Constriction Height Research Articles

Heat transport in magnetohydrodynamic physiological blood flow through a constricted artery

AbstractIn this paper, we study how the magnetohydrodynamic (MHD) pulsatile flow of blood and heat transfer works through a constricted artery with a flexible wall. The human circulatory network consists of veins and arteries that sometimes contain constrictions, allowing the impact of the applied magnetic field on flow fields to be observed. The walls of the flowing medium are considered to be a function of time. The flowing blood is hypothesized as shear‐thinning fluid, emulating Yeleswarapu's viscosity replica. Additionally, we consider the energy equation to understand the impact of a magnetic field on heat transfer rates for such flows. The vorticity transport equation along with the stream function equation is obtained using the vorticity–stream function technique. Numerical solutions of the governing nonlinear MHD equations and energy equation in addition to physically pertinent flow conditions were achieved by adapting a finite difference scheme. Considerable attention has been paid to ensure an accurate comparison between the current and previous results. The two sets of numbers appear to match closely. For an even deeper understanding of the flow and heat transport process, the effects of height of stenosis and diverse physiological parameters on time‐averaged wall shear stress (TAWSS), rate of heat transport, and so on are explored in depth through their graphical depiction. In the vicinity of the constriction, it is observed that the separation becomes longer with increasing constriction height. Higher magnetic force strength leads to a reduction in separation length. Newtonian fluids transfer heat more rapidly in their narrowing regions and downstream than fluids with non‐Newtonian behavior.

Multi-objective optimization of split and recombine micromixer using grey relational analysis method

PurposeThe effective, efficient and optimal design of micromixer is the need in the field of biochemical and biomedical diagnostic systems.Design/methodology/approachIn this paper, multi-objective optimization of split and recombine micromixer (SRM) with different geometrical configurations is carried out. The finite element method-based three-dimensional models are prepared and analyzed using COMSOL Multiphysics 5.0 Software. Taguchi’s design of experiment (DoE), main effect plot analysis, ANOVA and grey relational analysis (GRA) method are used to find out optimum condition. The five geometrical parameters with three levels, namely, angle between inlets, pillar size, pillar shape, aspect ratio and constriction height of SRM are considered as design variables. The mixing index (MXI) and pressure drop (∆P) are considered objective functions.FindingsThe MXI is significantly influenced by pillar shape and aspect ratio, whereas the pressure drop (∆P) by constriction height. Maximum MXI (0.97) with minimum pressure drop (64,587 Pa) is the optimal conditions and obtained at 180 deg angle between inlets, 50 µm of pillar size, 1.5 of aspect ratio, 100 µm of constriction height and ellipse shape pillar cross-section, respectively.Research limitations/implicationsThis optimized SRM can be combined with lab-on-a-chip for biochemical and biomedical analysis.Originality/valueThis work is useful to obtain optimal geometry of SRM for getting efficient performance of micromixer.

Enhance the mixing performance of water and ethanol at micro level using geometrical modifications

The mixing performance characteristics of water and ethanol in split and recombine micromixer (SARM) are significantly improved using topological modifications. Therefore, in this paper, effect of topological modifications on the mixing performance of water and ethanol in SARM with different configurations is reported. Finite Element Method based COMSOL Multiphysics 5.0 software was utilized for numerical analysis. The laminar flow and transport with diluted species physics were used for investigation of SARM. The influence of constriction height, angle between inlets and different pillar shape on the performance characteristics viz. mixing index, pressure developed and performance index was investigated. Initially numerical methodology applied for analysis was validated with results available in literature. Further, same code was utilized for the parametric analysis. From the study, it is concluded that U-shape pillar SARM showed best performance characteristics as compared with other configurations.

Oscillatory Blood Flow in Convergent and Divergent Channels, Part 1: Effects of Pulse Amplitude and Local Constriction Height

Oscillatory Blood Flow in Convergent and Divergent Channels, Part 1: Effects of Pulse Amplitude and Local Constriction Height

English

A two-layer fluid model is proposed to study the transport of mucus in the trachea and air motion by considering mucus as a viscoelastic fluid. The effect of air flow due to inspiration and expiration is considered by prescribing shear stress at the mucus-air interface. The resistance to flow has been computed for different constriction length and for different constriction height. Shear stress distribution along the axial distance has been computed for different constriction height. It has been shown that, axial velocity profile, resistance flow, wall shear stress and concentration increases as the size of the constricted trachea increases.

Methane adsorption and diffusion in a model nanoporous carbon: an atomistic simulation study

A constricted slit model was introduced to improve, one step further, the performance of the simple slit model in prediction of the adsorption and diffusion behavior of simple molecules in the nanoporous carbons (NPCs). The grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations are performed to study the adsorption and diffusion behavior of methane within the constricted slit models. The models are called slit-1, 2, and 3 with constriction heights 5, 7, and 9 A respectively. For comparison, we used the slit-0 name for the simple slit without constriction. Adsorption results show that at low pressures, the constriction increases the adsorbed amount irrespective of its height. Slit-2 with a constriction height as a molecular diameter has the greatest heat of adsorption and has highest loading at pressures up to 3,000 kPa. At high pressures, when all pores are filled, the adsorption trend is in line with the pore volumes of slits where slit-0 with higher pore volume is dominant. The density profiles in the models were calculated and examined. The spatial distribution of adsorbed methane molecules was examined by various radial distribution functions calculated by MD. Also, MD simulation results show that the diffusion coefficient of methane decreases in constricted slits. The calculated diffusion coefficients in slit-2 in the direction of the constriction are one order of magnitude smaller than the calculated one in the simple slit model but it is far from the experimental values in the NPCs.

Shape Deformation and Recovery of Multilayer Microcapsules after Being Squeezed through a Microchannel

The deformation and recovery behaviors of multilayer microcapsules were investigated after being forced to flow through a microchannel. The microchannel device with a constriction (5.7 μm in depth) in the middle was designed, and the multilayer microcapsules with different size and layer thickness (and thereby different mechanical strength) were used. Deformation in the microchannel was observed for all the capsules with a size larger than the constriction height, and its extent was mainly governed by the difference between capsule size and constriction height. The squeezed microcapsules could recover their original spherical shape when the deformation extent was smaller than 16%, whereas permanent physical deformation took place when the deformation extent was larger than 34%. The capsules filled with polyelectrolytes could greatly enhance their shape recovery ability due to the higher osmotic pressure in the capsule interior and could well maintain the preloaded low-molecular-weight dyes regardless of the squeezing.

PULSATILE FLOW AND HEAT TRANSFER OF A MAGNETO-MICROPOLAR FLUID THROUGH A STENOSED ARTERY UNDER THE INFLUENCE OF BODY ACCELERATION

With an aim to investigate the effect of externally imposed body acceleration and magnetic field on pulsatile flow of blood through an arterial segment having stenosis is under consideration in this article. The flow of blood is presented by an unsteady micropolar fluid, and the heat-transfer characteristics have been taken into account. The nonlinear equations that govern the flow are solved numerically using finite difference technique by employing a suitable coordinate transformation. The numerical results have been observed for axial and microrotation component of velocity, fluid acceleration, wall shear stress (WSS), flow resistance, temperature, and the volumetric flow rate. It thus turns out that the rate of heat transfer increases with the increase of Hartmann number H, while the WSS has a reducing effect on the Hartmann number H and an enhancing effect on the ratio of viscosity K as well as on the constriction height δ.

Simulation of Pharyngeal Airway Interaction with Air Flow Using Low‐Re Turbulence Model

This paper aims to simulate the interaction between a simplified tongue replica with expiratory air flow considering the flow in the pharyngeal airway to be turbulent. A three‐dimensional model with a low‐Re SST turbulence model is adopted. An Arbitrary Eulerian‐Lagrangian description for the fluid governing equation is coupled with the Lagrangian structural solver via a partitioned approach, allowing deformation of the fluid domain to be captured. Both the three‐dimensional flow features and collapsibility of the tongue are presented. In addition, examining initial constriction height ranging from 0.8 mm to 11.0 mm and tongue replica modulus from 1.25 MPa to 2.25 MPa, the influence of both of these parameters on the flow rate and collapsibility of the tongue is also investigated and discussed. Numerical simulations confirm expected predisposition of apneic patients with narrower airway opening to flow obstruction and suggest much severe tongue collapsibility if the pharyngeal flow regime is turbulent compared to laminar.

Numerical computation of pulsatile flow through a locally constricted channel

This paper deals with the numerical solution of a pulsatile laminar flow through a locally constricted channel. A finite difference technique has been employed to solve the governing equations. The effects of the flow parameters such as Reynolds number, flow pulsation in terms of Strouhal number, constriction height and length on the flow behaviour have been studied. It is found that the peak value of the wall shear stress has significantly changed with the variation of Reynolds numbers and constriction heights. It is also noted that the Strouhal number and constriction length have little effect on the peak value of the wall shear stress. The flow computation reveals that the peak value of the wall shear stress at maximum flow rate time in pulsatile flow situation is much larger than that due to steady flow. The constriction and the flow pulsation produce flow disturbances at the vicinity of the constriction of the channel in the downstream direction.

On quasi‐steady laminar flow separation in the upper airways

AbstractAccurate prediction of the position of flow separation along a constriction is important to model fluid–structure interaction phenomena in the upper airways such as phonation and obstructive sleep apnea. Flow assumptions underlying common flow descriptions along the upper airways are formulated. Flow separation positions obtained from theories with different degrees of complexity are qualitatively and quantitatively discussed. In particular, geometrical and flow features determining the influence of viscosity are varied. Increasing the constriction degree and the constriction length is shown to affect the position of flow separation. Boundary layer solutions and simulations with the two‐dimensional Navier Stokes equations result in an accurate quantitative prediction of flow separation. Furthermore, Jeffery–Hamel flow solutions qualitatively predict the effect of both constriction height and length on the position of flow separation. The ad hoc assumption applied in quasi‐one‐dimensional flow descriptions does not accurately predict flow separation. Copyright © 2008 John Wiley & Sons, Ltd.

Effect of constriction height on flow separation in a two-dimensional channel

We studied numerically the effect of the constriction height on viscous flow separation past a two-dimensional channel with locally symmetric constrictions. A numerically stable scheme in primitive variables (velocity and pressure) for the solution of two-dimensional incompressible time-dependent Navier–Stokes equations is employed using finite-difference approximation in staggered grid. The wall shear stresses at different heights of the constriction are computed and presented graphically. It is noticed that the maximum stress and the length of the recirculating region associated with two shear layers of the constriction increase with the increase of the area reduction of the constriction. The critical Reynolds number for symmetry breaking bifurcation for the 50%, 60% and 70% area reduction are obtained numerically. The flow field separates after the symmetry breaking bifurcation and the symmetry of the flow depends on the Reynolds number and the height of the constriction.