Effect Of Coalescence Research Articles

Modeling of gas–liquid mass transfer in a stirred tank bioreactor agitated by a Rushton turbine or a new pitched blade impeller

A combined computational fluid dynamics (CFD) and population balance model (PBM) approach has been applied to simulate hydrodynamics and mass transfer in a 0.18m(3) gas-liquid stirred bioreactor agitated by (1) a Rushton turbine, and (2) a new pitched blade geometry with rotating cartridges. The operating conditions chosen were motivated by typical settings used for culturing mammalian cells. The effects of turbulence, rotating flow, bubbles breakage and coalescence were simulated using the k-ε, multiple reference frame (MRF), Sliding mesh (SM) and PBM approaches, respectively. Considering the new pitched blade geometry with rotating aeration microspargers, [Formula: see text] mass transfer was estimated to be 34 times higher than the conventional Rushton turbine set-up. Notably, the impeller power consumption was modeled to be about 50% lower. Independent [Formula: see text] measurements applying the same operational conditions confirmed this finding. Motivated by these simulated and experimental results, the new aeration and stirring device is qualified as a very promising tool especially useful for cell culture applications which are characterized by the challenging problem of achieving relatively high mass transfer conditions while inserting only low stirrer energy.

Enzyme-catalyzed synthesis of heptyl-β-glycosides: Effect of water coalescence at high temperature

Alkyl glycosides can be synthesized by glycosidases in organic media with limited amounts of water. These systems, however, limit the solubility of the sugar substrates and decrease reaction yields. Herein we report the enzymatic synthesis of heptyl-β-glycosides in heptanol catalyzed by a hyperthermophilic β-glycosidase at 90°C. Our results indicate that dispersion of water in heptanol changes with time producing coalescence of water at the bottom of the reactor, playing a key role in the reaction yield. Water-soluble substrate, enzyme and products are concentrated in the aqueous phase, according to their partition coefficients, promoting side reactions that inactivate the enzyme. Reaction yield of heptyl-β-glycosides was 35% relative to lactose, at 7% water. The increase in the water phase to 12% diminished the enzyme inactivation and increased the heptyl-β-glycosides yield to 52%. Surface-active compounds, SDS and octyl glucoside, increased water dispersion but were unable to prevent coalescence.

Experimental study of the bubble size distribution in a pseudo-2D bubble column

This work presents an experimental study of the bubble size distribution of a bubbly flow using digital image analysis (DIA). In order to facilitate the image measurement technique a pseudo-2D bubble column is chosen for the experiments. To obtain well-defined inlet conditions a gas sparger, consisting of 20 needles, is used. By employing DIA, the bubble size distribution (BSD) has been measured for a range of superficial gas velocities. The resulting BSD's are expressed in terms of a probability density function (PDF). For low superficial gas velocities of 5 and 10mm/s the PDF has a unimodal shape, while for higher superficial gas velocities of 15 and 20mm/s the PDF has a bimodal shape. The effects of coalescence and break-up of bubbles are visible by evaluating the changes of the resulting BSDs for increasing superficial gas velocity. A comparison of gas hold-ups is made between the calculated BSD and the liquid expansion height. This comparison shows how well the BSD obtained with DIA describes the actual gas hold-up in the column.

Study of the thermal mixing between two non-isothermal sprays using combined three-color LIF thermometry and phase Doppler analyzer

The aim of this experimental work was to demonstrate the ability of three-color laser-induced fluorescence (3cLIF) thermometry to study the thermal mixing of two non-isothermal water sprays. Combined 3cLIF-phase Doppler analyzer measurements were also implemented to derive correlations between droplet size and temperature. Both sprays had different characteristics in terms of flow rate and droplet size distribution. The liquid spray was successively pre-heated, and the other spray was maintained and injected at ambient temperature. The thermal mixing will be discussed in light of a wide set of experimental results obtained under various experimental conditions, including different liquid flow rates, droplet size distributions and droplet concentrations. To analyze the potential effect of droplet coalescence on the mean local liquid temperature, both sprays were alternatively seeded with fluorescent dye. Main results show that significant heating of cold spray is possible when the hot spray is injected with the higher flow rate. Moreover, this heating affects only the smallest droplets.

Effect of group-III donors on high-resolution photoluminescence and morphology of ZnO nanowires grown by metalorganic vapour phase epitaxy

Extremely sharp low temperature photoluminescence (PL) linewidths as low as 0.17 meV are observed in nominally undoped ZnO nanowires grown by metalorganic vapour phase epitaxy (MOVPE). These are among the narrowest lines reported for ZnO PL, even for bulk growth, despite growth on highly mismatched sapphire substrates. MOVPE allows the control of group III dopants over a wide range of doping levels. At low concentrations the addition of indium and aluminum dopant resulted in the appearance of their corresponding neutral and ionized donor bound exciton transitions with linewidths comparable to those of nominally undoped material. At higher dopant levels, the axial growth rate decreases and the lateral growth rate increases for both dopants, resulting in eventual coalescence of the nanowires as well as a strong reduction in PL efficiency. The onset of lateral growth also coincides with the elimination of the so-called Y-line defect luminescence previously attributed to excitons localized at structural defects. Because of the lack of appreciable substrate induced strain, coupled with very high crystalline quality, nanowires provide an excellent tool for investigation of shallow dopant effects in ZnO by PL spectroscopy.

Phylogenetic Signal Variation in the Genomes of Medicago (Fabaceae)

Genome-scale data offer the opportunity to clarify phylogenetic relationships that are difficult to resolve with few loci, but they can also identify genomic regions with evolutionary history distinct from that of the species history. We collected whole-genome sequence data from 29 taxa in the legume genus Medicago, then aligned these sequences to the Medicago truncatula reference genome to confidently identify 87 596 variable homologous sites. We used this data set to estimate phylogenetic relationships among Medicago species, to investigate the number of sites needed to provide robust phylogenetic estimates and to identify specific genomic regions supporting topologies in conflict with the genome-wide phylogeny. Our full genomic data set resolves relationships within the genus that were previously intractable. Subsampling the data reveals considerable variation in phylogenetic signal and power in smaller subsets of the data. Even when sampling 5000 sites, no random sample of the data supports a topology identical to that of the genome-wide phylogeny. Phylogenetic relationships estimated from 500-site sliding windows revealed genome regions supporting several alternative species relationships among recently diverged taxa, consistent with the expected effects of deep coalescence or introgression in the recent history of Medicago.

Numerical Analysis of Drops Coalescence and Breakage Effects on De-Oiling Hydrocyclone Performance

This work investigated the effects of breakage and coalescence on de-oiling hydrocyclone performance utilizing Computational Fluid Dynamics (CFD). It was found that an increase in the entrance flow rate with low entrance oil concentration not only did not increase the separation performance of the hydrocyclone but it also decreased the separation efficiency. On the contrary, the hydrocyclone performance was enhanced with increasing the inlet velocity. Furthermore, a comparison between the standard design and the conical inlet chamber design was drawn in terms of separation efficiency for low entrance oil concentration; the results depicted that the conical design had higher separation efficiency.

Observation of Quantum Tunneling between Two Plasmonic Nanoparticles

The plasmon resonances of two closely spaced metallic particles have enabled applications including single-molecule sensing and spectroscopy, novel nanoantennas, molecular rulers, and nonlinear optical devices. In a classical electrodynamic context, the strength of such dimer plasmon resonances increases monotonically as the particle gap size decreases. In contrast, a quantum mechanical framework predicts that electron tunneling will strongly diminish the dimer plasmon strength for subnanometer-scale separations. Here, we directly observe the plasmon resonances of coupled metallic nanoparticles as their gap size is reduced to atomic dimensions. Using the electron beam of a scanning transmission electron microscope (STEM), we manipulate pairs of ~10-nm-diameter spherical silver nanoparticles on a substrate, controlling their convergence and eventual coalescence into a single nanosphere. We simultaneously employ electron energy-loss spectroscopy (EELS) to observe the dynamic plasmonic properties of these dimers before and after particle contact. As separations are reduced from 7 nm, the dominant dipolar peak exhibits a redshift consistent with classical calculations. However, gaps smaller than ~0.5 nm cause this mode to exhibit a reduced intensity consistent with quantum theories that incorporate electron tunneling. As the particles overlap, the bonding dipolar mode disappears and is replaced by a dipolar charge transfer mode. Our dynamic imaging, manipulation, and spectroscopy of nanostructures enables the first full spectral mapping of dimer plasmon evolution and may provide new avenues for in situ nanoassembly and analysis in the quantum regime.

The Role of Coalescence in Inkjet Printing Functional Films: An Experimental Study

For the past several decades inkjet technology has been shown to be a useful tool for fabricating anything from three dimensional objects to electrical devices and biological sensors. From a manufacturing perspective, it is important to functionalize a substrate with material in as timely a manner as possible while maintaining optimal functionality and satisfying hardware limitations. Of particular interest in previous work has been the effect of drop coalescence on print quality. This work examines how coalescence affects the uniformity of printed pairs of drops and printed lines as well as the functional performance of printed lines of a Pd based ink on Silicon and oxidized Silicon substrates. The results indicate that the ink migration resulting from Marangoni flows can be minimized by avoiding coalescence of adjacently deposited drops, thus increasing film uniformity and improving functional performance.

Eulerian versus Lagrangian simulation of unsteady two-way coupled coalescing two-phase flows in solid propellant combustion

Solid rocket motor flows depend strongly on alumina granulometry, which spreads up with coalescence. Solving droplet sizes in unsteady flows is a modeling and numerical challenge, specially when high loadings generate retrocoupling. As an alternative to Lagrangian approaches, the Eulerian Multi-Fluid model describes polydispersity with size-sorted droplet fluids called sections. A two size moment method, that spares sections, is implemented in the CEDRE code. A new transport and coupling method allows to capture moderately dense spray structures with low diffusion. The aim is threefold: compare CEDREʼs Lagrangian and new Eulerian two-phase approaches, prove the feasibility of unsteady and complex motor flow simulations, and show the effect of coalescence on instabilities.

Atomically-Coherent-Coalescence of Two Growth-Fronts in Ge Stripes on Insulator by Rapid-Melting Lateral-Crystallization

High-quality Ge-on-insulator (GOI) is a key structure for integrating high-speed transistors and optical- and spintronic-devices on Si-platform. Effects of coalescence of two growth-fronts on crystallinity of GOI-stripes during rapid-melting lateral-crystallization are investigated as a function of growth-distance. For long growth-distance (≥150 μm), grain-boundaries are generated in coalesced regions due to tilting growth-fronts (1-3°). On the other hand, for short distance (≤5 μm), lattice-structures coherently align without strains. Moreover, for intermediate distance (5–150 μm), lattice-structures of growth-fronts coherently align without any defects, though heterogeneous lattice-strains are locally induced due to slightly tilting growth-fronts (∼0.5°). Such atomically-coherent-coalescence for growth-distance <150 μm shows significant advantage of rapid-melting-crystallization over vapor and solid-phase techniques.

Evolution of dispersed drops during the mixing of mineral oil and water phases in a stirringtank

In this paper, a focused beam reflectance method is used to investigate the evolution of dispersed droplets at various dispersed volume fractions for an Exxsol D80 mineral oil–water dispersion in a stirring tank. Two types of inversion experiments are compared, the direct and continuous mixing of the oil–water phases. The number density of the chord lengths and distributions are identified as the main parameters for comparison. The drop coalescence is dominant slightly before inversion, at which point the measured mean square weighted (Sqr-wt) chord length increases significantly. The way of mixing will also influence the effect of drop coalescence and result in different inversion processes.

Quantification of vesicle characteristics in some diatreme-filling deposits, and the explosivity levels of magma–water interactions within diatremes

Vesicles within juvenile fragments in mafic pyroclastic deposits contain important information about the state of the magma at the time of fragmentation. There have been few vesicle studies of juvenile pyroclasts from mafic phreatomagmatic deposits, however, and none we can find from maar–diatreme volcanoes. In this paper we document the vesicularity and vesicle-population characteristics of juvenile fragments sampled from non-bedded lithified deposits of the Coombs Hills diatreme complex, part of the Ferrar large igneous province, Antarctica. The diatreme-filling pyroclastic deposits, dominated by lapilli tuffs and tuff breccias, contain typically abundant lithic clasts derived mostly from the enclosing sedimentary sequence, and several types of juvenile clasts ranging from blocky to fluidal or “raggy”.In the samples measured, 77–80% of the juvenile pyroclasts ranging in size from 0.5mm to fine lapilli is in the ‘non-vesicular’ to ‘incipiently vesicular’ range (<20% vesicles). Such low vesicularities are expected for pyroclasts from maar–diatreme volcanoes where fragmentation takes place at depth in the diatreme or root zone due to magma–water interaction. A few juvenile clasts, however, are more vesicular, and seven of these were chosen and sectioned for 2D analysis of vesicle shapes and orientation, vesicle number densities (Nv), and vesicle volume distributions. The shapes of the vesicles in the studied sections are mostly elliptical (sometimes polylobate), with mean aspect ratios ranging between 0.67 and 0.72. Circular statistics are used to test for trends in the vesicle long-axis orientation data; non-uniformity of orientations is found in most cases, but the trends are weak. Vesicle volume distributions are often bimodal due to variable coalescence. Total Nv values range from 1.0×102 to 5.7×103mm−3; taking the effects of bubble coalescence into account, these values are similar to those found in pyroclasts from other phreatomagmatic volcanoes, although they also overlap partly with those seen in fire fountain deposits and some basaltic Plinian eruptions.Fluidal- or rag-shaped juvenile clasts, some circular vesicles, and the lack of microlites all suggest that the Coombs Hills magma had a relatively low viscosity prior to fragmentation, despite the basaltic andesite composition. This low viscosity allowed parts of the magma to be fragmented in a non-brittle fashion during phreatomagmatic explosions and to form fluidal clasts. Phreatomagmatic explosions in diatremes can therefore produce diverse types of juvenile clasts simultaneously, and the proportions of each will depend on the explosivity of the magma–water (slurry) interaction and other factors. Recycling of fragments is also thought to be an important factor in generating mixtures of different types of juvenile fragments in diatremes.

Observation of ion coalescence in Orbitrap Fourier transform mass spectrometry

Similar to other mass spectrometric technologies based on ion trapping in a spatially restricted area, the performance of Orbitrap Fourier transform mass spectrometry (FTMS) is affected by the interaction between the trapped ion clouds. One of the effects associated with Coulombic interaction inside the ion trap is the ion cloud coupling, known in ion cyclotron resonance (ICR) FTMS as coalescence, or a phase-locking phenomenon. Nevertheless, the direct observation of ion coalescence has not been reported for Orbitrap FTMS yet. We have performed experiments on ion coalescence with a pair of isobaric peptides in the state-of-the-art hybrid linear ion trap high-field compact Orbitrap Elite FT mass spectrometer using both standard and advanced signal processing modes. For the instrument configuration employed in this work we found that ion coalescence occurs when two singly charged peptides with the mass difference of 22 mDa and molecular weight of about 1060 Da have the total abundance of at least 7.5*10(4) charges. We experimentally demonstrate the existence of the ion coalescence phenomenon in Orbitrap FTMS for peptides for a wide range of total trapped ion population. Using the applicable modeling of the phase-locking threshold we estimate the effect of ion coalescence on the performance of Orbitrap FTMS.

Bubble coalescence at constant wall temperatures during subcooled nucleate pool boiling

Bubble coalescence during subcooled nucleate pool boiling was investigated experimentally using constant wall temperature boundary conditions while the wall heat flux was measured at various locations to understand the effects of coalescence on the heat transfer. The effects of the subcooling on the coalesced bubble shape, size and departure time were also investigated. The observations showed that the coalesced bubble moved and oscillated on the heater surface with significant heat transfer variations prior to departure. The coalesced (or departure) bubble size and departure frequency decreased as the subcooling increased. The heat flux for boiling with coalescence fluctuated much more than for single bubble boiling with the heat flux fluctuations due to oscillations of the coalesced bubble on the heater surface resulting in frequent rewetting of the heated surfaces. In some cases, many additional small bubbles nucleated very near a larger bubble and then rapidly coalesced with the larger bubble which enhanced the overall heat transfer. The observations also showed coalescence with no increase in the heat transfer rate for very fast bubble coalescence such as would occur for large surface superheats as the boiling conditions approach CHF. A mechanistic model comparing the inertia and heat flux controlled bubble growth phases for inhomogeneous bubble growth shows that this coalescence without increased heat transfer corresponds to the inertial growth phase.

Visualization of the emergence of the pseudogap state and the evolution to superconductivity in a lightly hole-doped Mott insulator

Scanning tunnelling microscopy images of the evolution of the pseudogap phase of a hole-doped cuprate superconductor suggest that it emerges in localized clusters that grow with increasing doping. Moreover, the eventual coalescence of these clusters coincides with the emergence of superconductivity.

Investigations on Thermal Stress Relief Mechanism Using Air-Gapped SiO2 Nanotemplates during Epitaxial Growth of Ge on Si and Corresponding Hole Mobility Improvement

We demonstrate the implementation of air-gapped SiO2 nanotemplates embedded in epitaxially grown Ge on Si for relieving stress caused by the thermal expansion coefficient mismatch between Ge and Si. The air-gap is formed around the SiO2 template during growth and eventual coalescence of adjacent Ge islands merging over the template. The stress map obtained from finite element modeling corroborates the experimental observation, suggesting that the thermal stress can be reduced nearly by half. The templates also filter threading dislocations propagating from the underlying Ge-Si interface, reducing the defect density from 9.8×108 to 4.4×107 cm-2 in the demonstration case. We further investigate the influence of threading dislocation density on the effective hole mobility in undoped Ge between substrates grown with the template and without the template. Using the Hall mobility measurements, we have obtained a peak effective hole mobility of 925 cm2/V-s at room temperature for Ge grown with the template, compared to 297 cm2/V-s for Ge grown without the template.

The effects of load condition on void coalescence in FCC single crystals

To investigate the effects of load condition on void coalescence in FCC crystals, void coalescence under constant strain control was studied by using three-dimensional crystal plasticity finite element method, which was implemented with rate dependent crystal plasticity theory as user material subroutine. By comparison the width of inter-void ligament in single crystals, significant effects of load condition on void coalescence were revealed: (1) Crystallographic orientation plays a role in void coalescence, and the role is different under various load conditions. (2) The deformation is localized around voids under triaxial applied strain load condition, and the slip systems in soft orientation are easy to be activated, so voids in soft orientation grains tend to coalesce much easier than that in hard orientation, and the void growth direction has only a minor role in influencing the coalescence effect for different crystallographic orientations. (3) Under low biaxial applied strain load condition, the deformation localization is not serious, and the global deformation of soft orientation is homogeneous, so soft orientation shows less coalescence effect in general.

Mixing and atomization characteristics in an internal-mixing twin-fluid atomizer

Twin-fluid atomizers have been successfully used in many industrial applications. This paper presents experimental studies on internal mixing and atomization in a water–air internal-mixing atomizer. Two-phase mixing process and flow patterns in the internal mixing chamber were visually studied through high speed CCD. Observation reveals that internal mixing was dominated by Gas to Liquid mass Ratio (GLR). As GLR increased, the flow patterns changed from slug flow to annular flow. The Oshinowo and Charles’ map can be used to predict the flow patterns for the designed atomizer. Droplet Sauter Mean Diameter (SMD) spatial distributions were measured with Phase Doppler Analyzer (PDA) at different operating conditions. Droplet SMD decreased with the increase of GLR at all operating pressure and locations. In the undeveloped region, a close relationship was observed between flow pattern transformation in internal mixing chamber and droplet SMD distribution, and there was an optimized pressure ranging from 0.2MPa to 0.3MPa for atomization since liquid films became thicker under a higher pressure. In the developed region, pressure promoted to generate finer atomization. Possibility Density Function (PDF) distribution of droplet size at different axial locations was analyzed to quantitatively represent the effect of droplet coalescence and breakup. As axial distance increased, PDF of both fine droplets and large droplets decreased. The particle size with the maximum PDF increased with the axial distance as well. The results imply that best atomization performance was acquired in the undeveloped region.

Energy Towers – The effect of droplet coalescence on power and the environment

The Energy Tower concept is a renewable energy source suitable for dry and hot climates. It consists in cooling air by spraying water at the top of a tower approximately 1000m high and thus creating a downdraft with a velocity of approximately 15m/s. At the bottom of the tower the air goes through turbines and is subsequently exhausted through diffusers to the environment. In this work the influence of heat transfer from the droplets to the air is analyzed, the effect of coalescence being described using the O’Rourque model. It is shown that coalescence is substantial inside the tower and results in the droplets being an order of magnitude larger at the tower bottom and that there is a slight adverse effect on the energy performance, since evaporation from larger droplets is substantially less than from smaller droplets. In the case however that the water spray is a saline solution – which is the only possibility in view of unsalted water being as scarce a resource as energy – it makes it possible to keep the deposited salt inside the tower and the diffuser and in the immediate vicinity of the construction.