Flow characteristics of dc wire-non-parallel plate electrohydrodynamic gas pumps

Atherosclerosis induced narrowing of arteries reduces blood flow to critical regions, contributing to conditions such as ischemia, angina, and strokes. Curvature is observed in blood vessels at various locations. The sinusoidal stenotic surface provides additional curvature and a point of maximum shear, which varies with the cross-section. This research extends the cylindrical form of the Navier-Stokes equations in a polar coordinate system to incorporate effective viscosity and axial curvature, enabling the analysis of blood flow behavior in curved arteries with sinusoidal stenosis. The blood flow behavior was studied by taking different blood parameters using an extended blood flow model. Moreover, aspects of blood flow such as velocity profile, volumetric flow rate, pressure drop, and shear stress have been studied in relation to blood flow around curved arteries with sinusoidal stenosis, variations in the radii of the artery, thickness of the stenosis, hematocrit, and viscosity. The findings reveal that increasing the values of curvature, hematocrit, viscosity, and thickness of stenosis can quickly reduce velocity and volumetric flow rate while amplifying shear stress and pressure drop. This research considers flow conditions consistent with prior studies and opens routes for exploring unsteady and three-dimensional effects in similar geometries.

This article presents a numerical study on oscillating peristaltic flow of generalized Maxwell fluids through a porous medium. A sinusoidal model is employed for the oscillating flow regime. A modified Darcy-Brinkman model is utilized to simulate the flow of a generalized Maxwell fluid in a homogenous, isotropic porous medium. The governing equations are simplified by assuming long wavelength and low Reynolds number approximations. The numerical and approximate analytical solutions of the problem are obtained by a semi-numerical technique, namely the homotopy perturbation method. The influence of the dominating physical parameters such as fractional Maxwell parameter, relaxation time, amplitude ratio, and permeability parameter on the flow characteristics are depicted graphically. The size of the trapped bolus is slightly enhanced by increasing the magnitude of permeability parameter whereas it is decreased with increasing amplitude ratio. Furthermore, it is shown that in the entire pumping region and the free pumping region, both volumetric flow rate and pressure decrease with increasing relaxation time, whereas in the co-pumping region, the volumetric flow rate is elevated with rising magnitude of relaxation time.

Power law approximations to gas volume fraction and velocity profiles in low void fraction vertical gas–liquid flows

The effect of electrode orientation in an electrohydrodynamic (EHD) gas pump inside a square channel is experimentally examined for its effective use in thermal management. The two-stage gas pump with electrodes flush mounted on two parallel walls in each stage is powered by DC voltages ranging from 24 to 28 kV. In addition to the volume flow rate produced, the performance of the pump is evaluated using an energy efficiency factor, which is defined as the volume flow rate delivered by a unit power input. It is found that this parameter has a larger value for the EHD pump with aligned electrodes. However, the EHD pump with offset electrodes can produce more mixing of flow inside the channel, which may be more favorable for the application in thermal management. Most importantly, EHD gas pumps with either electrode configuration have a greater energy efficiency than conventional fans, and thus have a greater advantage for applications in the thermal management. This advantage is even more prominent when pumps are operated with uneven applied voltages.

EHD gas pump as a cooling device for electronic components in a horizontal channel

A series of 50 experiments was performed to investigate particle size and yield from three laboratory spray dryers with two-fluid nozzles, using an aqueous solution of egg albumin as the feed. First principles theory suggests that the main parameters affecting final particle size should be atomization gas flowrate and velocity, feed solution flowrate, solution concentration, and inlet and outlet gas temperature. The experiments demonstrated that atomization gas velocity at the nozzle correlated better than volumetric gas flowrate to the final particle size obtained. Increasing atomization gas flow gave a decrease in particle size, levelling off at high nozzle gas velocities approaching sonic values. Liquid flowrate had little effect, and hybrid ratios such as the ALM (atomization gas to liquid flow ratio) did not correlate well to measured final particle size for this system. This seems likely to apply to aqueous systems with temperature limitations, where liquid flowrates will be relatively low compared to gas flowrates (both atomization and main gas flow). Particle size generally increased with solution concentration, and in some cases scaled exactly, assuming a constant initial droplet size and final particle density. All experiments were performed below the boiling point and therefore temperature had little effect. Particles of 2–3 microns were obtained at high atomization gas flows, indicating initial droplet sizes of 4–7 microns at most, while lower flowrates gave substantially larger particles and a wider size distribution.

In this study, fluid flow induced by a two stage electrohydrodynamic (EHD) gas pump in a square channel has been evaluated by experimental measurement and numerical simulations. This study is implemented for a two stage EHD gas pump with three emitting electrode configurations: 8, 24, and 56 respectively to seek the relation between the number of stages and emitting electrodes. The EHD pump is evaluated for a wide range of operating voltages starting from 20 kV up to 28 kV for further improvement in its performance over a single stage. To achieve the maximum enhancement, the emitting electrodes of the EHD gas pump are flush mounted on the channel walls so that the corona wind produced directly disturbs the boundary layer thickness and improves the heat transfer. This is leading to a higher velocity near the channel walls and resulting in an inverted parabolic velocity profile at the center of the channel, which is opposite to the fully developed velocity profile of a forced flow. Velocities are measured at three cross-sections along the tube length and then integrated to obtain the volume flow rate. The results show that EHD technique has a great potential for many engineering applications.

Comparison of two axial fans for cooling of electromechanical actuators at variable pressure

Drag reduction (DR) is critical to the success of hydraulic fracturing operations with slickwater, and it is a challenge to accurately predict DR due to the problem of high injection rates. Although a practical pipe diameter model is frequently used to predict the field DR based on laboratory experimental data, there exist many limitations. This study, on account of dynamic similarity, shows two novel general models for the prediction of field DR, and such two models can give reliable predictions when the laboratory and field Reynolds numbers (Re) are the same. For general model 1, the DR can be predicted by using the laboratory volumetric flow rate, pipe diameter and pressure drop, and the field volumetric flow rate, with a deviation ranging from −10 to 10%. For general model 2, it is simpler than general model 1, and the DR can be predicted by using the laboratory pipe diameter and the field volumetric flow rate, with a deviation ranging from −6 to 6%. The two novel general models can be used for more scenarios than the existing reported ones.

DTM Simulation of Peristaltic Viscoelastic Biofluid Flow in Asymmetric Porous Media: A Digestive Transport Model

Motivated by the objective of improving an understanding of the complex rheological fluid dynamics in fluid engineering and biomedical engineering, we consider the creeping flow of Burgers’ fluid with a fractional model through a peristaltic tube in the present article. Homotopy analysis method is used to solve the problem and obtain the approximate analytical solution in terms of axial velocity, volumetric flow rate, pressure gradient, stream function and mechanical efficiency under the long wavelength approximation. It is assumed that the cross-section of the tube varies sinusoidally along the length of tube. The impacts of fractional parameters, material constants, time and amplitude on the pressure difference, frictional force across one wavelength and trapping, are depicted numerically. It is found that the second material constant helps the flow pattern, whereas the other three material constants resist it through the peristaltic tube. The effects of fractional parameters on flow pattern are found to be opposite to each other.

This paper discusses the effect of different geometric representations of stenosis on the numerical solution of one-dimensional unsteady blood flow in stenotic blood vessel (or stenosis) taking into account fluid-structure interaction. In the formulation, a collapsible pressure-area constitutive relation is added to the coupled mass and momentum equations to allow for the interaction between the cross sectional area, volumetric flow rate and pressure of the flow and hence the prevalence of the one-dimensional fluid-structure interaction. The formulation is stabilized by employing Streamline-Upwind Petrov-Galerkin scheme. Non-reflecting boundary conditions are imposed based on the method of characteristics. Flow characteristics and the geometrical effects of the stenosis are then discussed. Numerical results show that stenosis with irregular shape is more prone to collapse as compared to the smooth one for a given baseline conditions. This study, thus, highlights the importance of representing the shape of the stenosis as close as possible as it might give information otherwise missing in the simplistic smooth representation of the stenosis.

This chapter aims to present a theoretical study of the fluid flow in porous media, with particular reference to manufacturing of polymer composites reinforced with fibers via resin transfer molding process. The mass and momentum conservation equations, including the effect of resin sorption by the fibers, and Darcy's law, are presented, and the analytical solution of the governing equation is obtained via method of separation of variables. Predicted results of the flow front, velocity, volumetric flow rate and pressure fields of the resin inside the model, during the injection process, are presented, and the effects of the injection pressure, resin viscosity and sorption term, are also analyzed.

Steady-state 2-D electrohydrodynamic pumping through bipolar hetero-charge conduction phenomenon has been investigated numerically. In order to validate the presented numerical algorithm, the pump geometry was chosen to be identical to the device whose experimental data is available in the literature. The concentrations of the positive and negative ions and the electric field distribution of the pump were calculated. The resulting static pressure generation of the pump was predicted for the refrigerant R-123 at different applied voltages ranging between 2 to 20kV DC. The comparison between the predicted static pressure generation and the previous experimental results in the absence of fluid flow shows a good agreement with a maximum deviation of 12.5% at 20 kV applied voltage. In the present work, the electrical conductivity of R-123 was assumed to be the most recent proposed value of σ=7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> S/m. Assuming this value of electrical conductivity, the numerical model predicts the hetrocharge layer thicknesses in the order of gap spacing even at low applied voltage and weak field regime. By increasing the applied voltage, above ~15kV, the heterocharge layers of the opposite electrodes extend to the entire gap spacing and create an overlapping region. Assuming three orders of magnitude higher value of electrical conductivity for R-123 in the previous numerical studies, the thickness of the hetrocharge layer and pressure generation was underestimated by almost two orders of magnitude. Through extensive numerical experiments, the electrical conductivity of the working fluid was found to be an important parameter to determine the heterocharge layer thickness, electric body force, and predicted static pressure. The issues related to the scaling of the conduction pump when the heterocharge layers create an overlapping region in the reduced gap spacing are discussed.

The application of nuclear magnetic resonance imaging (NMRI) to the direct three‐dimensional measurement of flow in rough‐walled water‐saturated rock fractures is presented for the first time. The study demonstrates the abilities of NMRI to noninvasively measure rock‐water interfaces and water flow velocities in these fractures and investigates the effects of wall morphology on flow patterns inside a typical rock fracture. Two‐ and three‐dimensional flow‐encoded spin‐echo pulse sequences were applied. The stability and reproducibility of the water flow patterns were confirmed by analyzing two‐dimensional velocity images. A variety of geometrical and hydraulic features were determined from three‐dimensional velocity images, including the rock‐water interfaces, the fracture aperture distribution, and the critical aperture path; velocity profiles and volumetric flow rates; flow and stagnant regions; and the critical velocity path. In particular, the effects of a sharp step discontinuity of the fracture walls and the applicability of the cubic law were examined. As a result of the complex three‐dimensional geometry, velocity profiles are generally parabolic but often highly asymmetric, with respect to the fracture walls. These asymmetric velocity profiles are clustered together, with significant correlations; they are not just local random phenomena. However, theoretical considerations indicate that the effects of the measured asymmetry on volumetric flow rates and hydraulic conductivities are insignificant, in that the overall flow inside rough fractures still obeys the cubic law. The features discussed in this study emphasize the strong heterogeneity and the highly three‐dimensional nature of the flow patterns in natural rock fractures and consequently the need for three‐dimensional flow analysis.