Coalescence Phenomena Research Articles

Fabrication and characterization of bioinspired nanohydroxyapatite scaffolds with different porosities

This study aimed to fabricate and characterize bovine nanohydroxyapatite (nano-HAp) scaffolds at a low sintering temperature. The compact bone/starch systems were formed using the inorganic matrix of trabecular bone powder and achira isolated starch. To generate the macroporosity, 0, 10, 15, and 20% achira starch granules were added. To obtain nano-HAp scaffolds, the compact bone/starch systems were incinerated at 600 °C, removing organic material. The scaffolds exhibit the presence of Ca, P, Sr, Ba, Fe, Na, Mg, K, and Si came from the HAp with a slight K increase because of the mineral contribution of the starch. Infrared spectroscopy helped determine the elimination of organic materials and evidenced carbonated nano-HAp. X-ray diffraction allows to determine the presence of nano-HAp crystals. Moreover, the X-ray tomography revealed an increased macroporosity (30–38%) for the scaffolds as the starch percentage increased and scanning electron microscopy (SEM) average pore length size for HAp, HAp-A10, HAp-A15, and HAp-A20 were 356.71 ± 156.71, 548.91 ± 131.99, 620.94 ± 147.93, and 728.16 ± 160.98 μm, respectively. In the same way, SEM images of the scaffolds evidenced the presence of micro and nano porosities. The N2 adsorption-desorption analysis corroborated the presence of mesoporosity with average pore diameters of 3.66 and 3.32 nm in the samples before and after the calcining process, respectively. Thus, thermal treatments did not significantly affect the mesoporous size. In addition, effective Young's modulus is governed by the intrinsic properties of HAp, while the porosity governs the plastic and breaking point. The coalescence phenomena create the scaffold macro architecture.

Simulation of coalescence dynamics of droplets on surfaces with different wettabilities

The head-on-collision coalescence dynamics for droplets on surfaces with different wettabilities was numerically investigated by using the method of coupled level set and volume of fluid, and a high-speed video experiment was used to validate the simulation results. The simulated coalescence behavior of droplets is consistent with the experiment results. We compared droplets with different Weber numbers (3.67 ≤ We ≤ 50) coalescing on solid surfaces of different wettabilities and contact angles (80° ≤ α ≤ 160°). The result is a regional division diagram that relates Weber number and contact angle based on different coalescence phenomena. The factors causing droplet deposition, air entrapment, bounce, and partial bounce during collision coalescence are described based on an analysis of interactions involving inertial forces, surface tension, and wall adhesion forces. Furthermore, the effect of Weber number and contact angle on droplet coalescence behavior is elaborated by analyzing the relationship between coalescence time and wettability radius under different Weber numbers and contact angles. Finally, through an energy analysis, we explain the maximum spreading radius and oscillation of droplets with different Weber numbers on solid surfaces with different wettabilities and in the process of head-on-collision coalescence.

Probing the Coalescence Mechanism of Oil Droplets in Fluids Produced by Oil Wells and the Microscopic Interaction between Molecules in Oil Films

The microscopic interactions between oil droplets during the coalescence process have an important impact on the stability of the emulsion. In this paper, a model that can present the phenomenon of coalescence of oil droplets was established. Experiments were carried out to evaluate the stability of the emulsion. Combined with molecular dynamics simulation technology, the coalescence behaviors of emulsified oil droplets in fluids produced by oil wells were studied. Factors affecting the coalescence of emulsified oil droplets were analyzed. The results show that the fluid velocity was relatively high at the position where two oil droplets were close to each other. After the coalescence of oil droplets was completed, the emulsion system became stable. There was no obvious correlation between oil droplet size and coalescence time. When two adjacent oil droplets with different radii coalesced, the larger oil droplet moved a shorter distance overall. At the initial moment, there was a clear boundary between the oil film and the water phase. The longer the carbon chain, the more stable the emulsion. Among the following four crude oil molecules with the same number of carbon atoms, chain-like saturated hydrocarbons were the most stable, followed by chain-like carbon–carbon double bonds in component crude oil. Crude oils containing chain-like carbon–carbon triple bonds were the third most stable. Cyclane were the least stable. An increase in the asphaltene content was an important reason for the enhancement of the emulsifying ability and stability in the emulsion system. This work can help improve oil–water separation efficiency, thus reducing storage and transportation burden of crude oil.

Numerical study on gas–liquid two phase flow characteristic of multistage electrical submersible pump by using a novel multiple-size group (MUSIG) model

Electrical submersible pumps (ESPs) face enormous challenges in the petroleum industry while handling gas–liquid two-phase flow. The major difficulty is caused by the accumulation of gas bubbles inside ESP-impellers, which results in mild to severe degradation in pump performance. Therefore, to analyze the influence of gas entrainment and bubble size, a combination of experimental and numerical analysis is performed on a five-stage mixed-flow ESP in the present study. The experiments are first conducted to analyze the performance of ESP under pure water conditions at different rotating speeds, followed by the gas–liquid two-phase flow experiments that are performed at constant rotating speed (1475 r/min) and for a wide range of inlet gas void fractions (IGVFs). For numerical calculations, a novel multiple-size group (MUSIG) model is applied in ANSYS CFX to analyze the performance and different flow patterns in ESP in different IGVFs and understand the coalescence and breakup phenomena of gas bubbles in the impeller flow passage. The simulation results from the MUSIG model are compared with the Euler–Euler two-fluid model and test results. The MUSIG model can more accurately predict the changes in the performance and internal flow-field of ESP under two-phase flow conditions. Moreover, when the MUSIG model is used to calculate the two-phase flow of the ESP, the first-stage impeller has a higher head than other stages because the flow inside the second and other stages is affected by the disoriented flow coming from the first-stage diffuser and other return channels. Furthermore, this study gives an insight into the comprehensive application of the novel MUSIG model for complex turbo-machine designs such as ESP.

High vacuum applied during malaxation in oil industrial plant: Influence on virgin olive oil extractability and quality

Vacuum technology was applied for the first time at industrial scale to the mechanical extraction processes of virgin olive oil (VOO). The study was carried out using an industrial plant with a working capacity of 4 tons of olives. The use of high vacuum conditions during the malaxation process induced an intense mass transfer into the olive paste that improved the coalescence phenomena of oil droplets with a significant increase in oil extractability for four different cultivars (Arbequina, Arbosana, Koroneiki and Picual). The evaluation of the quality characteristics of the Picual VOO showed an enhancement in the hydrophilic phenol fraction mainly related to the oleacein content. The low temperature set during the vacuum treatment (16 ± 1 °C for 30 min of malaxation) limited the stripping process of the main aldehydes, alcohols and esters. In contrast, other negative volatile compounds related to off-flavoured VOO (ethanol, 3-methyl-1-butanol, ethyl acetate and acetic acid) were significantly reduced.

Quasi-continuous-wave laser directed energy deposition on inclined NV E690 steel plates: Melt pool and temperature evolution

A quasi-continuous-wave direct metal deposition (QCW-DMD), one of directed energy deposition (DED), with different pulse frequencies and duty cycles was performed on an inclined NV E690 steel plate. Comprehensive effects including the humping effect, the melt pool evolution process, the coalescence phenomenon, the deposition morphology, and the thermal behavior were investigated. The results show that during the continuous-wave direct metal deposition (CW-DMD) and the QCW-DMD with the pulse frequency of 1 Hz, the gravity-induced humping effect and the coalescence phenomenon contribute to the increase and decrease of the melt pool numbers, respectively. A small duty cycle leads to a decrease in the average melt pool numbers. Besides, the coalescence of melt pools is formed by establishing a liquid bridge which is first mainly driven by the surface tension and then by gravity. The humping effect is overcome when the pulse frequency ranges from 5 Hz to 50 Hz, presenting a small height variation. Furthermore, the QCW mode laser can modulate the powder catchment efficiency and produce a higher cooling rate that resulted in a higher microhardness.

Bubble size distribution and gas holdup in bubble columns employing non‐Newtonian liquids: A CFD study

AbstractThe hydrodynamics involved with the rise of air bubbles in shear‐thinning non‐Newtonian liquids in bubble columns was investigated using computational fluid dynamics (CFD). In bubble columns, the bubble size distribution (BSD) and gas holdup significantly affect the mass transfer rates and the reactor design. Consequently, the influence of superficial gas velocity, flow index, consistency index, sparger bubble size, and yield stress were analyzed on a local and global scale. The bubble sizes and the coalescence and breakage phenomena were incorporated using the homogeneous discrete method of the population balance model (PBM). The bubbles underwent coalescence during ascent and exhibited bimodal distribution. The radial homogeneity of the gas phase increased axially. Moreover, the zones of low liquid dynamic viscosity produced zones of a high gas holdup. Though the dual effect of viscosity on gas holdup was non‐existent, the gas holdup surged after 35.1 mPa s at the mid‐zone and remained constant thereafter. The noteworthy differences in simulation results put further emphasis upon the importance of sparger bubble size in CFD modelling. A decrease in the overall gas holdup and the axial air velocity with yield stress was observed. CFD simulation proved capable of providing results in reasonable agreement with experiments.

Morpho-dynamic evolution due to inertia-mediated impact of a compound drop on a deep liquid pool

A compound drop impacting on a liquid pool exhibits intriguing coalescence patterns that are primarily attributable to the complicated interplay of inertia with other physical parameters such as radius ratio of core to shell drop and density and viscosity contrasts of the two fluids. By executing comprehensive numerical investigations, here, we identify three different regimes based on the radius ratio of compound drop, viz., secondary drop pinch-off without bubble bursting, secondary drop pinch-off after bubble bursting, and compound breakage. Our findings also depict a transition in the shape of a secondary droplet from prolate to oblate or vice versa, a phenomenon non-trivially culminated by secondary drop pinch-off timing, neck radius, and amplitude and wavelength of capillary wave propagation. Our results bring out the fact that higher wavelength and amplitude of capillary waves are responsible for secondary drop pinch-off without bubble bursting. Furthermore, in the case of highly viscous core drop and surrounding fluid, we observe both complete and partial coalescence phenomena, which are critically dictated by the confluence of inertia and radius ratio of a compound drop leading to three different regimes, viz., complete coalescence without bubble bursting, complete coalescence with bubble bursting, and partial coalescence with bubble bursting, distinctively different from the observations for single droplet based investigations reported in earlier studies. These implications are likely to be beneficial in illustrating the physical functionalities accompanying the targeted release of encapsulated biological or pathological entities when they are transmitted under the action of an inertial force into another fluidic medium, a paradigm that has hitherto remained unexplored.

Significance of viscous coalescence in migmatites of the Assam-Meghalaya Gneissic Complex, eastern India

ABSTRACT The magnetite ocelli preserved in the Chandrapur area of the Assam-Meghalaya Gneissic Complex, eastern India, display viscous coalescence. The viscous coalescence phenomenon generally occurs below a critical capillary number, which is governed by the size of the coalescing droplets. The smaller the size of the coalescing droplets, the greater the possibility that they will exhibit viscous coalescing. From our results we infer that intrusion of younger pegmatitic magma into the much older polyphase deformed quartzofeldspathic gneiss of Chandrapur initiated localized partial melting in the gneissic rocks surrounding the intrusions. This localized partial melting produced small magma pools or leucocratic neosome, which was followed by intermingling between the in situ melt (leucocratic neosome) and external melt (pegmatite), leading to chaotic mixing between the two magmatic phases. Chaotic mixing produced thin veins or filaments of the pegmatitic magma as a result of stretching and folding dynamics. Gradually, the thin filaments underwent capillary instability to produce discrete viscous swirls or ocelli. The ocelli consist of leucocratic minerals like K-feldspar, plagioclase, and quartz, with crystals of magnetite at the center representing magnetite ocelli. The mineralogical assemblage of the ocelli matches that of the pegmatitic rocks. After their formation, some of the smaller magnetite ocelli underwent very gentle collisions due to the effect of capillary and viscous forces. Such collisions produced pairs, clusters, or linear structures that are now preserved in the migmatites of the study area.

Multifunctional roles of hairs and spines in old man of the Andes cactus: Droplet distant coalescence and mechanical strength

Cactaceae have adapted to harsh environments by resisting intense solar radiation, retaining and collecting water. Some cacti species have hairs on them along with distinctive spines to serve different functions. In this study, we characterized the Old Man of Andes cactus (Oreocereus trolli). We examined the surface morphology and estimated roughness and adhesion force of both spines and hairs. They both consist of longitudinal microgrooves. The condensation experiments carried out on spines showed that there is a particular phenomenon of distant coalescence (DC): smaller droplets flow totally or partially into larger ones through the microgrooves with consequent accumulation of water in a few large drops. An earlier study (Bintein et al., 2019) has shown that artificial micro-grooved surfaces that exhibit DC are more efficient than flat ones at collecting and sliding dew, and thus cactus spines could act as soil dew conveyors. The agreement between our analytical model and experimental data verifies that the flow is driven by the Laplace pressure difference between the drops. This allowed us to obtain a general criterion for predicting the total or partial emptying of the smaller drops as a function of the dynamic contact angles of a surface. With the Wilhelmy method, we determined that hairs are less hydrophilic than spines. We also estimated the mechanical properties of both the spines and hairs to evaluate their possible role in physical defense. This study aids in better understanding the physical attributes and the condensation interaction with microstructures, and suggests some functional roles.

High-order exceptional point in a quantum system of two qubits with interaction

<sec>As one of the essential features in non-Hermitian systems coupled with environment, the exceptional point has attracted much attention in many physical fields. The phenomena that eigenvalues and eigenvectors of the system simultaneously coalesce at the exceptional point are also one of the important properties to distinguish from Hermitian systems. In non-Hermitian systems with parity-time reversal symmetry, the eigenvalues can be continuously adjusted in parameter space from all real spectra to pairs of complex-conjugate values by crossing the phase transition from the parity-time reversal symmetry preserving phase to the broken phase. The phase transition point is called an exceptional point of the system, which occurs in company with the spontaneous symmetry broken and many novel physical phenomena, such as sensitivity-enhanced measurement and loss induced transparency or lasing. Here, we focus on a two-qubit quantum system with parity-time reversal symmetry and construct an experimental scheme, prove and verify the features at its third-order exceptional point, including high-order energy response induced by perturbation and the coalescence of eigenvectors.</sec><sec>We first theoretically study a two-qubit non-Hermitian system with parity-time reversal symmetry, calculate the properties of eigenvalues and eigenvectors, and prove the existence of a third-order exceptional point. Then, in order to study the energy response of the system induced by perturbation, we introduce an Ising-type interaction as perturbation and quantitatively demonstrate the response of eigenvalues. In logarithmic coordinates, three of the eigenvalues are indeed in the cubic root relationship with perturbation strength, while the fourth one is a linear function. Moreover, we study the eigenvectors around exceptional point and show the coalescence phenomenon as the perturbation strength becomes smaller.</sec><sec>The characterization of the response of eigenvalues at high-order exceptional points is a quite difficult task as it is in general difficult to directly measure eigenenergies in a quantum system composed of a few qubits. In practice, the time evolution of occupation on a particular state is used to indirectly fit the eigenvalues. In order to make the fitting of experimental data more reliable, we want to determine an accurate enough expressions for the eigenvalues and eigenstates. To this aim, we employ a perturbation treatment and show good agreement with the numerical results of states occupation obtained by direct evolution. Moreover, we find that after the system evolves for a long enough time, it will end up to one of the eigenstates, which gives us a way to demonstrate eigenvector coalescence by measuring the density matrix via tomography and parity-time reversal transformation.</sec><sec>To show our scheme is experimentally applicable, we propose an implementation using trapped <inline-formula><tex-math id="M2">\begin{document}$ ^{171} {\rm{Yb}}^{+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220716_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220716_M2.png"/></alternatives></inline-formula> ions. We can map the parity-time reversal symmetric Hamiltonian to a purely dissipative two-ion system: use microwave to achieve spin state inversion, shine a 370 nm laser to realize dissipation of spin-up state, and apply Raman operation for Mølmer-Sørensen gates to implement Ising interaction. By adjusting the corresponding microwave and laser intensity, the spin coupling strength, the dissipation rate and the perturbation strength can be well controlled. We can record the probability distribution of the four product states of the two ions and measure the density matrix by detecting the fluorescence of each ion on different Pauli basis.</sec>

High-order exceptional point in a quantum system of two qubits with interaction

As one of the essential features in non-Hermitian systems coupled with environment, the exceptional point has attracted much attention in many physical fields. The phenomena that eigenvalues and eigenvectors of the system simultaneously coalesce at the exceptional point are also one of the important properties to distinguish from Hermitian systems. In non-Hermitian systems with parity-time reversal symmetry, the eigenvalues can be continuously adjusted in parameter space from all real spectra to pairs of complex-conjugate values by crossing the phase transition from the parity-time reversal symmetry preserving phase to the broken phase. The phase transition point is called an exceptional point of the system, which occurs in company with the spontaneous symmetry broken and many novel physical phenomena, such as sensitivity-enhanced measurement and loss induced transparency or lasing. Here, we focus on a two-qubit quantum system with parity-time reversal symmetry and construct an experimental scheme, prove and verify the features at its third-order exceptional point, including high-order energy response induced by perturbation and the coalescence of eigenvectors.<br/>We first theoretically study a two-qubit non-Hermitian system with parity-time reversal symmetry, calculate the properties of eigenvalues and eigenvectors, and prove the existence of a third-order exceptional point. Then, in order to study the energy response of the system induced by perturbation, we introduce an Ising-type interaction as perturbation and quantitatively demonstrate the response of eigenvalues. In logarithmic coordinates, three of the eigenvalues are indeed in the cubic root relationship with perturbation strength, while the fourth one is a linear function. Moreover, we study the eigenvectors around exceptional point and show the coalescence phenomenon as the perturbation strength becomes smaller.<br/>The characterization of the response of eigenvalues at high-order exceptional points is a quite diffcult task as it is in gneneral diffcult to directly measure eigenenergies in a quantum system composed of a few qubits. In practice, the time evolution of occupation on a particular state is used to indirectly fit the eigenvalues. In order to make the fitting of experimental data more reliable, we want to determine an accurate enough expressions for the eigenvalues and eigenstates. To this aim, we employ a perturbation treatment and show good agreement with the numerical results of states occupation obtained by direct evolution. Moreover, we find that after the system evolves for a long enough time, it will end up to one of the eigenstates, which gives us a way to demonstrate eigenvector coalescence by measuring the density matrix via tomography and parity-time reversal transformation.<br/>To show our scheme is experimentally applicable, we propose an implementation using trapped <sup>171</sup>Yb+ ions. We can map the parity-time reversal symmetric Hamiltonian to a purely dissipative two-ion system:use microwave to achieve spin state inversion, shine a 370 nm laser to realize dissipation of spin-up state, and apply Raman operation for Mølmer-Sørensen gates to implement Ising interaction. By adjusting the corresponding microwave and laser intensity, the spin coupling strength, the dissipation rate and the perturbation strength can be well controlled. We can record the probability distribution of the four product states of the two ions and measure the density matrix by detecting the fluorescence of each ion on different Pauli basis.

Drop coalescence during condensation on viscous slippery and viscoelastic coatings

Coatings of viscous oil or viscoelastic polymer on a rigid surface transform the condensation phenomena differently. When the viscous oil is infused on low-energy rigid surfaces, the surface shows excellent water repellent behavior. On the other hand, the viscoelastic material coating exhibits a high affinity with water drop resulting in more contact angle hysteresis (CAH). We focused on the drop coalescence phenomena during condensation on viscous slippery and viscoelastic coated metallic samples in this work. We have observed that the drop coalescence on lubricant infused surfaces (LIS) significantly depends on the viscosity of the lubricant and the stability of droplet interface bilayers between the drops. The lifetime of the non-coalescence event of the droplets during condensation on high viscous liquid infused surfaces (50 cst and 500 cst) surfaces was found to be in 1–3 orders of magnitude longer compared to low viscous liquid infused surface (5 cst). Coalescence induced motion during condensation was significantly observed in high viscous liquid infused surfaces (50 cst and 500 cst) compared to low viscous lubricant infused surface (5 cst). On soft viscoelastic coating, drop coalescence during condensation event undergoes through merging of the droplets followed by relaxation of the coalesced drop by the capillary induced movement of the contact line. Key findings of this work would be helpful to comprehend the drop coalescence phenomena on viscous slippery and viscoelastic coatings in a detailed manner.

Hydrodynamic density functional theory for mixtures from a variational principle and its application to droplet coalescence.

Dynamic density functional theory (DDFT) allows the description of microscopic dynamical processes on the molecular scale extending classical DFT to non-equilibrium situations. Since DDFT and DFT use the same Helmholtz energy functionals, both predict the same density profiles in thermodynamic equilibrium. We propose a molecular DDFT model, in this work also referred to as hydrodynamic DFT, for mixtures based on a variational principle that accounts for viscous forces as well as diffusive molecular transport via the generalized Maxwell-Stefan diffusion. Our work identifies a suitable expression for driving forces for molecular diffusion of inhomogeneous systems. These driving forces contain a contribution due to the interfacial tension. The hydrodynamic DFT model simplifies to the isothermal multicomponent Navier-Stokes equation in continuum situations when Helmholtz energies can be used instead of Helmholtz energy functionals, closing the gap between micro- and macroscopic scales. We show that the hydrodynamic DFT model, although not formulated in conservative form, globally satisfies the first and second law of thermodynamics. Shear viscosities and Maxwell-Stefan diffusion coefficients are predicted using an entropy scaling approach. As an example, we apply the hydrodynamic DFT model with a Helmholtz energy density functional based on the perturbed-chain statistical associating fluid theory equation of state to droplet and bubble coalescence in one dimension and analyze the influence of additional components on coalescence phenomena.

Numerical investigation on the direct contact condensation of oxygen jets in a cryogenic pipe

In the present study, the direct contact condensation (DCC) performance of the superheat GOX in subcooling LOX is explored by numerical simulations based on the VOF two-phase model. The flow condensation characteristics are analyzed in a practical condenser of a cryogenic liquid rocket. The coalescence phenomenon of the GOX streams is examined. The possible regimes of the coalescence are summarized and their effects on the condensation performance are explored. Besides, an improved GOX entrance layout is proposed to avoid the coalescence phenomenon and improve condensation performance. The main conclusions are concluded as follows: The gas condensation is the main heat transfer form in most of the pipe region. The bending section of the condenser pipe that connects the vertical section and horizontal section is the most active region for DCC. It is found that there can be two types of coalescences namely, transverse coalescence and longitudinal coalescence. Both coalescence regimes have strong negative effects on the heat transfer ability and condensation performance of the condenser pipe. The improved entrance layout can successfully avoid the coalescence of the GOX streams and reduce the flow distance of the GOX by about 93%. It is also concluded that an improvement of the condenser pipe should be effectively accomplished by controlling the coalescence of the GOX streams after injection.

O/W Pickering Emulsions Stabilized with Cellulose Nanofibrils Produced through Different Mechanical Treatments.

This work aimed at studying the stabilization of O/W Pickering emulsions using nanosized cellulosic material, produced from raw cellulose or tomato pomace through different mechanical treatments, such as ball milling (BM) and high-pressure homogenization (HPH). The cellulose nanofibrils obtained via HPH, which exhibited longer fibers with higher flexibility than those obtained via ball milling, are characterized by lower interfacial tension values and higher viscosity, as well as better emulsion stabilization capability. Emulsion stability tests, carried out at 4 °C for 28 d or under centrifugation at different pH values (2.0, 7.0, and 12.0), revealed that HPH-treated cellulose limited the occurrence of coalescence phenomena and significantly slowed down gravitational separation in comparison with BM-treated cellulose. HPH-treated cellulose was responsible for the formation of a 3D network structure in the continuous phase, entrapping the oil droplets also due to the affinity with the cellulose nanofibrils, whereas BM-treated cellulose produced fibers with a more compact structure, which did adequately cover the oil droplets. HPH-treated tomato pomace gave similar results in terms of particle morphology and interfacial tension, and slightly lower emulsion stabilization capability than HPH-treated cellulose, suggesting that the used mechanical disruption process does not require cellulose isolation for its efficient defibrillation.

Effect of Acoustic Parameters and Microbubble Concentration on the Likelihood of Encapsulated Microbubble Coalescence

Microbubble contrast agents are commonly used for therapeutic and diagnostic imaging applications. Under certain conditions, these contrast agents can coalesce on ultrasound application and form larger bubbles than the initial population. The formation of large microbubbles potentially influences therapeutic outcomes and imaging quality. We studied clinically relevant ultrasound parameters related to low-pressure therapy and contrast-enhanced ultrasound imaging to determine their effect on microbubble coalescence and subsequent changes in microbubble size distributions in vitro. Results indicate that therapeutic ultrasound at low frequencies, moderate pressures and high duty cycles are capable of forming bubbles greater than two times larger than the initial bubble distribution. Furthermore, acoustic parameters related to contrast-enhanced ultrasound imaging that are at higher frequency, low-pressure and low-duty cycle exhibit no statistically significant changes in bubble diameter, suggesting that standard contrast ultrasound imaging does not cause coalescence. Overall, this work suggests that the microbubble coalescence phenomenon can readily occur at acoustic parameters used in therapeutic ultrasound, generating bubbles much larger than those found in commercial contrast agents, although coalescence is unlikely to be significant in diagnostic contrast-enhanced ultrasound imaging. This observation warrants further expansion of parameter ranges and investigation of resulting effects.

Cultivation of Synechococcus HS-9 in a novel rectangular bubble column photobioreactor with horizontal baffle

As a source for third-generation biofuel, microalgae can assist island countries to overcome their energy crisis. In this study, a novel photobioreactor having three segments is designed and Synechococcus HS-9 growth in the photobioreactors with and without a baffle is compared. The aims of this study are to investigate how the baffle influences bubble size, distribution, and velocity, to explain the bubble coalescence phenomena, and verify the effect of the baffle on Synechococcus HS-9 growth. The results showed that bubble size distribution in the photobioreactors paralleled the increasing air flow rate. At a flow rate of 1.0 L/min, most bubbles had a diameter of 200–400 μm; however, at 2.5 L/min, the typical size was 1400–2000 μm. Bubble velocity was observed through imaging techniques. The intake air flow rate of 1 LPM has a mass transfer coefficient value of 0.00075 m/s for the photobioreactor without the baffle and 0.00089 m/s for the baffle-bearing photobioreactor. The Sauter mean diameters at three different heights (A, B and C section) in the photobioreactors were 675 μm, 1001 μm, and 1125 μm. Synechococcus HS-9 growth was 2.17 times higher in the baffle-bearing photobioreactor than that in the photobioreactor without the baffle.

Parametric numerical study and optimization of mass transfer and bubble size distribution in a gas-liquid stirred tank bioreactor equipped with Rushton turbine using computational fluid dynamics

Abstract Designing and optimizing a bioreactor can be an especially challenging process. Computational modelling is an effective tool to investigate the effects of various operating parameters on bioreactor performance and identify the optimum ones. In this work, a computational fluid dynamics-population balance model (CFD-PBM) was developed to elucidate the effect of different geometrical and operating parameters on the hydrodynamics and mass transfer coefficient of a batch stirred tank bioreactor. The validated model was projected to predict the effect of different parameters including the gas flow rate, the impeller off-bottom clearance, the number of agitator blades, and rotational speed of the impeller on the velocity profiles, air volume fraction, bubble size distribution, and the local gas mass transfer coefficient (K l a) in the bioreactor. Air bubble breakup and coalescence phenomena were considered in all simulations. Factorial experimental design approach was employed to statistically investigate the impacts of the aforementioned operating and geometrical parameters on K l a and bubble size distribution in the bioreactor in order to determine the most significant parameters. This can give an essential insight into the most impactful factors when it comes to designing and scaling up a bioreactor.

Disparity in recrystallization of α- & γ-fibers and its impact on Cube texture formation in non-oriented electrical steel

An investigation into the recovery and recrystallization of the two major texture fibres, namely α and γ, during annealing yielded subtle differences between the two. It is reported that with thermal activation static recovery occurs, where dislocation free sub-grains are formed and tend to grow, coalesce, or bulge out. This can form new strain-free recrystallisation nuclei, with the coalescence or bulging phenomenon depending on stored energy and geometrically dislocation density (GND). Due to low lattice curvature or otherwise, it was found α-fiber has low stored energy and GND values which favours bulging into neighbouring deformed grains as opposed to subgrain coalescence. In contrast, γ-fiber tends to undergo rapid subgrain coalescence due to high lattice curvature, i.e., GND and stored energy. The newly formed grains from both texture fibers were also found to typically differ in size, as γ-fiber has a much higher nucleation rate with rapid subgrain coalescence. Furthermore, it was discovered that Cube texture component though nucleating in higher rates within α-fiber, nucleates in all regions of high dislocation densities but will only survive in regions with low recovery and nucleation rates, typically α-fiber. Moreover, Goss texture component was found to preferentially nucleate from γ-fiber.