Drag Effect Research Articles

Effect of nano-TiC/TiB2 on recrystallization, texture and mechanical properties of Al–Cu–Li alloy during solid-solution treatment

The evolution of the microstructure, texture and mechanical properties of the Al–Cu–Li alloy sheets by nanoscale TiC + TiB2 ceramic particles during solid solution treatment was systematically investigated by characterization, texture measurements and mechanical performance tests. The yield strength, tensile strength, and elongation of the A1 alloy with the addition of nanoscale TiC + TiB2 ceramic particles under T4P conditions were 312 MPa, 420 MPa, and 21.9%, respectively, which were 35.6%, 27.6%, and 2.8% higher than those of the A0 alloy, respectively. The recrystallization mechanism of both alloys was mainly the particle stimulated nucleation (PSN) mechanism, but the nanoscale TiC + TiB2 in the A1 alloy led to a stronger Zener dragging effect, which hindered the growth of CubeND nuclei, and P-oriented grains dominated. Thus, the A0 alloy sheet was dominated by CubeND components, while the A1 alloy sheet was dominated by P recrystallized grains, which led to the two alloy sheets showing opposite variation trends of the deep drawing properties with increasing solid solution treatment time. The short-time solid-solution process is more likely to provide better properties to the alloy with TiC + TiB2 added particles better properties in terms of various aspects, such as microstructure, mechanical properties, and electrical conductivity.

A novel approach to regulate the microstructure of laser-clad FeCrNiMnAl high entropy alloy via CeO2 nanoparticles

In this work, the mechanical mixing process was successfully used to inoculate FeCrNiMnAl powder with CeO2 nanoparticles, which contributed to the heterogeneous nucleation of fine equiaxed grains. In this way, the nano-CeO2/FeCrNiMnAl HEA composite coating with low dilution, cracks-free was successfully fabricated. The effects of different addition of nano-CeO2 (0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%) on the microstructure and properties of HEA composite coatings were mainly explored. The thermodynamic calculations on HEA composite coatings with different contents of CeO2 were conducted to predicted their phase composition. With the modification of nano-CeO2, the microstructure exhibited homogenous, fine-grained and equiaxed. To further reveal the effect of CeO2 on the microstructure, this work studied the columnar-to-equiaxed transition (CET) behavior of HEA coating during solidification process. As a comparison, the heterogeneous nucleation behavior of fine equiaxed grains induced by nano-CeO2 in HEA composite coatings was studies. The results showed that CeO2 nanoparticles were enriched at the grain boundaries of HEA composite coating, and it not only had a drag effect, but also hindered the growth and development of grains. However, excessive nano-CeO2 (2.0 wt% CeO2) could affect the forming quality of HEA coating and have a negative impact on the mechanical properties. After regulating the grain structure, the mechanical properties of HEA composite coating have been greatly improved. While 1.0 wt% nano-CeO2 was added, the microhardness of HEA composite coating reached to the maximum (670.4 HV0.2). Compared with substrate, the average microhardness has increased almost 91.5 %. The friction performance of 1.0 wt% CeO2/FeCrNiMnAl HEA composite coating was the optimal as well and the wear rate reached 3.12 × 10−6 mm3/N m. The tribo-oxide layer was produced on the worn surface of HEA composite coating.

Coulomb effects in electronic transport

AbstractCharge transport in metals and semiconductors is often dominated by electron‐impurity and electron–phonon scattering. Coulomb effects could be found in small corrections to the leading behavior, drag effects in specially fabricated samples, compensated semimetals, and hydrodynamic phenomena in ultra‐pure materials. In contrast, electrical resistivity in strongly correlated systems is poorly understood. Understanding the fate of electron–phonon scattering in these materials may offer a route towards future advancements.

Breaking the high-temperature strength-ductility trade-off in TiAl alloys through microstructural optimization

Designing a novel microstructure with higher strength-ductility than lamellar microstructure (LM), which has been considered the most valuable engineering application in the service temperature range, is desired for lightweight TiAl alloys. Our prior publication reported a three-phase tri-modal (T-T) structure for Ti-43.5Al-4Nb-1Mo-0.1B(.at%) with superior mechanical properties than LM at room temperature (Ref: Acta Mater. 225 (2022) 117,585). However, its strength-ductility at working temperature has yet to be fully exploited. This work fills the much-needed gap. The qualitative and quantitative optimizations indicate that the T-T structure's yield strength increases first and then decreases with increasing pearlitic-like microstructure (PM, which consist of three-phase (α2, γ and βo phase) with clear orientation relationships that form in a lamellar/cellular manner) content while the ductility keeps rising. When the T-T structure contains ∼20 % PMs, it exhibits a yield strength about 130MPa higher than LM coupling with doubled ductility at 750 °C. PMs can induce a prominent twinning induced plasticity and dislocation jog dragging (TWIP&DJD) effect, resulting in better strength-ductility below 700°C; above this temperature, the TWIP&DJD effect significantly plasticizes the alloys. The higher strength of the T-T structure at 750 °C is caused by hetero-deformation-induced strengthening between LMs and PMs, which cannot be offset by the plasticizing caused by PM when the volume fraction of PMs is less than 50 %. This study demonstrates that introducing an appropriate amount of plasticizing structures (similar to PM) with excellent work hardening capacity is a promising strategy for enhancing the strength-ductility synergy of TiAl and possibly other brittle materials.

Secondary vortex drag reduction and heat transfer enhancement of nanofluids in hierarchical microchannels applied to thermal management of electronic components

In order to improve the heat dissipation performance of electronic components, two hierarchical microchannel structures with curve and straight corners are proposed, and semi-circular and trapezoidal secondary flow structures are introduced into the structure with the best performance. The effects of coolant (Fe3O4-water nanofluid), layered structure and secondary flow structure on the comprehensive performance of MCHS were studied by numerical simulation. Results showed that deionized water is more suitable for the heat dissipation of microchannels at this scale. The hierarchical structure has the effect of enhancing heat transfer, and Nu can be increased by up to 67.32 %. The introduction of secondary flow structure has drag reduction effect in a certain Reynolds number range. The hierarchical MCHS with semi-circular secondary flow structure has drag reduction effect in the Reynolds number range of Re = 200–400, and the pressure drop can be reduced by up to 1.89 %. The hierarchical MCHS with trapezoidal secondary flow structure always has a drag reduction effect in the range of Reynolds number Re = 200–600, and the maximum pressure drop can be reduced by 2.46 %, showing excellent drag reduction ability. In addition, the introduction of trapezoidal secondary flow in MCHS increases the Nusselt number by 9.70 %, the comprehensive performance index reaches 1.10, and the cooling performance and comprehensive performance are optimal. The combination of hierarchical structure and secondary flow structure has excellent drag reduction and heat transfer enhancement effects, and has broad application prospects in the field of thermal management of electronic devices.

Effects of separation distance, lateral offset, and yaw on the drag of a truck and SUV platoon

The recent popularity of electric vehicles and upcoming governmental regulations on emissions are forcing automotive manufacturers to build more efficient vehicles. An approach to improve the efficiency of a road vehicle is by reducing its aerodynamic resistance. One way of achieving this is through platooning, vehicles drive in close-proximity. Despite of the extensive literature available on platooning of multiple vehicle types, most studies have focused on the drag and flow effects around the truck only. This work aims to increase the understanding and recognize the usefulness of a truck-SUV platoon system as a whole using wind tunnel measurements on two scale models and CFD simulations. From the results of this study, it was found that the effects on the SUV are large and contribute to a significant portion of the drag reduction of the system, especially at short inter-vehicle distances where the drag of the car can become negative. The drag reduction for the truck is generally limited as the truck is a much larger vehicle. For the system, the results show that for very short distances it is beneficial for the truck to lead the platoon, while at longer separations there is no preferable order.

The effect of terrain-influenced winds on fire spread in QUIC-Fire

In this manuscript, we describe the implementation of the terrain-following version of QUIC-URB into QUIC-Fire and a demonstration of the impacts of terrain-influenced winds on QUIC-Fire-simulated fire spread. No changes to the underlying QUIC-Fire fire spread algorithm were made other than what was required to correctly account for the inclusion of terrain. This paper summarizes simulations used to understand how the QUIC-URB terrain-influenced winds affect upslope fire behavior without additional changes to the QUIC-Fire fire spread algorithm. Previously published FIRETEC results are compared to simulation results from the modified QUIC-Fire (incorporating terrain-influenced winds) that use the same topographies and fuels. QUIC-Fire results showed overall similar behaviors in terms of how the topographies affected fire shapes and trends in spread rates. Due to the terrain-following version of QUIC-URB being unable to generate flow separations at the crest of hills, fire spread rates in these regions across all non-flat topographies were over-predicted when compared to FIRETEC. Lateral fire growth showed similar trends with FIRETEC between topographies but did not capture the increase in spread due to a diagonal interface between grassland and forested fuel regions in the test domain. These simulations suggest possible refinements that are necessary to improve QUIC-Fire and thus guide ongoing efforts related to: how flame tilt angle is accounted for, the incorporation of non-local drag effects, and the inclusion of the wake-eddy parameterizations that are used in QUIC-URB.

Austenite-Grain-Growth Kinetics and Mechanism in Type 347H Alloy Steel for Boiler Tubes

Abstract The research material (type 347H alloy steel) has been characterized using optical microscopy and an EDS/SEM system. Annealing experiments have been conducted at temperatures range of 600–1050°C for 30 min–20 h by using an atmosphere-controlled furnace. Normal grain growth with intermediate grain size has been related to the favouring of creep resistance to recommend the material suitable for boiler tubes at operating temperatures up to 750°C for long duration. The kinetics of grain growth in the 347H has been shown to behave similar to a pure metal in the initial stage of annealing in the range of 0–30 min, beyond which the grain-growth process was found to be suppressed due to second-phase (NbC) particle-pinning and solute drag effects. The grain-growth exponent n is computed to be in the range of 0.117–0.313; the deviation from ideal kinetic behavior (n=0.5) has been scientifically justified. The activation energy for grain growth Qg, for the investigated alloy, has been graphically computed and validated.

Preparation of dense ThO2-based ceramics by Sc doping and simple sintering method

The Th1-xScxO2-x/2 (0 ≤ x ≤ 0.1) ceramic system with high density was originally prepared via a co-precipitation route and simple sintering method. XRD analysis indicates that the Th1-xScxO2-x/2 ceramics exhibited a single cubic fluorite structure and a slight increase of cell parameters. SEM images show that Sc doping contributed a decreasing pores and more uniform grain distribution. The calculated relative densities could reach up to a value higher than 99.0% for x = 0.01 during the isothermal process while the maximum actual relative density was only about 77.4% during the non-isothermal sintering process. And the analysis of grain growth kinetics demonstrates that Th1-xScxO2-x/2 was a solid solution with a high solubility of Sc for x = 0.01 and a low solubility of Sc for both x = 0.05 and x = 0.1, which resulted in a strongly slow grain growth for x = 0.1 due to the solute drag effect. The sintering mechanism investigation also illustrates that low amount (x = 0.01) of Sc doping could significantly enhance the densification sintering of ThO2-based ceramics and reduce the sintering temperature by nearly 150 °C. Such strategy has issued the bottleneck problem existed in the densification sintering of ThO2-based ceramics at a lower temperature without any other special sintering atmosphere, which even could be applicable for other ceramics difficult to sinter.

Atomistic analysis of temperature-dependent dislocation dynamics in Ni3Al-based intermetallic alloys

In this study, we investigate the dynamics of superlattice edge dislocations composed of partial dislocations, complex stacking faults, and antiphase boundaries in binary and ternary Ni-based alloys (γ’ phase) with the L12 structure. In the case of Ni3Al, the dislocation velocity decreases with increasing temperature at low applied shear stress, mainly owing to the phonon drag effect. Meanwhile, in the case of ternary alloys constructed by exchanging Ni atoms with Co atoms in Ni3Al, the effects of temperature on dislocation motion are more complex. At low applied shear stress, the dislocation motion is disturbed by solute Co (i.e., solid-solution strengthening). In this case, the temperature promotes dislocation motion because the potential energy barrier dominates the thermally activated dislocation dynamics. In contrast, when the applied shear stress increases, the temperature suppresses dislocation motion owing to the phonon drag effect. The drag effect also increases with increasing Co concentration. The origin of the energy barrier due to solute atoms at low applied shear stress can be explained by the interaction between the partial dislocation and solute Co. Meanwhile, the origin of the drag effect on the superlattice dislocation dynamics is discussed on the basis of atomic vibrational motions and wavy dislocation behaviors. In this study, we propose and construct a map showing the dominant effects on complex superlattice dislocation dynamics. The map has energy-barrier-dominated, phonon-drag-dominated, and sound velocity-dominated regions, suggesting that the dominant factor changes depending on the applied shear stress, temperature, and strength of the solute–dislocation interaction.

Research on Oil–Gas Two-Phase Flow Characteristics and Improvement of Aero-Engine Bearing Chamber

In order to study the oil–gas two-phase flow characteristics of an aero-engine bearing chamber and improve the scavenge effect of lubricating oil, the two-phase flow solution model of a bearing chamber based on the Euler–Euler method was established. Three improvement schemes were proposed for the ventilation structure and scavenge structure of the bearing chamber. The flow characteristics and scavenge characteristics of a conventional bearing chamber and three improvement schemes under different working conditions were analyzed in depth. The results show that after the conventional bearing chamber ventilation structure is embedded (Embed) and improved, with the increase in the embedding depth, the oil in the cavity is further blocked in the cavity, the amount of oil flowing out from the vent is further reduced, and the scavenge efficiency is further improved. After the slope improvement of the scavenge structure of the conventional bearing chamber, due to the increase in the depth of the oil return groove, the drag effect of the air shear force in the cavity on the oil in the oil return groove is further weakened, and the oil accumulation area on the right side of the scavenge port is further suppressed. The volume fraction of the oil in the cavity is further reduced, and the scavenge efficiency is further improved. The combined improvement scheme (ES) can take into account the advantages of embedding and slope improvement schemes, and further improve the scavenge efficiency. Compared to the conventional bearing chamber, when the oil flow rate is 200 L/h and the speed is 15,000 r/min, the oil return efficiency of the embedded (h = 12 mm), slope (l = 56 mm) and combined improvement schemes are increased by 20.19%, 13.43%, and 37.94%, respectively.

An Analysis Model for Predicting Windage Power Loss of Aviation Spiral Bevel Gears Under Optimal Injection Jet Layout

With the increasing rotating speed of aviation spiral bevel gears, the load-independent windage power loss caused by hydrodynamic behavior has a greater impact on transmission efficiency. An analytical model is established to predict the windage power loss of spiral bevel gears with oil injection lubrication. The improved model regards the total windage losses as the sum of oil–gas dragging effects on the tooth flank, toe/heel, circular cone surface, circumference of the teeth, and tooth root. Then the numerical method and analytical method are combined to calculate windage losses. A multi-objective NSGA-II optimization algorithm is used to optimize the jet layout parameters. The rationality and accuracy of this model are verified by comparing the calculation results of an example with data sets of existing experimental findings and computational fluid dynamics (CFD) simulation results. The calculation results show that compared with the tooth profile assumption method in the existing literature, the improved calculation formula of windage dragging effect on tooth flank can better reflect the influence of oil injection lubrication layout parameters on windage loss and make the windage loss calculation more accurate. Finally, the influence of gear body parameters, working conditions parameters, geometric parameters, and injection lubrication layout parameters on the windage loss is examined. This research provides a theoretical basis and methodological guidance for optimization design of reducing windage power loss.

Mechanistic investigation on the voltage collapse of polymer electrolyte membrane fuel cell under high-temperature and low-humidity conditions

Polymer electrolyte membrane fuel cell (PEMFC) operating under high-temperature and low-humidity (HTLH) conditions enables more efficient and compact fuel cell system through smaller radiators (less parasitic power) and smaller humidifier, but exerts negative influence on conductivity of perfluorosulfonic acid (PFSA) membrane, which is the most commercial proton conductor for PEMFC at current state. Although great progress has been made on the R&D of advanced PFSA-based material, a huge gap from material to PEMFC still exists due to its complicated physico-chemical processes. In this work, after a slight rise of operation temperature, we observe the unexpected voltage collapse of PEMFC under HTLH conditions and non-active zone (nearly zero local current density) is found to fast propagate from air inlet to the rest area during this period. For the first time, temporal–spatial numerical reconstruction of this dynamic process reveals that the current in-plane redistribution raises the local mass transfer losses but make limited contribution. Instead, the water being transferred from anode to cathode due to proton's dragging effect leads to severe anode ionomer dehydration, dominating such process. Finally, suggestions are provided as following: (a) raising membrane conductivity under dry condition or reducing proton's dragging coefficient could significantly improve PEMFC's performance under HTLH condition; (b) particular attention should be paid to the water content of anode ionomer for PEMFC design and system control.

Large-Eddy Simulation of Utility-Scale Wind Farm Sited over Complex Terrain

The realm of wind energy is a rapidly expanding renewable energy technology. Wind farm developers need to understand the interaction between wind farms and the atmospheric flow over complex terrain. Large-eddy simulations provide valuable data for gaining further insight into the impact of rough topography on wind farm performance. In this article, we report the influence of spatial heterogeneity on wind turbine performance. We conducted numerical simulations of a 12×5 wind turbine array over various rough topographies. First, we evaluated our large-eddy simulation method through a mesh convergence analysis, using mean vertical profiles, vertical friction velocity, and resolved and subgrid-scale kinetic energy. Next, we analyzed the effects of surface roughness and dispersive stresses on the performance of fully developed large wind farms. Our results show that the ground roughness element’s flow resistance boosts the power production of large wind farms by almost 68% over an aerodynamically rough surface compared with flat terrain. The dispersive stress analysis revealed that the primary degree of spatial heterogeneity in wind farms is in the streamwise direction, which is the “wake-occupied” region, and the relative contribution of dispersive shear stress to the overall drag may be about 45%. Our observation reveals that the power performance of the wind farm in complex terrain surpasses the drag effect. Our study has implications for improving the design of wind turbines and wind farms in complex terrain to increase their efficiency and energy output.

INFLUENCE OF THE GAUGE FIELD ON TRANSPORT PHENOMENA IN CONDUCTIVE INHOMOGENEOUS MAGNETIC STRUCTURES

The influence of the gauge ("accompanying"), spin-dependent electric field and force induced magnetization dynamics of conducting inhomogeneous magnetic structures, on transport phenomena. It is shown that the transport phenomena, associated with the manifestation of a spin-dependent electric field, lead to the effect of spin Coulomb drag of carriers charge.

The development and validation of the Inhomogeneous Wind Scheme for Urban Street (IWSUS-v1)

Abstract. The layout of urban buildings shows significant heterogeneity, which leads to the significant spatial inhomogeneity of the wind field in and over the canopy of urban street canyons. However, most of the current urban canopy models do not fully consider the heterogeneity of the urban canopy. Large discrepancies thus exist between the wind speeds simulated by the current urban canopy models and those observed in the street canyon. In this study, a parameterization scheme for wind fields, Inhomogeneous Wind Scheme for Urban Street (IWSUS), is developed to better characterize the heterogeneity of the urban canopy. We use a computational fluid dynamics method to generate the IWSUS scheme and compare it with observations of the wind profile and turbulent flux in and over the street canyon for validation. In IWSUS, the wind speed vertical profiles at six representative positions located in a typical street canyon (i.e., the windward or leeward side of a long straight street or the inflow or outflow end) are parameterized separately. The wind profile by IWSUS thus can better describe the horizontal heterogeneity of the urban near-surface wind field, e.g., the dynamic drag effect of buildings in the lower atmospheric layer over the urbanized land use. The validation based on observations shows that the performance of simulation results by IWSUS is better than that by the exponential–logarithmic (exp-log) law widely used in the current urban schemes. We consider typical building arrangement and specific street orientations in IWSUS for wind field simulations, which can better match the distribution characteristics of street canyons around the observation point in the street canyon. The averaged wind profiles and turbulence energy fluxes in the model grids of urban areas by IWSUS are also nearer to the observations than those by the exp-log law. The normalized mean errors (NMEs) between the simulated and the observed vertical average wind speed are 49.0 % for IWSUS and 56.1 % for exp-log law in the range from the ground to 4 times the average height of the buildings and 70 % for IWSUS and 285.8 % for exp-log law in the street canyon (range from the ground to building top). This study proves that the accuracy of simulations of land surface processes and near-ground meteorological processes over the urban canopy can be improved by fully considering the heterogeneity of the urban canopy layout structures and the inhomogeneity of wind field distributions in and over the street canyon. IWSUS is expected to be coupled with mesoscale atmospheric models to improve the accuracy of the wind field, land surface energy budget, meteorological and atmospheric chemistry simulations.

Microstructure and mechanical properties of Nb microalloyed high‑carbon pearlitic steels subjected to isothermal transformation

Niobium (Nb) is mainly added to low-carbon steels, in which the main microstructure is ferrite and/or bainite, to refine grains and improve their properties. However, the studies on Nb in high-carbon pearlitic steels are insufficient, and there are some debates regarding the existing studies. High-carbon pearlitic steel is widely used in bars, wires, and steel rails. The role of Nb in high-carbon steels may differ for different steel grades and under different heat treatments. Hence, further detailed studies are required to improve the properties of high-carbon pearlitic steels. In this study, two series of high-carbon pearlitic steels (68C and 75C series) were designed and subjected to isothermal pearlite transformation at different austenitization and isothermal transformation temperatures. The microstructures and mechanical properties of the steels were investigated by optical microscopy, field-emission scanning electron microscopy, electron backscatter diffraction, scanning transmission electron microscopy, and hardness tests. The results showed that the pearlite lamellae were refined by the addition of Nb to high-carbon pearlitic steels, which was attributed to the solute drag effect of Nb. The pearlite colony and nodule sizes also became finer with the addition of Nb because of the finer prior austenite grains and smaller pearlite growth rates. However, the refinement of the pearlite lamellae, nodules, and colonies by the addition of Nb was not significantly enhanced by increasing the Nb content from 0.014 wt% to 0.027 wt% in 75C series samples. In addition, the pearlite interlamellar spacing and colony and nodule sizes of the samples decreased with decreasing isothermal and austenitization temperatures. Moreover, the addition of Nb to high-carbon steels increased their hardness and yield strength. The main strengthening mechanisms of Nb in high-carbon steel are grain refinement strengthening and precipitation strengthening in the samples austenitized at 900 °C, whereas the improvement of strength is mainly attributed to grain refinement strengthening in the samples austenitized at 1180 °C. This study systematically characterized the pearlite morphology of Nb microalloyed high-carbon steels and analyzed the strengthening mechanism, providing a theoretical reference for the development of Nb-containing high-carbon pearlitic steels.

Drag and heat transfer effect of grooved hydrophobic bluff bodies

This research delves into an examination of the potential reduction in friction drag within turbulent channel flow through the implementation of superhydrophobic surfaces. The focus lies on considering the effect of the hydrophobic surface as a slip boundary condition along the wall. Consequently, this newly introduced boundary condition becomes an integral part of the Large Eddy Simulation (LES) equations. The projected outcome suggests a substantial drag reduction of approximately 15% at Re = 5000-8000 and enhanced heat transfer by 20%, aligning harmoniously with the findings derived from Direct Numerical Simulation (DNS). Significantly, this discovery holds implications regarding the modification of near-wall turbulence structures through the introduction of streamwise slip velocity. Moreover, it becomes evident that the turbulence structure experiences a discernible transformation when the slip length exceeds a specific threshold value.

Relative and absolute on-board optimal formation acquisition and keeping for scientific activities in high-drag low-orbit environment

In this paper, a novel Model Predictive Control (MPC) technique for multi-satellite formation flying geometry acquisition and maintenance in high-drag environment is presented. The proposed MPC relies on a linearized and convexified quasi-nonsingular Relative Orbital Elements (ROE) model based on state transition matrices propagation, allowing to include the effect of perturbations in the prediction to optimize fuel efficiency and tracking accuracy. The formation is controlled with respect to a non-decaying orbiting point to perform absolute and relative station keeping simultaneously. For this purpose, a new dedicated plant matrix to include drag effects on ROE in the propagation is derived and validated with respect to numerical results. In all simulations, the satellites are assumed to be equipped with a single low-thrust propulsion unit, therefore, specific constraints are included in the controller to obtain a feasible solution in a real operational scenario. Moreover, a collision avoidance constraint is added in case of close proximity operations exploiting a linear mapping between the set of ROE and cartesian coordinates expressed in the Local-Vertical-Local-Horizontal (LVLH) reference frame. The controller response is simulated in several realistic mission contexts with a high-fidelity orbital propagator and the results are validated for fuel efficiency by comparing them to similar approaches available in literature and to optimal solutions obtained respectively with a direct single shooting algorithm and with a closed-form impulsive formulation.

Role of molybdenum disulfide (MoS2) nanosheets doping position on the thin-film nanocomposite (TFN) membrane during brackish water treatment

Brackish water desalination based on nanofiltration (NF) has been regarded asa feasible solution to address the scarcity of freshwater. However, the trade-off effect and membrane fouling are challenges for the thin-film composite NF membranes, restricting their further application in desalination. Herein, modified thin-film nanocomposite (TFN) membranes were constructed with molybdenum disulfide (MoS2) nanosheets incorporated either into the polyamide layer (P-TFN) or as an interlayer (I-TFN). The surface morphology, chemical element, electronegativity, pore size, hydrophilicity, separation performance and antifouling property of the membranes were systematically evaluated and compared. The P-TFN membrane exhibited superior salt rejection of Na2SO4 up to 98.4% and preeminent flux recovery ratios (FRRs) of 95.4% and 92.2% for humic acid (HA) and bovine serum albumin (BSA) filtration, respectively, which possessed high electronegativity and small effective pore size. While, without compromising its salt retention and foulant resistance, the I-TFN membrane exhibited 51% better permeability than the control TFC membrane, due to its unique crumpled structure of the PA layer and the “dragging effect” of the interlayer on water molecules. Furthermore, we elaborated on the mechanism underlying the differences in surface properties, and verified the effectiveness of the modified membranes in authentic brackish water desalination. Significantly, the comparison provides novel insight for the customization and regulation of the PA layer.