Rectilinear Channel Research Articles

Exploring sperm cell rheotaxis in microfluidic channel: the role of flow and viscosity

Rheotaxis is a fundamental mechanism of sperm cells that guides them in navigating towards the oocyte. The present study investigates the phenomenon of sperm rheotaxis in Newtonian and non-Newtonian fluid media, which for the first time explores a viscosity range equivalent to that of the oviductal fluid of the female reproductive tract in rectilinear microfluidic channels. Three parameters, the progressive velocity while performing rheotaxis, the radius of rotation during rheotaxis, and the percentage of rheotactic sperm cells in the bulk and near-wall regions of the microfluidic channel were measured. Numerical simulations of the flow were conducted to estimate the shear rate, flow velocity, and the drag force acting on the sperm head at specific locations where the sperms undergo rheotaxis. Increasing the flow velocity resulted in a change in the position of rheotactic sperm from the bulk center to the near wall region, an increase and subsequent decrease in the sperm's upstream progressive velocity, and a decrease in the radius of rotation. We observed that with an increase in viscosity, rheotactic sperms migrate to the near wall regions at lower flow rates, the upstream progressive velocity of the sperm decreases for Newtonian and increases for non-Newtonian media, and the radius of rotation increases for Newtonian and decreases for non-Newtonian media. These results quantify the effects of fluid properties such as viscosity and flow rate on sperm rheotaxis and navigation, thereby paving the way for manipulating sperm behavior in microfluidic devices, potentially leading to advancements in assisted reproduction techniques.

Стационарное протекание несжимаемой вязкой жидкости сквозь двухмерный разветвленный канал

The results of a numerical experiment for the problem of an incompressible viscous fluid stationary flow through a branched planar (two-dimensional) channel are presented. The region in which the flow occurs simulates either blood vessels or a river delta. The finite element method and a modification of the penalty method, as well as the splitting method, are used for calculations. The implementation of the calculation algorithm is using with the help the package FreeFem++. The main goal, in addition, of course, to study the properties and structure of the stationary flow, is to demonstrate the effectiveness of the proposed modification of the penalty method. It is assumed that the region has one input boundary section through which the liquid flows into the region, and several (five) boundary sections through which the liquid flows out of the region. The remaining sections of the region boundary are considered impermeable to liquid. The boundary condition corresponding to the Poiseuille flow in a plane rectilinear channel is set at the input section. Three types of boundary conditions are considered on the output boundary secctions. 1. The boundary conditions correspond to the conditions of conservation of motion of luid particles i. e. the material derivative of the velocity is zero. 2. The boundary conditions correspond to the setting of the flow velocity. 3. The boundary conditions correspond to the setting of the same pressure. The stationary solution is constructed by the relaxation method. In fact, a non-stationary problem is solved over a sufficiently large time interval. As an initial condition for a non-stationary problem, a flow is chosen that is a Poiseuille flow in some region near the input boundary. The dependence of the convergence rate of the relaxation method on the initial data is investigated. It is found that the Poiseuille flow, given at the input section of the boundary of the region, induces similar Poiseuille flows at the output boundaries sections of the region in all these cases of boundary conditions. For a region with five sections of the output boundaries for some configuration of the region, the presence of stationary vortex flows (‘maelstorm’) is found.

Elastic instability in a family of rectilinear viscoelastic channel flows devoid of centerline symmetry

Elastic instability in a family of rectilinear viscoelastic channel flows devoid of centerline symmetry

Variations in hydraulic efficiency of the subglacial drainage landsystem control surging and streaming regimes of outlet glaciers

AbstractSurging and streaming of glaciers are modulated by meltwater availability and pressure which controls mechanical coupling at their beds. Using laboratory-scale experimental modelling and palaeoglaciological mapping, we explore how subglacial drainage landsystems control meltwater drainage efficiency and ice flow velocities for terrestrial-based ice lobes resting on flat horizontal and permeable beds. Two end-members regimes, surging and streaming, appear in our experiments. The surge regime is characterised by a rapid increase of drainage efficiency through development of tunnel valleys and their tributaries, thus reducing the duration of ice flow speed-up events by lowering water pressures and increasing ice-bed coupling. Tunnel valleys connected to ice lobe margins, submarginal thrust moraines, reduced ice lobe extensions and ephemeral shear margins are the most distinctive characteristics of this regime. The stream regime is characterised by disconnected channels of smaller dimensions unable to evacuate all the meltwater: this prolonged drainage inefficiency leads to sustained high ice flow velocity and steady shear margins. Small and rectilinear meltwater channels devoid of tributaries, often disconnected from ice lobe margins, and lineation swarms are diagnostic of this regime.

On the Use of Viscous Micropumps for the Transport of Yield-Stress Liquids in Microfluidic Systems

• A fluid's yield stress is predicted to negatively affect the performance of viscous micropumps. • The drop in performance depends on the Bn number and is estimated to be around 60% for Bn = 10 and 20% for Bn = 2. • Viscous micropumps can be used for pumping weakly-viscoplastic liquids in microfluidic systems. The effect of a fluid's yield stress is numerically studied on the performance of a single-rotor, I-shaped viscous micropump. The device comprises a long cylindrical rotor which rotates in a two-dimensional rectilinear channel filled with a yield-stress fluid. A net flow is established for viscous fluids provided that the cylinder is installed in an off-center position across the channel. Having assumed that the viscoplastic fluid of interest obeys the Bingham-Papanastasiou model we have obtained converged results for Bingham numbers (Bn) up to 10. Numerical results obtained at low Reynolds numbers (typical of microfluidic systems) have revealed that a fluid's yield stress has a negative effect on the device performance. Specifically, the flow rate of the micropump is decreased while its driving torque is increased the larger Bn number. At the maximum Bn number tried in this work (i.e., Bn = 10) the drop in performance is predicted to be around 60%. For Bn < 1, however, it is predicted to be less than 20% suggesting that viscous micropumps can still be regarded as a viable option for the transport of weakly-viscoplastic liquids in microfluidic systems.

Influence of the Physical State of Microencapsulated PCM on the Pressure Drop of Slurry in a Circular Channel.

Phase Change Material (PCM) is mainly used in thermal energy storage. The addition of small PCM particles to the working fluid circulating in the heat exchange systems allowed to increase the amount of transported energy thanks to the use of latent heat—the heat of phase change. Encapsulating PCM in microcapsules avoids the disadvantages of PCM emulsions and makes the resulting slurry an attractive heat energy carrier. The paper presents the effect of the aggregate state of PCM enclosed in microcapsules on the flow resistance of the slurry through a rectilinear tubular channel. The tests were carried out with the use of a tube with an internal diameter of 4 mm and a measuring section length of 400 mm. A slurry of 21.5 wt.% PCM microcapsules (MPCM) was used as the working fluid in distilled water. A slurry with temperatures of 18.4 °C (PCM encapsulated in a solid state), 26.1 °C (PCM is in a phase change), and 30.5 °C (PCM in a liquid state) flowed through the measuring section. The mass flow rate of the MPCM slurry reached 70 kg/h (Remax = 2150). It was shown that the higher the Re number, the higher the value of the flow resistance, and the more clearly this value depended on the temperature of the slurry. Detailed analyses indicate that the observed changes were not the result of a change in the viscosity of the slurry, but its density depending on the state of the PCM. Significant changes in the density of the slurry in the range of the phase transition temperature are the result of significant changes in the volume of the microcapsule containing the phase change material in different aggregate states.

Acoustofluidic-mediated molecular delivery to human T cells with a three-dimensional-printed flow chamber.

Cell-based therapies have garnered significant interest to treat cancer and other diseases. Acoustofluidic technologies are in development to improve cell therapy manufacturing by facilitating rapid molecular delivery across the plasma membrane via ultrasound and microbubbles (MBs). In this study, a three-dimensional (3D) printed acoustofluidic device was used to deliver a fluorescent molecule, calcein, to human T cells. Intracellular delivery of calcein was assessed after varying parameters such as MB face charge, MB concentration, flow channel geometry, ultrasound pressure, and delivery time point after ultrasound treatment. MBs with a cationic surface charge caused statistically significant increases in calcein delivery during acoustofluidic treatment compared to MBs with a neutral surface charge (p < 0.001). Calcein delivery was significantly higher with a concentric spiral channel geometry compared to a rectilinear channel geometry (p < 0.001). Additionally, calcein delivery was significantly enhanced at increased ultrasound pressures of 5.1 MPa compared to lower ultrasound pressures between 0-3.8 MPa (p < 0.001). These results demonstrate that a 3D-printed acoustofluidic device can significantly enhance intracellular delivery of biomolecules to T cells, which may be a viable approach to advance cell-based therapies.

Modulation of acoustofluidic parameters to assess effect on molecular loading in human T cells

T-cell therapies are rapidly emerging for treatment of cancer and other diseases but are limited by inefficient non-viral delivery methods. Acoustofluidic devices are in development to enhance non-viral delivery to cells. The effect of acoustofluidic parameters, such as channel geometry, on molecular loading in human T cells was assessed using 3D-printed acoustofluidic devices. Devices with rectilinear channels (1- and 2-mm diameters) were compared directly with concentric spiral channel geometries. Intracellular delivery of a fluorescent dye (calcein, 100 μg/ml) was evaluated in Jurkat T cells using flow cytometry after ultrasound treatment with cationic microbubbles (2.5% v/v). B-mode ultrasound pulses (2.5 MHz, 3.8 MPa output pressure) were generated by a P4-1 transducer on a Verasonics Vantage ultrasound system. Cell viability was assessed using propidum iodine staining (10 μg/ml). Intracellular molecular delivery was significantly enhanced with acoustofluidic treatment in each channel geometry, but treatment with the 1-mm concentric spiral geometry further enhanced delivery after acoustofluidic treatment compared to both 1- and 2-mm rectilinear channels (ANOVA p < 0.001, n = 6/group). These results indicate that 3D-printed acoustofluidic devices enhance molecular delivery to T cells, and channel geometry modulates intracellular loading efficiency. This approach may offer advantages to improve manufacturing of T cell therapies.

Resistance of Tangential Swirlers with Rectilinear Channel Walls

Resistance of Tangential Swirlers with Rectilinear Channel Walls

LES of H2-air jet combustion in high enthalpy supersonic crossflow

Here, we report on large eddy simulation (LES) of supersonic flow, mixing, self-ignition, and combustion in a supersonic hydrogen jet in a crossflow configuration. The configuration has been experimentally investigated at Stanford and consists of a rectilinear channel with a ramp inlet in which a hydrogen jet discharges at a 90° angle to the high enthalpy supersonic crossflow. This configuration has been extensively studied by several research groups and constitutes a good validation case for model development and physics elucidation. The LES model used is based on an unstructured finite volume discretization of the filtered mass, momentum, species, and energy equations and an explicit flow solver. In this study, we investigate the effects of the jet-to-crossflow momentum ratio, the chemical reaction mechanism, and the combustion subgrid model by comparing predictions and by comparing with experimental data including OH* chemiluminescence images and jet penetration data. In general, good agreement is found but with some departures for the smallest reaction mechanisms and some of the LES combustion models. The LES results are also used to elucidate the flow, mixing, and combustion features of this configuration.

Channel morphodynamics of the Selenga River

The article presents the experimental data of the channel morphodynamics of the Selenga River and the Chikoy River mouth over a 100-year period within the 23.5 km long stretch from the Termyn-Tatur channel to Gustovskii Island. We analyzed changes in the planned pattern of the channel and systemized channel processes for three time sections – 1914, 1987 and 2019 on the stretch from the Termyn-Tatur channel to the Gustovskii Island. The main changes over more than a century have manifested themselves in the form of changes in the elements, types and shapes of bends, dynamics of the width and number of arms, as well as in degradation processes and appearance of new arms, redistribution of the main flow from one arm to another. The most stable areas turned out to be areas of relatively rectilinear channel of undivided and divided types located near the valley side, which was a limiting factor in the development of horizontal deformation. We determined the time of the most significant channel deformations-from 1914 to 1987. This is explained by the number of high-water periods in this period, the total duration of which was 43 years and possibly by the intensification of anthropogenic impact and the associated increase in suspended sediment discharge. The longest period of decrease in the manifestations of channel deformations occurred from 1987 to 2019, and it coincides with a prolonged dry period that began in 1995.

On a property of curves given by the determining equations

The motion of a mechanical system consisting of a carrier and a load is considered. The carrier, located all the time in a horizontal plane, can move translationally along a rectilinear trajectory. The carrier has a rectilinear channel through which the load can move. The load is considered further on as a material point. The load can move in the channel according to a predetermined motion law. The channel axis is located in a vertical plane passing through the trajectory of the carrier. The Coulomb dry friction model is applied for simulation the forces of resistance to the motion of the carrier from the side of the underlying plane. In the conditions of the carrier motion along horizontal plane without detachment, the carrier motion differential equations are a system of three linear second-order differential equations. The influence of the system parameters on the motion of the carrier from the rest state is studied in the point of view of determining functions. An important property of the determining expressions is proved: the existence of a single intersection point of the curves given by the determining equations, which corresponds to the zero angle of setting of the channel along which the load moves.

Hydraulic Resistance of Tangential Swirlers

The hydraulic resistance of nine tangential swirlers with rectilinear and sectional channels is measured. A comparison of the hydraulic resistance coefficients of the different swirlers is and it is established that the structural parameters of the swirlers and Reynolds number together exert a significant influence on the hydraulic resistance. It is shown that the resistance coefficient increases with increasing width of the swirler channel gap due to a decrease in the gas velocity and an increase of the force of viscous friction. A relationship for calculating the resistance coefficient of the swirlers is obtained.

Algorithm for determination the type of bilateral motions of a carrier with a mobile load along a horizontal plane

The motion of a mechanical system consisting of a carrier and a load is considered. The carrier, located all the time in a horizontal plane, can move translationally along a rectilinear trajectory. The carrier has a rectilinear channel through which the load can move. The load is considered further on as a material point. The load can move in the channel according to a predetermined motion law. The channel axis is located in a vertical plane passing through the trajectory of the carrier. The Coulomb dry friction model is applied for simulation the forces of resistance to the motion of the carrier from the side of the underlying plane. In the conditions of the carrier motion along horizontal plane without detachment, the carrier motion differential equations are a system of three linear second-order differential equations. The influence of the system parameters on the motion of the carrier from the rest state is studied. In the considered mechanical system (carrier + load) only two types of motion are possible: regular motions in which the relative moments of time being the switching times from one of the three differential equations to the other are unchanged, and the irregular motions when such switching times are different in each of the half-periods of the load motion. Definitive expressions allowing determine the type of carrier motion for the studied systems are derived. An algorithm for classifying two-sided carrier motions for a predetermined load motion law in a channel is presented based on the values of the defining expressions. Examples of specific systems are considered and the results of computational experiments are presented.

AARF: Any-Angle Routing for Flow-Based Microfluidic Biochips

Flow-based microfluidic biochips are promising with significant applications for automating and miniaturizing laboratory procedures in biochemistry. Automated design methods for flow-based microfluidic biochips are becoming increasingly important due to the advancement in both integration scale and design complexity for complicated biochemical applications. Though the multilayer soft lithography fabrication provides flexibility to route both flow and control channels in any angle, existing routing algorithms still adopt Manhattan routing metrics, which design channel in either vertical or horizontal direction only. Moreover, based on the computational fluid dynamics analysis, rectilinear channels with 90° bends have the following issues: 1) reduced the fluidic flow rate, which degrades the performance of the biochip and may even result in the erroneous outcome of the whole procedure and 2) increased pressure at the right-angle bend, which negatively affects the reliability of the biochip. To fully utilize the routing flexibility, this paper proposes the first any-angle routing algorithm for flow-based microfluidic biochip, called AARF. Computational simulation results show that compared with traditional Manhattan routing method, the proposed AARF significantly improves the total wirelength and total effective wirelength (considering the turning angles) by 17.11% and 35.91%, respectively, which prove the effectiveness of the AARF routing flow.

ANALYSIS OF MORPHOLOGICAL AND HYDROLOGICAL CHANGES IN THE CORRENTES RIVER

Meandering rivers have a number of features that differentiate them from rectilinear and anastomosing channels, such as the rapid change of course, which is the result of continuous adjustments of hydro-sedimentary factors. Studying these changes helps to inform on the potential future changes, and generates valuable data for landuse planning. This study aims to identify the morphological changes in the lower Correntes River between 1984 and 2016, and generate information that is currently scarce about the watershed. A temporal analysis of migrating meanders using remote sensing, literature search, and field work was conducted. This river is highly mobile with lateral and downstream migration, exhibiting a rectilinear channel tendency as shown by the decreased sinuosity between 1984 and 2016. This trend reflects channel adjustment in relation to hydro-sedimentary factors. Because the upstream hydroelectric dam retained sediment and enhanced flow velocity, erosion and meander migration increased. In addition to the channel modification, the dam caused observable changes to the river stage and discharge

Motion of a carrier with a mobile load along a rough inclined plane

The mechanical system consisting of a carrier and a load is considered. The load can move respectively the carrier according to the preset given motion law. The carrier motion from rest caused the load motion is investigated. The carrier can move translationally along rectilinear trajectory along rough inclined plane. The trajectory is the line of the greatest descent. The axis of rectilinear channel along which the load moves is situated in vertical plane containing the carrier trajectory. The Coulomb model is taken to describe the friction forces on sloped plane. Differential equations of motion of carrier with load are obtained. The sufficient condition of the carrier motion without detachment from inclined plane is given. For two special cases of the channel installation angle and the plane inclination angle combination the motion types are described. The computation experiments results are presented: the carrier motions in the special cases are illustrated, the phase portraits for some types of motions are constructed.

The pulsating laminar flow in a rectangular channel

The finite difference method is used to solve the task of the developed pulsating laminar flow in a rectangular channel. The optimum of the difference scheme parameters was determined. Data on the amplitude and phase of the longitudinal velocity oscillations, the hydraulic and friction drag coefficients, the shear stress on the wall have been obtained. Using the dimensionless value of the frequency pulsations two characteristic regimes — the quasisteady-state regime and the high-frequency regime have been identified. In the quasi-steady-state regime, the values of all hydrodynamic quantities at each instant of time correspond to the velocity value averaged over the cross section at a given moment of time. It is shown that in the high-frequency regime, the dependences on the dimensionless oscillation frequency of oscillating components of hydrodynamic quantities are identical for rectilinear channels with a different cross-sectional form (round pipe, flat and a rectangular channels). The effect of the aspect ratio of the rectangular channel sides channel on the pulsating flow dynamics has been analyzed.

Hydrodynamics and heat transfer for pulsating laminar flow in channels

The problem about laminar pulsating flow and heat transfer with high pulsation amplitudes of average cross-section velocity in a round tube and in a flat channel is solved using the finite element method. The difference scheme’s optimal parameters are determined. Data on the pulsation amplitude and phase are obtained for the hydraulic friction coefficient, tangential stress on the wall, liquid temperature, heat flux on the wall qw (at ϑw = const), and wall temperature ϑw (at qw = const) are obtained. Two characteristic modes, namely, quasi steady-state and high-frequency ones are separated based on the value of dimensionless pulsation frequency. During operation in the quasi steady-state mode, the values of all hydrodynamic and thermal quantities correspond to the values of time-average velocity at the given time instant. For operation in the high-frequency mode, it is shown that the dependences of the pulsating components of hydrodynamic and thermal quantities on the dimensionless pulsation frequency have the same pattern for rectilinear channels having different shapes of their cross section. It is found that certain nodal points exist on the distribution of thermal characteristics along the tube (liquid temperature, heat flux density on the wall at ϑw = const, and wall temperature at qw = const) in which the values of these quantities remain unchanged. The distances between the nodal points decrease with increasing the pulsation frequency. The pulsations of thermal quantities decay over the tube length.

Simulation of magnetohydrodynamic effects during large-scale vortices generation in a liquid-metal coolant

This investigation is aimed at establishing the interrelation between the generation of a large-scale vortical motion and magnetohydrodynamic (MHD) effects in liquid-metal nuclear power plant coolants. The subjects of the study are three-dimensional liquid sodium flows in the presence of an external transverse magnetic field in bent and in rectilinear cylindrical channels with obstacles inside of them with different geometries that generate a large-scale vortical motion. To establish the governing dimensionless criteria and their influence on the distribution of the velocity and the magnetic fields, analytical solutions of the Hartmann problem were found to a 2D approximation. A numerical 3D simulation identified the regions of the most intensive induced magnetic field for the 3D Hartmann flow under consideration. The spatial distributions of the fields of the velocities, the vorticity, and the magnetic induction are obtained considering the position of the flow disturbance source. A correlation is found between the vortex formation effects in channels with a complex geometry and the fluctuations of the magnetic field induced in the area where the vortical structures are localized on imposition of a static magnetic field.