High-throughput particle focusing and separation in split-recombination channel

Inertial microfluidic has been widely applied to manipulate particles or bio-sample based on the inertial lift force and Dean Vortices. This technology provides significant advantages over conventional technologies, including simple structure, high throughput and freedom from an external field. Among many inertial microfluidic systems, the straight microchannel is commonly used to produce inertial focusing, which is a phenomenon that particles or cells are aligned and separated based on their size under the influence of inertial lift force. Besides the inertial lift force, flow drag forces induced by the geometrical structures of microchannel can also affect particle focusing. Herein, a split-recombination microchannel, consisting of curved and straight channels, is proposed to focus and separate particles at high flow rate. As compared with the straight channel, the particle focusing in the split-recombination channel is greatly improved, which results from the combined effects of the inertial lift force, the curvature-induced Dean drag force and the structure of split and recombination. Moreover, the distribution of different-sized particles in designed microchannel is investigated. The results indicate that the proposed microchannel not only enhances the particle focusing but also enables the separation of different-sized particles with high throughput. Finally, it is discovered that the larger length of straight channel and curvature radius of curved channel can result in a more efficient particle separation. Another important feature of designed split-recombination microchannel is that it can be arranged in parallel to handle large-volume samples, holding great potential in lab-on-a-chip 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.

Flow and heat transport phenomenon for dynamics of Jeffrey nanofluid past stretchable sheet subject to Lorentz force and dissipation effects

Survey of literature unveils that nanofluids are more efficient for heat transport in comparison to the traditional fluids. However, the enlightenment of developed techniques for the augmentation of heat transport in nanomaterials has considerable gaps and, consequently, an extensive investigation for aforementioned models is vital. The ongoing investigation aims to study the 2-D, incompressible Jeffrey nanofluid heat transference flow due to a stretchable surface. Furthermore, the effect of dispersion of graphene nanoparticles in base liquid ethylene glycol (EG) on the performance of flow and heat transport using the Tawari-Das model in the existence of Ohmic heating (electroconductive heating) and viscous heat dissipation is contemplated. The boundary-layer PDEs are reconstituted as ODEs employing appropriate similarity transformation. Keller-Box Method (KBM) is utilized to determine the numerical findings of the problem. Graphene conducts heat greater in rate than all of the other materials and it is a good conductor of electrical energy. Graphene/EG nanofluid is employed to look out the parametric aspects of heat transport flow, drag coefficient, and heat transference rate phenomena with the aid of graphs and tables. The numerical outcomes indicate that concentration and magnetic field abate the shear stresses for the nanofluid. An increase of Graphene nanoparticle volume fraction parameter can boost the heat transport rate. The effect of Prandtl Number is to slow down the rate of heat transport as well as decelerate the temperature. Additionally, the rate of heat transportation augments on a surface under Deborah's number. Results indicate that the temperature of the graphene-EG nanofluid is greater than the convectional fluid hence graphene-EG nanofluid gets more important in the cooling process, biosensors and drug delivery than conventional fluids.

Evaluation of Anti-Icing Performance for an NACA0012 Airfoil with an Asymmetric Heating Surface

Heating devices on airfoil surfaces are widely used as an anti-icing technology. This study investigated the aerodynamic performance with a static heating surface based on the modified extended Messinger model. The predicted ice shape was validated through a comparison with the experimental results for HAARP-II. A reasonable agreement was found for both the icing area and the ice mass on the suction surface. Then, the prediction method was adopted for an NACA0012 airfoil at an attack angle of 4.0∘ under a glaze ice condition. An asymmetric heating area was imposed on the suction and pressure surfaces considering a temperature of 10∘C near the leading edge. As a result of heating, the round ice formation when was no longer observed, and the formed ice volume decreased. However, bump-shaped pieces of ice were formed downstream of the heater owing to runback water; these bump-shaped pieces of ice formed on the suction surface significantly increased the flow drag and reduced the lift. The results indicated that extending the heating area on the suction surface can improve the aerodynamic performance. Consequently, the overall aerodynamic performance is deteriorated by adding static heating compared to the case without heating.

Monolithic polymeric porous superhydrophobic material with pneumatic plastron stabilization for functionally durable drag reduction in blood-contacting biomedical applications

Superhydrophobic (SHP) surfaces can provide substantial reductions in flow drag forces and reduce blood damage in cardiovascular medical devices. However, strategies for functional durability are necessary, as many SHP surfaces have low durability under abrasion or strong fluid jetting or eventually lose their air plastron and slip-flow capabilities due to plastron gas dissolution, high fluid pressure, or fouling. Here, we present a functional material that extends the functional durability of superhydrophobic slip flow. Facile modification of a porous superhydrophobic polytetrafluoroethylene (PTFE, Teflon) foam produced suitable surface structures to enable fluid slip flow and resist protein fouling. Its monolithic nature offered abrasion durability, while its porosity allowed pressurized air to be supplied to resist fluid impalement and to replenish the air plastron lost to the fluid through dissolution. Active pore pressure control could resist high fluid pressures and turbulent flow conditions across a wide range of applied pressures. The pneumatically stabilized material yielded large drag reductions (up to 50%) even with protein fouling, as demonstrated from high-speed water jetting and closed loop pressure drop tests. Coupled with its high hemocompatibility and impaired protein adsorption, this easily fabricated material can be viable for incorporation into blood-contacting medical devices.

Study on the Law of Pseudo-Cavitation on Superhydrophobic Surface in Turbulent Flow Field of Backward-Facing Step

Superhydrophobic surface is regarded as important topic in the field of thermal fluids today due to its unique features on flow drag reduction and heat transfer enhancement. In this study, the pseudo-cavitation phenomenon on the superhydrophobic surface in the backward-facing step turbulent flow field is observed through experiments. The underlying reason for this phenomenon is studied with experimental observation and analysis, and the time variant mechanisms of this phenomenon with various Reynolds number is summarized. The research results indicate that the superhydrophobic surface and the backward-facing step provide the material basis and dynamic condition for the generation of pseudo-cavitation. The pseudo-cavitation induces a large bubble on the superhydrophobic surface below the backward-facing step. The size, position, shape, oscillation amplitude, detachment, and splitting of the large bubble show regularity with the changes of Reynolds number. Meanwhile, the bubble growth, oscillation, detachment, split, and regeneration over time also show regularity. The study of bubble generation and development laws can be used to better control the perturbation of the flow field. Importantly, the present study has meaning in better understanding the flow mechanisms and gas coverage of superhydrophobic surface under condition of backward-facing step, paving the way for studying the flow drag reduction effect of superhydrophobic surface.

A note to further explain the mechanism of turbulent flow drag reduction by polymer from chemistry view

In our previous work regarding the mechanism of drag reduction and degradation by flexible linear polymers, we proposed a correlation based on the Fourier series to predict the drag reduction and its degradation, where a phase angle was involved, but the physical meaning for the correlation especially of the employed phase angle was not clear, which is however important for reasonable explanation of the drag reduction mechanism over flexible linear polymers. This letter aims to clarify this issue. We use several steps of deduction from the viscoelastic theory, and conclude that the Fourier series employed to predict the drag reduction and its degradation is due to viscoelastic property of drag-reducing polymer solution, and the phase angle represents the hysteresis of polymer in turbulent flow. Besides, our new view of drag reduction by flexible polymers can also explain why a maximum drag reduction in rotational flow appears before degradation happens.

Vortex chip incorporating an orthogonal turn for size-based isolation of circulating cells

Label-free separation of rare cells (e.g. circulating tumor cells (CTCs)) based on their size is attractive due to its wider applicability, simpler sample preparation, faster turnaround, better efficiency and higher purity. Amongst cognate protocols for the same, vortex-trapping based techniques offer high throughput but operate at high flow velocities where the resulting hydrodynamic shear stress is likely to damage cells and compromise their viability for subsequent assays. We present here an orthogonal vortex chip which can carry out size-differentiated trapping at significantly lower (38% of previously reported) flow velocities. Fluid flowing through the chip is constrained to exit the trapping chamber at right angles to that of its entry. Such a flow configuration leads to the formation of vortex in the chamber. Above a critical flow velocity, larger particles are trapped in the vortex whereas smaller particles get ejected with the flow: we call this phenomenon the turn-effect. We have characterized the critical velocities for trapping of cells and particles of different sizes on chips with distinct entry-exit configurations. Optimal architectures for stable vortex trapping at low flow velocities are identified. We explain how shear-gradient lift, centrifugal and Dean flow drag forces contribute to the turn-effect by acting on cells which pushes them into specific vortices in a size- and velocity-dependent fashion. Finally, we demonstrate selective trapping of human breast cancer cells mixed with whole blood at low-concentration. Our findings suggest that the device shows promise for the gentle isolation of rare cells from blood.

Dielectrophoretic Crossover Frequency of Single Particles: Quantifying the Effect of Surface Functional Groups and Electrohydrodynamic Flow Drag Force

We present a comprehensive comparison of dielectrophoretic (DEP) crossover frequency of single particles determined by various experimental methods and theoretical models under the same conditions, and ensure that discrepancy due to uncertain or inconsistent material properties and electrode design can be minimized. Our experiment shows that sulfate- and carboxyl-functionalized particles have higher crossover frequencies than non-functionalized ones, which is attributed to the electric double layer (EDL). To better understand the formation of the EDL, we performed simulations to study the relationship between initial surface charge density, surface ion adsorption, effective surface conductance, and functional groups of both functionalized and nonfunctionalized particles in media with various conductivities. We also conducted detailed simulations to quantify how much error may be introduced if concurrent electrohydrodynamic forces, such as electrothermal and electro-osmotic forces, are not properly avoided during the crossover frequency measurement.

Computational and Experimental Investigation of Camber-Morphing Airfoils for Reverse Flow Drag Reduction on High-Speed Rotorcraft

Through computational fluid dynamics simulations and wind tunnel tests, this study examines a NACA 63-218 airfoil in reverse flow at Rec=375,000 and demonstrates reduction in reverse flow drag through the introduction of reflex camber. Of the three contributors to drag—ram pressure on the upper surface near the trailing edge, suction on the lower surface near the trailing edge, and bluff body separation at the rounded nose—reflex camber (where the camber line near the trailing edge of the airfoil is deflected upward) influences the first two, reducing exposure to ram drag on the upper surface while rotating the suction on the lower surface away from the direction of drag. Particle image velocimetry and surface pressure measurements were utilized in experiment to directly compare with the results obtained through simulation. As expected, the flow was dominated by separation over the sharp trailing edge, where at moderate angles of attack (α <190°), a separation bubble was observed; the use of reflex camber reduced the extent of this separation. The simulations (unsteady Reynolds-averaged Navier–Stokes with and without the Spalart–Allmaras turbulence model) captured the reduction in separation at the trailing-edge well, as there was good agreement between the velocity fields when compared to experiments. This yielded maximum drag reductions near 60% for a 10° reflex camber, compared to reductions near 50% in experiments. Even greater percentage reductions in drag (up to 70%) were observed with a larger 15° reflex angle (not tested experimentally) for nose-up pitch angles greater than 5°in reverse flow. With simulations at a higher Reynolds number (1.5 million) showing very similar drag reductions, using reflex camber over inboard blade sections appears to have significant promise for alleviating reverse flow drag on edgewise rotors at high advance ratio.