Presence Of Fluid Flow Research Articles

Enhanced cancer cell invasion caused by fibroblasts when fluid flow is present.

It has been demonstrated that interstitial fluid (IF) flow can play a crucial role in tumor cell progression. Swartz and collaborators (Cancer Cell 11: 526-538, Shields et al. 2007) demonstrated that cells that secrete the lymphoid homing chemokines CCL21/CCL19 and express their receptor CCR7 could use flow to bias the secreted chemokine, causing pericellular gradients that stimulate cells to migrate in the direction of the flow. In a further work by Shieh et al. (Cancer Res 71: 790-800, 2011), a synergetic enhancement of tumor cell invasion caused by interaction between tumor cells and fibroblasts in the presence of fluid flow was reported. In the present work, we extend a previous proposed cell-fluid mathematical model for autologous chemotaxis (Chem Eng Sci 191: 268-287, Waldeland and Evje 2018) to also include fibroblasts. This results in a cell-fibroblast-fluid model. Motivated by the experimental findings by Shieh et al, the momentum balance equation for the fibroblasts involves (1) a stress term that accounts for chemotaxis in the direction of positive gradients in secreted growth factor TGF-[Formula: see text]; (2) a fibroblast-ECM interaction term; (3) a cancer cell-fibroblast interaction term. Imposing reasonable simplifying assumptions, we derive an explicit expression for the cancer cell velocity [Formula: see text] that reveals a balance between a fluid-generated stress term, a chemotactic-driven migration term (autologous chemotaxis), and a new term that accounts for the possible mechanical interaction between fibroblasts and cancer cells. Similarly, the model provides an expression for the fibroblast velocity [Formula: see text] as well as the IF velocity [Formula: see text]. The three-phase model is then used for comparison of the simulated output with experimental results to elucidate some of the possible mechanism(s) behind the reported fibroblast-enhanced tumor cell invasion.

An Immersed Boundary-Lattice Boltzmann Prediction for Particle Hydrodynamic Focusing in Annular Microchannels**Supported by the National Natural Science Foundation of China under Grant Nos 51728601 and 51771118, and the Natural Science Foundation of Jiangsu Province under Grant No BK20150600.

We numerically study the dynamics of particle crystals in annular microchannels by the immersed-boundary (IB) lattice Boltzmann (LB) coupled model, analyze the fluid-particle interactions during the migration of particles, and reveal the underlying mechanism of a particle focusing on the presence of fluid flows. The results show that the Reynolds and Dean numbers are key factors influencing the hydrodynamics of particles. The particles migrate onto their equilibrium tracks by adjusting the Reynolds and Dean numbers. Elliptical tracks of particles during hydrodynamic focusing can be predicted by the IB-LB model. Both the small Dean number and the small particle can lead to a small size of the focusing track. This work would possibly facilitate the utilization of annular microchannel flows to obtain microfluidic flowing crystals for advanced applications in biomedicine and materials synthesis.

Magnetohydrodynamic micropolar fluid flow in presence of nanoparticles through porous plate: A numerical study

This study numerically investigates Magnetohydrodynamic (MHD) convective and chemically reactive unsteady micropolar fluid flow with nanoparticles through the vertical porous plate with mass diffusion, thermal radiation, radiation absorption and heat source. A flow model is established by employing the well-known boundary layer approximations. To obtain the non-similar equation, the boundary layer governing equations including continuity, momentum, energy and concentration balance were nondimensionalised by usual transformation. A non-similar approach is applied to the flow model. To optimize the parametric values, the stability and convergence analysis (SCA) have been analysed for the Prandtl number (Pr) and Lewis number (Le). It is observed that with initial boundary conditions, U =V =T = C= 0 and for Delta tau = 0.005, Delta X = 0.20 and Delta Y = 0.25, the system converged at Prandtl number, P-r >= 0.356 and Lewis number, L-e >= 0.16. The coupled non-linear partial differential equations are solved by explicit finite difference method (EFDM) and the numerical results have been calculated by Compaq Visual FORTRAN 6.6a. Evaluation of the thermal and momentum boundary layer thickness with isotherms and streamlines analysis of boundary layer flows have been shown for the thermal radiation parameter (R). The effects of various parameters entering the problem on velocity, angular velocity, temperature and concentration are shown graphically.

Chemotactic behavior of spermatozoa captured using a microfluidic chip.

Chemotaxis, as a mechanism for sperm guidance in vivo, is an enigma which has been difficult to demonstrate. To address this issue, various devices have been designed to study sperm chemotaxis in vitro. Limitations of traditional chemotaxis devices were related to the inability to maintain a stable concentration gradient as well as track single sperm over long times. Microfluidics technology, which provides superior control over fluid flow, has been recently used to generate stable concentration gradients for investigating the chemotactic behavior of several cell types including spermatozoa. However, the chemotactic behavior of sperm has not been unequivocally demonstrated even in these studies due to the inability to distinguish it from rheotaxis, thermotaxis, and chemokinesis. For instance, the presence of fluid flow in the microchannels not only destabilizes the concentration gradient but also elicits a rheotactic response from sperm. In this work, we have designed a microfluidic device which can be used to establish both, a uniform concentration and a uniform concentration gradient in a stationary fluid. By facilitating measurement of sperm response in ascending, descending ,and uniform chemoattractant concentration, the assay could isolate sperm chemotactic response from rheotaxis and chemokinesis. The device was validated using acetylcholine, a known chemoattractant and further tested with rat oviductal fluid from the estrus phase.

Impact of catholyte recirculation on different 3-dimensional stainless steel cathodes in microbial electrolysis cells

While stainless steel (SS) cathodes have shown great promise due to their low cost and high specific surface areas in microbial electrolysis cells (MECs), they have mainly been examined under static (no flow) conditions. Several different SS materials with different 3-dimensional structures (mesh, fiber felt, wool, and brushes) were compared in the absence and presence of fluid flow (0.05, 0.1 and 0.2 cm/s) past the cathode by catholyte recirculation. MECs with wool produced the highest hydrogen production rate with 1.3 ± 0.3 L-H2/L-reactor/d, which was the same as the Pt control at a catholyte recirculation of 40 mL/min (applied voltage of 0.9 V). In the absence of flow, hydrogen production rates of SS materials decreased by 52% (wool) to 28% (brush). The high hydrogen production rate using wool was likely a result of its high specific surface area (480 m2/m3-reactor volume), and reduced cathode overpotential due to gas removal by catholyte recirculation.

Naturally convective Casson fluid flow in presence of nano particle through porous plate with thermal radiation and MHD effects

Naturally convective Casson fluid flow in presence of nano particle through porous plate with thermal radiation and MHD effects

Study on the Time-Dependent Evolution of Pitting Corrosion in Flowing Environment

Pitting corrosion is one of the most destructive forms of localized corrosion in oil-gas pipelines. Due to being obscured by corrosion products and little loss of material with small effect on the surface, this kind of corrosion is extremely insidious. In this work, a novel multi-physics model is proposed to investigate the growth behavior of pitting corrosion in the presence of fluid flow. Various physical and chemical phenomena are taken into account in a coupled scheme, including chemical reactions, electrochemical reactions, flow disturbance and the mass transport of species. The mass transport is attributed to diffusion, electro-migration and convection. The time-dependent evolution of the pit morphology is implemented via an arbitrary Lagrangian-Eulerian method. The mechanism of the pitting corrosion is revealed with the integration of flow field, local chemical environment and the electrochemical behavior within the pit hole. Special emphasis is put on the relationship between the flowing fluid and the corrosion behavior. The results show that the flowing fluid would result in an asymmetric distribution of the species concentration and corrosion current density within the pit hole. It is found that the pit growth dynamics is determined by the combined effect of solution chemistry and electrical field. It is also indicated that the pH in the bulk solution and the flow rate have a significant coupling influence on the pitting corrosion behavior.

Making the cut: Innovative methods for optimizing perfusion-based migration assays.

Application of fluid shear stress to adherent cells dramatically influences their cytoskeletal makeup and differentially regulates their migratory phenotype. Because cytoskeletal rearrangements are necessary for cell motility and migration, preserving these adaptations under in vitro conditions and in the presence of fluid flow are physiologically essential. With this in mind, parallel plate flow chambers and microchannels are often used to conduct in vitro perfusion experiments. However, both of these systems currently lack capacity to accurately study cell migration in the same location where cells were perfused. The most common perfusion/migration assays involve cell perfusion followed by trypsinization which can compromise adaptive cytoskeletal geometry and lead to misleading phenotypic conclusions. The purpose of this study was to quantitatively highlight some limitations commonly found with currently used cell migration approaches and to introduce two new advances which use additive manufacturing (3D printing) or laser capture microdissection (LCM) technology. The residue-free 3D printed insert allows accurate cell seeding within defined areas, increases cell yield for downstream analyses, and more closely resembles the reported levels of fluid shear stress calculated with computational fluid dynamics as compared to other residue-free cell seeding techniques. The LCM approach uses an ultraviolet laser for "touchless technology" to rapidly and accurately introduce a custom-sized wound area in otherwise inaccessible perfusion microchannels. The wound area introduced by LCM elicits comparable migration characteristics compared to traditional pipette tip-induced injuries. When used in perfusion experiments, both of these newly characterized tools were effective in yielding similar results yet without the limitations of the traditional modalities. These innovative methods provide valuable tools for exploring mechanisms of clinically important aspects of cell migration fundamental to the pathogenesis of many flow-mediated disorders and are applicable to other perfusion-based models where migration is of central importance. © 2016 International Society for Advancement of Cytometry.

Thermal diffusion and chemical reaction effects on unsteady flow past a vertical porous plate with heat source dependent in slip flow regime

The present study investigates an analytical solution of free convective unsteady fluid flow in presence of thermal diffusion and chemical reaction effects past a vertical porous plate with heat source dependent in slip flow regime. The plate is assumed to move with a constant velocity in the direction of fluid flow, while free stream velocity is assumed to follow exponentially increasing small perturbation law. The velocity, temperature and concentration profiles are presented graphically for different values of the parameters entering into the problem. Finally the effects of pertinent parameters on the skin friction coefficient, Nusselt number and Sherwood numbers distributions are derived and have shown through graphs and tables by using perturbation technique.

Suppression of Chemotactic Explosion by Mixing

Chemotaxis plays a crucial role in a variety of processes in biology and ecology. In many instances, processes involving chemical attraction take place in fluids. One of the most studied PDE models of chemotaxis is given by Keller-Segel equation, which describes a population density of bacteria or mold which attract chemically to substance they secrete. Solution of Keller-Segel equation can exhibit dramatic collapsing behavior, where the density concentrates positive mass in a measure zero region. A natural question is whether presence of fluid flow can affect singularity formation by mixing the density thus making concentration harder to achieve. In this paper, we consider parabolic-elliptic Keller-Segel equation in two and three dimensions with additional advection term modeling ambient fluid flow. We prove that for any initial data, there exist incompressible fluid flows such that the solution to the equation stays globally regular. On the other hand, it is well known that when the fluid flow is absent, there exist initial data leading to finite time blow up. Thus presence of fluid can prevent the singularity formation. We discuss two classes of flows that have the explosion arresting property. Both classes are known as very efficient mixers. The first class are relaxation enhancing (RE) flow. These flows are stationary. The second class of flows are Yao-Zlatos optimal mixing flows, which are time dependent. The proof is based on the nonlinear version of the relaxation enhancement construction of the paper by Peter Constantin, Alexander Kiselev, Lenya Ryzhik, Andrej Zlatos, and on some variations of global regularity estimate for Keller-Segel model.

Effects of Rayleigh Number on MHD Heat Transfer and Fluid Flow in Two-Dimensional Open Square Cavity with Heat Generation

The present work is devoted to investigating heat transfer and fluid flow in a two dimensional square open cavity containing a heated circular cylinder at the centre. A constant heat flux is set at the left sidewall; high and low temperatures are fixed at the bottom and top walls of the cavity respectively. The right side of the cavity is open. Galerkin Weighted Residual Finite Element Analysis is used to visualize the heat transfer and fluid flow solving two-dimensional governing mass, momentum and energy equations for steady state, heat transfer and fluid flow in presence of magnetic field in side an open square cavity. A uniformly heated circular cylinder is placed at the centre of the cavity as a heat source. To find the effects of Rayleigh number (Ra) on the thermal fields and fluid flow in presence of magnetic field and a heated circular cylinder as heat source by visualization and line graphs is the objective of this study. Numerical results are presented in graphical and tabular form. The study is conducted for different values of Rayleigh number, some fixed Hartmann numbers (Ha) and heat flux (q). In the conclusion it has been observed that the temperature field and fluid flow pattern are functions of the parameters Rayleigh number and Hartmann number.

Flow-driven morphology control in the cobalt–oxalate system

The presence of fluid flow by maintaining the density gradient and controlling the flow rate provides a simple method to modify the microstructure of cobalt oxalate.

Lymphocytes can self-steer passively with wind vane uropods

A wide variety of cells migrate directionally in response to chemical or mechanical cues, however the mechanisms involved in cue detection and translation into directed movement are debatable. Here we investigate a model of lymphocyte migration on the inner surface of blood vessels. Cells orient their migration against fluid flow, suggesting the existence of an adaptive mechano-tranduction mechanism. We find that flow detection may not require molecular mechano-sensors of shear stress, and detection of flow direction can be achieved by the orientation in the flow of the non-adherent cell rear, the uropod. Uropods act as microscopic wind vanes that can transmit detection of flow direction into cell steering via the on-going machinery of polarity maintenance, without the need for novel internal guidance signalling triggered by flow. Contrary to chemotaxis, which implies active regulation of cue-dependent signalling, upstream flow mechanotaxis of lymphocytes may only rely on a passive self-steering mechanism.

Flow effects in the laser-induced thermal loading of optical traps and optofluidic devices.

Flow effects on the thermal loading in different optofluidic systems (optical trap and various microfluidic channels) have been systematically explored by using dye-based ratiometric luminescence thermometry. Thermal images obtained by fluorescence microscopy demonstrate that the flow rate plays a key role in determining both the magnitude of the laser-induced temperature increment and its spatial distribution. Numerical simulations were performed in the case of the optical trap. A good agreement between the experimental results and those predicted by mathematical modelling was observed. It has also been found that the dynamics of thermal loading is strongly influenced by the presence of fluid flow.

Dynamic self-assembly of particles in an expanding channel flow

Microfluidic particle crystals, which were previously observed in experiment, can be formed under the mediation of fluid flow. In this letter, we numerically investigated the dynamics of multi particles in an expanding channel, analyzed the fluid-particle interactions during the self-assembling, and revealed the underlying mechanism of the dynamic self-assembly of particles in the presence of fluid flow. Our results show that a pearls-string-like chain can be formed at low Reynolds numbers without external force fields. This research will possibly facilitate the utilization of expanding channel flows to obtain the microfluidic particle crystals for advanced applications in biomedicine and materials synthesis.

MR elastography of the human abdominal aorta: A preliminary study

PurposeTo investigate the feasibility of using MR elastography (MRE) for the evaluation of the stiffness of in vivo aortic wall.Materials and MethodsTo validate the experimental approach for imaging the aorta in vivo, a gel phantom with an embedded porcine aorta was imaged in the presence of fluid flow within the aorta. The potential changes in the elasticity of the vessel wall with changes in pressure were investigated. The feasibility of performing MRE of abdominal aorta was assessed in five volunteers (age, 22–40 years; body mass index, 21.5–25.2 kg/m2). The pulse‐gated cine MRE technique was used to study the wave propagation along the aorta throughout the cardiac cycle and provide estimates of aortic stiffness in diastole.ResultsIn the phantom study, the wave propagation was well visualized within the porcine aorta embedded in the gel phantom. An increase of the Young's modulus‐wall thickness (E*t) product with the increase in static pressure was observed. In the in vivo study, the waves were well visualized within the lumen of abdominal aorta in the five volunteers in diastolic phase, but they were not well visualized during systole.ConclusionMRE is feasible for noninvasively assessing the stiffness of the abdominal aorta and merits further investigation. J. Magn. Reson. Imaging 2013;38:1549–1553. © 2013 Wiley Periodicals, Inc.

Phase field simulation of multi-dendrite growth in a coupled thermal-solute-convective environment

To study the complexities in multi-dendrite growth during solidification, a fully coupled thermal-solute-convective phase field model and a parallel multigrid computing scheme have been developed for the first time for the simulation of multi-dendrite growth in a condition involving coupled heat/solute transfer, and flow convection. The interplay between fluid flow and heat/solute transfer and the resultant effects on dendrite growth, such as the effects of recirculating eddies, solute pile-up on the growth of primary and higher-order dendrite arms, and the final multi-dendrite morphology have been analysed and are discussed in detail. In particular, the development of multi-dendrites with four and six-fold symmetry in the presence of fluid flow is studied and contrasted.

Solid-State Microrefrigeration in Conjunction With Liquid Cooling

Thermal design requirements are mostly driven by the peak temperatures. Reducing or eliminating hot spots could alleviate the design requirement for the whole package. Combination of solid-state and liquid cooling will allow removal of both hot spots and background heating. In this paper, we analyze the performance of thin film Bi2Te3 microcooler and the 3D SiGe-based microrefrigerator, and optimize the maximum cooling and cooling power density in the presence of a liquid flow. Liquid flow and heat transfer coefficient will change the background temperature of the chip but they also affect the performance of the solid-state coolers used to remove hot spots. Both Peltier cooling at interfaces and Joule heating inside the device could be affected by the fluid flow. We analyze conventional Peltier coolers as well as 3D coolers. We study the impact of various parameters such as thermoelectric leg thickness, thermal interface resistances, and geometry factor on the overall system performance. We find that the cooling of a conventional Peltier cooler is significantly reduced in the presence of fluid flow. On the other hand, 3D SiGe cooler can be effective to remove high power density hot spots up to 500 W/cm2. 3D microrefrigerators can have a significant impact if the thermoelectric figure-of-merit, ZT, could reach 0.5 for a material grown on silicon substrate. It is interesting to note that there is an optimum microrefrigerator active region thickness that gives the maximum localized cooling. For liquid heat transfer coefficient between 5000 and 20,000 W m−2 K−1, the optimum is found to be between 10 μm and 20 μm.

Experimental and numerical investigation of orbital atherectomy: absence of cavitation

A definitive, quantitative investigation has been performed to determine whether orbital atherectomy gives rise to cavitation. The investigation encompassed a synergistic interaction between in vitro experimentation and numerical simulation. The experimentation was performed in two independent fluid environments: 1) a transparent tube having a diameter similar to that of the superficial femoral artery and 2) a large, fluid-filled, open-topped container. All of the experimental and simulation work was based on the geometric model of the Diamondback 360 atherectomy device (Cardiovascular Systems, Inc., St. Paul, MN). Rotational speeds ranged from 80,000 to 214,000 rpm. The presence or absence of cavitation in the experiments was assessed by means of high-speed photography. The photographic images clearly display the fact that there was no cavitation. Flow visualization revealed the presence of fluid flows driven by pressure gradients created by the geometry of the rotating crown. The numerical simulations encompassed the fluid environments and the operating conditions of the experiments. The key result of the numerical simulation is that the minimum fluid pressure due to the rotational motion was approximately 50 times greater than the saturation vapor pressure of the fluid. Since the onset of cavitation requires that the fluid pressure falls below the saturation vapor pressure, the computational outcome strongly supports the experimental findings.

Numerical simulation of the effect of fluid flow on solute distribution and dendritic morphology

The presence of bulk and interdendritic flow during solidification can alter the microstructure, potentially leading to the formation of defects. In this paper, a numerical model is presented for the direct simulation of dendritic growth in the presence of fluid flow in both liquid and mushy zones. The Navier–Stokes equations are solved for multiphase flow using a projection method. The energy conservation and solute diffusion equations are solved via a combined stochastic nucleation approach and finite difference solution to simulate dendritic growth. The predicted microstructures illustrate typical asymmetric dendritic growth behaviour under forced convection, which is consistent with prior similar simulations of a single dendrite during unconstrained growth (both 2D and 3D). The micromodel was coupled with a macromodel to investigate the effects of forced fluid flow on equiaxed dendritic growth and micro-segregation during vacuum arc remelting.