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Showing papers on "Marangoni effect published in 2022"


Journal ArticleDOI
TL;DR: In this paper , an infinite porous disk was used to communicate the Marangoni convection flow of hybrid nanomaterials by using Von Kamran variables and Darcy-Forchheimer law.

58 citations


Journal ArticleDOI
TL;DR: In this article, an NAB/15-5-PH interface without cracks and lack of fusion was achieved, which was characterized with an interlayer of FexAl dendrites.
Abstract: Additive manufacturing (AM) of a nickel-aluminum-bronze (NAB)/15-5 PH multimaterial by laser-powder directed energy deposition (LP-DED) accomplished a combination of excellent mechanical performance and high corrosion resistance. An NAB/15-5 PH interface without cracks and lack of fusion was achieved, which was characterized with an interlayer of FexAl dendrites. The formation of the interfacial characteristics was attributed to a synthetic effect of liquid phase separation, Marangoni convection, and atom diffusion. A miscibility gap was generated by a high degree of supercooling in the melt pool, and 15-5 PH solidified prior to NAB to form a dendritic interlayer. Marangoni convection occurred to promote the Al atom diffusion from NAB to 15-5 PH, contributing to the formation of the FexAl phase at the interface. The multimaterial sample possessed higher ultimate tensile strength of 754.64 MPa in the transverse direction and 854.57 MPa in the longitudinal direction as compared to that of copper/steel counterparts fabricated by AM. The multimaterial printed by LP-DED exhibited different deformation mechanisms in the transverse and longitudinal directions. In the transverse direction, NAB contributed more deformation than 15-5 PH and determined the improved ductility of the multimaterial; in the longitudinal direction, the brittle FexAl dendrites constrained the deformation of NAB and 15-5 PH, which resulted in the early failure of the multimaterial. The multimaterial tended to undergo cracking at the interface of the FexAl and Cu phases under stress concentration, which was induced by their crystal incoherence.

44 citations


Journal ArticleDOI
TL;DR: In this paper , an NAB/15-5 PH interface without cracks and lack of fusion was achieved, which was characterized with an interlayer of FexAl dendrites.
Abstract: Additive manufacturing (AM) of a nickel-aluminum-bronze (NAB)/15-5 PH multimaterial by laser-powder directed energy deposition (LP-DED) accomplished a combination of excellent mechanical performance and high corrosion resistance. An NAB/15-5 PH interface without cracks and lack of fusion was achieved, which was characterized with an interlayer of FexAl dendrites. The formation of the interfacial characteristics was attributed to a synthetic effect of liquid phase separation, Marangoni convection, and atom diffusion. A miscibility gap was generated by a high degree of supercooling in the melt pool, and 15-5 PH solidified prior to NAB to form a dendritic interlayer. Marangoni convection occurred to promote the Al atom diffusion from NAB to 15-5 PH, contributing to the formation of the FexAl phase at the interface. The multimaterial sample possessed higher ultimate tensile strength of 754.64 MPa in the transverse direction and 854.57 MPa in the longitudinal direction as compared to that of copper/steel counterparts fabricated by AM. The multimaterial printed by LP-DED exhibited different deformation mechanisms in the transverse and longitudinal directions. In the transverse direction, NAB contributed more deformation than 15-5 PH and determined the improved ductility of the multimaterial; in the longitudinal direction, the brittle FexAl dendrites constrained the deformation of NAB and 15-5 PH, which resulted in the early failure of the multimaterial. The multimaterial tended to undergo cracking at the interface of the FexAl and Cu phases under stress concentration, which was induced by their crystal incoherence.

39 citations


Journal ArticleDOI
TL;DR: A review of the most recent and significant developments in this rapidly growing field can be found in this article , focusing on the mathematical and physical modeling of these intriguing droplets, together with their experimental design and characterization.
Abstract: Microscopic active droplets are able to swim autonomously in viscous flows. This puzzling feature stems from solute exchanges with the surrounding fluid via surface reactions or their spontaneous solubilization and from the interfacial flows resulting from these solutes’ gradients. Contrary to asymmetric active colloids, these isotropic droplets swim spontaneously by exploiting the nonlinear coupling of solute transport with self-generated Marangoni flows; such coupling is also responsible for secondary transitions to more complex individual and collective dynamics. Thanks to their simple design and their sensitivity to physico-chemical signals, these droplets are fascinating to physicists, chemists, biologists, and fluid dynamicists alike in analyzing viscous self-propulsion and collective dynamics in active-matter systems, developing synthetic cellular models, or performing targeted biomedical or engineering applications. I review here the most recent and significant developments of this rapidly growing field, focusing on the mathematical and physical modeling of these intriguing droplets, together with their experimental design and characterization. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 55 is January 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

31 citations


Journal ArticleDOI
TL;DR: In this article, the influence of laser power, scanning speed, hatch spacing and layer thickness on the surface quality and internal hole defect of SLMed 18Ni300 maraging steel was investigated, and the thermal and physical behaviour and instability of the molten pool, as well as the formation and distribution behaviour of internal hole defects were also analyzed and discussed.

23 citations


Journal ArticleDOI
TL;DR: In this paper , a noncontact light-driven droplet manipulation method by using photothermally active droplets is introduced, which is induced by local photothermal heating via near infrared (NIR) irradiation resulting in an internal flow that drives the droplets.
Abstract: Marangoni flow, a surface shear flow, is a promising option for propulsion when controlling liquid droplet motion on solid substrates. However, the applicability of Marangoni flow induced by heating the substrate for droplet manipulation is limited by low precision of motion control and a narrow range of substrate types. Herein, a novel noncontact light‐driven droplet manipulation method by using photothermally active droplets is introduced. Marangoni flow is induced by local photothermal heating via near‐infrared (NIR) irradiation resulting in an internal flow that drives the droplets. The photothermally active droplets slide away from the NIR light and the direction of motion can be precisely controlled by changing the irradiation position remotely. In addition, it is demonstrated that the addition of a miscible liquid to the droplets can reverse the direction of motion. Moreover, the authors show that spherical droplets on conventional liquid repellent surfaces move through a rolling mechanism instead of sliding. It is believed that this droplet manipulation method can provide a general way of droplet transportation on solid surfaces.

19 citations


Journal ArticleDOI
TL;DR: A validated CFD model coupling the multiple phases and multiple physics was developed for the dynamic simulation of pulse wave laser welding (PWLBW) process of 1.2mm-thick Ti-6Al-4V alloy sheets assembled in butt joint with a reserved air gap as mentioned in this paper.
Abstract: A validated CFD model coupling the multiple phases and multiple physics was developed for the dynamic simulation of pulse wave laser welding (PWLBW) process of 1.2 mm-thick Ti-6Al-4V alloy sheets assembled in butt joint with a reserved air gap. A laser spot diameter of 700 μm was used to compensate for the energy loss with the clearance applied at 0.2 mm and therefore improve the gap bridging ability. The distributions and evolutions of temperature, velocity, phase interface and weld pool dimensions were characterized and discussed to reveal the joining mechanism and the heat and flow behaviors during welding. The results show that the liquid bridges firstly occur in the middle height of sheets as the welding begins, and rapidly extend to the whole thickness with the increasing heat input. The reduction on laser power causes the rebounding of keyhole surface and the backfilling of molten metal. The keyhole closes at root surface and rebounds completely in 2 microseconds, leading to the merging of liquid bridges, bottom-up moving of high temperature area, and temporarily enlargement on weld pool size at root surface. During the pulse interval, the weld pool volume shrinks significantly and the molten metal slows down from Marangoni vortexes to thermal buoyance flows. The proposed process parameters allow an air gap accounting for 16.67% of specimen thickness and result in a well-formed and defect-free weld bead.

18 citations


Journal ArticleDOI
TL;DR: A validated CFD model coupling the multiple phases and multiple physics was developed for the dynamic simulation of pulse wave laser welding (PWLBW) process of 1.2 mm-thick Ti-6Al-4V alloy sheets assembled in butt joint with a reserved air gap as discussed by the authors .
Abstract: A validated CFD model coupling the multiple phases and multiple physics was developed for the dynamic simulation of pulse wave laser welding (PWLBW) process of 1.2 mm-thick Ti-6Al-4V alloy sheets assembled in butt joint with a reserved air gap. A laser spot diameter of 700 μm was used to compensate for the energy loss with the clearance applied at 0.2 mm and therefore improve the gap bridging ability. The distributions and evolutions of temperature, velocity, phase interface and weld pool dimensions were characterized and discussed to reveal the joining mechanism and the heat and flow behaviors during welding. The results show that the liquid bridges firstly occur in the middle height of sheets as the welding begins, and rapidly extend to the whole thickness with the increasing heat input. The reduction on laser power causes the rebounding of keyhole surface and the backfilling of molten metal. The keyhole closes at root surface and rebounds completely in 2 microseconds, leading to the merging of liquid bridges, bottom-up moving of high temperature area, and temporarily enlargement on weld pool size at root surface. During the pulse interval, the weld pool volume shrinks significantly and the molten metal slows down from Marangoni vortexes to thermal buoyance flows. The proposed process parameters allow an air gap accounting for 16.67% of specimen thickness and result in a well-formed and defect-free weld bead.

17 citations


Journal ArticleDOI
TL;DR: In this article , the authors investigated the swimming motion of a two-dimensional drop that is determined by two dimensionless parameters, the Péclet number and Damköhler number.
Abstract: Abstract Chemically active droplets often show intriguing self-propulsion behaviour in a surfactant solution. The drop motion is controlled by the nonlinear coupling among chemical transport in the bulk fluid, consumption of surfactant at the drop surface, and the fluid flow driven by the self-generated Marangoni stress. To quantify the underlying hydrodynamics, this work investigates the swimming motion of a two-dimensional drop that is determined by two dimensionless parameters, the Péclet number ($Pe$) and Damköhler number ($Da$). The weakly nonlinear analysis shows that near the instability threshold, the drop undergoes a supercritical bifurcation with velocity $U\sim \sqrt {Pe-Pe_c}$, where $Pe_c$ is the critical Péclet number for the onset of dipole mode. In the highly nonlinear regime, the drop transits from steady translation of pusher swimming to unsteady motion of mixed pusher–puller swimming along zigzaging trajectories of quadrangle and/or triangle waves. Mode decomposition shows that the zigzag motion is directly related to the interaction between the secondary wake of low surfactant concentration and the primary wake.

15 citations


Journal ArticleDOI
TL;DR: In this article , a radial basis function (RBF) meshless method was proposed for numerical simulation of the thermal convection and vapor absorption in aqueous LiBr solution problems.

14 citations



Journal ArticleDOI
TL;DR: In this paper, the authors present a new concept to strongly enhance the conversion of ambient thermal fluctuations into electric power using the Marangoni effect, which can be applied to conditions where the phase change material (PCM) has a free surface.

Journal ArticleDOI
TL;DR: In this paper , a channelless patterning method for fabricating elastomeric wearable sensors is demonstrated to detect motions of liquid metals (LMs) on a 2D plane.
Abstract: The ability to control interfacial tension electrochemically is uniquely available for liquid metals (LMs), in particular gallium‐based LM alloys. This imparts them with excellent locomotion and deformation capabilities and enables diverse applications. However, electrochemical oxidation of LM is a highly dynamic process, which often induces Marangoni instabilities that make it almost impossible to elongate LM and manipulate its morphology directly and precisely on a 2D plane without the assistance of other patterning methods. To overcome these limitations, this study investigates the use of an LM–iron (Fe) particle mixture that is capable of suppressing instabilities during the electrochemical oxidation process, thereby allowing for superelongation of the LM core of the mixture to form a thin wire that is tens of times of its original length. More importantly, the elongated LM core can be manipulated freely on a 2D plane to form complex patterns. Eliminating Marangoni instabilities also allows for the effective spreading and filling of the LM–Fe mixture into molds with complex structures and small features. Harnessing these excellent abilities, a channel‐less patterning method for fabricating elastomeric wearable sensors is demonstrated to detect motions. This study shows the potential for developing functional and flexible structures of LM with superior performance.

Journal ArticleDOI
TL;DR: In this article , the authors presented a new concept to strongly enhance the conversion of ambient thermal fluctuations into electric power using the Marangoni effect, which can be used as a foundation for further improvements to optimize the output of thermoelectric devices to power low-consumption electronics.

Journal ArticleDOI
TL;DR: In this article , through modeling the metal powder melting and subsequent solidification under the conduction mode, it was found that the molten liquid near the gas-liquid interface flows centrifugally and vortices including a clockwise and an anticlockwise vortex are produced.
Abstract: The formation of pores can severely deteriorate the quality of parts fabricated by laser powder bed fusion (LPBF) technology. However, how the pores formation relates to melt pool and gas bubble dynamics is still not well understood. Here, through the modeling of the metal powder melting and the subsequent solidification under the conduction mode, it was found that the molten liquid near the gas-liquid interface flows centrifugally and vortices including a clockwise and an anticlockwise vortex are produced. The anticlockwise vortex dominates the molten liquid when laser turns off. The motion of gas bubbles originating from the powder bed voids follows the melt pool flow synchronously, where bubbles can coalesce, and some escape from the top and sides of the melt pool, and some remain as pores in the solidified part. For the positive value of surface tension gradient, the centripetal Marangoni convection drives the melt pool to flow in the dual clockwise circulation and obstructs the escaping orbit of bubbles, leading to higher porosity and surface humping. The present study enhances the further understanding of multi-physics in LPBF process.

Journal ArticleDOI
TL;DR: In this paper , the authors optimized the heat and mass transfer characteristics of Marangoni convection in a nanoliquid flowing on an infinite disk with Stefan blowing and activation energy using the Taguchi method.

Journal ArticleDOI
TL;DR: In this paper , three different micro-fluidics-suitable fluid behavior phenomena have been studied on the ISS that might further facilitate the manipulation of fluids in space: capillary-driven flow, thermocapillary Marangoni forces, and electrolytic gas evolution driven flow.
Abstract: Fluid transport and handling in extraterrestrial conditions, i.e. microgravity, require significantly different system engineering than here on Earth. On Earth, a notable part of fluid processing units inherently relies on buoyancy to transport and handle fluids. In space, however, buoyancy effects are negligible due to the strong diminishment of gravity, resulting in the domination of surface tension forces. Surface tension forces are also dominating micro-scale processes in gravity, making microfluidics a promising technology for fluidic transport and handling in microgravity. Recently, three different microfluidics-suitable fluid behavior phenomena have been studied on the ISS that might further facilitate the manipulation of fluids in space: capillary-driven flow, thermocapillary Marangoni forces, and electrolytic gas evolution-driven flow. Furthermore, attention is drawn for strategies to eliminate unwanted bubbles from liquid bodies in space, as they can damage sensitive equipment: Mesh-screen capillarity and open wedge channels have been identified as promising approaches. Finally, the relevance of fluid handling in space is illustrated with everyday activities during space missions, such as drinking, plant watering, and gathering biometric data.

Journal ArticleDOI
TL;DR: In this paper , a novel eutectic galliumindium (EGaIn)/polyaniline (PANI) complex (EP) and cellulose nanocrystals (CNCs) are explored as the light absorber for broadband light absorbing and the dispersant for particles uniformity.
Abstract: Solar‐driven evaporation is a promising strategy to relieve fresh water stress in the world. For an evaporator, it is necessary to be equiped with novel photothermal conversion materials and regulate heat energy loss in the solar‐driven generation process for evaporation efficiency. Herein, a novel eutectic gallium‐indium (EGaIn)/polyaniline (PANI) complex (EP) and cellulose nanocrystals (CNCs) are explored as the light absorber for broadband light absorbing and the dispersant for particles uniformity. Based on the Bénard–Marangoni effect, a dual‐network poly(vinyl alcohol)/poly(acrylamide) (PM) hydrogel as the evaporator and water/ethylene glycol as the solvent to regulate heat transfer. Specifically, with CNCs and EP incorporated, the hydrogel is endowed with excellent mechanical properties, photothermal conversion performance, and electrical characteristics. Surface temperature of the hydrogel can reach to ≈38.7 °C in water under 1 sun illumination for 1 h. Based on combination of broadband light absorption and the Bénard–Marangoni effect, its evaporation rate is higher than 1.50 kg m–2 h–1. The engineered synergy also gives the hydrogels with multiple sensory capabilities, skin‐like function, and power generation. This work demonstrates novel EGaIn‐based photothermal conversion particles and a new approach to regulate the heat transfer for highly solar‐driven evaporation, with a focus on the integration of multifunctional solar evaporation systems.

Journal ArticleDOI
TL;DR: In this paper , the effect of fiber laser welding parameters on temperature distribution, weld bead dimensions, melt flow velocity, and microstructure was investigated by finite volume and experimental methods in order to detect the temperature history during continuous laser welding, two thermocouples were considered at a distance of 2 mm from the welding line.
Abstract: In these days, laser is a useful and valuable tool. Low input heat, speed, accuracy, and high controllability of laser welding have led to widespread use in various industries. Nickel-based superalloys are creep-resistant materials used in high-temperature conditions. Also, these alloys have high strength, fatigue, and suitable corrosion resistance. Inconel 625 is a material that is strengthened by a complex deposition mechanism. Therefore, the parameters related to laser welding affect the microstructure and mechanical properties. Therefore, in this study, the effect of fiber laser welding parameters on temperature distribution, weld bead dimensions, melt flow velocity, and microstructure was investigated by finite volume and experimental methods. In order to detect the temperature history during continuous laser welding, two thermocouples were considered at a distance of 2 mm from the welding line. The heat energy from the laser beam was modeled as surface and volumetric heat flux. The results of numerical simulation showed that Marangoni stress and buoyancy force are the most important factors in the formation of the flow of liquid metal. Enhancing the laser power to 400 W led to the expansion of the width of the molten pool by 1.44 mm, which was in good agreement with the experimental results. Experimental results also showed that increasing the temperature from 500 °C around the molten pond leads to the formation of a coarse-grained austenitic structure.

Journal ArticleDOI
TL;DR: In this paper , two numerical models are implemented: one dynamic model based on lubrication theory and one quasi-stationary model, that allows for arbitrary contact angles, and they are mutually validated by comparing their results in cases where both are valid.

Journal ArticleDOI
TL;DR: In this paper , a flow focusing microfluidic device was studied for capillary numbers between 10 −4 and 10 −1 and the effect of the continuous phase viscosity on droplet size and flow fields inside the drop was investigated.

Journal ArticleDOI
04 Apr 2022-Langmuir
TL;DR: In this paper , the evaporation of water-ethanol binary sessile droplets loaded with alumina nanoparticles on a critically inclined heated surface and compare it to the noloading condition was investigated.
Abstract: We experimentally investigate the evaporation of water-ethanol binary sessile droplets loaded with alumina nanoparticles on a critically inclined heated surface and compare it to the no-loading condition. In contrast to a droplet of pure fluids, several distinct and interesting phenomena observed in a binary-nanofluid droplet on a critically inclined substrate are reported for the first time. The critical angle at which a droplet begins to slide increases for ethanol-rich binary droplets up to 0.6 wt % nanoparticle loading. The critical angle for binary droplets also increases as the substrate temperature increases and as the ethanol concentration decreases for modest loading conditions. It is observed that the advancing side of a binary droplet is pinned in both the loading and no-loading scenarios, whereas the receding side is pinned in the loading case but shrinks continuously in the no-loading case. The pinning effect caused by nanoparticles results in a larger perimeter and surface area for the nanoparticle-laden droplets, enhancing the evaporation rates and significantly decreasing the lifetime of the nanoparticle-containing droplets compared to the no-loading case. Increasing the ethanol percentage in the binary droplet placed on an inclined substrate produces complex thermosolutal Marangoni convection, which becomes more affluent in the case of nanoparticles loading than the no-loading condition. The radial symmetry of the circular coffee ring structure observed on a horizontal surface is shattered in the inclined case because the droplet elongates and preferentially deposits toward the advancing side of the triple line due to the action of the body force. Despite its fundamental nature, the present study can contribute to understanding many practical applications.

Journal ArticleDOI
TL;DR: In this paper , the spontaneous self-induced solutal Marangoni flow of an evaporating binary mixture droplet has been widely investigated and used to suppress coffee-ring patterns in ink-jet printing technology.
Abstract: Currently, quantum dot light‐emitting diodes (QD‐LEDs) are receiving extensive attention. To maximize their luminous performance, the uniformity of the QD‐LEDs is crucial. Although the spontaneously self‐induced solutal Marangoni flow of an evaporating binary mixture droplet has been widely investigated and used to suppress coffee‐ring patterns in ink‐jet printing technology, unfortunately, ring shapes are still present at the edges, and the Marangoni flow generated by the selective evaporation of volatile liquid components cannot be controlled due to its nonlinear instabilities. In this work, polygonal coffee‐ring‐less QD microarrays are created using two spontaneous and sequential solutal Marangoni flows. During the initial evaporation, internal circulating flows are controlled by polygonal‐shaped droplets. After that, sequential interfacial flows are generated by the captured volatile vapors. A theoretical model and scaling analysis are provided to explain the working mechanisms. It is expected that the newly designed printing system can be applied to the mass production of QD‐LEDs.

Journal ArticleDOI
TL;DR: In this article , the effect of convection flow on the as-solidified material microstructure is investigated using a process-microstructure model and comparative simulation cases to identify the effects of convective flow on melt pool geometry, solidification conditions, and as solidified grain structure formation.

Journal ArticleDOI
TL;DR: In this paper, a flow focusing microfluidic device was studied for capillary numbers between 10−4 and 10−1, and the addition of a cationic surfactant to the dispersed phase and the effect of the continuous phase viscosity on droplet size, neck kinetics and flow fields inside the drop was investigated.

Journal ArticleDOI
TL;DR: In this paper , a two-dimensional hybrid thermal lattice Boltzmann (LB) method coupled with the leaky dielectric model was firstly presented to study droplet evaporation on a heated substrate under the influence of an electric field.

Journal ArticleDOI
TL;DR: In this article , the significances of bio-convection for the Carreau nanofluid flow over a stretched cylinder were investigated by suggesting the contribution of melting phenomenon and chemical reaction are also addressed.

Journal ArticleDOI
TL;DR: In this paper , the surface tension of pure iron and 304L stainless steel was measured under different gas mixtures (pure argon and Ar-2.5 %vol. H2).

Journal ArticleDOI
TL;DR: In this article , the keyhole dynamics in the laser powder bed fusion (LPBF) process and its relationship with driving forces of surface tension, Marangoni force and recoil pressure have not been well addressed and quantified.

Journal ArticleDOI
TL;DR: In this paper , the complex evaporation kinetics of saline sessile droplets on surfaces with elevated temperatures were investigated and it was shown that on heated surfaces, the saline droplets evaporate slower than the water counterpart, thereby posing a counter-intuitive phenomenon.
Abstract: We report the complex evaporation kinetics of saline sessile droplets on surfaces with elevated temperatures. Our previous studies show that on non-heated substrates, saline sessile droplets evaporate faster compared to the water counterparts. In the present study, we discover that on heated surfaces, the saline droplets evaporate slower than the water counterpart, thereby posing a counter-intuitive phenomenon. The reduction in the evaporation rates is directly dependent on the salt concentration and the surface wettability. Natural convection around the droplet and thermal modulation of surface tension is found to be inadequate to explain the mechanisms. Flow visualizations using particle image velocimetry (PIV) reveal that the morphed advection within the saline droplets is a probable reason behind the arrested evaporation. Infrared thermography is employed to map the thermal state of the droplets. A thermo-solutal Marangoni based scaling analysis is put forward and the major governing non-dimensional numbers have been accounted for in the analysis. It is observed that the Marangoni flow and internal advection borne of thermal and solutal gradients are competitive, thereby leading to the overall decay of internal circulation velocity compared to the equivalent pure water case, which reduces the evaporation rates. The theoretically proposed advection velocities conform to the experimental results. This study sheds rich insight on a novel species transport behaviour in saline droplets.