scholarly journals SIMULATION OF A PERFECT DIELECTRIC DROP IN ELECTRO-OSMOTIC FLOW OF AN ELECTROLYTE THROUGH A MICROCHANNEL

2017 ◽  
Vol 3 (3) ◽  
pp. 294-319
Author(s):  
Michelle Magalhães Barbosa Felisberto ◽  
Alvaro Vianna Novaes de Carvalho Teixeira
Keyword(s):  
Weber Number ◽  
Vortex Flow ◽  
Fluid Dynamic ◽  
Computational Fluid Dynamic Model ◽  
Horizontal Deformation ◽  
Charged Drop ◽  
Drop Flow ◽  
Wall Charge ◽  
Electro Osmotic Flow ◽  
Positively Charged

This research uses a computational fluid dynamic model to simulate motion and deformation of a dielectric drop in electrolyte solution in a microchannel. Wall charge density, the Debye-Hückel parameter and the Weber number are varied for uncharged, positively and negatively charged drop interfaces. Drop flow and deformation were analysed and the effects of charge distribution, electric field and permittivity jump were discussed. For a positively charged channel wall, negatively charged drops moved faster and positively charged drops moved slower than an uncharged drop. This effect increased for a higher We. Vortex flow was observed inside the drop.  For a low surface tension, the drops were elongated due to electric forces acting on its surface with the charged drops deforming more than the uncharged one. When the permittivity component of the force was removed, the drop had a horizontal deformation that was sufficiently high to cause the negatively charged drop to break up.

scholarly journals Pengaruh Kekasaran Permukaan terhadap Performa Slider Bearing Bertekstur dengan Menggunakan Pendekatan CFD

ROTASI ◽  
2019 ◽  
Vol 21 (1) ◽  
pp. 56
Author(s):  
Mohammad Tauviqirrahman ◽  
Mufti M. Suryaman ◽  
Muchammad Muchammad
Keyword(s):  
Dynamic Model ◽  
Computational Fluid Dynamic ◽  
Fluid Dynamic ◽  
Computational Fluid Dynamic Model ◽  
Slider Bearing ◽  
Multi Phase

Dalam teori pelumasan klasik hidrodinamika, asumsi permukaan kontak bearing yang benar-benar halus sering kali digunakan. Meskipun demikian, telah dibuktikan bahwa asumsi tersebut tidak realistis dikarenakan pada umumnya, tidak ada permukaan bearing yang benar-benar halus. Tulisan ini membahas pengaruh kekasaran permukaan terhadap performa slider bearing bertektur dengan menggunakan pendekatan CFD (computational fluid dynamic). Model kavitasi multi-phase digunakan untuk memodelkan fenomena kavitasi yang lebih riil. Performa slider bearing dengan tingkat kekasaran permukaan tertentu dibandingkan dengan slider bearing halus dengan menvariasikan kondisi inersia. Berdasarkan hasil simulasi, ditemukan bahwa tekanan hidrodinamik dan daya dukung beban berkurang dengan bertambahnya kekasaran permukaan. Selain itu, jika bearing dirancang agar memiliki kondisi inersia yang rendah, daya dukung beban akan menjadi lebih besar.

Shielding Nozzle Design and Analysis for Atomization-Based Cutting Fluid Systems in Micromachining

2015 ◽  
Vol 3 (2) ◽  
Author(s):  
Andressa Lunardelli ◽  
John E. Wentz ◽  
John P. Abraham ◽  
Brian D. Plourde
Keyword(s):  
Fluid Dynamic ◽  
Continuous Phase ◽  
Computational Fluid Dynamic Model ◽  
Parameter Analysis ◽  
Cutting Fluid ◽  
Nozzle Design ◽  
Fluid Systems ◽  
Cutting Surface ◽  
Droplet Tracking ◽  
Cooling And Lubrication

Atomization-based cutting fluid systems (ACFs) are increasingly being used in micromachining applications to provide cooling and lubrication to the tool–chip interface. In this research, a shielding nozzle design is presented. A computational fluid dynamic model is developed to perform parameter analysis of the design. The numerical simulations were accomplished using the Eulerian approach to the continuous phase and a Lagrangian approach for droplet tracking. Based on the results of the simulations it is determined that the shielding nozzle is effective at providing droplets to the cutting surface at an appropriate speed and size to create a lubricating microfilm.

scholarly journals A Numerical Model of the Onset of Stall Flutter in Cascades

1995 ◽  
Author(s):  
William S. Clark ◽  
Kenneth C. Hall
Keyword(s):  
Unsteady Flow ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Computational Fluid Dynamic Model ◽  
Navier Stokes ◽  
Aeroelastic Stability ◽  
Blade Vibration ◽  
Navier Stokes Equations ◽  
The Mean ◽  
Stall Flutter

In this paper, we present a computational fluid dynamic model of the unsteady flow associated with the onset of stall flutter in turbomachinery cascades. The unsteady flow is modeled using the laminar Navier-Stokes equations. We assume that the unsteadiness in the flow is a small harmonic disturbance about the mean or steady flow. Therefore, the unsteady flow is governed by a small-disturbance form of the Navier-Stokes equations. These linear variable coefficient equations are discretized on a deforming computational grid and solved efficiently using a multiple-grid Lax-Wendroff scheme. A number of numerical examples are presented which demonstrate the destabilizing influence of viscosity on the aeroelastic stability of airfoils in cascade, especially for torsional modes of blade vibration.

scholarly journals An Actuator Disc Analysis of a Ducted High-Solidity Tidal Turbine in Yawed Flow

2019 ◽  
Author(s):  
Mitchell G. Borg ◽  
Qing Xiao ◽  
Atilla Incecik ◽  
Steven Allsop ◽  
Christophe Peyrard
Keyword(s):  
Fluid Dynamic ◽  
Computational Fluid Dynamic Model ◽  
Hydrodynamic Performance ◽  
Speed Ratio ◽  
Angular Range ◽  
Power Development ◽  
Tip Speed Ratio ◽  
Power Increase ◽  
Actuator Disc ◽  
Tidal Turbine

Abstract This work elaborates a computational fluid dynamic model utilised in the investigation of the hydrodynamic performance concerning a ducted high-solidity tidal turbine in yawed inlet flows. Analysing the performance at distinct bearing angles with the axis of the turbine, increases in torque and mechanical rotational power were acknowledged to be induced within a limited angular range at distinct tip-speed ratio values. Through multiple yaw iterations, the peak attainment was found to fall between bearing angles of 15° and 30°, resulting in a maximum power increase of 3.22%, together with an extension of power development to higher tip-speed ratios. In confirmation, these outcomes were subsequently analysed by means of actuator disc theory, attaining a distinguishable relationship with blade-integrated outcomes.

Lubrication theory for electro-osmotic flow in a microfluidic channel of slowly varying cross-section and wall charge

2002 ◽  
Vol 459 ◽  
pp. 103-128 ◽  
Author(s):  
SANDIP GHOSAL
Keyword(s):  
Cross Section ◽  
Microfluidic Channel ◽  
Lubrication Theory ◽  
Wall Material ◽  
Channel Cross Section ◽  
Microfluidic Channels ◽  
Osmotic Flow ◽  
Axial Variation ◽  
Wall Charge ◽  
Electro Osmotic Flow

Electro-osmotic flow is a convenient mechanism for transporting fluid in microfluidic devices. The flow is generated through the application of an external electric field that acts on the free charges that exist in a thin Debye layer at the channel walls. The charge on the wall is due to the particular chemistry of the solid–fluid interface and can vary along the channel either by design or because of various unavoidable inhomogeneities of the wall material or because of contamination of the wall by chemicals contained in the fluid stream. The channel cross-section could also vary in shape and area. The effect of such variability on the flow through microfluidic channels is of interest in the design of devices that use electro-osmotic flow. The problem of electro-osmotic flow in a straight microfluidic channel of arbitrary cross-sectional geometry and distribution of wall charge is solved in the lubrication approximation, which is justified when the characteristic length scales for axial variation of the wall charge and cross-section are both large compared to a characteristic width of the channel. It is thereby shown that the volume flux of fluid through such a microchannel is a linear function of the applied pressure drop and electric potential drop across it, the coefficients of which may be calculated explicitly in terms of the geometry and charge distribution on the wall. These coefficients characterize the ‘fluidic resistance’ of each segment of a microfluidic network in analogy to the electrical ‘resistance’ in a microelectronic circuit. A consequence of the axial variation in channel properties is the appearance of an induced pressure gradient and an associated secondary flow that leads to increased Taylor dispersion limiting the resolution of electrophoretic separations. The lubrication theory presented here offers a simple way of calculating the distortion of the flow profile in general geometries and could be useful in studies of dispersion induced by inhomogeneities in microfluidic channels.

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