When the process of extraction of oil from an offshore oilfield enters the advanced stages,the water content in the extracted fluid can be above 90%.The water quality is complex with many types of pollutants and highl...When the process of extraction of oil from an offshore oilfield enters the advanced stages,the water content in the extracted fluid can be above 90%.The water quality is complex with many types of pollutants and highly emulsified water.Therefore,a key consideration in the production process of offshore oilfields is the efficient and economical treatment of the oil-containing produced water to make it suitable for discharge and recover oil pollutants.In this study,we developed a hydrophilic and hydrophobic combined fiber coalescence separator with composite fiber shapes using fiber induction and X/Uweaving.The separator is designed based on experimental observations of the mechanism of structure coalescence in the physical oil removal method.A pilot test was performed on an oil exploration platform in the Bohai Sea.At the designed flow rate,the separator reduced the total concentration of petroleum in the produced water from 2000 to 3000 mg/L to below 60 mg/L,with an average oil removal efficiency of 98.24%.Furthermore,it effectively reduced the number of organic compounds present in the water from 120 to 17 and removed 70% of the SS.The test results show that the proposed device can be used fr produced-water treatment on offshore platforms.展开更多
The mechanism of microdroplet coalescence is a fundamental issue for droplet-based microfluidics. We developed an asymmetric expansion(a rectangular groove) along one side of a microchannel to achieve multiple-microdr...The mechanism of microdroplet coalescence is a fundamental issue for droplet-based microfluidics. We developed an asymmetric expansion(a rectangular groove) along one side of a microchannel to achieve multiple-microdroplet trapping, collision, and coalescence. Compared with reported symmetric expansions, this asymmetric groove could easily trap microdroplets and control two or three microdroplet coalescences precisely without a requirement for temporal and spatial synchronization. To reveal the mechanisms of multiple-droplet coalescences in a groove, we observed five different coalescence patterns under different flow conditions. Moreover, we characterized the flow behavior quantitatively by simulating the velocity vector fields in both the microdroplets and continuous phase, finding good agreement with experiments. Finally, a map of coalescence forms with different capillary numbers(0.001 < C a < 0.016) and flow ratios(0.1 < e < 0.9) was obtained. The results could provide a useful guidance for the design and application of droplet-based microfluidic devices.展开更多
Discharging untreated oily wastewater into the environment disrupts the ecological balance,which is a global problem that requires urgent solutions.Superhydrophilic and superoleophilic fibrous medium(FM)effectively se...Discharging untreated oily wastewater into the environment disrupts the ecological balance,which is a global problem that requires urgent solutions.Superhydrophilic and superoleophilic fibrous medium(FM)effectively separated oil–water emulsion as it was hydrophobic underwater.But its separation efficiencies(SEs)first increased to 98.9%,then dropped to 97.6%in 10 min because of oil-fouling.To tackle this problem,FM deposited with 0%–10%silica nanoparticle(NPsFMs),then coated by fluorocarbon polymer(X-[CH_(2)CH_(2)O]nCH_(2)CH_(2)O-Y-NH-COOCH_(2)C4F9)(FCNPs FMs),was used to enhance its roughness and regulate its initial wettability to improve the anti-fouling property.FCFM and FCNPs FMs were hydrophobic and oleophobic in air and oleophobic underwater.Their water contact angles,oil contact angles and oil contact angles were 115.3°–121.1°,128.8°–136.5°,and 131.6°–136.7°,respectively,meeting the requirement of 90°–140°for coalescence separation.FCNPs FM-5 had the best separation performance with a constant value of 99.8%in 10 min,while that of FCNPs FM-10 slightly decreased to 99.5%.Theoretical released droplet(TRD)diameter,calculated by the square root of the product of pore radius and fiber diameter,was used for the evaluation of coalescence performance.Analyzed by two ideal models,TRD diameter and fiber diameter showed a parabola type relationship,proving that the separation efficiency was a collaborative work of wettability,pore size and fiber diameter.Also,it explained the SEs reduction from FCNPs FM-5 to FCNPs FM-10 was revelent to the three parameters.Moreover,FCNPsFMs effectively separated emulsions stabilized by cationic surfactant CTAB(SEs:97.3%–98.4%)and anionic surfactant SDBS(SEs:91.3%–93.4%).But they had an adverse effect on nonionic surfactant Tween-80 emulsion separation(SEs:94.0%–71.76%).Emulsions made by diverse oils can be effectively separated:octane(SEs:99.4%–100%),rapeseed oil(SEs:97.3%–98.8%),and diesel(SEs:95.2%–97.0%).These findings provide new insights for designing novel materials for oil–water separation by coalescence mechanism.展开更多
Bubble coalescence reduces specific area and weakens the work performance of bubble column. The bubble coalescence near gas sparger which is caused mainly by bubble growing is different from the ones occurring in majo...Bubble coalescence reduces specific area and weakens the work performance of bubble column. The bubble coalescence near gas sparger which is caused mainly by bubble growing is different from the ones occurring in major liquid. Bubble coalescence efficiency near gas sparger is influenced by many factors including sparger configuration, gas flow rate, bubble deformation, solution composition, etc. This work has conducted a set of visual experiments to study the coalescence characteristics near multi-orifice plate. The experiment parameters cover a wide range of conditions including large scope of gas flow rate,different kinds of solution and orifice configurations. The experimental results suggest that coalescence time is applicable to reflect the influence of the pitch of orifices and gas flow rate on bubble coalescence efficiency. As the number of orifices increases, bubble coalescence efficiency is reduced by the disturbance from the bubbles at adjacent orifices. A hindering coefficient is used to consider the hindering effect of additives on bubble coalescence efficiency. Finally a new calculation expression is established to predict bubble coalescence efficiency near multi-orifice plate whose fundamental form is based on the logistic curve of binary response. The calculated values that refer to this calculation expression are well consistent with the experimental results.展开更多
A novel and high-efficiency coalescence membrane enhanced by nano-sized polyvinylidene fluoride(PVDF)nanofibers based on polyester(PET)substrate was fabricated using electrospinning method.The properties of the electr...A novel and high-efficiency coalescence membrane enhanced by nano-sized polyvinylidene fluoride(PVDF)nanofibers based on polyester(PET)substrate was fabricated using electrospinning method.The properties of the electrospun nanofibers such as roughness and surface morphology greatly affected the oil droplet interception efficiency and surface wettability of the membrane.A series of coalescence units were prepared with different layers of nanofibrous membrane and the separation efficiencies at different initial concentrations,flow rates,and oil types were tested.It is very interesting that the obtained nanofibrous membrane exhibited superoleophilicity in air but poor oleophilicity under water,which was beneficial to the coalescence process.The coalescence unit with four membrane layers had excellent performances under different initial concentrations and flow rates.The separation efficiency of the 4-layers unit remained above 98.2%when the initial concentration reached up to 2000 mg·L-1.Furthermore,the unit also exhibited good performance with the increasing oil density and viscosity,which is promising for large-scale oil wastewater treatment.展开更多
Based on the volume of fluid(VOF) method, we conduct a numerical simulation to study the hydrodynamic binary coalescence of droplets under air flow in a hydrophobic rectangular microchannel. Two distinct regimes, coal...Based on the volume of fluid(VOF) method, we conduct a numerical simulation to study the hydrodynamic binary coalescence of droplets under air flow in a hydrophobic rectangular microchannel. Two distinct regimes, coalescence followed by sliding motion and that followed by detaching motion, are identified and discussed. Additionally, the detailed hydrodynamic information behind the binary coalescence is provided, based on which a dynamic mechanical analysis is conducted to reveal the hydrodynamic mechanisms underlying these two regimes. The simulation results indicate that the sliding motion of droplets is driven by the drag force and restrained by the adhesion force induced by the interfacial tension along the main flow direction. The detachment(i.e., upward motion) of the droplet is driven by the lift force associated with an aerodynamic lifting pressure difference imposed on the coalescent droplet, and also restrained by the adhesion force perpendicular to the main flow direction. Especially, the lift force is mainly induced by an aerodynamic lifting pressure difference imposed on the coalescent droplet. Two typical regimes can be quantitatively recognized by a regime diagram depending on Re and We. The higher Re and We respectively lead to relatively larger lift forces and smaller adhesion forces acting on the droplet, both of which are helpful to detachment of the coalesced droplet.展开更多
Novel preparation method of microencapsules was developed on the basis of the liquid coalescence method followed by phase separation. Oil droplets of limonene dissolving expanded polystyrene as a shell material were f...Novel preparation method of microencapsules was developed on the basis of the liquid coalescence method followed by phase separation. Oil droplets of limonene dissolving expanded polystyrene as a shell material were forced to collide and coalesce with the Isopar oil droplets of core material in the continuous wates phase. When two kinds of oil droplets are collided and coalesced with each other, expanded polystyrene dissolved in the limonene oil may be phase-separated in the oil droplets newly formed to form the microcapsule shell, because the Isopar oil was a poor solvent for expanded polystyrene but a good solvent for the limonene oil. In the experiment, the diameter (or number) of limonene oil droplets dissolving expanded polystyrene was mainly changed, because the coalescence frequency between the droplets is strongly dependent on the number of droplets. Favorable core shell types of microcapsules with the shell thickness from 1.0 to 5.0 μm were able to be prepared under all the experimental conditions adopted here.展开更多
1 INTRODUCTIONThe rate of coalescence between bubbles is important to the stability of foams,the mo-bility control in tertiary oil recovery,and a broad class of operations in which gas orvapor is the dispersed phase.T...1 INTRODUCTIONThe rate of coalescence between bubbles is important to the stability of foams,the mo-bility control in tertiary oil recovery,and a broad class of operations in which gas orvapor is the dispersed phase.Therefore,it is very important that the mechanism of thecoalescence process be understood,so that the effects of the physical properties oncoalescence can be assessed.展开更多
A fast coalescence mechanism is proposed to account for the wall effect on the formation of gradient morphologyin phase separated polymer blends during quiescent annealing. The existence of solid wall with high polari...A fast coalescence mechanism is proposed to account for the wall effect on the formation of gradient morphologyin phase separated polymer blends during quiescent annealing. The existence of solid wall with high polarity is believed tochange the potential field around the dispersed particles near the wall. This additional potential interaction between the solidwall and the dispersed particles causes faster coalescence of the dispersed particles near the wall than in the bulk. Thegradient phase morphology thus formed can be predicted by combining the wall-particle interaction and the touch-coalescence mechanism. The effect of interfacial tension on the gradient morphology is also discussed.展开更多
Droplet coalescence in liquid steel was carefully investigated through observations of the distribution pattern of inclusions in solidified steel samples. The process of droplet coalescence was slow, and the critical ...Droplet coalescence in liquid steel was carefully investigated through observations of the distribution pattern of inclusions in solidified steel samples. The process of droplet coalescence was slow, and the critical Weber number(We) was used to evaluate the coalescence or separation of droplets. The relationship between the collision parameter and the critical We indicated whether slow coalescence or bouncing of droplets occurred. The critical We was 5.5, which means that the droplets gradually coalesce when We ≤ 5.5, whereas they bounce when We > 5.5. For the carbonate wire feeding into liquid steel, a mathematical model implementing a combined computational fluid dynamics(CFD)–discrete element method(DEM) approach was developed to simulate the movement and coalescence of variably sized droplets in a bottom-argon-blowing ladle. In the CFD model, the flow field was solved on the premise that the fluid was a continuous medium. Meanwhile, the droplets were dispersed in the DEM model, and the coalescence criterion of the particles was added to simulate the collision-coalescence process of the particles. The numerical simulation results and observations of inclusion coalescence in steel samples are consistent.展开更多
In this paper,dynamic caustic method is applied to analyze the blast-induced crack propagation and distribution of the dynamic stress field around an empty circular hole in polymethyl methacrylate(PMMA)material under ...In this paper,dynamic caustic method is applied to analyze the blast-induced crack propagation and distribution of the dynamic stress field around an empty circular hole in polymethyl methacrylate(PMMA)material under delayed ignition blasting loads.The following experimental results are obtained.(1)In directional-fracture-controlled blasting,the dynamic stress intensity factors(DSIFs)and the propagation paths of the blast-induced cracks are obviously influenced by the delayed ignition.(2) The circular hole situated between the two boreholes poses a strong guiding effect on the coelesence of the cracks,causing them to propagate towards each other when cracks are reaching the circular hole area.(3)Blast-induced cracks are not initiated preferentially because of the superimposed effect from the explosive stress waves on the cracking area.(4) By using the scanning electron microscopy(SEM)method,it is verified that the roughness of crack surfaces changes along the crack propagation paths.展开更多
The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same vi...The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratioηof two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when1<η<6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time(Tdr)and critical capillary number(Ca)c)were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size difference and viscosity ratio of the two droplets:Tdr~(ld)^(0.25±0.04)and Tdr~(η)^(﹣0.1±0.02).For droplet coalescence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac=0.48λ^(0.26)l^(﹣2.64),while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac=0.11η^(﹣0.07)ls^(﹣2.23)l^(0.16)_(d).展开更多
A computational study was carried out on bubble dynamic behaviors and bubble size distributions in a pressurized lab-scale gas-solid fluidized bed of Geldart A particles.High-resolution 3-D numerical simulations were ...A computational study was carried out on bubble dynamic behaviors and bubble size distributions in a pressurized lab-scale gas-solid fluidized bed of Geldart A particles.High-resolution 3-D numerical simulations were performed using the two-fluid model based on the kinetic theory of granular flow.A finegrid,which is in the range of 3–4 particle diameters,was utilized in order to capture bubble structures explicitly without breaking down the continuum assumption for the solid phase.A novel bubble tracking scheme was developed in combination with a 3-D detection and tracking algorithm(MS3 DATA)and applied to detect the bubble statistics,such as bubble size,location in each time frame and relative position between two adjacent time frames,from numerical simulations.The spatial coordinates and corresponding void fraction data were sampled at 100 Hz for data analyzing.The bubble coalescence/break-up frequencies and the daughter bubble size distribution were evaluated by using the new bubble tracking algorithm.The results showed that the bubble size distributed non-uniformly over cross-sections in the bed.The equilibrium bubble diameter due to bubble break-up and coalescence dynamics can be obtained,and the bubble rise velocity follows Davidson’s correlation closely.Good agreements were obtained between the computed results and that predicted by using the bubble break-up model proposed in our previous work.The computational bubble tracking method showed the potential of analyzing bubble motions and the coalescence and break-up characteristics based on time series data sets of void fraction maps obtained numerically and experimentally.展开更多
The interaction of a falling drop(diluted aqueous solution of ink in various concentrations)with a target fluid(partially degassed tap water)has been tracked by means of high-resolution video recording and photography...The interaction of a falling drop(diluted aqueous solution of ink in various concentrations)with a target fluid(partially degassed tap water)has been tracked by means of high-resolution video recording and photography.The experimental setup has carefully been prepared in order to preserve the axial symmetry of initial conditions.Three regimes of interaction have been identified accordingly(depending on the drop velocity as controlled by the distance of fall):rapid droplet coalescence,rebound with the conservation of the drop volume and shape,and partial coalescence.Previous findings are recovered and confirmed,and enriched with heretofore unseen observations of complex partial coalescence.An extensive set of data is reported to support understanding of the observed dynamics and their repeatability and reproducibility.The overall study has been carried out with the express intent to spur the future development of detailed mathematical models and numerical methods suited for this kind of problems.展开更多
Grain coalescence has been applied in many areas of nanofabrication technology, including modification of thinfilm properties, nanowelding, and self-assembly of nanostructures. However, very few systematic studies of ...Grain coalescence has been applied in many areas of nanofabrication technology, including modification of thinfilm properties, nanowelding, and self-assembly of nanostructures. However, very few systematic studies of selfassembly using the grain coalescence, especially for threedimensional(3D) nanostructures, exist at present. Here, we investigate the mechanism of plasma triggered grain coalescence to achieve the precise control of nanoscale phase and morphology of the grain coalescence induced by exothermic energy. Exothermic energy is generated through etching a silicon substrate via application of plasma. By tuning the plasma power and the flow rates of reactive gases, different etching rates and profiles can be achieved, resulting in various morphologies of grain coalescence. Balancing the isotropic/anisotropic substrate etching profile and the etching rate makes it possible to simultaneously release 2D nanostructures from the substrate and induce enough surface tension force,generated by grain coalescence, to form 3D nanostructures.Diverse morphologies of 3D nanostructures have been obtained by the grain coalescence, and a strategy to achieve self-assembly, resulting in desired 3D nanostructures, has been proposed and demonstrated.展开更多
Partial coalescence is a complicated flow phenomenon.In the present study,the coalescence process is simulated with the volume of fluid(VOF)method.The numerical results reveal that a downward high-velocity region play...Partial coalescence is a complicated flow phenomenon.In the present study,the coalescence process is simulated with the volume of fluid(VOF)method.The numerical results reveal that a downward high-velocity region plays a significant role in partial coalescence.The high-velocity region pulls the droplet downward continuously which is an important factor for the droplet turning into a prolate shape and the final pinch-off.The shift from partial coalescence to full coalescence is explained based on the droplet shape before the pinch-off.With the droplet impact velocity increasing,the droplet shape will get close to a sphere before the pinch-off.When the shape gets close enough to a sphere,the partial coalescence shifts to full coalescence.The effect of film thickness on the coalescence process is also investigated.With large film thickness,partial coalescence happens,while with small film thickness,full coalescence happens.In addition,the results indicate that the critical droplet impact velocity increases with the increase of surface tension coefficient but decreases with the increase of viscosity and initial droplet diameter.And there is a maximum critical Weber number with the increase of surface tension coefficient and initial droplet diameter.展开更多
Fractal interpolation function (FIF) is a special type of continuous function which interpolates certain data set and the attractor of the Iterated Function System (IFS) corresponding to a data set is the graph of the...Fractal interpolation function (FIF) is a special type of continuous function which interpolates certain data set and the attractor of the Iterated Function System (IFS) corresponding to a data set is the graph of the FIF. Coalescence Hidden-variable Fractal Interpolation Function (CHFIF) is both self-affine and non self-affine in nature depending on the free variables and constrained free variables for a generalized IFS. In this article, graph directed iterated function system for a finite number of generalized data sets is considered and it is shown that the projection of the attractors on is the graph of the CHFIFs interpolating the corresponding data sets.展开更多
Directional solidification methods are being used f or in-situ production of metallic immiscible composites. A quantitative understa nding of the dynamic behavior and growth kinetics of the nucleated second phase duri...Directional solidification methods are being used f or in-situ production of metallic immiscible composites. A quantitative understa nding of the dynamic behavior and growth kinetics of the nucleated second phase during solidification is necessary to produce homogeneous dispersion in solidifi ed composites. This paper presents a mathematical model for describing the grow th of nucleated dispersed phase in the two-liquid phase region ahead of the sol idification front and the entrapment of these droplets by the moving solid-liqu id interface in vertical unidirectional solidification systems. The model has t wo components. A macro-heat transfer model for describing the temperature prof iles and the rate of advance of the solidification front. The dynamic behavior and coalescence and growth of nucleated droplets in the two-liquid phase region under the influence of effective gravity and thermocapillary forces were repres ented through the solution the droplet momentum and mass conservation equations in particle space. These two components of the models were coupled through a sp ecial algorithm for tracking the particle location and size with respect to movi ng solidification front in the solidification time scale. The model is used to study the particle size distribution in unidirectional solidified Zn-Bi hypermo notectic alloys at reduced gravity conditions. It has been found that the parti cle size and distribution in the solidified alloy depends on solidification rate and the ratio of effective gravity to thermocapillary forces. It was also foun d that uniform dispersion could only be obtained in a very narrow range of effec tive gravity values near zero gravity. The model predictions were compared agai nst experimental measurements obtained at different effective gravity conditions in a novel unidirectional solidification apparatus that uses electromagnetic fo rces to modulate gravitational forces. The model was found to reasonably predic t the experimentally measured particle size and distribution over the entire ran ge of effective gravity investigated as well as gravity conditions for settling and flotation of the second phase during solidification. The practical signific ance of these findings will be discussed.展开更多
In shallow crust, faults often consist of a series of secondary fractures. Based on experimental micro features in rock mechanics and macro structures in field, the progressive coalescence model, in which a brittle fa...In shallow crust, faults often consist of a series of secondary fractures. Based on experimental micro features in rock mechanics and macro structures in field, the progressive coalescence model, in which a brittle fault evolved from micro crack, stylolitic fracture, large fault to super large fault, is founded, and its forming mechanism is discussed by variation of stress field. At last the undulation, branches of faults and the phenomenon that the angle between fractures and the principal stress axis decreases gradually are explained by the G.C.Sih model.展开更多
基金This work is supported by the National Natural Science Foundation of China(Grant Nos.52025103).
文摘When the process of extraction of oil from an offshore oilfield enters the advanced stages,the water content in the extracted fluid can be above 90%.The water quality is complex with many types of pollutants and highly emulsified water.Therefore,a key consideration in the production process of offshore oilfields is the efficient and economical treatment of the oil-containing produced water to make it suitable for discharge and recover oil pollutants.In this study,we developed a hydrophilic and hydrophobic combined fiber coalescence separator with composite fiber shapes using fiber induction and X/Uweaving.The separator is designed based on experimental observations of the mechanism of structure coalescence in the physical oil removal method.A pilot test was performed on an oil exploration platform in the Bohai Sea.At the designed flow rate,the separator reduced the total concentration of petroleum in the produced water from 2000 to 3000 mg/L to below 60 mg/L,with an average oil removal efficiency of 98.24%.Furthermore,it effectively reduced the number of organic compounds present in the water from 120 to 17 and removed 70% of the SS.The test results show that the proposed device can be used fr produced-water treatment on offshore platforms.
基金supported by the Beijing Municipal Natural Science Foundation (Grant 7152012)the General Program of Science and Technology Development Project of the Beijing Municipal Education Commission (Grant KM201610005002)+2 种基金the National Natural Science Foundation of China (Grant 11572013)the China Scholarship Council (Grant 201406545031)the Training Plan of New Talent of Beijing University of Technology (Grant 2015-RX-L02)
文摘The mechanism of microdroplet coalescence is a fundamental issue for droplet-based microfluidics. We developed an asymmetric expansion(a rectangular groove) along one side of a microchannel to achieve multiple-microdroplet trapping, collision, and coalescence. Compared with reported symmetric expansions, this asymmetric groove could easily trap microdroplets and control two or three microdroplet coalescences precisely without a requirement for temporal and spatial synchronization. To reveal the mechanisms of multiple-droplet coalescences in a groove, we observed five different coalescence patterns under different flow conditions. Moreover, we characterized the flow behavior quantitatively by simulating the velocity vector fields in both the microdroplets and continuous phase, finding good agreement with experiments. Finally, a map of coalescence forms with different capillary numbers(0.001 < C a < 0.016) and flow ratios(0.1 < e < 0.9) was obtained. The results could provide a useful guidance for the design and application of droplet-based microfluidic devices.
基金supported by the National Key Research and Development Program of China under the contract number of 2017YFB0308000Program of Innovation Academy for Green Manufacture,CAS(IAGM2020C04)+1 种基金the State Key Laboratory of Heavy Oil Processing(SKLOP201903001)Key Research and Development Program of Hebei Province,China(20374001D)。
文摘Discharging untreated oily wastewater into the environment disrupts the ecological balance,which is a global problem that requires urgent solutions.Superhydrophilic and superoleophilic fibrous medium(FM)effectively separated oil–water emulsion as it was hydrophobic underwater.But its separation efficiencies(SEs)first increased to 98.9%,then dropped to 97.6%in 10 min because of oil-fouling.To tackle this problem,FM deposited with 0%–10%silica nanoparticle(NPsFMs),then coated by fluorocarbon polymer(X-[CH_(2)CH_(2)O]nCH_(2)CH_(2)O-Y-NH-COOCH_(2)C4F9)(FCNPs FMs),was used to enhance its roughness and regulate its initial wettability to improve the anti-fouling property.FCFM and FCNPs FMs were hydrophobic and oleophobic in air and oleophobic underwater.Their water contact angles,oil contact angles and oil contact angles were 115.3°–121.1°,128.8°–136.5°,and 131.6°–136.7°,respectively,meeting the requirement of 90°–140°for coalescence separation.FCNPs FM-5 had the best separation performance with a constant value of 99.8%in 10 min,while that of FCNPs FM-10 slightly decreased to 99.5%.Theoretical released droplet(TRD)diameter,calculated by the square root of the product of pore radius and fiber diameter,was used for the evaluation of coalescence performance.Analyzed by two ideal models,TRD diameter and fiber diameter showed a parabola type relationship,proving that the separation efficiency was a collaborative work of wettability,pore size and fiber diameter.Also,it explained the SEs reduction from FCNPs FM-5 to FCNPs FM-10 was revelent to the three parameters.Moreover,FCNPsFMs effectively separated emulsions stabilized by cationic surfactant CTAB(SEs:97.3%–98.4%)and anionic surfactant SDBS(SEs:91.3%–93.4%).But they had an adverse effect on nonionic surfactant Tween-80 emulsion separation(SEs:94.0%–71.76%).Emulsions made by diverse oils can be effectively separated:octane(SEs:99.4%–100%),rapeseed oil(SEs:97.3%–98.8%),and diesel(SEs:95.2%–97.0%).These findings provide new insights for designing novel materials for oil–water separation by coalescence mechanism.
基金Supported by the Fundamental Research Funds for the Central Universities(HEUCFP201855)
文摘Bubble coalescence reduces specific area and weakens the work performance of bubble column. The bubble coalescence near gas sparger which is caused mainly by bubble growing is different from the ones occurring in major liquid. Bubble coalescence efficiency near gas sparger is influenced by many factors including sparger configuration, gas flow rate, bubble deformation, solution composition, etc. This work has conducted a set of visual experiments to study the coalescence characteristics near multi-orifice plate. The experiment parameters cover a wide range of conditions including large scope of gas flow rate,different kinds of solution and orifice configurations. The experimental results suggest that coalescence time is applicable to reflect the influence of the pitch of orifices and gas flow rate on bubble coalescence efficiency. As the number of orifices increases, bubble coalescence efficiency is reduced by the disturbance from the bubbles at adjacent orifices. A hindering coefficient is used to consider the hindering effect of additives on bubble coalescence efficiency. Finally a new calculation expression is established to predict bubble coalescence efficiency near multi-orifice plate whose fundamental form is based on the logistic curve of binary response. The calculated values that refer to this calculation expression are well consistent with the experimental results.
基金supported by the National Key Research and Development Program of China(No.2017YFB0308000)the National Natural Science Foundation of China(No.21706259)+3 种基金the State Key Laboratory of Heavy Oil Processing(SKLOP201903001)Guizhou Science Technology Support Program([2019]2839)the Natural Science Youth Foundation of Shanxi Province(No.201701D221033)Program of Innovation Academy for Green Manufacture,CAS(IAGM2020C04)。
文摘A novel and high-efficiency coalescence membrane enhanced by nano-sized polyvinylidene fluoride(PVDF)nanofibers based on polyester(PET)substrate was fabricated using electrospinning method.The properties of the electrospun nanofibers such as roughness and surface morphology greatly affected the oil droplet interception efficiency and surface wettability of the membrane.A series of coalescence units were prepared with different layers of nanofibrous membrane and the separation efficiencies at different initial concentrations,flow rates,and oil types were tested.It is very interesting that the obtained nanofibrous membrane exhibited superoleophilicity in air but poor oleophilicity under water,which was beneficial to the coalescence process.The coalescence unit with four membrane layers had excellent performances under different initial concentrations and flow rates.The separation efficiency of the 4-layers unit remained above 98.2%when the initial concentration reached up to 2000 mg·L-1.Furthermore,the unit also exhibited good performance with the increasing oil density and viscosity,which is promising for large-scale oil wastewater treatment.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51876184,51706193,and 51776037)the National Natural Science Foundation of China–NSAF(Grant No.U1530260)+2 种基金the China Postdoctoral Science Foundation(Grant No.2017M621835)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.17KJB470014)Jiangsu Planned Projects for Postdoctoral Research Funds,China(Grant No.1701188B)
文摘Based on the volume of fluid(VOF) method, we conduct a numerical simulation to study the hydrodynamic binary coalescence of droplets under air flow in a hydrophobic rectangular microchannel. Two distinct regimes, coalescence followed by sliding motion and that followed by detaching motion, are identified and discussed. Additionally, the detailed hydrodynamic information behind the binary coalescence is provided, based on which a dynamic mechanical analysis is conducted to reveal the hydrodynamic mechanisms underlying these two regimes. The simulation results indicate that the sliding motion of droplets is driven by the drag force and restrained by the adhesion force induced by the interfacial tension along the main flow direction. The detachment(i.e., upward motion) of the droplet is driven by the lift force associated with an aerodynamic lifting pressure difference imposed on the coalescent droplet, and also restrained by the adhesion force perpendicular to the main flow direction. Especially, the lift force is mainly induced by an aerodynamic lifting pressure difference imposed on the coalescent droplet. Two typical regimes can be quantitatively recognized by a regime diagram depending on Re and We. The higher Re and We respectively lead to relatively larger lift forces and smaller adhesion forces acting on the droplet, both of which are helpful to detachment of the coalesced droplet.
文摘Novel preparation method of microencapsules was developed on the basis of the liquid coalescence method followed by phase separation. Oil droplets of limonene dissolving expanded polystyrene as a shell material were forced to collide and coalesce with the Isopar oil droplets of core material in the continuous wates phase. When two kinds of oil droplets are collided and coalesced with each other, expanded polystyrene dissolved in the limonene oil may be phase-separated in the oil droplets newly formed to form the microcapsule shell, because the Isopar oil was a poor solvent for expanded polystyrene but a good solvent for the limonene oil. In the experiment, the diameter (or number) of limonene oil droplets dissolving expanded polystyrene was mainly changed, because the coalescence frequency between the droplets is strongly dependent on the number of droplets. Favorable core shell types of microcapsules with the shell thickness from 1.0 to 5.0 μm were able to be prepared under all the experimental conditions adopted here.
基金Supported by the National Natural Science Foundation of China.
文摘1 INTRODUCTIONThe rate of coalescence between bubbles is important to the stability of foams,the mo-bility control in tertiary oil recovery,and a broad class of operations in which gas orvapor is the dispersed phase.Therefore,it is very important that the mechanism of thecoalescence process be understood,so that the effects of the physical properties oncoalescence can be assessed.
基金This work was supported by research grants from the National Natural Science Foundation of China and The Special Funds for Major State Basic Research Projects (G199906408).
文摘A fast coalescence mechanism is proposed to account for the wall effect on the formation of gradient morphologyin phase separated polymer blends during quiescent annealing. The existence of solid wall with high polarity is believed tochange the potential field around the dispersed particles near the wall. This additional potential interaction between the solidwall and the dispersed particles causes faster coalescence of the dispersed particles near the wall than in the bulk. Thegradient phase morphology thus formed can be predicted by combining the wall-particle interaction and the touch-coalescence mechanism. The effect of interfacial tension on the gradient morphology is also discussed.
基金financially supported by the National Natural Science Foundation of China (No. 51374081)
文摘Droplet coalescence in liquid steel was carefully investigated through observations of the distribution pattern of inclusions in solidified steel samples. The process of droplet coalescence was slow, and the critical Weber number(We) was used to evaluate the coalescence or separation of droplets. The relationship between the collision parameter and the critical We indicated whether slow coalescence or bouncing of droplets occurred. The critical We was 5.5, which means that the droplets gradually coalesce when We ≤ 5.5, whereas they bounce when We > 5.5. For the carbonate wire feeding into liquid steel, a mathematical model implementing a combined computational fluid dynamics(CFD)–discrete element method(DEM) approach was developed to simulate the movement and coalescence of variably sized droplets in a bottom-argon-blowing ladle. In the CFD model, the flow field was solved on the premise that the fluid was a continuous medium. Meanwhile, the droplets were dispersed in the DEM model, and the coalescence criterion of the particles was added to simulate the collision-coalescence process of the particles. The numerical simulation results and observations of inclusion coalescence in steel samples are consistent.
基金Supported by the Opening Fund of the State Key Laboratory of Explosion Science and Technology of Beijing Institute of Technology(KFJJ17-01M)
文摘In this paper,dynamic caustic method is applied to analyze the blast-induced crack propagation and distribution of the dynamic stress field around an empty circular hole in polymethyl methacrylate(PMMA)material under delayed ignition blasting loads.The following experimental results are obtained.(1)In directional-fracture-controlled blasting,the dynamic stress intensity factors(DSIFs)and the propagation paths of the blast-induced cracks are obviously influenced by the delayed ignition.(2) The circular hole situated between the two boreholes poses a strong guiding effect on the coelesence of the cracks,causing them to propagate towards each other when cracks are reaching the circular hole area.(3)Blast-induced cracks are not initiated preferentially because of the superimposed effect from the explosive stress waves on the cracking area.(4) By using the scanning electron microscopy(SEM)method,it is verified that the roughness of crack surfaces changes along the crack propagation paths.
基金supported by the National Natural Science Foundation of China(92034303,91834303 and 21776200)the aid of Program of Introducing Talents of Discipline to Universities(BP0618007)。
文摘The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratioηof two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when1<η<6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time(Tdr)and critical capillary number(Ca)c)were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size difference and viscosity ratio of the two droplets:Tdr~(ld)^(0.25±0.04)and Tdr~(η)^(﹣0.1±0.02).For droplet coalescence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac=0.48λ^(0.26)l^(﹣2.64),while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac=0.11η^(﹣0.07)ls^(﹣2.23)l^(0.16)_(d).
基金supported by the National Natural Science Foundation of China(21908062)。
文摘A computational study was carried out on bubble dynamic behaviors and bubble size distributions in a pressurized lab-scale gas-solid fluidized bed of Geldart A particles.High-resolution 3-D numerical simulations were performed using the two-fluid model based on the kinetic theory of granular flow.A finegrid,which is in the range of 3–4 particle diameters,was utilized in order to capture bubble structures explicitly without breaking down the continuum assumption for the solid phase.A novel bubble tracking scheme was developed in combination with a 3-D detection and tracking algorithm(MS3 DATA)and applied to detect the bubble statistics,such as bubble size,location in each time frame and relative position between two adjacent time frames,from numerical simulations.The spatial coordinates and corresponding void fraction data were sampled at 100 Hz for data analyzing.The bubble coalescence/break-up frequencies and the daughter bubble size distribution were evaluated by using the new bubble tracking algorithm.The results showed that the bubble size distributed non-uniformly over cross-sections in the bed.The equilibrium bubble diameter due to bubble break-up and coalescence dynamics can be obtained,and the bubble rise velocity follows Davidson’s correlation closely.Good agreements were obtained between the computed results and that predicted by using the bubble break-up model proposed in our previous work.The computational bubble tracking method showed the potential of analyzing bubble motions and the coalescence and break-up characteristics based on time series data sets of void fraction maps obtained numerically and experimentally.
基金supported by the Russian Science Foundation(Project 19-19-00598“Hydrodynamics and energetics of drops and droplet jets:formation,motion,break-up,interaction with the contact surface”).
文摘The interaction of a falling drop(diluted aqueous solution of ink in various concentrations)with a target fluid(partially degassed tap water)has been tracked by means of high-resolution video recording and photography.The experimental setup has carefully been prepared in order to preserve the axial symmetry of initial conditions.Three regimes of interaction have been identified accordingly(depending on the drop velocity as controlled by the distance of fall):rapid droplet coalescence,rebound with the conservation of the drop volume and shape,and partial coalescence.Previous findings are recovered and confirmed,and enriched with heretofore unseen observations of complex partial coalescence.An extensive set of data is reported to support understanding of the observed dynamics and their repeatability and reproducibility.The overall study has been carried out with the express intent to spur the future development of detailed mathematical models and numerical methods suited for this kind of problems.
基金supported by an NSF CAREER Award(CMMI-1454293)a Grant-In-Aid(GIA)program/a start-up fund at the University of Minnesota,Twin Cities+2 种基金Parts of this work were carried out in the Characterization Facility,University of Minnesota,a member of the NSF-funded Materials Research Facilities Network(www.mrfn.org)via the MRSEC programA portion of this work was also carried out in the Minnesota Nano Center which receives partial support from the NSF through the NNCI programthe 3M Science and Technology Fellowship
文摘Grain coalescence has been applied in many areas of nanofabrication technology, including modification of thinfilm properties, nanowelding, and self-assembly of nanostructures. However, very few systematic studies of selfassembly using the grain coalescence, especially for threedimensional(3D) nanostructures, exist at present. Here, we investigate the mechanism of plasma triggered grain coalescence to achieve the precise control of nanoscale phase and morphology of the grain coalescence induced by exothermic energy. Exothermic energy is generated through etching a silicon substrate via application of plasma. By tuning the plasma power and the flow rates of reactive gases, different etching rates and profiles can be achieved, resulting in various morphologies of grain coalescence. Balancing the isotropic/anisotropic substrate etching profile and the etching rate makes it possible to simultaneously release 2D nanostructures from the substrate and induce enough surface tension force,generated by grain coalescence, to form 3D nanostructures.Diverse morphologies of 3D nanostructures have been obtained by the grain coalescence, and a strategy to achieve self-assembly, resulting in desired 3D nanostructures, has been proposed and demonstrated.
基金the National Natural Science Foundation of China(Grant No.51876102)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51621062).
文摘Partial coalescence is a complicated flow phenomenon.In the present study,the coalescence process is simulated with the volume of fluid(VOF)method.The numerical results reveal that a downward high-velocity region plays a significant role in partial coalescence.The high-velocity region pulls the droplet downward continuously which is an important factor for the droplet turning into a prolate shape and the final pinch-off.The shift from partial coalescence to full coalescence is explained based on the droplet shape before the pinch-off.With the droplet impact velocity increasing,the droplet shape will get close to a sphere before the pinch-off.When the shape gets close enough to a sphere,the partial coalescence shifts to full coalescence.The effect of film thickness on the coalescence process is also investigated.With large film thickness,partial coalescence happens,while with small film thickness,full coalescence happens.In addition,the results indicate that the critical droplet impact velocity increases with the increase of surface tension coefficient but decreases with the increase of viscosity and initial droplet diameter.And there is a maximum critical Weber number with the increase of surface tension coefficient and initial droplet diameter.
文摘Fractal interpolation function (FIF) is a special type of continuous function which interpolates certain data set and the attractor of the Iterated Function System (IFS) corresponding to a data set is the graph of the FIF. Coalescence Hidden-variable Fractal Interpolation Function (CHFIF) is both self-affine and non self-affine in nature depending on the free variables and constrained free variables for a generalized IFS. In this article, graph directed iterated function system for a finite number of generalized data sets is considered and it is shown that the projection of the attractors on is the graph of the CHFIFs interpolating the corresponding data sets.
文摘Directional solidification methods are being used f or in-situ production of metallic immiscible composites. A quantitative understa nding of the dynamic behavior and growth kinetics of the nucleated second phase during solidification is necessary to produce homogeneous dispersion in solidifi ed composites. This paper presents a mathematical model for describing the grow th of nucleated dispersed phase in the two-liquid phase region ahead of the sol idification front and the entrapment of these droplets by the moving solid-liqu id interface in vertical unidirectional solidification systems. The model has t wo components. A macro-heat transfer model for describing the temperature prof iles and the rate of advance of the solidification front. The dynamic behavior and coalescence and growth of nucleated droplets in the two-liquid phase region under the influence of effective gravity and thermocapillary forces were repres ented through the solution the droplet momentum and mass conservation equations in particle space. These two components of the models were coupled through a sp ecial algorithm for tracking the particle location and size with respect to movi ng solidification front in the solidification time scale. The model is used to study the particle size distribution in unidirectional solidified Zn-Bi hypermo notectic alloys at reduced gravity conditions. It has been found that the parti cle size and distribution in the solidified alloy depends on solidification rate and the ratio of effective gravity to thermocapillary forces. It was also foun d that uniform dispersion could only be obtained in a very narrow range of effec tive gravity values near zero gravity. The model predictions were compared agai nst experimental measurements obtained at different effective gravity conditions in a novel unidirectional solidification apparatus that uses electromagnetic fo rces to modulate gravitational forces. The model was found to reasonably predic t the experimentally measured particle size and distribution over the entire ran ge of effective gravity investigated as well as gravity conditions for settling and flotation of the second phase during solidification. The practical signific ance of these findings will be discussed.
文摘In shallow crust, faults often consist of a series of secondary fractures. Based on experimental micro features in rock mechanics and macro structures in field, the progressive coalescence model, in which a brittle fault evolved from micro crack, stylolitic fracture, large fault to super large fault, is founded, and its forming mechanism is discussed by variation of stress field. At last the undulation, branches of faults and the phenomenon that the angle between fractures and the principal stress axis decreases gradually are explained by the G.C.Sih model.
