Breakup Process Research Articles

Numerical investigation on the hole characteristics and perforation mechanism of conical liquid sheet

The conical liquid sheet formed by a swirl nozzle was numerically investigated by volume-of-fluid (VOF) in this paper. With increase of Reynolds number (Re), the breakup process of the conical liquid sheet was dominated successively by rim, rim-perforation, perforation, perforation-wave and wave disintegration modes, which agreed well with the experiment results. For the perforation disintegration mode, several kinds of hole in the liquid sheet were successfully predicted, such as isolated holes and group holes. The expansion speed of the hole varied with the time in an exponential form at the initial stage of hole growing, and then kept constant at Taylor-Culick speed. That was the reason why there were two views on the expansion speed of the hole. A model to predict the expansion speed and the rim radius of the hole was proposed and well validated by the numerical results. The flow instability in the conical liquid sheet was successfully predicted, and its wave length was corresponding with Reitz wave instability model. Based on such flow instability, the mechanism of perforation formation was revealed. At the superimposed position of surface wave troughs, fluid migration from this position to its surrounding stretched the liquid sheet thinner and thinner, and finally made it collapsing. Thus, the perforation of the liquid sheet was an intrinsic performance induced by flow instability of liquid sheet itself, rather than the environmental factors. Furthermore, based on the such perforation mechanism, a perforation-time model is proposed, which is reasonable to predict the formation process of hole.

Lattice Boltzmann modeling of primary liquid film breakup at the prefilmer edge: Effects of surface wettability

In this paper, numerical predictions are performed for a planar prefilming atomizer using the lattice Boltzmann (LB) method. The main target is to inspect the effects of surface wettability on the primary liquid film breakup at the prefilmer edge. To this end, a phase-field-based multiple-relaxation-time LB model for two-phase flow is derived and verified for the present study, as well as the wetting boundary scheme. After that, the effects of surface wettability are assessed by specifying different contact angles during the simulations. Numerical results indicate that the whole primary breakup process of the liquid film can be roughly divided into three interactive stages: (i) liquid accumulation at the trailing edge; (ii) ligament formation and its flapping movements; (iii) ligament breakup and droplet formation. It is visible that the liquid accumulation and the following ligament breakup show similar periodic patterns with quite consistent frequencies. Besides, when the contact angle is increased, the volume of liquid accumulated at the prefilmer edge declines, the maximum flapping region of ligaments shrinks, the ligament breakup length reduces, but the ligament breakup frequency increases. Based on the above-mentioned results, it can be concluded that the prefilmer with hydrophobic surfaces benefits the primary liquid film breakup in the close vicinity of the prefilmer edge.

Computational Evaluation of Shock Wave Interaction with a Liquid Droplet

This article represents the natural continuation of the work by Rossano and De Stefano (2021), dealing with the computational fluid dynamics analysis of a shock wave interaction with a liquid droplet. Differently from our previous work, where a two-dimensional approach was followed, fully three-dimensional computations are performed to predict the aerodynamic breakup of a spherical water body due to the impact of a traveling shock wave. The present engineering analysis focuses on capturing the early stages of the breakup process under the shear-induced entrainment regime. The unsteady Reynolds-averaged Navier–Stokes approach is used to simulate the mean turbulent flow field in a virtual shock tube device with circular cross section. The compressible-flow-governing equations are numerically solved by means of a finite volume method, where the volume of fluid technique is employed to track the air–water interface. The proposed computational modeling approach for industrial gas dynamics applications is verified by making a comparison with reference numerical data and experimental findings, achieving acceptably accurate predictions of deformation and drift of the water body without being computationally cumbersome.

Stratigraphic record of continental breakup, offshore NW Australia

AbstractContinental breakup involves a transition from rapid, fault‐controlled syn‐rift subsidence to relatively slow, post‐breakup subsidence induced by lithospheric cooling. Yet the stratigraphic record of many rifted margins contain syn‐breakup unconformities, indicating that episodes of uplift and erosion interrupt this transition. This uplift has been linked to mantle upwelling, depth‐dependent extension and/or isostatic rebound. Deciphering the breakup processes recorded by these unconformities and their related rock record is challenging because uplift‐associated erosion commonly removes the strata that help constrain the onset and duration of uplift. We examine three major breakup‐related unconformities and the intervening rock record in the Lower Cretaceous succession of the Gascoyne and Cuvier margins, offshore NW Australia, using seismic reflection and borehole data. These data show the breakup unconformities are disconformable (non‐erosive) in places and angular (erosive) in others. Our recalibration of palynomorph ages from rocks underlying and overlying the unconformities shows: (i) the lowermost unconformity developed between 134.98–133.74 Ma (Intra‐Valanginian), probably during the localisation of magma intrusion within continental crust and consequent formation of continent–ocean transition zones (COTZ); (ii) the middle unconformity formed between ca. 134 and 133 Ma (Top Valanginian), possibly coincident with breakup of continental crust and generation of new magmatic (but not oceanic) crust within the COTZs; and (iii) the uppermost unconformity likely developed between ca. 132.5 and 131 Ma (i.e. Intra‐Hauterivian), coincident with full continental lithospheric breakup and the onset of seafloor spreading. During unconformity development, uplift was focussed along the continental rift flanks, likely reflecting flexural bending of the crust and landward flow of lower crust and/or lithospheric mantle from beneath areas of localised extension towards the continent (i.e. depth‐dependent extension). Our work supports the growing consensus that the ‘breakup unconformity’ is not always a single stratigraphic surface marking the onset of seafloor spreading; multiple unconformities may form and reflect a complex history of uplift and subsidence during continent–ocean transition.

The dynamics of the tip and hub vortices shed by a propeller: Eulerian and Lagrangian approaches

Large Eddy Simulation on a grid composed of 3.8 billion points is utilized to reproduce the wake of a marine propeller. Results are compared against Particle Imaging Velocimetry experiments. The study is based on a core analysis for the tip and hub vortices, using both Eulerian and Lagrangian methodologies. Results show that the instability of the tip vortices is first triggered by their shear with the wake of the neighboring blades. This promotes short- and long-wave oscillations of the trajectory of the tip vortices and eventually mutual inductance phenomena between them. Then, the process of instability and break-up of the coherence of the tip vortices is accelerated by the interaction with the hub vortex, which is the largest coherent structure shed by the propeller, dominating its wake system and expanding radially as the wake develops downstream. The break-up of the helical structures shed from the tip of the propeller blades results in a substantial increase of turbulence at the wake outer boundary and especially in its diffusion. This process is even enhanced by the energy provided by the hub vortex, associated with its fluctuations at low frequencies. The instability process of the hub vortex is slower than the one experienced by the tip vortices. Although the former develops growing fluctuations around the wake axis, it keeps coherent further downstream, in comparison with the latter. Therefore, within a few diameters from the propeller plane, turbulence at the wake axis keeps decreasing downstream of the onset of the hub vortex.

Further investigation of the irreversible floc breakup in flocculation kinetics modelling

Abstract Recent research has shown that the equilibrium between aggregation and breakup in flocculation kinetics modelling may not hold due to irreversible floc breakup. This work investigated the influence of the coagulant/particle ratio and average velocity gradient () in the occurrence of this phenomenon with a different water matrix than previous research. Jar test assays were conducted with low (≈15 NTU), medium (≈50 NTU) and high (≈100 NTU) turbidity synthetic raw water, using alum as coagulant and kaolin as primary particles. Results were analyzed using Argaman and Kaufman's model and values for KA (aggregation constant) and KB (breakup coefficient) were determined with the evolutionary convergence method. Model fitting was satisfactory when the Al/particle ratio varied between 10 and 27 mg Al3+/g. Outside this range, residual turbidity increased after equilibrium, attributed to the irreversible floc breakup process and not adequately described by the model. A two-factor analysis of variance (ANOVA) was conducted, and the results indicated a plausible correlation between pKA (–log KA) and Al/particle ratio. As for pKB (–log KB), the results indicated a possible correlation with both Al/particle ratio and . The results suggest that the irreversible floc breakup may occur regardless of the water matrix composition.

Primary breakup of shear‐thickening suspension jet by an annular air jet

AbstractAn experimental investigation is conducted to study the influence of shear‐thickening behavior on the primary breakup process of suspension jets. The primary breakup morphologies of cornstarch–water suspension are observed via a high‐speed camera. The unique hardened breakup mode only occurs when the suspension exhibits discontinuous shear thickening (DST). During hardened breakup mode, the oscillating portion of the suspension jet becomes perpendicular to the air direction and keeps cylindrical instead of deforming into a thin sheet or membrane structure. The suspension jets break off into large pieces rather than tiny droplets. The dimensionless number N is established to describe the relative magnitude of the increment of the viscous force and aerodynamic force during the primary breakup process. The primary breakup regime map of Newtonian fluids and shear‐thickening suspensions is also promoted based on the dimensionless number N and the Weber number We.

Numerical investigation on the coupled mechanisms of bubble breakup in a venturi-type bubble generator

ABSTRACT The bubble breakup mechanism in a venturi-type bubble generator is a hot research topic, and the bubble breakup mechanisms induced by the axial regional flow field characteristics has long been studied and debated. A coupled volume of fluid and large eddy simulation numerical simulation method was conducted within the OpenFOAM® framework to track the two-phase interfaces and transient turbulence characteristics of the flow field in a venturi-type bubble generator. A turbulence inlet database was established to ensure the reliability of the numerical solution and the economy of the calculation. The results indicated that the bubble breakup induced by the axial regional flow field characteristics of the divergent section can be divided into a steady-state disturbed breakup pattern and an unsteady-state disturbed breakup pattern macroscopically, the latter playing a dominant role in generating fine bubbles. Furthermore, a series of typical bubble breakup processes were captured via a Lagrangian approach that showed that interfacial instability played an important role at each stage of bubble transport: Kelvin–Helmholtz instability caused bubbles to detach from the gas film during the steady-state disturbed breakup pattern, and Rayleigh–Taylor instability induced the deformation of detached bubbles in the unsteady-state disturbed region. Additionally, viscous shear force strengthened the interfacial instability in the binary breakup process, and turbulent fluctuations and collisions contributed to the shattering of defective bubbles. Moreover, a shearing-off process tended to occur in regions with small vorticity fluctuations, therefore playing a small role in creating large clusters of bubbles.

A Comparison of Convective and Stratiform Precipitation Microphysics of the Record-breaking Typhoon In-Fa (2021)

In July 2021, Typhoon In-Fa attacked eastern China and broke many records for extreme precipitation over the last century. Such an unrivaled impact results from In-Fa’s slow moving speed and long residence time due to atmospheric circulations. With the supports of 66 networked surface disdrometers over eastern China and collaborative observations from the advanced GPM satellite, we are able to reveal the unique precipitation microphysical properties of the record-breaking Typhoon In-Fa (2021). After separating the typhoon precipitation into convective and stratiform types and comparing the drop size distribution (DSD) properties of Typhoon In-Fa with other typhoons from different climate regimes, it is found that typhoon precipitation shows significant internal differences as well as regional differences in terms of DSD-related parameters, such as mass-weighted mean diameter (Dm), normalized intercept parameter (Nw), radar reflectivity (Z), rain rate (R), and intercept, shape, and slope parameters (N0, µ, Λ). Comparing different rain types inside Typhoon In-Fa, convective rain (Nw ranging from 3.80 to 3.96 mm−1 m−3) shows higher raindrop concentration than stratiform rain (Nw ranging from 3.40 to 3.50 mm−1 m−3) due to more graupels melting into liquid water while falling. Large raindrops occupy most of the region below the melting layer in convective rain due to a dominant coalescence process of small raindrops (featured by larger ZKu, Dm, and smaller N0, µ, Λ), while small raindrops account for a considerable proportion in stratiform rain, reflecting a significant collisional breakup process of large raindrops (featured by smaller ZKu, Dm, and larger N0, µ, Λ). Compared with other typhoons in Hainan and Taiwan, the convective precipitation of Typhoon In-Fa shows a larger (smaller) raindrop concentration than that of Taiwan (Hainan), while smaller raindrop diameter than both Hainan and Taiwan. Moreover, the typhoon convective precipitation measured in In-Fa is more maritime-like than precipitation in Taiwan. Based on a great number of surface disdrometer observational data, the GPM precipitation products were further validated for both rain types, and a series of native quantitative precipitation estimation relations, such as Z–R and R–Dm relations were derived to improve the typhoon rainfall retrieval for both ground-based radar and spaceborne radar.

Lake ice phenology variations and influencing factors of Selin Co from 2000 to 2020

湖冰作为湖泊-大气界面能量和物质交换的结果，其物候变化对揭示区域气候变化和湖泊响应过程具有重要意义.本研究基于2000-2020年色林错边界矢量数据、Terra MODIS和Landsat TM/ETM+/OLI遥感影像并结合气象数据及湖泊资料，利用RS和GIS手段综合分析了色林错湖冰物候变化特征及其影响因素.结果表明：①色林错于11月下旬到12月上旬开始冻结，在12月下旬到1月上旬完全冻结，封冻时间约一个月左右.湖冰在每年的3月下旬到4月上旬开始消融，历经半个月左右，至4月下旬完全消融.②近20 a来，色林错开始冻结日期整体呈现逐渐推迟的波动趋势，推迟率约为11.3 d/10 a.湖冰冻结期呈缩短趋势；湖冰存在期整体上呈缩短趋势，缩短率为13.5 d/10 a.③色林错冻结先从北部和东部湖岸处开始逐渐向中部湖心处扩张，解冻时湖冰中心先破裂，向湖岸边逐渐消融.④色林错湖冰物候受气候和湖泊自身理化性质综合影响.冬半年平均气温是影响湖冰消融和封冻期的关键因素；风速和降水对湖冰的冻结和消融亦有一定影响.近20 a来，随着色林错面积扩张、浑浊度上升及透明度下降，湖冰开始冻结时间推迟，湖冰封冻期缩短.全球变暖背景下，包含色林错在内的青藏高原湖泊有加速扩张趋势，本研究结果可为理解变化环境下湖冰物候信息的气候指示意义及湖泊反馈过程提供参考.;As a result of energy and material exchange at the lake-atmosphere interface, the variations of lake ice phenology are of great significance for indicating regional climate change and lake response process. Based on the boundary data of Selin Co, some multi-source remote sensing (RS) datasets including Terra MODIS and Landsat TM/ETM+/OLI product, combined with meteorological records and lake data to analyze spatiotemporal variations of ice phenology of Selin Co and its relationship with climate factors and physical and chemical factors between 2000 and 2020 by applying both RS and GIS technology. The main research conclusions are as follows:(1) Freeze-up start (FUS) and freeze-up end (FUE) of lake ice appears in late November-early December, and late December-early January, respectively. The duration of lake ice freeze-up is about a month. The time of break-up start (BUS) and break-up end (BUE) of lake ice appears in late March-early April, and late April, respectively. The duration of lake ice break-up is about half a month. (2) Data show that FUS dates of lake ice have been delayed at a rate of 11.3 d/10 a from 2000 to 2020. FUD (freeze-up duration) time of lake ice showed an increasingly shortening trend. Ice cover duration had been shortened at a rate of 13.5 d/10 a. (3) Selin Co can be characterized by opposite spatial patterns in both freeze-up and break-up processes. Lake ice freezes from the northern and eastern lakeshore and gradually expands to the center of lake. Instead, lake ice break-up begins in the center of the lake. (4) Ice phenology of Selin Co is influenced by climate and physico-chemical factors of the lake itself. The average temperature of winter half-year (between November and the following April) plays a dominant role in ice phenology variations of Selin Co. Wind speed and precipitation both also some influences on the formation and melting of lake ice cover and also cannot be neglected. In the recent 20 years, with the expansion of Selin Co area, the increase of turbidity and the decrease of water clarity, the freezing dates of lake ice were gradually delayed. Under the background of global warming, the area expansion of lakes on the Tibetan Plateau, including Selin Co, has accelerated. The results of this study can provide a reference for understanding the climate indicator significance of lake ice phenology information and the feedback process of lakes under the changing environment.

Numerical study of asymmetric breakup behavior of bubbles in Y-shaped branching microchannels

Microfluidic technology based on microchannel two-phase flow has been widely used. The precise control of the bubble or droplet size in the channel plays a crucial role in designing the microfluidic systems. In this work, the bubble breakup behavior in Y-shaped microchannel is reconstructed based on the volume of fluid method (VOF), and the effects of bubble dimensionless size (1.2–2.7), outlet flow ratio (1–4) and main channel Reynolds number (100–600) on the bubble breakup behavior are systematically investigated. The bubble asymmetric breakup process is found to be divided into three stages: extension stage, squeeze stage, and rapid pinch-off stage. In the case of small initial bubble size or relatively high outlet flow rate, the bubble does not break, but only experiences the extension stage and the squeezing stage. Four flow patterns of bubble breakup are further revealed for the bubbles with different sizes and outlet flow ratios: tunnel-tunnel breakup, obstruction-obstruction breakup, tunnel-obstruction breakup, and non-breakup. With the increase of outlet flow ratio, the breakup process of the bubble gradually becomes asymmetrical, and the flow pattern shifts along the tunnel-tunnel breakup and the obstruction-obstruction breakup, gradually turns toward the tunnel-obstruction breakup and non-breakup. On this basis, the critical flow ratio of bubble breakup and the variation of daughter bubble volume ratio with outlet flow ratio are obtained for different Reynolds numbers and initial bubble sizes, and the corresponding criterion correlation equation is refined, which can provide theoretical guidance for accurately regulating the daughter bubble size after breakup.

Identification of free-stream and boundary layer correlating events in free-stream turbulence-induced transition

Boundary layer receptivity to free-stream disturbances plays a crucial role in forming coherent structures, whose breakup drives the laminar to turbulent flow transition. In the present work, an extended proper orthogonal decomposition (E-POD) procedure is applied to particle image velocimetry (PIV) data to identify correlating events between the free-stream velocity field and transitional boundary layers for flow configurations typical of low-pressure turbine blades. Data collected in two wall-parallel planes were ordered along the homogeneous spanwise coordinate so that the dominant POD coefficients provide the most energetic spanwise wavelengths in the free-stream and the near-wall regions. Then, the cross-correlation matrix of the POD spanwise coefficients computed independently in both measuring planes directly identifies the free-stream scales showing the highest degree of correlation with the boundary layer structures. Low-order reconstructions of the original PIV data show that the most correlating events are directly linked to the formation and the successive breakup process of streaky structures. Otherwise, larger-scale structures which are not involved in the transition process are filtered out. Interestingly, free-stream disturbances appear as organized wave packets with significant elongation in the streamwise direction when the velocity fields are reconstructed considering only the most correlating modes. The effect due to the Reynolds numbers, the pressure gradient, and the free-stream turbulence variation on the free-stream modes affecting the formation of coherent structures in the boundary layer is discussed in the paper.

Fragmentation and atomization characteristics of near-orifice liquid jet under transverse gas film

In order to understand the fragmentation and atomization characteristics of the liquid jet in transverse gas film, a pintle injection element using air and water as simulants is designed. The two-phase flow large eddy simulation and backlight imaging are used to study the liquid-jet breakup process and spray-field dynamic characteristics in the nearorifice area of pinte injection element under the atmospheric environment. The primary fragmentation process of the liquid jet dominated by surface wave is obtained by large eddy simulation, which reveals the establishment process of the spray field in near-orifice area of the gas-liquid pintle injector. After the subsonic airflow leaves the slit, it expands and accelerates into supersonic state. Then the deceleration and pressurization phenomenon occurs once the supersonic airflow passes through the detached bow shock upstream of the liquid jet. The liquid jet bends downstream due to the difference in pressure between upstream and downstream, and the Rayleigh-Taylor (R-T) unstable surface wave appears on the jet windward surface. As the surface wave develops, the penetration of the wave trough by airflow causes the continuous liquid jet to fragment. Proper orthogonal decomposition (POD) method can effectively reconstruct spray snapshot. The POD mode shows that the low-frequency spray oscillation in near-orifice area is caused by the overall expansion/contraction process of the spray field, while the high-frequency one is due to the “impact wave” movement of the liquid block or liquid mist group on the windward side. The latter is produced by the R-T unstable surface wave before the jet breakup, and can be categorized as traveling wave structure. The dimensionless traveling wave wavelength has a power-law relationship with Weber number.

High-speed visualization measurement for breakup process of liquid metal with solidification

In recent years, Additive Manufacturing (AM) technology such as 3D printing has attracted much attention. In order to produce high-quality metal powders as printing materials, it is necessary to elucidate the phenomena of liquid metal splitting accompanied by solidification, which is manifested in the powder manufacturing process. So far, various experiments have been conducted on the atomization method, but the mechanism for determining powder properties has not been clarified. In particular, there is insufficient knowledge about the phenomenon of molten metal splitting along with solidification. Therefore, in this study, we investigate the breakup process of a single ligament of 42Sn-58Bi, which is a kind of fusible alloy with a melting point of 139 ℃. A high-speed camera is used to visualize the pinch-off process of the ligament. The variation of the neck diameter of the ligament is traced during the fragmentation process. When the initial temperature is high, we found that the neck diameter thins down following a power law of 2/3, corresponding to the trend derived from capillary time scale. On the other hand, as the initial temperature gets lower, the neck diameter becomes thinner than that predicted by the capillary time scale just before breaking up, which is attributed to the influence of solidification.

Effects of fuel properties and aerodynamic breakup on spray under flash boiling conditions

• Sprays of four single component fuels under flash boiling conditions were studied. • Spray collapses at R p of 0.28 for isooctane, hexane and ethanol, and 0.18 for pentane. • Ethanol has relatively larger near-field angle, far-field angle and SMD. • Aerodynamic breakup still plays an important role under low flash boiling conditions. • Isooctane, hexane and pentane under R p of 0.28 show a similar SMD value of 10 µm. The main purpose of this work is to conduct detailed comparisons of spray behavior among four important components of gasoline and to investigate the effects of fuel properties and aerodynamic breakup on spray behavior under flash boiling conditions. Isooctane, hexane, pentane, and ethanol were used as test fuels. Pressure ratio ( R p ) was used as an indicator for the superheated degree and varied from 0.14 to 1.1 by adjusting the ambient pressure. Both Diffused Backlight Imaging (DBI) and Phase Doppler Anemometry (PDA) measurements were used to obtain macroscopic and microscopic characteristics of sprays. Four dimensionless numbers were used to evaluate the aerodynamic breakup processes. The results showed that as the reduction of R p , the flash boiling intensity increased, leading to dramatic spray morphology changes and smaller droplet size, regardless of fuel type. Spray plumes merged into the spray center when lowering R p from 1.0. Spray collapsed at an R p of 0.28 for isooctane, hexane, and ethanol, and at an R p of 0.18 for pentane. Fuel properties also had significant effects on spray behaviors. Spray with pentane had the smallest penetration length, and a dramatic far-field angle reduction was observed at R p between 0.2 and 0.4, due to its higher vapor pressure and lower latent heat of vaporization. Under the same R p , ethanol sprays had relatively larger near-field angles, far-field angles, and Sauter mean diameter (SMD), due to its high latent heat of vaporization. All the dimensionless numbers showed that the spray with pentane had the largest aerodynamic breakup intensity, followed by hexane and isooctane, while ethanol had the lowest aerodynamic breakup intensity under the tested conditions. Aerodynamic breakup still played an important role under low flash boiling intensity conditions ( R p over 0.8). Microscopic results showed that SMD of isooctane, hexane, and pentane under an R p of 0.28 had a similar value of 10 µm.

Analysis of Flow State in Venturi Tube for Fine Bubble Generation

Bubbles with a diameter of 100 μm or less are called fine bubbles, which have been applied widely in the industrial fields due to its strong detergent, bactericidal effect, and bioactivity. Ballast water is the seawater to stabilize the center of gravity of a ship. In water purification, a technology has been developed to reduce the dissolved oxygen (D.O.) concentration and pH by mixing water with gas to deaerate D.O. and dissolving CO2, but gas is mixed with such water. When purifying water quality, it is important to reduce the bubble diameter when gas is mixed with water, and to improve the efficiency of dissolving CO2 by degassing D.O.. In this research, a method to improve the mixing efficiency of ballast water treatment equipment by improving the fine bubble generation efficiency of the venturi tube is investigated by experiment and simulation analysis. We design venturi tubes with different divergent angles and investigate the optimized geometric combination by experiment and numerical simulation for improving the fine bubble size and volume. From the experimental results, we find that in the nozzles with small divergent angles the low pressure region becomes longer and the pressure recovery slows down, which promote the breakup of bubbles. The simulation results show that in the nozzles with the divergent angles of 15°and 20°, the affection region of gas-liquid two-phase flow becomes larger, and the concentration of bubbles near the wall or near the center of the nozzle will promote the breakup process of bubbles.

Study on particle cluster behavior in the multistage circulating fluidized bed

Particle clusters play a significant role in gas-solid flow systems. Cluster motions are experimentally studied in a multistage circulating fluidized bed. Cluster characteristics including spatial distribution, breakup process, and size are discussed. Dynamic parameters (frequency, duration, and time fraction) are also obtained to characterize cluster behavior by employing the digital image analysis method. The results show that cluster motions gradually weaken along radial and axial directions in the enlarged section. Cluster breakup tends to increase in the enlarged section due to gas turbulence and cluster collision. Cluster frequency, duration, and time fraction decrease with the increasing gas velocity but increase with the increasing solid mass flux. Compared with the conventional riser, cluster size reduces in the enlarged section. Furthermore, the analysis results from cluster dynamic parameters indicate that cluster motions are restricted under the low solid loading.

Secondary droplet size distribution upon breakup of a sub-milimeter droplet in high speed cross flow

The droplet breakup behaviors under the action of shock wave are frequently observed in liquid-fueled detonation-based engines. In this work, the secondary droplet size distribution after the breakup of a sub-milimeter droplet under high velocity cross flow conditions (the gas flow velocity is 105.64 m/s) was experimentally determined on a horizontal shock tube with the developed digital in-line holography technique. During the droplet breakup process, the spatial (two-dimensional, three-dimensional) and droplet size distributions of two characteristic stages (early and late stages) were majorly concerned based on the reconstructed droplet cloud field. At the early stage, the liquid-mist field appeared as the barrel shape, and the probability distribution of the droplet number in the cross-stream direction presented as “M shape”. While the secondary droplet cloud field appeared as the conical shape, and the probability distribution presented as the parabolic shape at the late stage. Both the probability distribution of the droplet number along the flow direction increased firstly then decreased at the early and late stages with the increasing of distance. In addition, the peak position of the droplet number probability distribution also changed with time. The secondary droplets mainly distributed in the range of 0∼20 μm for the early and late stages, and its number accounted for more than 93%. Meanwhile, the corresponding volume probabilities changed from 12% to 72%, due to the consistent stripping process. In addition, the droplet size distribution could be well described by the log-normal and root-normal distribution curves at both stages. The study of the spatial and droplet size distributions is believed to be of importance for corresponding droplet breakup modeling.

Novel glass capillary microfluidic devices for the flexible and simple production of multi-cored double emulsions

HypothesisDouble emulsions with many monodispersed internal droplets are required for the fabrication of multicompartment microcapsules and tissue-like synthetic materials. These double emulsions can also help to optically resolve different coalescence mechanisms contributing to double emulsion destabilization. Up to date microfluidic double emulsions are limited to either core–shell droplets or droplets with eight or less inner droplets. By applying a two-step jet break-up within one setup, double emulsion droplets filled with up to several hundred monodispersed inner droplets can be achieved. ExperimentsModular interconnected CNC-milled Lego®-inspired blocks were used to create two separated droplet break-up points within coaxial glass capillaries. Inner droplets were formed by countercurrent flow focusing within a small inner capillary, while outer droplets were formed by co-flow in an outer capillary. The size of inner and outer droplets was independently controlled since the two droplet break-up processes were decoupled. FindingsWith the developed setup W/O/W and O/W/O double emulsions were produced with different surfactants, oils, and viscosity modifiers to encapsulate 25–400 inner droplets in each outer drop with a volume percentage of inner phase between 7% and 50%. From these emulsions monodispersed multicompartment microcapsules were obtained. The report offers insights on the relationship between the coalescence of internal droplets and their release.

Опыт разработки методики долгосрочного прогноза сроков вскрытия ото льда рек бассейна р. Вятки

An attempt is made to develop a method for long-term forecasting of the ice breakup time for the Vyatka River basin, to identify the impact of the distribution of sea surface temperature and geopotential height in the informative regions at the levels H100 and H500 over the Northern Hemisphere on the river ice breakup. The location and boundaries of the informative regions in the fields of H100 and H500 were revealed by the discriminant analysis, the EOF expansion coefficients of the fields of anomalies of monthly mean values of H100 and H500 for January and February and the anomalies of monthly mean sea surface temperature in the North Atlantic and Northwest Pacific were used as potential predictors. The stepwise regression analysis allowed deriving good and satisfactory (S/σ = 0.45–0.73) complex prognostic equations for forecasting the ice breakup time for the Vyatka River basin. The essential influence of H100 and H500 geopotential height fields and the spatial distribution of sea surface temperature anomalies in the North Atlantic and Northwest Pacific in January and February on the river ice breakup time is revealed. It is proposed to improve the method by considering the impact of air temperature, maximum ice thickness per winter, and other indirect characteristics on the processes of river ice breakup in the Vyatka River basin. Keywords: ice regime, long-range forecast, river ice breakup, expansion coefficients, geopotential height fields, spring ice phenomena, energy-active zones of the oceans, complex prognostic equation