Saffman Force Research Articles

Dynamic behavior of DNA molecules in microchannels: exploring deflective, elliptical, and spin motions induced by Saffman and Magnus forces.

Precise manipulation of individual DNA molecules entering and leaving the channel ports, as well as their smooth passage across the channel, is essential for the detection and screening of DNA molecules using nano-/micro-fluidic technologies. In this paper, by combining single-molecule fluorescence imaging and numerical simulations, the motion states of DNA molecules translocating through a microfluidic channel under the action of the applied electric field are monitored and analyzed in detail. It is found that, under certain conditions of the applied electric field DNA molecules exhibit various motion states, including translation crossing, deflection outflow, reverse outflow, reciprocal movement, and elliptical movement. Simulations indicate that, under the action of Saffman force, DNA molecules can only undergo deflective motion when they experience a velocity gradient in the microchannel flow field; and they can only undergo elliptical motion when their deflective motion is accompanied by a spin motion. In this case, the Magnus force also plays an important role. The detailed study and elucidation of the movement states, dynamic characteristics and mechanisms of DNA molecules such as the deflective and elliptical motions under the actions of Saffman and Magnus forces have helpful implications for the development of related DNA/gene nano-/microfluidic chips, and for the separation, screening and detection of DNA molecules.

Contribution of rational design and fractional rheology on magnetic nanoparticle-based drug targeting in a microvessel with Saffman force

Magnetic nanoparticles based drug targeting is one of the prominent drug targeting methods due to non-invasive treatments, and recovery efficiency. The aim of the present problem is to analyze the trajectories of drug carrier particles and the total volume fraction of magnetic nanoparticles required for capturing purposes close to the tumor region. Due to the complex nature of blood, the viscoelastic Maxwell fluid relation is used to describe blood, and the flow of nanoparticles is investigated using momentum equations with the time-variant Caputo-Fabrizio fractional order expression to capture memory effects. The rational design of the nanoparticles such as size and shape with different aspect ratio along particle-particle interaction, Saffman force and external magnetic force are incorporated in the governing equation. The velocity profile of the fluid is represented in the form of the inverse of Laplace and Hankel transform. The velocity profile is solved by numerical integration and trajectories of the drug carrier particles analyzed by using the fourth order Runge-Kutta method by developing an algorithm. The conclusion drawn from the study shows that drug carriers lead towards the tumor region with long term memory effects, and it is easily captured at the tumor region. Viscoelastic rheology capture possibly opposes the drugs carrying magnetic nanoparticles to capture at tumor regions following a similar phenomenon by Saffman force. Spherical shaped drugs carrying magnetic nanoparticles are more prominent to be targeted to the tumor region than other shaped drugs carrying magnetic nanoparticles. The present study will help biomedical engineers and nanomedicine researchers develop magnetic devices and the next generation of drug carrier particles to treat cancerous tumors.

A gas dynamic perspective on particle lifting in electrostatic discharge-like devices using multiphase particle-in-cell approach

Although particle–laden electrostatic discharges are widely used in laboratories as well as in industrial applications, the mechanism of particle lifting for particles initially at rest in such highly unsteady systems is not well understood. A multiphase gas–particle solver is developed using the multiphase particle-in-cell (MP-PIC) approach to emulate the interaction of a compressible shock-dominated gas phase with the dense particle phase. First, the two-way coupled solver is initially used to study the interaction of a planar traveling shock with a vertical curtain of particulates. The gas and particle phase evolution was found to be in good agreement with a similar experimental study in Ling et al. [Phys. Fluids 24, 113301 (2012)]. Second, the MP-PIC code is used to study the interaction of an expanding blast wave with a thick bed of particles. The simulation considered forces such as quasi-steady drag, pressure-gradient, added-mass, Saffman, and Magnus forces. We observe that the vertical liftoff particles close to the shock impingement point in this configuration are associated with the quasi-steady drag, pressure gradient, and added-mass forces. Also, the Saffman lift and Magnus forces contribute to lifting particles located radially farther away from the shock impingement point. In addition, the study finds a decrease in particle lifting efficiency with decreasing plasma kernel length and shock strength.

ADVECTION AND DEPOSITION OF MICRODROPLETS IN STAGNATION POINT FLOW

We investigate trajectories of microscale evaporating droplets in a stagnation point flow near a wall of a respiratory airway. The configuration is motivated by the problem of advection and deposition of microscale droplets of respiratory fluids in human airways during transmission of infectious diseases, such as tuberculosis and COVID-19. Laminar boundary layer equations are solved to describe the airflow while the equations of motion of the droplet include contributions from gravity, aerodynamic drag, and Saffman force. Evaporation is accounted for at both the droplet surface and the wall of the respiratory airway and is shown to delay droplet deposition as compared to the predictions of isothermal models. Evaporation at the airway wall has a stronger effect on droplet trajectories than evaporation at the droplet surface, leading to droplets being advected away by the flow and thus avoiding deposition in the stagnation point flow region.

Investigation of dust lifting by a moving shock wave based on compressible multiphase particle-in-cell method

A dust lifting process by shock waves performs high complexity and is of significance for industrial safety. To develop an in-depth understanding of an inherent physical mechanism of dust lifting, this study presents a detailed consideration regarding particle force models. First, a set of compressive force models of those that may affect lifting is distinguished, which afterwards is integrated into the original compressible multiphase particle-in-cell (CMP-PIC) method. Second, the value of the restitution coefficient is determined using the sensitivity analysis method. Good agreement of the dust lifting height is achieved between the numerical and different experimental results, which demonstrate the reliability of the CMP-PIC method. Then, the contributions of different kinds of forces to dust lifting are qualitatively and quantitatively analyzed. Flow field analysis shows that the shock-induced flow produces downward drag and pressure gradient forces on the particles to inhibit the rise of the particles, while the Magnus and Saffman forces perform a promoting role. Additionally, the compression wave and its reflected wave in the granular medium are clearly observed. Specially, when the reflected wave reaches the surface, huge collision forces on the particles and significantly promotes the initial lifting of particles. Moreover, the histories of forces acting on the particles at different layers of dust are discussed. The results show that different kinds of forces perform intense space-time dependent characteristics, and the dominant forces at different stages of dust lifting are identified. A dimensionless analysis of the force model qualitatively justifies the simulation results. The influence of the shock strength is also discussed.

Compressible gas-droplet flow and heat transfer behind a condensation shock in an expanding channel

A two-fluid mathematical model of a supersonic gas-droplet mixture flow with account of droplet growth due to vapor condensation behind a condensation shock in a plane expanding channel is constructed. The flow structure in both the inviscid core and the two-phase boundary layer assumed to be laminar is studied numerically. The range of flow parameters is considered in which the spontaneous condensation zone (“condensation shock”) is fairly narrow, and just behind this shock thermal parameters of the phases almost reach thermodynamic equilibrium. Downstream, the droplet radius continues to grow due to the flow expansion and further vapor condensation. Of primary concern is the flow region where the droplets become sufficiently inertial to travel with a velocity slip, and hence to model adequately the velocity and temperature fields in both phases a two-fluid model is required. In addition to the Stokes drag, the Saffman lifting force exerted on the droplets in the boundary layer is taken into account. The Saffman force results in droplet deposition and the formation of a thin liquid film on the channel walls. A parametric numerical analysis of the two-phase flow structure in the inviscid flow region and in the near-wall boundary layer is performed, and the effects of phase transitions (droplet condensation and evaporation, as well as the film formation) on the reduction of the adiabatic channel wall temperature are analyzed.

Large eddy simulation of aerosol particle dispersion mechanism in aircraft exhaust plume

Aerosol Infrared Stealth Technology is a novel method to suppress the infrared by releasing aerosol particles around the hot exhaust plume. However, the Infrared Radiation (IR) suppression rate is much lower in flight tests, which is caused by the unclear particle dispersion mechanism in high-speed non-isothermal shear flow. Hence, the large eddy simulation (LES) and particle discrete phase model (DPM) are coupled to solve the turbulent shear flow and the aerosol particle motion. The effects of aircraft flight speed on the turbulent flow characteristics and particle motion behaviors are systematically studied. It is found that the Mach rings appear in flight conditions, and they are getting blurry when increasing the flight speed. Both γ-like vortex and horseshoe-like vortex are observed when Ma < 1, and the horse-like could disappear when Ma > 1. The aerosol particle distribution is closely related to the turbulent gas vortices. The particle lateral dispersion is obviously restricted with the rising flight speed. Besides, the drag force plays a dominant role, the Saffman force and the thermophoretic force are of the same order of magnitude, all of these three forces are much greater than the gravity.

Impact of drug carrier shape, size, porosity and blood rheology on magnetic nanoparticle-based drug delivery in a microvessel

Background and objectiveIn the drug targeting delivery, the mesoporous materials known as biomaterials exhibit a more significant drug loading and drug release capacity at a specific location are controlled by the external magnetic field. This article theoretically investigates the effects of a high specific surface, pore volume and unique pore size enrich mesoporous materials as carriers for magnetic drug targeting delivery. We analyze the trajectory of a porous drug carrier embedded with the magnetic nanoparticles are transported with the blood flow through the microvessel. MethodsThe governing equations for blood flow and the motion of the magnetic nanoparticles are solved analytically in terms of the Bessel function. The solutions have been computed numerically to discuss the effects of size and permeability of the carrier particle, the volume fraction of embedded magnetic nanoparticles, distance of the magnetic from the axis of the microvessel,the intensity of the magnetic field, blood rheology, the shape of the carrier particles and Saffman force on flow analysis. ResultsThe permeability of the drug carrier and the peripheral region support the drug carrier to capture near the tumor zone, while the stress jump is constant and Saffman parameter shows an opposite phenomenon. Due to symmetricity, the spherical particles easily capture at the tumor zone rather than the arbitrarily shaped drug carrier. Blood rheology based yield stress reduces the efficiency of the drug carrier to capture close to the tumor region. The trajectories of the drug carrier towards the tumor are restricted with an increase in the aspect ratio of the cylinder. The same phenomena are observed for the increased aspect ratio of the prolate ellipsoid. The outcomes of the present analysis will help to develop biomaterials in the drug delivery applications.

Modeling the Filler Phase Interaction with Solidification Front in Al(TiC) Composite Produced by the In Situ Method.

This paper presents simulation results of the interaction of TiC nanoparticle in liquid aluminum. The behavior of the TiC particle in the frontal interaction region stems from the operation of a system of such forces as gravity, viscous flow drag force, and Saffman force. The difference in density between the TiC and the aluminum matrix makes the particle fall, regardless of the radius dimension; while the Saffman force—which accounts for the local velocity gradient of the liquid aluminum—causes that particles with the smallest radii considered in the calculations 6.4 × 10−8 m; 7 × 10−8 m; 7.75 × 10−8 m; 9.85 × 10−8 m are repelled from the solidification front and the particles with 15.03 × 10−8 m are attracted to it. The viscosity growth in the course of casting caused by the lowering temperature reduces this effect, though the trend is maintained. The degree to which the particle is attracted to the front clearly depends on the velocity gradient of the liquid phase. For a very small gradient of 0.00001 m/s, the particle is at its closest position relative to the front.

Parabolic velocity profile causes shape-selective drift of inertial ellipsoids

Understanding particle drift in suspension flows is of the highest importance in numerous engineering applications where particles need to be separated and filtered out from the suspending fluid. Commonly known drift mechanisms such as the Magnus force, Saffman force and Segré–Silberberg effect all arise only due to inertia of the fluid, with similar effects on all non-spherical particle shapes. In this work, we present a new shape-selective lateral drift mechanism, arising from particle inertia rather than fluid inertia, for ellipsoidal particles in a parabolic velocity profile. We show that the new drift is caused by an intermittent tumbling rotational motion in the local shear flow together with translational inertia of the particle, while rotational inertia is negligible. We find that the drift is maximal when particle inertial forces are of approximately the same order of magnitude as viscous forces, and that both extremely light and extremely heavy particles have negligible drift. Furthermore, since tumbling motion is not a stable rotational state for inertial oblate spheroids (nor for spheres), this new drift only applies to prolate spheroids or tri-axial ellipsoids. Finally, the drift is compared with the effect of gravity acting in the directions parallel and normal to the flow. The new drift mechanism is stronger than gravitational effects as long as gravity is less than a critical value. The critical gravity is highest (i.e. the new drift mechanism dominates over gravitationally induced drift mechanisms) when gravity acts parallel to the flow and the particles are small.

Study of particle lifting mechanisms in an electrostatic discharge plasma

Although particle-laden electrostatic discharges are widely used in research as well as in industrial applications, the mechanisms of particle lifting for a particle initially at rest in such highly unsteady flows are not well understood. A multiphase plasma flow is modeled by solving the continuum conservation equations and particles as discrete entities in a Lagrangian approach. The gas phase solver is used to study the generation of shock waves and the high temperature plasma kernel. A one-way coupling approach between the two phases is used and various Lagrangian sub-models are developed to study the particle phase evolution in the system. Comparison with shock tube measurements where a planar shock wave perpendicular to the shock tube wall interacts with particles residing on the wall showed that the predominant mechanism of particle lifting is the Saffman force generated on particles due to velocity gradients in the gas boundary layer. A second configuration with an overhead spherical blast wave generated by an electrostatic discharge (ESD) interacting with a polydisperse distribution of spherical particles placed at three wall-electrode distances was considered. The predicted particle lifting heights and velocities are found to compare well with measurements in an ESD configuration initiated by the dielectric breakdown of ambient air.

Numerical Simulation on Saffman Force Controlled Inclusions Removal during the ESR Process

Electroslag remelting (ESR) is an effective method for removing nonmetallic inclusions from steels or alloys. The main stage of inclusion removal during ESR is the aggregation of liquid metal film (LMF) to form droplets at the consumable electrode tip. In this study, a lab-level ESR experiment was carried out. The number and size of inclusions at the characteristic position of the electrode were quantitatively counted. The number of inclusions in the center position of LMF were larger than that in other regions. To elucidate these phenomena, a two-dimensional mathematical model was established to study the migration of inclusions in LMF. The results indicate that due to the large velocity gradient in LMF, the Saffman force is strong enough to offset the buoyant force and drag the inclusions toward the slag/LMF interface (SFI), where the inclusions will be dissolved in the SFI region by the molten slag. This study demonstrates that the Saffman force plays a key role in the removal of nonmetallic inclusions in LMF during the ESR process.

On the Role of Saffman Force in Inertial Microfluidics

In this brief review article, the effects of Saffman force in inertial microfluidics-based systems are discussed and investigated. A short discussion regarding the applications of microfluidics, especially inertial microfluidics, is given. Then, the importance of the present investigation is illustrated. The Saffman force is mathematically formulated based on matched asymptotic expansion approach.

Dynamics analysis of microparticles in inertial microfluidics for biomedical applications

Inertial microfluidics-based devices have recently attracted much interest and attention due to their simple structure, high throughput, fast processing and low cost. They have been utilised in a wide range of applications in microtechnology, especially for sorting and separating microparticles. This novel class of microfluidics-based devices works based on intrinsic forces, which cause microparticles to migrate laterally and locate at their equilibrium positions. In this article, a comprehensive theoretical formulation is presented for the dynamics of ultrasmall particles in microfluidics-based devices. Explicit expressions are presented for various important forces, which act on a microparticle, such as drag, Magnus, Saffman and wall-induced forces. In addition, the drag coefficient, diffusion phenomenon and Peclet number are formulated. Finally, the influences of particle size, as a crucial parameter, on various intrinsic forces including drag, Magnus and Saffman forces as well as the wall-induced force, are investigated. It is found that the drag, wall-induced and Saffman forces have an important role to play in the dynamics of microparticles in inertial microfluidics while the effects of Magnus force and diffusion can be ignored in most applications.

The Droplets Condensate Centering in the Vapour Channel of Short Low Temperature Heat Pipes at High Heat Loads

The results of experimental studies of the process of condensate microdroplets centering contained in the moving moist vapour in the vapour channel of short heat pipes (HPs) for large thermal loads are presented. A vapour channel formed by capillary-porous insert in the form of the inner Laval-liked nozzle along the entire length of the HP. In the upper cover forming a condensation surface in the HP, on the diametrical line are installed capacitive sensors, forming three capacitors located at different distances from the longitudinal axis of the vapour channel. With increasing heat load and the boil beginning in the evaporator a large amount of moist vapour in the vapour channel of HP occur the pressure pulsation with frequency of 400-500 Hz and amplitude up to 1·104Pa. These pulsations affect the moving of the inertial droplets subsystem of the vapour and due to the heterogeneity of the velocity profile around the particle flow in the vapour channel at the diameter of microdroplets occurs transverse force, called the Saffman force and shear microdroplets to the center of vapour channel. Using installed in the top cover capacitors we can record the radial displacement of the condensable microdroplets.

Identification of dust storm origin in South \u2013West of Iran

BackgroundDeserts are the main sources of emitted dust, and are highly responsive to wind erosion. Low content of soil moisture and lack of vegetation cover lead to fine particle’s release. One of the semi-arid bare lands in Iran, located in the South-West of Iran in Khoozestan province, was selected to investigate Sand and Dust storm potential.MethodsThis paper focused on the metrological parameters of the sampling site, their changes and the relationship between these changes and dust storm occurrence, estimation of Reconaissance Drought Index, the Atterberg limits of soil samples and their relation with soil erosion ability, the chemical composition, size distribution of soil and airborne dust samples, and estimation of vertical mass flux by COMSALT through considering the effect of saffman force and interparticle cohesion forces during warm period (April–September) in 2010. The chemical compositions are measured with X-ray fluorescence, Atomic absorption spectrophotometer and X-ray diffraction. The particle size distribution analysis was conducted by using Laser particle size and sieve techniques.ResultsThere was a strong negative correlation between dust storm occurrence and annual and seasonal rainfall and relative humidity. Positive strong correlation between annual and seasonal maximum temperature and dust storm frequency was seen. Estimation of RDIst in the studied period showed an extremely dry condition. Using the results of particle size distribution and soil consistency, the weak structure of soil was represented. X-ray diffraction analyses of soil and dust samples showed that soil mineralogy was dominated mainly by Quartz and calcite. X-ray fluorescence analyses of samples indicated that the most important major oxide compositions of the soil and airborne dust samples were SiO2, Al2O3, CaO, MgO, Na2O, and Fe2O3, demonstrating similar percentages for soil and dust samples. Estimation of Enrichment Factors for all studied trace elements in soil samples showed Br, Cl, Mo, S, Zn, and Hg with EF values higher than 10.ConclusionThe findings, showed the possible correlation between the degree of anthropogenic soil pollutants, and the remains of Iraq-Iran war. The results expressed sand and dust storm emission potential in this area, was illustrated with measured vertical mass fluxes by COMSALT.

Permeability and stress-jump effects on magnetic drug targeting in a permeable microvessel using Darcy model

In the present paper, we investigated the influence of permeability of the carrier particle and stress jump condition on the porous spherical surface in magnetic drug targeting through a permeable microvessel. The nature of blood is defined by non-Newtonian Casson fluid in the core region of the microvessel and Newtonian fluid in the peripheral region which is located near the surface of the wall of the microvessel. The magnetic particles are considered as spherical and in nanosize, embedded in the carrier particle along with drug particles. A magnet is placed near the tumor position to generate a magnetic field. The relative motion of the carrier particle is the resultant of the fluidic force, magnetic force and Saffman drag force which are calculated for the spherical carrier particle. Trajectories of the carrier particle along the radial and axial direction are calculated. Effect of different parameters such as stress-jump constant, permeability of the carrier particle, pressure gradient, yield stress, Saffman force, volume fraction of the embedded magnetic nanoparticles, permeability of the microvessel wall, and the radius of the carrier particle on the trajectory of the carrier particle are discussed and displayed graphically.

Simulation of Air Flow and Particle Trajectories in the Head–Disk Interface

A numerical method is presented to study the air-flow pattern and particle trajectory in the head–disk interface (HDI) in this paper. It first solves the generalized steady-state Reynolds equation with slip boundary conditions to get the slider attitude. Then, it solves the reduced Navier–Stokes equation to get the air flow velocity distribution in the HDI. The motion equations of particles are solved to obtain the particle trajectory in the HDI by using the fourth-order Runge–Kutta method. Air flow characteristics and particle behaviors are investigated to illustrate the relationship between the air flow and particle trajectory. The effect of the particle release height is also studied. The simulation results show that particle trajectories basically overlap air flow streamlines in the horizontal plane. The particle moves a longer horizontal distance at a lower particle release height. The difference between the horizontal velocity of the particle and the air flow indicates that the Saffman force points to the disk in the transition region close to the leading edges of leading pads. Moreover, the peak values of the air flow vertical velocity in the previously mention location increase with the reduction of the particle release height. And the air flow vertical velocity along the particle trajectory is almost two times larger than that of the particle at the leading edges of leading pads. The results also show that the drag force of the air flow mainly drives particles up toward the air bearing surface at the leading edges of leading pads, but not the Saffman force.

Tunable Particle Focusing in a Straight Channel with Symmetric Semicircle Obstacle Arrays Using Electrophoresis-Modified Inertial Effects

In this work, a novel microfluidic platform for tunable particle focusing in a straight channel with symmetric semicircle obstacle arrays using electrophoresis (EP)-modified inertial effects was presented. By exerting an EP force on the charged microparticles, a relative velocity gap between microspheres and fluid in a straight channel with symmetric semicircle obstacle arrays was implemented. The relative velocity and fluid shear will induce shear-slip lift force (Saffman lift force) perpendicular to the mainstream direction. Therefore, the focusing pattern can be altered using the electrophoresis-induced Saffman force. The effects of electric field direction, flow rate, electric field magnitude, and particle size were also studied. This demonstrates the possibility of adjusting the particle inertial focusing pattern in a straight channel with with symmetric semicircle obstacle arrays using electrophoresis. Manipulation of the lateral migration of focusing streaks increases controllability in applications such as blood cell filtration and the separation of cells by size.

Dynamic analysis of a liquid droplet and optimization of helical angles for vortex drainage gas recovery

Downhole vortex drainage gas recovery is a new gas production technology. So far, however, the forces and motions of liquid phase in the swirling flow field of wellbores during its field application have not been figured out. In this paper, the forces of liquid droplets in the swirling flow field of wellbores were analyzed on the basis of two-phase fluid dynamics theories. Then, the motion equations of fluid droplets along axial and radical directions were established. Magnitude comparison was performed on several typical acting forces, including Basset force, virtual mass force, Magnus force, Saffman force and Stokes force. Besides, the formula for calculating the optimal helical angle of vortex tools was established according to the principle that the vertical resultant force on fluid droplets should be the maximum. And afterwards, each acting force was comprehensively analyzed in terms of its origin, characteristics and direction based on the established force analysis model. Magnitude comparison indicates that the forces with less effect can be neglected, including virtual mass force, Basset force and convection volume force. Moreover, the vertically upward centrifugal force component occurs on the fluid droplets in swirling flow field instead of those in the conventional flow field of wellbores, which is favorable for the fluid droplets to move upward. The reliability of optimal helical angle calculation formula was verified by means of case analysis. It is demonstrated that with the decrease of well depth, the fluid-carrying capability of gas and the optimal helical angle increase. The research results in this paper have a guiding significance to the optimization design of downhole vortex tools and the field application of downhole vortex drainage gas recovery technology.