Suspended Droplets Research Articles

First Report of Colletotrichum gloeosporioides and Colletotrichum siamense, Causing Anthracnose Disease on coffee trees, in Saudi Arabia.

Coffee (Coffea arabica L.) is a promising agricultural commodity in many countries including Saudi Arabia, but crop production is often constrained by diseases. In December 2021, coffee trees had symptoms of anthracnose disease (CAD) were observed in Jazan Province, Saudi Arabia (17°19'00.8"N 43°11'26.8"E), and the incidence was 55%. Affected trees showed dieback and leaves necrosis. On green and ripening berries, slightly sunken and dark brown lesions were occurred; the berries finally become mummified (Fig. S1). For pathogen isolation, symptomatic tissues (4×4mm) of 30 diseased branches and berries samples were surface-sterilized in 1% sodium hypochlorite for 2 min, followed by 70% ethanol for 20 s, rinsed in sterile distilled water and placed on potato dextrose agar (PDA). Cultures were incubated at 26℃ for 8 days in the dark. Eighteen isolates were recovered, and 2 representative single spore isolates (KSU-CgM17, KSU-CsM42) were used for further study. PDA culture of KSU-CgM17 had aerial white mycelium at first and later became gray to grayish black; light salmon to orange conidial masses were observed on the mycelium plate surface as the cultures aged (Fig. S2). Colony produced by KSU-CsM42 was off-white to gray with cottony mycelia and grayish-white on the undersides of the culture after 10 days at 28° (Fig. S2). Conidial shape of these two isolates were both aseptate, cylindrical to nearly straight, hyaline, rounded at both ends. Conidia (n = 50) measurements were 16 to 18.0 µm long × 4.8 to 6.4 µm wide for KSU-CgM17 and 12.6 to 17.5 µm long × 3.2 to 4.5 μm wide for KSU-CsM42. The microscopic and culture features fitted those for Colletotrichum gloeosporioides species complex (Weir et al. 2012). To further identify these isolates, four genomic DNA loci including the partial ITS rDNA region, and CAL, TUB2, and GAPDH genes were amplified and sequenced (Hu et al., 2015). All sequences were deposited into GenBank under accession numbers: OQ791412 & OQ791413 (ITS), OQ786847 & OQ786851 (CAL), OQ786849 & OQ786850 (TUB2), and OQ786848 & OQ786852 (GAPDH) for KSU-CgM17and KSU-CsM42, respectively (Tables S1& S2). A BLAST search of GenBank showed that these pathogens were identified as C. gloeosporioides (KSU-CgM17) and C. siamense (KSU-CsM42). The pathogenicity was tested on detached coffee leaves or green and red berries (Coa et al., 2019). For inoculation, healthy leaves and berries were wounded with a sterilized needle, placed inside petri dishes containing moist filter paper, and then inoculated with a 10-µl droplet of conidial suspension (106 spores/ ml). Sterile distilled water was used as a negative control. Six replicates were tested per isolate and the experiment was repeated once. The inoculated materials were incubated at 25°C and 100% relative humidity for 8 days. Necrotic lesions developed on 100% of the inoculated coffee materials 6 days later, whereas the negative controls were asymptomatic (Fig. S2). Koch's postulates were fulfilled when typical colonies of these species were successfully re-isolated from the from symptomatic tissues. These pathogens were reported previously to affect coffee in Vietnam (Nguyen et al., 2010), China (Cao et al., 2019), and Puerto Rico (Serrato-Diaz et al., 2020). To our knowledge, this is the first record of C. gloeosporioides and C. siamense causing CAD in Saudi Arabia. Further studies on the epidemiology of CAD on arabica coffee plantations as well as effective strategies for managing this disease are needed.

The Influence of Gravity and Mass Loading on the Coalescence of Aerodynamically Interacting Droplets in Homogeneous Isotropic Turbulence

Abstract The collision–coalescence of cloud droplets in atmospheric turbulent flow is analyzed numerically using direct numerical simulation coupled to a Lagrangian particle tracking. The droplet aerodynamic interactions (AI) are represented for employing two complementary approaches. For large separations, the interaction forces are evaluated by the superposition of Stokes disturbance velocities generated by moving particles. When the distance between droplets is comparable to their mean radii, lubrication forces are additionally considered. Simulation results show that without gravitational acceleration, aerodynamic interactions decrease the kinetics of the coalescence process but do not significantly impact the size spectrum broadening. The influence of AI on the coalescence kinetics is more complex in the presence of gravity and depends on the mass loading and on droplet inertia. Long-range aerodynamic interactions reduce the coalescences in dilute suspensions but increase the collision rate in dense suspensions of high-inertia droplets. In contrast, lubrication forces decrease the collision rate regardless of the mass loading. The collision efficiency induced by aerodynamic interactions additionally is influenced by the radius ratio of colliding droplets and the mechanisms leading to raindrops formation and growth. In cloud-like conditions, both long- and short-range AI decrease the fraction of raindrops created by collisions between droplets (autoconversion) while promoting raindrops growth by accretion (collection by settling drops). In turn, aerodynamic interactions favor the growth of a limited number of droplets and promote the broadening of the droplet size spectrum. This effect is stronger in dilute suspensions of weakly inertial droplets, corresponding to the flow properties encountered in developing precipitation.

Cross-infection risk assessment in dental clinic: Numerical investigation of emitted droplets during different atomization procedures

Cross-infection risk induced by the emitted droplets and bioaerosols during dental procedures has challenged service providers and patients alike. The present study aims to investigate the transmission mechanism of emitted droplets during the dental atomization procedures: vibration ultrasonic scaling (vUS) and rotation high-speed drilling (rHSD) and propose the risk assessment. Computational fluid dynamics (CFD) simulation was performed, and the experimentally recorded droplet velocity and diameter distribution during the atomization procedures were defined as initial boundary conditions. The droplet transmission in the dental clinic was analyzed from the final fate (deposition, suspension, and escape) and fallow time (FT) of emitted droplets. The results revealed that the diameter threshold for the droplet deposition and suspension was 60μm, and the fraction of deposited droplets would be stable at 79.5% for rHSD and 85% for vUS. The primary contamination distance was generally within 0.28 m and 0.4 m from the treatment position for the atomization procedures of rHSD and vUS, respectively. An increment of about 2% in the fraction of escaped droplets was noted when conducting the rHSD. The median of estimated FT for the atomization procedure of rHSD, 34 min, was longer than that of vUS, 30.6 min. In general, cross-infection risk during rHSD can be regarded as “higher” than vUS. The contribution of the present study can serve as guidance to decrease the cross-infection risk in dental clinics.

Numerical Evaluation of the Effect of Buoyancy-Driven Flow on the Migration of Respiratory Droplets

The understanding of the impact of buoyancy-driven flow on the migration of respiratory droplets remains limited. To investigate this phenomenon, the Lagrangian–Eulerian approach (k-ε turbulent model and discrete phase model) was employed to analyze the interaction between buoyancy-driven flow and coughing activity. The simulation approach was validated by simulating a jet problem in water. Although this problem describes the jet penetration in water, the governing equations for this problem are the same as those for coughing activity in the air. The results demonstrated that an umbrella-shaped airflow was generated above a person and a temperature stratification existed in the room. The buoyancy-driven flow significantly altered the dispersion pattern of the droplets. Notably, for large droplets with an initial diameter of 100 μm, the flow in the boundary layer led to an increased deposition time by about five times. Conversely, for small droplets with an initial diameter of 20 μm, the umbrella-shaped airflow resulted in a more rapid dispersion of droplets and subsequently facilitated their quicker removal by the room walls. After a duration of 300 s, the suspended droplet number of the case with buoyancy-driven flow was 33.4% smaller than that of the case without buoyancy-driven flow. Two or three persons being in the room resulted in a faster droplet removal.

Antimicrobial mechanism of cuprous oxide (Cu2O) coatings

Some very effective antimicrobial coatings exploit copper or cuprous oxide (Cu2O) as the active agent. The aim of this study is to determine which species is the active antimicrobial – dissolved ions, the Cu2O solid, or reactive oxygen species. Copper ions were leached from Cu2O into various solutions and the leachate tested for both dissolved copper and the efficacy in killing Pseudomonas aeruginosa. The concentration of copper species leached from Cu2O into aqueous solution varied greatly with the composition of the aqueous solution. For a range of solution buffers, killing of P. aeruginosa was highly correlated with the concentration of copper in the leachate. Further, 10 µL bacterial suspension droplets were placed on Cu2O coatings, with or without a polymer barrier layer, and tested for bacterial kill. Killing occurred without contact between bacterium and solid, demonstrating that contact with Cu2O is not necessary. We therefore conclude that soluble copper species are the antimicrobial agent, and that the most potent species is Cu+. The solid quickly raises and sustains the concentration of soluble copper species near the bacterium. Killing via soluble copper ions rather than contact should allow copper coatings to kill bacteria even when fouled, which is an important practical consideration.

An integrated simulation approach for demulsification of water-in-oil emulsions by medium coalescence

Medium coalescence, as a low energy consumption demulsification method, has been widely applied in many industries. During the water-in- oil emulsions flowing through medium bed, the dispersed water droplets not only collide and aggregate with each other, but also deposit and wet on the hydrophilic medium surface. Moreover, the formed large droplets may also breakup into small ones by the turbulent flow or the tiny fibers. Thus, an integrated approach is needed to predict the demulsification performance of water-in-oil (W/O) emulsion by medium coalescence. In this work, the population balance model (PBM) with considering Boltzmann motion and differential settlement was used to predict suspension droplets aggregation. The interaction between dispersed droplets and medium bed was calculated by a modified deposition model. Moreover, a published breakage model was selected to simulate the complex droplet breakage process. Then, the demulsification performance of W/O emulsion can be obtained by the variation of droplet size profile. To verify the integrated simulation approach, the existing experimental datasets were compared with the simulation results. After that, a sensitivity analysis was carried out to study parameters that affect the demulsification performance, such as flow velocity, capillary size, and continuous viscosity. The integrated approach proposed in this paper fills in the blank of the demulsification simulation of W/O emulsion by medium coalescence. It provides an in-depth understanding of the relationship between droplets behaviors and medium coalescence performance.

Role of volatiles in intrusion emplacement and sulfide deposition in the supergiant Norilsk-Talnakh Ni-Cu-PGE ore deposits

Abstract The Norilsk-Talnakh orebodies in Siberia are some of the largest examples on Earth of magmatic Ni–Cu–platinum group element (PGE) deposits, formed by segregation of immiscible sulfide melts from silicate magmas. They show distinctive features attributable to degassing of a magmatic vapor phase during ore formation, including: vesiculation of the host intrusions, widespread intrusion breccias, and extensive hydrofracturing, skarns, and metasomatic replacement in the country rocks. Much of the magmatic sulfide was generated by assimilation of anhydrite and carbonaceous material, leading to injection of a suspension of fine sulfide droplets attached to gas bubbles into propagating tube-like host sills (“chonoliths”). Catastrophic vapor phase exsolution associated with a drop in magma overpressure at the transition from vertical to horizontal magma flow enabled explosive propagation of chonoliths, rapid “harvesting” and gravity deposition of the characteristic coarse sulfide globules that form much of the ore, and extensive magmatic fluid interaction with country rocks.

Evaluation of the relative deviation for coagulation and gravitational sedimentation model from experimental results of submicron aerosol in water vapor environments

This paper evaluates the relative bias of submicron aerosol coagulation and gravity deposition experiments and model prediction results under water vapor conditions, and discusses the model prediction bias results at high steam fraction. When submicron aerosols are at room temperature and lower vapor molar ratios, the model predictions and experimental results are in good agreement. When the molar fraction of steam is high, the prediction results of the model are poor. Through analyzing thermal data and conducting gas superheating experiments, it was found that under saturated steam conditions in the experimental vessel, the number of suspended small droplets also increases with the increase of steam molar fraction. The presence of these droplets alters the coagulation and sedimentation results of submicron aerosols. Based on experimental data, this paper adds correction coefficients of coalescence and sedimentation to the original model, making it suitable for predicting submicron aerosol coagulation and sedimentation under high steam molar fraction.

Mechanical alloying and high-repetition-pulsed-laser based manufacturing method for nanostructured hydroxyapatite films on cobalt-chromium substrates

In this study, we report a manufacturing process for coating nanostructured and hierarchically porous Hydroxyapatite (HA) films on cobalt-chromium (CoCr) substrates. Nanoparticles of HAP are prepared using three different methods: ball milling of sol–gel synthesized HAP, mechanical alloying of calcium oxide (CaO) and diammonium phosphate (DAP), and mechanical alloying of eggshell and diammonium phosphate. The nanoparticle's characterization showed the presence of nanophase HAP in sol–gel synthesized powders and synthesis of apatite phases in mechanically alloyed powders. Small droplets of nanoparticle ethanol suspensions were injected on the substrate and irradiated with high-repetition-rate picosecond pulsed laser to coat the CoCr samples. Characterization of the deposited films showed bonding of HAP nanoparticles to a film with nanostructured morphology and hierarchical porosity and the incorporation of CoCr from the substrate into the first few deposited layers of HAP nanoparticles. The two-step manufacturing process results in bioactive and biocompatible HAP films with morphology that is desirable for the growth and infiltration of biological cells.

Disruption and microexplosion mechanisms of burning alcohol droplets with the addition of nanoparticles

Microexplosions of burning liquid fuels have been actively investigated and considered due to the advantage for substantially increasing the overall burning rate. This study concerns possible control of microexplosion occurrence by adding nanoparticles in alcohol fuel without effects of surfactant and ignitable particles as usually seen in the literature. In addition, the essential characteristics and differences between various particles on combustion are discussed. Specifically, we have added three types of ceramic nanoparticles into butanol and isopropanol droplets under different convection environments, i.e., forced convection and natural convection in normal gravity, and free convection in microgravity. A suspended droplet method was performed under convection-free and natural convective conditions while a free-falling droplet method provided a forced convection environment. It was observed that the combustion characteristics of droplets changed from extinction to burnout or from burnout to microexplosion by using different base fuels, by increasing the intensity of flow convection, or by using different kinds of nanoparticles. During combustion, droplets would deform due to the presence of gelation in the outer layer when Al2O3 or SiO2 nanoparticles were added, but not for TiO2. This yielded one of the key factors leading to microexplosions, in addition to the amount of heat absorption during the burning. For the latter, specifically, microexplosions happened when butanol/SiO2 droplets were tested, but not for butanol/Al2O3 droplets. By comparing the infrared absorptivity of Al2O3 and SiO2, distinct amount of absorbed infrared radiation was demonstrated. Such a difference in heat absorption was also key to the creation of microexplosion. As a consequence, microexplosions could be generated when nanoparticles were added into the fuel and formed gelation on the droplet surface, which trapped bubbles in the droplet, while sufficient heat was absorbed by the particles during the burning. The resulted consumption rate had increased by 46% compared to that of pure fuel.

First Report of Xanthomonas hydrangeae Causing Leaf Spot on Oakleaf Hydrangea (Hydrangea quercifolia) in Tuscany (Italy).

Hydrangeas (Hydrangea L.) are popular ornamental plants used in urban landscapes and gardens worldwide for the beauty of their large flowers. In June 2022, dark brown/purple and irregular water-soaked spots coalescing into large areas of necrosis were observed on the leaves of potted Hydrangea quercifolia Bartr. plants growing in two ornamentals nurseries in Pistoia, Tuscany, Italy. Isolations, using two symptomatic plants/nursery, were performed by excising small portions of leaf tissue from the margin of the lesions, and macerating them in 100 μl of sterile distilled water (SDW). After 15 min of incubation, a loopful of the resulting suspension was streaked on yeast extract-dextrose-CaCO3 agar (YDCA) amended with 60 mg L-1 cycloheximide. Mucoid, convex and yellow colonies appeared on YDCA after incubation at 28°C for 48h. After colony purification on yeast extract-nutrient-agar (YNA), two isolates from each nursery were subject to amplification and sequence analysis of the 16S rRNA using universal primers FD1/RD1, for genus identification (Vauterin et al. 2000; Weisburg et al. 1991). All 16S rRNA sequences (OP441051) were identical and BLASTn searches indicated that the isolates belong to the genus Xanthomonas [99.9% nucleotide identity with X. hydrangeae strain LMG 31885 (LR990741.1) and 99.8% with strain LMG 31884T (NR_181958.1)]. For classification at species level, fragments of the housekeeping genes gyrB, rpoD, dnaK, and fyuA, were amplified according to Young et al. (2008). Both strands were sequenced and the consensus sequences aligned using MUSCLE as implemented in MEGA X (Kumar et al. 2018). Homologous sequences were once again identical between the isolates. A neighbor joining phylogenetic analysis of the concatenated fragments, was carried out, using the Tuscan isolate HyQ-Tu1, the type/pathotype strains of the seven pathovars of X.hortorum, proposed by Morinière et al. (2020), the four X.hydrangeae strains characterized by Dia et al. (2021) and the type strain of X.populi as the outgroup. The analysis indicated that HyQ-Tu1 isolate clusters within the X. hydrangeae branch of the recently described X. hortorum - X. hydrangeae species complex (Morinière et al. 2020; Dia et al. 2021; 2022). In agreement with this result, isolates tested positive to the LAMP assay specific for members of the complex's clade C (X. hydrangeae) (Dia et al. 2022). Based on molecular evidence, the isolates were identified as X. hydrangeae (Dia et al. 2021; Oren and Garrity, 2022). Three healthy H. quercifolia potted plants were inoculated by rubbing a 10 µl droplet of a bacterial suspension of X. hydrangeae HyQ-Tu1 adjusted to an OD600 of 0.3 (approx. 108 CFU/ml) in SDW on the adaxial surface of two leaves per plant. Two control leaves/plant were inoculated with SDW. Each inoculated leaf was enclosed for 24h in a polyethylene bag and all plants were maintained in a greenhouse at 28°C. Nine days post inoculation (DPI), leaf spots similar to those observed on naturally infected plants started to become evident on the bacteria-inoculated leaves while control leaves remained asymptomatic throughout the trial (21 DPI). Koch's postulates were fulfilled by re-isolating the bacterium from the symptomatic tissues, obtaining a positive amplification with the clade C-specific LAMP assay (Dia et al. 2022), and confirming that the gyrB sequence was 100% identical to that of X. hydrangeae HyQ-Tu1. Housekeeping gene sequences were submitted to GenBank (OP456006-9). Members of the X. hortorum - X. hydrangeae species complex have been reported to affect H. quercifolia in the USA (Uddin et al. 1996) and H. quercifolia and H. arborescens L. in Belgium (Cottyn et al. 2021). To the best of our knowledge, this is the first documentation of X. hydrangeae causing disease on H. quercifolia in Italy. Further work is required to verify the presence of the bacterium in other European countries and to assess the economic impact that it causes within and outside nurseries.

Formation of an organic film on an electrode via a suspension of redox-active droplets in acidic aqueous solution

Previous electrochemical studies of redox emulsions have been mainly performed in the context of electro-organic synthesis. More recently, this research has been oriented towards applications of emulsions in flow batteries. Such biphasic systems seem to provide a suitable environment for reactions at the liquid–liquid interface. Taking an emulsion consisting of microdroplets of decamethylferrocene solution in a hydrophobic ionic liquid/toluene mixture in acidic aqueous solution as an example, we have demonstrated that an electrochemical redox reaction involving the hydrophobic redox probe occurs at the glassy carbon electrode|organic liquid film interface. This reaction is followed by ion exchange between liquid phases. This effect is explained by the instability of the emulsion. A portion of the organic liquid stays on the electrode surface after transfer to a purely aqueous electrolyte and remains electroactive.

Thermal analysis of suspended single droplet evaporation measurements with a coupled lumped parameter model

The measurement data of single droplet evaporation experiments are often biased due to the extra heat input through the fiber suspension and the presence of thermal radiation in hot environments. This encumbers model validation for heat and mass transfer simulations of liquid droplets. In this paper, a thermal analysis of this measurement layout is presented with a coupled lumped parameter model, considering heat conduction through the suspension. The model was validated by experimental data from the literature and good agreements were found. The thermal analysis focused on fiber material and geometry, and thermal radiation properties. Calculations were performed on a broad range of ambient conditions for liquids with different volatility characteristics. Temporal squared droplet diameter- and temperature-profiles, furthermore, droplet stationary evaporation rate were used to characterize vaporization phenomena. The thermal balance of the droplet is dominated by the convective heat rate from the environment in the early stage of evaporation. The effect of heat conduction through the fiber becomes important at the end of the droplet lifetime when the droplet size is decreased. Temperature sensor suspension may seriously bias droplet temperature due to the larger thermal conductivity compared to quartz fiber. Large droplets in high-temperature environments show significant sensitivity to thermal radiation properties, which should be considered in measurements and model validation.

Assessment of Experimental Artifacts in Evaporation Tests on Isolated, Suspended Droplets

The suspended droplet framework is commonly used to study liquid fuel evaporation and combustion. However, measurements at this facility can be affected by artifacts. This study examines their impact on butanol droplet evaporation. Thermal radiation and fiber conduction effects are specifically addressed. Results show that heat conduction through the fiber can significantly affect droplet evaporation, even causing internal bubbling in some cases.

Evaporation of Suspended Heavy Oil/1-Pentanol Droplets in Flame-like Conditions

In this work high temperature evaporation characteristics of isolated, suspended, ≈500 µm size droplets of heavy fuel oil/1-pentanol blends are experimentally studied. Flame-like ambient conditions are reproduced by developing a new suspended droplet facility such that the influence of major external effects is minimum.

Identification of Fusarium sacchari Causing Foliar Blight on Begonia semperflorens in China.

Begonia semperflorens Link et Otto (Begoniaceae) is a flowering, ornamental plant widely cultivated in China. In April of 2020, a foliar blight disease on B. semperflorens was observed in plant nurseries (∼0.2 ha), with ~ 20% disease incidence (n = 150) in Nanning, Guangxi Province, China. Initial symptoms included irregular to circular, grayish white spots surrounded by a dark brown halo, mainly scattered on the edges the leaves. In severe infections, the spots frequently coalesced to form large, blighted areas, followed by defoliation. To isolate the pathogen, three representative plants exhibiting symptoms were collected from the nurseries. Leaf tissues (5 × 5 mm) were cut from the margin of necrotic lesions (n = 18), surface disinfected in 1% NaOCl for 2 min, then rinsed three times in sterile H2O. Then the tissues were plated on potato dextrose agar (PDA), and incubated at 28°C (12 h photoperiod) for 3 days. Hyphal tips from recently germinated spores were transferred to PDA to purify fungal isolates. A total of 11 isolates (85% isolation frequency) with similar morphological characteristics were obtained. Colonies on PDA plates were villose, had a dense growth of white aerial mycelia and appeared pale but becoming violet with age. On Spezieller Nährstoffarmer Agar (SNA), the macroconidia were slender, slight falcate, two to three septate, and 23.5 to 48.8 × 2.8 to 4.8 μm (n = 60), and the microconidia were abundant and formed in false heads on monophialides or polyphialides, slim, oval, zero to one septate, and 7.8 to 22.4 × 2.4 to 4.0 μm (n = 60). For molecular identification, the internal transcribed spacer (ITS) region of rDNA, and partial translation elongation factor-1 alpha (TEF-1α), and RNA polymerase second largest subunit (RPB2) genes of the representative isolate HT-2B were amplified and sequenced using primer pairs ITS1/ITS4 (White et al. 1990), EF-1/EF-2 (O'Donnell et al. 1998), and 5f2/11ar (Liu et al. 1999, Reeb et al. 2004), respectively. The obtained sequences were deposited in NCBI GenBank under the accession numbers OQ048268 (TIS), OP994260 (TEF-1α), OP994262 (RPB2) and showed 99.4%, 99.8%, and 99.4% similarity with the corresponding sequences (X94168，AF160278，and JX171580, respectively) of Fusarium sacchari from type material. In addition, a phylogenetic analysis showed that HT-2B was grouped with F. sacchari. Therefore, based on morphological (Leslie et al. 2005) and molecular characteristics, the isolates were identified as F. sacchari. To test pathogenicity, three healthy leaves on each of three B. semperflorens plants were stab-wounded with a sterile syringe and inoculated with a 10-μl droplet of a conidial suspension (106 spores/ml) of the isolate HT-2B. As a control, another three leaves were wound inoculated with sterilized dH2O. All plants were enclosed in transparent plastic bags and incubated in a greenhouse at 28°C (12 h photoperiod, ~ 80% relative humidity). Six days post-inoculation, symptoms appeared on the inoculated leaves. No symptoms were detected on control plants. Experiments were replicated three times with similar results. To fulfill Koch's postulates, the F. sacchari isolates were consistently re-isolated from symptomatic tissue and confirmed by morphology and sequencing, whereas no fungus was isolated from the control plants. To our knowledge, this is the first report of F. sacchari causing foliar blight on B. semperflorens in China. This result will help develop management strategies for this disease.

Molecular dynamics simulation of oily wastewater treatment by air floatation

Molecular dynamics (MD) method was used to study the process of treating oily wastewater by air flotation. The bubbles generated by the machine combine the suspended oil droplets in the oily wastewater in the way of entrapment. In the process of upward movement, bubbles will collide with oil droplets suspended in water, the oil droplets will slightly deform on the surface of foam film, and the oil droplets will stick to the surface of foam film. Moreover, in the process of oil droplets floating up with bubbles, the foam film will further depress the position of oil droplets to the gas phase, and the closer oil droplets will coalesce in the depression, while the farther oil droplets will approach each other without coalescence.

On the flow of soft suspensions through orifices

The behavior of confined suspensions of soft droplets under pressure-driven flow, passing an obstacle within a planar channel, is investigated by means of a mesoscopic lattice Boltzmann model capable of simulating soft non-coalescing droplets. The simulations reveal that the threshold of the pore size, below which the flux vanishes, is between 1 and 2 droplet diameters, and increases with the packing fraction. Moreover, we show that the classical Beverloo relation between the total flux and the pore size is not suitable for the soft suspensions considered here.

Yield-stress transition in suspensions of deformable droplets.

Yield-stress materials, which require a sufficiently large forcing to flow, are currently ill-understood theoretically. To gain insight into their yielding transition, we study numerically the rheology of a suspension of deformable droplets in 2D. We show that the suspension displays yield-stress behavior, with droplets remaining motionless below a critical body-force. In this phase, droplets jam to form an amorphous structure, whereas they order in the flowing phase. Yielding is linked to a percolation transition in the contacts of droplet-droplet overlaps and requires strict conservation of the droplet area to exist. Close to the transition, we find strong oscillations in the droplet motion that resemble those found experimentally in confined colloidal glasses. We show that even when droplets are static, the underlying solvent moves by permeation so that the viscosity of the composite system is never truly infinite, and its value ceases to be a bulk material property of the system.

Advection-enhanced heat and mass transport from neutrally suspended droplet in simple shear flow

Advection-enhanced heat and mass transport from a single droplet neutrally suspended in a simple shear flow has been studied using high-fidelity numerical simulation. The capillary number ranges from 0.01 to 0.5, which encompasses the entire range of small deformation, large deformation, and breakup of the droplets. The Reynolds number is from 0.01 to 1, including regions of both weak and strong advection. The temperature and mass concentration are modeled as the concentration of a passive scalar released at the droplet surface. Two Schmidt numbers, 10 and 100, are considered, for which flow advection plays a role in the transport of passive scalar. For unbroken droplets, the interaction between the carrier fluid and the suspended droplet leads to several different flows around the droplet. The fluid motions together with scalar diffusion constitute a coupled transport mechanism for passive scalar. The dependence of scalar release rate on Reynolds and Peclet numbers can be roughly described by the correlation for a rigid sphere. For broken droplets, the basic flow features around the droplet during the process of elongation and breakup are similar to those of an unbroken droplet. The variation of the scalar release rate can be decomposed into several stages, corresponding to the process of droplet elongation and breakup. The variation of the scalar release rate exhibits a high correlation with the capillary, Reynolds, and Peclet numbers. This suggests that it is feasible to develop an empirical model that incorporates the effects of the number and size distributions of child droplets after breakup.