Variation Of Tension Research Articles

Thermophysical Properties of the Hydrogen Carrier System Based on Aqueous Solutions of Isopropanol or Acetone

One concept for the safe storage and transport of molecular hydrogen (H2) is the use of hydrogen carrier systems which can bind and release hydrogen in repeating cycles. In this context, the liquid system based on isopropanol and its dehydrogenated counterpart acetone is particularly interesting for applications in direct isopropanol fuel cells that are operated with an excess of water. For a comprehensive characterization of diluted aqueous solutions of isopropanol or acetone with technically relevant solute amount fractions between 0.02 and 0.08, their liquid density, liquid viscosity, and interfacial tension were investigated using various light scattering and conventional techniques as well as equilibrium molecular dynamics (EMD) simulations between (283 and 403) K. Polarization-difference Raman spectroscopy (PDRS) was used to monitor the liquid-phase composition during surface light scattering (SLS) experiments on viscosity and interfacial tension. For comparison purposes and to expand the database, capillary viscometry and dynamic light scattering (DLS) from bulk fluids with dispersed particles were also applied to determine the viscosity while the pendant-drop (PD) method allowed access to the interfacial tension. By adding isopropanol or acetone to water, density and, in particular, interfacial tension decrease significantly, while viscosity shows a pronounced increase. The behavior of viscosity and interfacial tension is closely related to the strong hydrogen bonding between the unlike mixture components and the pronounced enrichment of both solutes at the vapor–liquid interface, as revealed by EMD simulations. For an aqueous solution with an isopropanol amount fraction of 0.04, minor variations in interfacial tension and viscosity were found in the presence of pressurized H2 up to 7.5 MPa. Overall, the results from this study contribute to an extended database for diluted aqueous solutions of isopropanol or acetone, especially at temperatures above 323 K.

Multiscale simulation of water/oil displacement with dissolved CO[formula omitted]: Implications for geological carbon storage and CO[formula omitted]-enhanced oil recovery

This study combines molecular and pore-scale simulations to enhance our understanding of water, carbon dioxide (CO2), and oil flow in a porous system for high-efficiency geological carbon storage and enhanced oil recovery. We use molecular dynamics simulations to study the variation of interfacial tension (IFT), viscosity, and contact angle across varying system CO2 concentrations. The study reveals that the IFT simulation accuracy in the three-component mixture system relates positively to the volume-to-interfacial area ratio, and IFT decreases with CO2 concentration. Oil–CO2 mixture viscosity decreases and shows an intersection with water viscosity as CO2 concentration increases. The contact angle on the hydrophobic surface of kaolinite first increases and then decreases with CO2 concentration, while the hydrophilic surface contact angle is not sensitive to the CO2 concentration. Visualizing CO2 density distribution reveals its accumulation at fluid-fluid and fluid-solid interfaces and the combined effect results in the highest CO2 density at contact-line regions. Meanwhile, the elevated CO2 density at fluid-fluid interfaces reduces IFT, contributing to the initial contact angle increase, while the CO2 density increase at fluids-solid surface explains the subsequent contact angle decrease. These findings are then upscaled into a core-scale system using lattice Boltzmann simulations. The results are summarized into a phase diagram, which reveals the non-monotonic variations of the initial-residual (I-R) curves across different CO2 concentrations, and the residual saturation overall decreases with CO2 concentration for high initial saturations. These findings underscore the critical roles of system CO2 concentration and rock components, particularly kaolinite clay minerals, in subsurface multiphase seepage confronted in geological carbon storage and CO2-enhanced oil recovery, highlighting the importance of digital rock physical chemistry.

Investigation of surfactant-laden bubble migration dynamics in self-rewetting fluids using lattice Boltzmann method

Self-rewetting fluids (SRFs), such as aqueous solutions of long-chain alcohols, show anomalous nonlinear (quadratic) variations of surface tension with temperature involving a positive gradient in certain ranges, leading to different thermocapillary convection compared to normal fluids (NFs). They have recently been used for enhancing thermal transport, especially in microfluidics and microgravity applications. Moreover, surface-active materials or surfactants can significantly alter interfacial dynamics by their adsorption on fluid interfaces. The coupled effects of temperature- and surfactant-induced Marangoni stresses, which arise due to surface tension gradients, on migration bubbles in SRFs remain unexplored. We use a robust lattice Boltzmann method based on central moments to simulate the two-fluid motions, capture interfaces, and compute the transport of energy and surfactant concentration fields, and systematically study the surfactant-laden bubble dynamics in SRFs. When compared to motion of bubbles in NFs, in which they continuously migrate without a stationary behavior, our results show that they exhibit dramatically different characteristics in SRFs in many different ways. Not only is the bubble motion directed toward the minimum temperature location in SRFs, but, more importantly, the bubble attains an equilibrium position. In the absence of surfactants, such an equilibrium position arises at the minimum reference temperature occurring at the center of the domain. The addition of surfactants moves the equilibrium location further upstream, which is controlled by the magnitude of the Gibbs elasticity parameter that determines the magnitude of the surface tension variation with surfactant concentration. The parabolic dependence of surface tension in SRF is parameterized by a quadratic sensitivity coefficient, which modulates this behavior. The lower this quantity, the greater is the role of surfactants modifying the equilibrium position of the bubble in SRF. Furthermore, the streamwise gradient in the surfactant concentration field influences the transient characteristics in approaching the terminal state of the bubble. These findings provide new means to potentially manipulate the bubble dynamics, and especially to tune its equilibrium states, in microchannels and other applications by exploiting the interplay between surfactants and SRFs.

Variation of Surface Tension of Liquid Metal with Fluorides in Tungsten Inert Gas Welding

Real-time measuring and obtaining surface tension of liquid metal during the arc welding process is critical for studying the behavior of the weld pool, such as Marangoni flow and flow velocity. The dynamic variation of surface tension of weld pool during tungsten inert gas welding process with and without fluoride flux was measured by weld pool oscillation sensing system, and the effect of fluoride flux on surface tension and pool behavior was analyzed. The results show that the surface tension gradient of liquid metal can convert from a negative to a positive value in a critical arc time. The flow velocity of liquid metal and critical arc time significantly increased and decreased, respectively, with fluoride flux. The variation of surface tension, flow velocity, and critical arc time with fluoride flux was induced by arc temperature increasing.

Combined Freak Wave, Wind, and Current Effects on the Dynamic Responses of Offshore Triceratops

Offshore structures are exposed to various environmental loads, including extreme and abnormal waves, over their operational lifespan. The existence of wind and current can exacerbate the dynamic response of these structures, posing threats to safety and integrity. This study focuses on the dynamic responses of offshore triceratops under different environmental conditions characterized by the superimposition of freak waves, uniform wind, and current. The free surface profile of the freak wave was generated using the dual superposition model. The numerical model of the offshore platform designed for ultra-deep-water applications was developed using the ANSYS AQWA 2023 R2 modeler. Numerical investigations, including the free decay tests and time-domain analysis under random sea states, including freak waves, were initially carried out. Then, the combined effects of freak waves, wind, and current were studied in detail under different loading scenarios. The results revealed the increase in structural response under the freak wave action at the focus time. Wind action resulted in a mean shift in responses, while the inclusion of current led to a pronounced increase in the total response of the platform, encompassing deck and buoyant legs, alongside the tether tension variation. Notably, considerable variations in the response were observed after freak wave exposure under the combined influence of wind, freak wave, and current. The results underscore the profound effects induced by wind and current in the presence of freak waves, providing valuable insights for analyzing similar offshore structures under ultimate design conditions.

Revealing the Intrinsic Correlation between Cu Scales and Free Radical Chain Reactions in the Regulation of Catalytic Behaviour.

Defining the copper-based catalysts that are responsible for the catalytic behaviour of oil-paper insulation systems and implementing effective regulation are of great significance. Accelerated ageing experiments were conducted to reveal variations in copper scales and deterioration in insulation properties. As ageing progressed, TEM images demonstrated that copper species were adsorbed and aggregated on the fibre surface in the form of nanoparticles (NPs). The scale of NPs exhibited a continuous increase, from 27.06 nm to 94.19 nm. Cu(I) and Cu(II) species were identified as the active sites for inducing intense free radical reactions, which significantly reduced the activation energy, making the insulating oil more susceptible to oxidation. The role of the antioxidant di-tert-butyl-p-cresol (DBPC) in extending the insulation life was regulated by determining the optimal addition time based on variations in the interfacial tension. After the second addition of DBPC, the ageing rates of the dissipation factor, acidity, micro-water and breakdown voltage in the Cu+DBPC group decreased by 28.8%, 43.2%, 52.9% and 46.7%, respectively, compared to the Cu group. This finding not only demonstrates the crucial role of DBPC in preventing the copper-based catalyst-induced oxidation of insulating oil, but also furnishes a vital foundation for enhancing the long-term stability of transformer insulation systems.

Exploration of the interfacial tension variation behavior in different CO2/oil systems based on experimental and molecular dynamics simulation studies

Exploration of the interfacial tension variation behavior in different CO2/oil systems based on experimental and molecular dynamics simulation studies

Modeling and control of perturbation torques and mass distribution impact on a tethered system for a 12U CubeSat in sun-synchronous orbit

Tethered CubeSat systems are characterized by momentum exchange and gravity gradient stabilization, and encounter stability challenges, especially with shorter tethers in highly inclined and eccentric orbits. This study investigates the libration dynamics of a 12U CubeSat in its stowed configuration, which separates into two satellites connected via tether, throughout its deployment, station-keeping, and retrieval phases. Two deployed configurations, symmetrical 6U-6U, and asymmetrical 8U-4U connected by a non-conductive tether with a maximum length of 100m are analyzed. The study accounts for perturbations including Earth’s oblateness, atmospheric drag, solar radiation pressure, and lunisolar gravitation, modeling the tether as a rigid, extendable rod and the satellites as lumped masses. The translational and rotational dynamics are decoupled, assuming the system’s center of mass follows an unperturbed Keplerian Sun-synchronous orbit at altitudes between 400 and 600km. A tension control strategy based on Lyapunov’s direct method and supplemented by external actuation torques is explored. Results show high orbit eccentricity significantly affects the maximum in-plane libration angle. The 6U-6U system experiences smaller disturbance torques but greater tether tension variations than the 8U-4U system. Both configurations exhibit larger in-plane oscillations compared to near-zero out-of-plane oscillations, nonetheless, eclipse passages exacerbate the out-of-plane libration of the 8U-4U system. Relative stability is maintained during deployment, however, retrieval is chaotic, with notable oscillations in libration angles and tether tension. The tension control strategy effectively dampens oscillations during retrieval but loses effectiveness as tether tension approaches zero at retrieval’s conclusion. External actuation torques, ranging from 1-2mNm for deployment to 15mNm for retrieval, complement tension control.

Visualizing nuclear pore complex plasticity with Pan-Expansion Microscopy.

Cell-type specific and environmentally-responsive plasticity in nuclear pore complex (NPC) composition and structure is an emerging area of investigation, but its molecular underpinnings remain ill defined. To understand the cause and consequence of NPC plasticity requires technologies to visualize differences within individual NPCs across the thousands in a given nucleus. We evaluate the utility of Pan Expansion Microscopy (Pan-ExM), which enables 16-20 fold isotropic cell enlargement while preserving the proteome, to reveal NPC plasticity. NPCs are robustly identified by deep learning-facilitated segmentation as tripartite structures corresponding to the nucleoplasmic ring, inner ring with central transport channel, and cytoplasmic ring, as confirmed by immunostaining. We demonstrate a range of NPC diameters with a bias for dilated NPCs at the basal nuclear surface, often in local clusters. These diameter biases are eliminated by disrupting linker of nucleoskeleton and cytoskeleton (LINC) complex-dependent connections between the nuclear envelope (NE) and the cytoskeleton, supporting that they reflect local variations in NE tension. Pan-ExM further reveals that the transmembrane nucleoporin/nup POM121 resides specifically at the nuclear ring in multiple model cell lines, surprising given the expectation that it would be a component of the inner ring like other transmembrane nups. Remarkably, however, POM121 shifts from the nuclear ring to the inner ring specifically in aged induced pluripotent stem cell derived neurons (iPSNs) from a patient with C9orf72 amyotrophic lateral sclerosis (ALS). Thus, Pan-ExM allows the visualization of changes in NPC architecture that may underlie early steps in an ALS pathomechanism. Taken together, Pan-ExM is a powerful and accessible tool to visualize NPC plasticity in physiological and pathological contexts at single NPC resolution.

Interfacial Rheological Investigation of Modified Silica Nanoparticles with Different Alkyl Chain Lengths at the n-Octane/Water Interface.

The interfacial dilational rheology of silica nanoparticles (NPs) directly reflects the relationship between surface structure and interfacial behaviors in NPs, which has attracted significant attention in various industrial fields. In this work, modified silica nanoparticles (MNPs) with various alkyl chain lengths were synthesized and systematically characterized using Fourier transform infrared spectra, Zeta potential, and water contact angle measurements. It was found that the MNPs were successfully fabricated with similar degrees of modification. Subsequently, the interfacial behaviors of the MNPs in an n-octane/water system were investigated through interfacial dilational rheological experiments. The length of the modified alkyl chain dominated the hydrophilic-lipophile balance and the interfacial activity of the MNPs, evaluated by the equilibrium interfacial tension (IFT) variation and dilational elasticity modulus. In the large amplitude compression experiment, the balance between the electrostatic repulsion and interfacial activity in the MNPs was responsible for their ordered interfacial arrangement. The MNPs with the hexyl alkyl chain (M6C) presented the optimal amphipathy and could partly overcome the repulsion, causing a dramatic change in surface pressure. This was further confirmed by the variations in IFT and dilational elasticity during the compression path. The study provides novel insights into the interfacial rheology and interactions of functionally modified NPs.

Highly stable nanobubbles in the reduction of apparent viscosity of liquids during UF process

Nano-bubbles (NBs) have attracted more attention in various chemical processes due to their different physicochemical properties from macro-bubbles. However, little attention has been paid to the variations in physicochemical properties of the liquids caused by NBs. In this study, stable NBs in the range of 120–360 nm (mean diameters of 221 nm) are generated at an air pressure of 0.3 MPa. Meanwhile, the surface tension of H2O and sodium dodecyl sulfate (SDS) solution decrease with increasing amounts of NBs, indicating that NBs altered the physicochemical properties of liquids. Consistent with the variations in surface tension, the apparent viscosity of pure H2O and 400 mg L−1 sodium alginate (SA) solutions decreased by 5.6 % and 6.6 % after bubbling for 180 min, respectively, which can be attributed to the long retention time of NBs in the mixture of NB-liquids. The correlations between the apparent viscosity of the gas–liquid mixture (μ) and the gas holdups (V) are then deduced as μ=μ0(1-αV), where μ0 is the apparent viscosity of liquid in the absence of NBs and α is the correction factor. The CFD results further confirm that the apparent viscosity of the gas–liquid mixture decreases with increasing gas holdups. During the UF process, NBs significantly increase the normalized flux of NB-H2O from 1.00 to 1.35 and from 0.72 to 1.02 for NB-10 mg L−1 SA solution, which from the other side confirms that NBs decrease the apparent viscosity of the gas–liquid mixture, thus improving the normalized flux of filtrates. This study provides valuable clues for the significance of NBs in chemical processes.

Electric Buoyancy-driven convection in stable and unstable thermal stratifications

Thermo-electro-convective modes induced by a dielectrophoretic force in a differentially heated horizontal rectangular cavity have been investigated using direct numerical simulations in stable and unstable thermal stratifications. The variation of the electric tension applied to the plates of the cavity leads to multiple modes under microgravity as well as under both stable and unstable stratifications in terrestrial conditions. An effective electric Rayleigh number incorporating the effects of both the electric potential and the thermal stratification has been introduced in order to analyze the heat transfer induced by thermoelectric convection, leading to a unique curve of the variation of the Nusselt number with the effective electric Rayleigh number. The results can be used for modeling the heat transfer in microfluidic devices where the Archimedean buoyancy is very weak or to simulate natural convection at any planet using experiments performed on the Earth.

Hydrodynamic instability of shear imposed falling film over a uniformly heated inclined undulated substrate

Linear and weakly nonlinear stability analyses of an externally shear-imposed, gravity-driven falling film over a uniformly heated wavy substrate are studied. The longwave asymptotic expansion technique is utilized to formulate a single nonlinear free surface deflection equation. The linear stability criteria for the onset of instability are derived using the normal mode form in the linearized portion of the surface deformation equation. Linear stability theory reveals that the flow-directed sturdy external shear grows the surface wave instability by increasing the net driving force. On the contrary, the upstream-directed imposed shear may reduce the surface mode instability by restricting the gravity-driving force, which has the consequence of weakening the bulk velocity of the liquid film. However, the surface mode can be stabilized/destabilized by increasing the temperature-dependent density/surface-tension variation. Furthermore, the bottom steepness shows dual behavior on the surface instability depending upon the wavy wall's portion (uphill/downhill). At the downhill portion, the surface wave becomes more unstable than at the bottom substrate's uphill portion. Moreover, the multi-scale method is incorporated to obtain the complex Ginzburg–Landau equation in order to study the weakly nonlinear stability, confirming the existence of various flow regions of the liquid film. At any bottom portion (uphill/downhill), the flow-directed external shear expands the supercritical stable zones, which causes an amplification in the nonlinear wave amplitude, and the backflow-directed shear plays a counterproductive role. On the other hand, the supercritical stable region decreases or increases as long as the linear variation of density or surface tension increases with respect to the temperature, whereas the sub-critical unstable region exhibits an inverse trend.

Research on monitoring method for ice-covered state of transmission lines based on conductor end displacement

To efficiently and economically monitor the status of transmission lines in frozen rain areas, we propose a method, which can monitor the status of ice- covered transmission lines based on conductor end displacement. Firstly, we delve into the factors that contribute to icing on transmission lines and the subsequent mechanical implications. Subsequently, we propose an equal-height double-node conductor model that aptly captures the stress characteristics of transmission lines in frozen rain environments. This model utilizes the horizontal displacement of the mid-span endpoint and the wire's load as proxies for the variations in horizontal tension and sag. Furthermore, we establish the overall static balance equation for continuous overhead conductors, grounded in the principle of nodal force equilibrium. We then elaborate on the operational framework of our monitoring model. A comparative analysis with existing models reveals the superior accuracy and computational efficiency of our proposed model. To validate our approach, we construct a real-world transmission line setup and assess the economic viability of various monitoring strategies. Additionally, we examine the impact of varying icing thicknesses and locations on the transmission line's status. Our findings indicate that our model outperforms traditional counterparts in terms of accuracy, computational speed, and cost-effectiveness. Specifically, at ice-covered sections, the maximum sag and tension of the conductor exhibit a direct correlation with the ice thickness. Conversely, in non-ice-covered areas, the maximum sag inversely correlates with ice thickness, while the tension maintains a direct relationship.

Growth of a vapour bubble in a viscous, superheated Nanofluid under Effect of Variations in Surface Tension

This study analyzes the growth of a vapour bubble in a superheated nanofluid with variable surface tension at the bubble interface. The governing equations describing the problem are formulated, converted to a single integrodifferential equation, and solved analytically. The results are implemented in one of the favorable nanofluids, namely, Al2O3/water, since it is widely used in nanofluid applications, which include self-cooling devices and as a coolant in newly designed photovoltaic/thermal systems, because it has higher thermal and electrical physical properties than the base fluid and a lower economical preparation cost. The results showed that the growth process is proportional to the thermal diffusivity and the Jakob number, while it is inversely proportional to surface tension, dynamic viscosity, initial bubble radius, coefficient of the initial pressure difference, initial void fraction, and nanoparticle volume fraction. Moreover, we conducted a comparison to the experimental data obtained by Hamda and Hamed (2016), and our results achieved a better agreement with these data than some famous studies for both experiments for superheated Al2O3/water nanofluid and pure water (base fluid), because our model considered the effects of several parameters that were ignored in the previous theories, which have been derived as special cases of our result. Furthermore, the effects of nanoparticle characteristics and slip mechanisms; base fluid type and temperature; and the addition of surfactants on bubble growth rates are investigated. Implications drawn from this study may have consequences for the optimum design of thermal systems/devices based on nanofluid technology.

Experimental Investigation on the Interfacial Characteristics of Tight Oil Rocks Induced by Tuning Brine Chemistry.

Currently, research on enhancing imbibition oil recovery in tight oil reservoirs through the ion-tuning technique remains limited. Two critical parameters for capillary imbibition are the wettability and interfacial tension between oil and water. In this investigation, we manipulate the properties of two types of formation water for both aged and unaged samples by diluting brine and altering ion composition. Subsequently, we employ captive and pendant-drop methods to assess rock wettability and interfacial tension under varied brine conditions. Additionally, we elucidate the primary mechanisms underlying changes in rock wettability and interfacial tension. Meanwhile, we analyze capillarity characteristics and assess the relative significance of wettability and interfacial tension. Results indicate that there is a critical interfacial tension with progressive dilution of two types of formation water. However, modifying ion composition leads to a complex trend in interfacial tension, which can be explained qualitatively through the Gibbs adsorption isotherm. For unaged samples, the contact angle demonstrates a pronounced water-wet characteristic, showing a nonmonotonic trend with respect to dilution times. Remarkably, the rock surface exhibits the strongest water-wet, particularly evident in the case of FW-10, largely influenced by variations in interfacial tension. Conversely, aged samples demonstrate strong oil-wet, with a critical salinity resulting in the lowest contact angle, while altering brine ion types can alter rock wettability from strongly oil-wet to intermediate-wet, which is not sufficient to result in the wettability alteration. The removal of multivalent cations is proposed as the most effective method for wettability modification. Furthermore, capillarity variations among different brine cases are primarily contingent upon contact angle changes, and interfacial tension does not have a significant change when regulating the brine properties. Consequently, we emphasize the significance of wettability in the adoption of ion-tuned brine techniques for tight oil reservoirs. Overall, our study underscores the potential of reasonably regulating brine properties to enhance capillarity and, thereby, improve imbibition oil recovery.

Investigation of Lateral and Longitudinal Deformation of Submarine Nuclear Power Plant Water-Intake Tunnel on Non-Uniform Soft Soil during Earthquake

The safety-grade water-intake immersed tunnel plays a vital role in the nuclear power cooling system, and its seismic safety is crucial. This paper employs the response displacement method and dynamic time-history analysis using the finite element software ANSYS to construct a beam–spring model and a 3D finite element model of a shield tunnel and foundation. It also develops equivalent linear dynamic constitutive and viscoelastic boundary element subprograms. This study focuses on the weak joint sections of immersed tunnels, conducting a seismic performance analysis under extreme safety earthquake conditions (SL-2). The results indicate that the joint stiffness of immersed tunnels and the increase in seismic peak values do not affect the trend of joint opening variation with longitudinal position. The change in joint opening is primarily located where the thickness of the cover layer changes abruptly or where the soil hardness is unevenly distributed. The joint opening is mainly influenced by seismic forces when considering static and dynamic superposition. When the stiffness of the joint GINA water stop exceeds a certain value, the correlation between stiffness change and joint compression–tension variation gradually weakens. This research can provide a reference for the seismic design of similar projects.

Bubble rising in the presence of a surfactant at very low concentrations

This paper analyzes experimentally and numerically the steady bubble rising in water with a surfactant dissolved at very low concentrations. We explain how traces of surfactant can significantly change the bubble dynamics. The tiny surface tension variation produced by the surfactant monolayer has a negligible effect on the capillary pressure. However, this variation occurs within an extremely thin diffusive boundary layer, which produces a Marangoni stress three orders of magnitude larger than the tangential viscous stress in a surfactant-free bubble. Although the Marangoni stress is confined within the surface boundary layer, it manages to immobilize most of the bubble's south hemisphere. The increase in skin friction and the reduction of the terminal velocity cannot be attributed to the viscous stress exerted on the immobilized interface but to the stress in the diffusive surface boundary layer. The stagnant-cap approximation applies despite the small surfactant concentration considered.

Thermocapillary migration of a compound drop in an arbitrary viscous flow

The thermocapillary migration of a concentric compound drop in an arbitrary viscous flow under the consideration of negligible Reynolds number is investigated. The thermocapillary effect refers to the migration of a drop under the influence of a temperature gradient. The thermal and hydrodynamic problems are examined. The thermal field is governed by the heat conduction equation whereas the hydrodynamic fluid velocities are governed by the linearized Navier–Stokes equations. Presence of temperature gradient results in variation of the interfacial tension which is assumed to depend on temperature linearly. Variation of interfacial gradient leads to the coupling of the hydrodynamic problem with the thermal problem through the boundary condition. A complete general solution of Stokes equations is utilized to obtain closed-form expressions for the velocity vector and pressure. The hydrodynamic forces acting on the compound drop are obtained and expressed in terms of Fax́en’s law. Some important asymptotic limiting cases of hydrodynamic drag are also derived. The hydrodynamic drag for cases of uniform flow, shear flow, and heat source with the known ambient flow are derived and it is found that in the case of shear flow, the hydrodynamic drag is contributed only by the thermal component and the shear flow has no effect on it. The obtained results for drag and torque in the limiting cases are in agreement with the existing results in the literature. Furthermore, the migration velocity of the compound drop is obtained by equating the hydrodynamic drag force to zero. The results obtained for migration velocity are explained with the aid of graphs. The migration velocity is found to be a monotonic function of the Marangoni number and the radius of the innermost drop.

Eco-friendly efficient cleaning of oiled sand by phosphorylated cellulose nanocrystal-based composite

Oil from offshore oil spills may be stranded on beaches and exist for decades, requiring appropriate cleaning agents to adequately remove it. Herein, a phosphorylated cellulose nanocrystals (PCNCs) −Tween80 composite cleaning agent was developed by adding trace amounts of nonionic surfactant Tween80. Through the synergistic interaction of various components, the cleaning agent exhibited high oil removal efficiencies for the oiled sand at 25 ℃ and sea salt concentration of 3.5 wt%. The difference among the oil removal efficiencies of cleaning agents containing different components was mainly attributed to variations in the interfacial tension and the zeta potential. The oil removal efficiencies of the cleaning agent for contaminated sand containing engine oil were 81.2 % and 91.4 % at the cleaning speeds of 150 rpm and 300 rpm, respectively. Surprisingly, the composite cleaning agent reached an oil removal efficiency of 89.9 % at just 150 rpm for the real-world polluted system of the sand contaminated with crude oil. At a relatively mild cleaning speed of 150 rpm, the cleaning effect exceeded those reported in most previous studies at 300 rpm. Furthermore, the washing wastewater achieved rapid and efficient oil/water separation under flocculation of using polyaluminum chloride, which was expected to significantly reduce the discharge of wastewater and avoid secondary pollution. This work has developed a PCNCs-based cleaning agent with advantages of high efficiency, environment-friendliness, convenient preparation, low cost, and low discharge of wastewater, which can efficiently remove oil from oiled sand.