-explosion and combustion characteristics of multi-component fuel droplet cluster

The micro-explosion and combustion characteristics of n-butanol/n-pentanol/biodiesel blended fuel droplet cluster are investigated using high-speed backlit imaging technique. The droplet cluster includes 9 droplets with the same diameter, which are arranged in a 3 × 3 matrix equidistantly using the fiber support method. The results indicate that when the normalized droplet spacing (s/d0) is less than 3, the coalescence phenomenon caused by micro-explosions will occur between adjacent two or three droplets in the droplet cluster. For small s/d0 (2 ∼ 4.5), the droplet cluster sustains a fully enveloped flame. Within the range of s/d0 of 5 ∼ 7, two combustion modes emerge: transitioning from a fully enveloped flame to an independent flame, and merging independent flames into enveloped flames, eventually reverting to independent flames. At a s/d0 of 8, each droplet within the cluster maintains an independent flame. In addition, the combustion rate of droplets 1–3 and 7–9 reaches its maximum value at 4 ∼ 4.5 s/d0, about 30 % higher than single droplet. Most importantly, the droplet micro-explosion intensity at the center of the droplet cluster is higher than that of other droplets (similar to a single droplet), which is caused by the “group micro-explosion” effect.

Internalization of PEI-based complexes in transient transfection of HEK293 cells is triggered by coalescence of membrane heparan sulfate proteoglycans like Glypican-4

Polymer-cationic mediated gene delivery is a well-stablished strategy of transient gene expression (TGE) in mammalian cell cultures. Nonetheless, its industrial implementation is hindered by the phenomenon known as cell density effect (CDE) that limits the cell density at which cultures can be efficiently transfected. The rise in personalized medicine and multiple cell and gene therapy approaches based on TGE, make more relevant to understand how to circumvent the CDE. A rational study upon DNA/PEI complex formation, stability and delivery during transfection of HEK293 cell cultures has been conducted, providing insights on the mechanisms for polyplexes uptake at low cell density and disruption at high cell density. DNA/PEI polyplexes were physiochemically characterized by coupling X-ray spectroscopy, confocal microscopy, cryo-transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). Our results showed that the ionic strength of polyplexes significantly increased upon their addition to exhausted media. This was reverted by depleting extracellular vesicles (EVs) from the media. The increase in ionic strength led to polyplex aggregation and prevented efficient cell transfection which could be counterbalanced by implementing a simple media replacement (MR) step before transfection. Inhibiting and labeling specific cell-surface proteoglycans (PGs) species revealed different roles of PGs in polyplexes uptake. Importantly, the polyplexes uptake process seemed to be triggered by a coalescence phenomenon of HSPG like glypican-4 around polyplex entry points. Ultimately, this study provides new insights into PEI-based cell transfection methodologies, enabling to enhance transient transfection and mitigate the cell density effect (CDE).

Linking microbial community coalescence to ecological diversity, community assembly and species coexistence in a typical subhumid river catchment in northern China

Community coalescence denotes the amalgamation of biotic and abiotic factors across multiple intact ecological communities. Despite the growing attention given to the phenomenon of coalescence, there remains limited investigation into community coalescence in single and multiple source habitats and its impact on microbial community assemblages in sinks. This study focused on a major river catchment in northern China. We investigated microbial community coalescence across different habitats (i.e., water, sediment, biofilm, and riparian soil) and seasons (i.e., summer and winter). Using 16S rRNA gene amplicon sequence variants, we examined the relationship between community coalescence and microbial diversity, assembly processes, and species coexistence. The results showed that the intensity of microbial community coalescence was higher in the same habitat pairs compared to disparate habitat pairs in both summer and winter. During the occurrence of microbial community coalescence, the assembly processes regulated the intensity of coalescence. When the microbial community exhibited strong heterogeneous selection (heterogeneous environmental conditions leading to more dissimilar community structures), the intensity of community coalescence was low. With the assembly process shifted towards stochasticity, coalescence intensity increased gradually. However, when homogeneous selection (homogeneous environmental conditions leading to more similar community structures) predominantly shaped microbial communities, coalescence intensity exceeded the threshold of 0.25–0.30. Moreover, the enhanced intensity of community coalescence could increase the complexity of microbial networks, thereby enhancing species coexistence. Furthermore, the assembly processes mediated the relationship between community coalescence and species coexistence, underscoring the pivotal role of intermediate intensity of community coalescence in maintaining efficient species coexistence. In conclusion, this study highlights the crucial role of community coalescence originating from single and multiple source habitats in shaping microbial communities in sinks, thus emphasizing its central importance in watershed ecosystems.

The role of coalescence and ballistic growth on in-situ electrical conduction of cluster-assembled nanostructured Sn films

The electrical conduction of nanostructured Sn films assembled via Supersonic Cluster Beam Deposition is studied in-situ during film growth. The kinetic energy of Sn nanoparticles, in combination with low melting point of Sn, promotes coalescence phenomena, enabling the investigation of their impact on film morphology and on percolation threshold. A percolation threshold occurring at thicknesses much larger than the dimensions of Sn nanoparticles suggests that coalescence leads to the growth of disconnected, island-like structures. The deposition rate is found to influence coalescence dynamics during the early stages of film growth, allowing for the tuning of film microstructure from a more compact, island-like morphology to a more porous structure. The percolation threshold shifts accordingly from 24 nm to 3 nm film thickness. Upon completion of the percolation phase, film resistivity settles at values 2–3 orders of magnitude larger than that of bulk Sn, attributed to the nanogranular nature of cluster-assembled films. During the “3D conduction” phase, resistivity exhibits an increasing trend with thickness following a power law with an exponent value of 0.76–0.78. This behavior is attributed to the decrease in the density of interconnections between particles in the topmost layer during film growth, consistent with expectations in ballistic growth processes.

Curing temperature’s effect on argillite-metakaolin based geopolymer grouts

This study concerns the project of high and intermediate level radioactive waste disposal (Cigéo project for Centre Industriel de stockage GEOlogique). Millions of tons of argillite will be excavated during the construction of the site. Therefore, the aim of this work is to reuse this argillite in the formulation of an injectable geopolymer grout and study its evolution in different storage conditions (T = 20 and 80 °C). To achieve this challenge, a metakaolin and calcined Callovo-Oxfordian (COx) argillite were used with potassium silicate solutions. The grouts were successfully obtained from both metakaolin and COx argillite in both temperatures 20 and 80 °C. The range of viscosity of several mixtures respected the required specifications (viscosity ≤5 Pa s and setting time superior to 6 h). The metakaolin-based geopolymers didn’t display any major changes no matter the storage temperature, except for the pore size, a coalescence phenomenon was observed with the increase of temperature. In contrast, for argillite or argillite-metakaolin based samples, a decrease of pore size as well as in pH values were observed with the increase of temperature. This behaviour was attributed to the dissolution of argillite’s impurities such as illite, providing more oligomers to allow the formation of different geopolymer networks.

Coalescence as a key process in wafer-scale diamond heteroepitaxy

Due to fascinating physical properties powered by remarkable progress in chemical vapor deposition of high-quality epilayers, diamond thin films attract great attention for fabrication of nitrogen-vacancy-based solid-state spin systems capable of operating in ambient conditions. To date, diamond heteroepitaxy via bias-enhanced nucleation is an unavoidable method for reliable wafer-scale film manufacturing. In this work, we analyze the coalescence phenomena in nitrogen doped, heteroepitaxial diamond epilayers, with a particular focus on their specific role in the annihilation of macroscopic crystal irregularities such as grain boundaries, non-oriented grains, and twinned segments. Here, we also report on the growth mechanism for the “primary” crystal orientation along with a predominant formation of two different types of boundaries highlighting the {011}-type as a main source of the crystal lattice irregularities.

Cellular automata simulation of cavity growth during creep of Al–Mg alloy

Lifespan of high temperature services could seriously be affected by cavitation and thus, prediction of this phenomenon is considered as a significant task. A two-dimensional cellular automata approach coupled with governing equations for cavity nucleation and growth was developed to predict the size and distribution of cavities. Different growth mechanisms including diffusion and strain-controlled processes were taken into account and also, the coalescence phenomenon and the corresponding growth rate were considered in the model. The creep experiments were conducted on AA5052 under different temperatures and applied stresses such as 15 MPa at 300 °C, 20 MPa at 300 °C and 30 MPa at 270 °C for providing essential data points. Afterwards, the optical metallography and the scanning electron microscopy were performed to characterize the cavity size and distribution. The obtained results were then used to determine material constants and validate the simulation outcomes and a reasonable consistency was found between the predictions and experimental data. It was found that the strain-controlled growth is the dominant mechanism for strains larger than 0.04 while the coalescence of cavities might be significant when cavity volume fraction is higher than 0.5%. The simulations showed that the large cavity radius was observed when growth rate due to coalescence was implemented in the model.

Study on characteristics of gas–liquid two-phase flow in pump as turbine using multiple-size group model

The multi-size group (MUSIG) model is employed in this paper to simulate the gas–liquid two-phase flow in pump as turbine (PAT) since the traditional Eulerian–Eulerian two-fluid model is unable to take into account the phenomena of breakup and coalescence of bubbles. First, the simulation of gas–liquid two-phase flow in a square column is compared with the experiment to verify the accuracy of the MUSIG model. Then, the results of gas–liquid two-phase flow in PAT simulated by the MUSIG model are compared with those by the conventional uniform bubble (UB) model and find that the MUSIG model is more favorable to capture the flow pattern at high gas content compared to the UB model. Based on the MUSIG model, the internal flow characteristics, pressure fluctuation, and bubble size distribution of the PAT are analyzed. The rotation of the blades breaks a part of big bubbles into small bubbles in the volute, resulting in a smaller diameter of the bubbles entering the impeller. As the gas content increases, the number and size of vortices in the impeller flow channel increase. The vortex is formed at locations where the gas phase distribution in the impeller flow channel is concentrated. The outlet of the impeller is more prone to bubble consolidation under high gas content conditions. In conclusion, the MUSIG model can well predict the complex flow characteristics of gas–liquid two-phase inside the PAT and identify the key influencing factors of energy acquisition, which can provide support for improving the performance of the PAT design.

Coalescence of non-spherical drops with a liquid surface

We employ three-dimensional numerical simulations to explore the impact dynamics of non-spherical drops in a deep liquid pool by varying the aspect ratios (Ar) and Weber numbers (We). We observe that when a non-spherical drop is gently placed on a liquid pool, it exhibits a partial coalescence phenomenon and the emergence of a daughter droplet for Ar>0.67. In contrast to the prolate (Ar<1) and spherical drops (Ar=1), an oblate (Ar>1) drop with a high aspect ratio encapsulates air in a ring-like bubble within the pool and emerges a liquid column that undergoes Rayleigh–Plateau capillary instability, leading to the formation of two daughter droplets with complex shapes. When the parent drop is impacted with finite velocity, our observations indicate that increasing the Weber number leads to elevated crater heights on the free surface for all aspect ratios. A prolate drop produces a less pronounced wave swell and exhibits a prolonged impact duration owing to its negligible impact area. Conversely, an oblate drop generates a much wider wave swell than spherical and prolate drops. We analyze the relationship between rim formation dynamics and the kinetic and surface energies of the system. Finally, we establish an analogy by comparing the dynamics of a freely falling non-spherical drop, undergoing topological oscillations during its descent from a height, with the impact dynamics of parent drops of various shapes striking the liquid surface with an equivalent velocity. Our investigation involving non-spherical drops contrasts the extensive studies conducted by various researchers on the impact of a parent spherical drop just above the free surface of a liquid pool.

Development and Characterization of Pectin-Based Antimicrobial Packaging Films Containing Nanoemulsified Trans-Cinnamaldehyde

In this study, an antimicrobial plant-based film was developed using pectin which is incorporated by different percentages of nanoemulsified trans-cinnamaldehyde (TC). The nanoemulsion of TC was incorporated into pectin to form films containing TC at concentrations of 5.00%, 3.33%, 2.50% and 2.00% (w/w). The nanoemulsion of TC was formed by using soybean lecithin as an emulsifier and had a zeta potential of −57 mV and an average size of 106 nm. The analysis showed that the addition of emulsified TC enhanced the light barrier properties, but the opacity of films increased due to the increase in light absorption, coalescence, and light-scattering phenomena. Films containing the nanoemulsion of TC exhibited reduced tensile strength and elasticity due to structural discontinuities in the film network caused by the presence of the nanoemulsion of TC, while elongation at break increased for TC concentrations of 2.50% and 2.00%. The films retained their infrared spectra, but their thermal stability decreased slightly. The incorporation of TC nanoemulsion significantly reduced the glass transition temperature, as shown by the differential scanning calorimetry analysis. The active films showed antimicrobial activity against Listeria innocua and Escherichia coli, indicating their potential for various food applications.

Unraveling Partial Coalescence Between Droplet and Oil-Water Interface in Water-in-Oil Emulsions under a Direct-Current Electric Field via Molecular Dynamics Simulation.

When the electric field strength (E) surpasses a certain threshold, secondary droplets are generated during the coalescence between water droplets in oil and the oil-water interface (so-called the droplet-interface partial coalescence phenomenon), resulting in a lower efficiency of droplet electrocoalescence. This study employs molecular dynamics (MD) simulations to investigate the droplet-interface partial coalescence phenomenon under direct current (DC) electric fields. The results demonstrate that intermolecular interactions, particularly the formation of hydrogen bonds, play a crucial role in dipole-dipole coalescence. Droplet-interface partial coalescence is categorized into five regimes based on droplet morphology. During the contact and fusion of the droplet with the water layer, the dipole moment of the droplet exhibits alternating increases and decreases along the electric field direction. Electric field forces acting on sodium ions and the internal interactions within droplets promote the process of droplet-interface partial coalescence. High field strengths cause significant elongation of the droplet, leading to its fragmentation into multiple segments. The migration of hydrated ions has a dual impact on the droplet-interface partial coalescence, with both facilitative and suppressive effects. The time required for droplet-interface partial coalescence initially decreases and subsequently increases as the field strength increases, depending on the competitive relationship between the extent of droplet stretching and the electric field force. This work provides molecular insights into the droplet-interface coalescence mechanisms in water-in-oil emulsions under DC electric fields.

Size-dependent coalescence of nanobubbles in pure water

Previously, we experimentally demonstrated that similar-sized bulk nanobubbles (NBs) preferentially coalesce when the NB size is ∼100 nm. To explain this peculiar NB coalescence phenomenon, we performed a nanoparticle trajectory analysis to determine the size distribution profile and time-dependent concentration of the bulk NBs generated by pressurizing a porous alumina thin film with ordered straight nanoholes. Furthermore, we propose a physical model based on the hypothesis that the repulsive energy increases when two NBs establish contact, and that coalescence occurs when the kinetic energy of the NBs overcomes the repulsive energy. We simulated the observed NB-size distribution by using the proposed model. The simulation results explained the observed NB-size distribution and lifetime of the NBs. They further indicated that NB coalescence was suppressed for small NBs with diameters of approximately 100 nm or less, resulting in their long lifetimes.