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slip-boundary-conditions
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Development of a consistent slip boundary condition at the inlet of microchannels
, Article 44th AIAA Aerospace Sciences Meeting 2006, Reno, NV, 9 January 2006 through 12 January 2006 ; Volume 10 , 2006 , Pages 7087-7096 ; 1563478072 (ISBN); 9781563478079 (ISBN) ; Vakilipour, S ; Schneider, G. E ; Sharif University of Technology
2006
Abstract
The fast progress in Microelectromechanical systems has drawn the attention of many numerical workers to provide sufficient numerical tools to analyze the micro flows accurately. Besides many ambiguities behind the slip boundary condition research which are normally encountered in the vicinity of the solid walls (and are necessary to provide the suitable bridge between the macro and micro behaviors), there are serious uncertainties at the inlet of channels where the microflow enters into the conduit. Indeed, the macro inlet flow have been long investigated by the past workers; however, there is little effort to clarify the issue in micro inlet flow cases. In this research, we utilize the...
One Dimensional and Two Dimensional Numerical Investigation of Micro Scale Combustion
, M.Sc. Thesis Sharif University of Technology ; Saidi, Mohammad Said (Supervisor) ; Saidi, Mohammad Hasan (Supervisor) ; Shafii, Mohammad Behshad (Supervisor)
Abstract
In this paper, a one-dimensional and two-dimensional numerical approach is used to study the effect of various parameters such as micro combustor height, mass flow rate and external convection heat transfer coefficient on the temperature and species mass fraction profiles. A premixed mixture of H2-Air with a multi-step chemistry (9 species and 19 reactions) is used. The transient gas phase energy and species conservation equations result in an Advection-Diffusion-Reaction system (A-D-R) that leads to two stiff systems of PDEs, which can not be solved by conventional Computational Fluid Dynamics (CFD) methods. In the present work, Strang splitting method, which is suitable for nonlinear stiff...
Pore-scale Simulation of Flow around a Micro-porous Square Cylinder, Using Hybrid LBM-FVM, Considering Slip Condition Inside Porous Media
, M.Sc. Thesis Sharif University of Technology ; Tayyebi Rahni, Mohammad (Supervisor)
Abstract
In recent years, application of porous media is highlighted among researchers due to their wider use in micro-scale problems, such as in gas reservoirs, micro-filtering, and heat exchangers. In such applications, accurate description of flow behavior, using governing equations based on continuum assumption, is not valid, since mean free path has the same order as the characteristic length of the problem. In such cases, imposing appropriate slip condition on the fluid-solid interface of porous media (in pore-scale level), based on kinetics theory, is an appropriate approach. For this purpose, pore-scale simulation of flow inside porous media in slippery and transient regimes is carried out...
Gaseous slip flow mixed convection in vertical microducts with constant axial energy input
, Article Journal of Heat Transfer ; Vol. 136, issue. 3 , 2014 ; ISSN: 00221481 ; Baghani, M ; Saidi, M. H ; Sharif University of Technology
Abstract
The present investigation is devoted to the fully developed slip flow mixed convection in vertical microducts of two different cross sections, namely, polygon, with circle as a limiting case, and rectangle. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The velocity and temperature discontinuities at the boundary are incorporated into the solutions using the first-order slip boundary conditions. The method considered is mainly analytical in which the governing equations in cylindrical coordinates along with the symmetry conditions and finiteness of the flow parameter at the origin are exactly satisfied. The first-order slip boundary...
Buoyancy effects on gaseous slip flow in a vertical rectangular microchannel
, Article Microfluidics and Nanofluidics ; Vol. 16, issue. 1-2 , 2014 , pp. 207-224 ; ISSN: 16134982 ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
Abstract
Consideration is given to the buoyancy effects on the fully developed gaseous slip flow in a vertical rectangular microduct. Two different cases of the thermal boundary conditions are considered, namely uniform temperature at two facing duct walls with different temperatures and adiabatic other walls (case A) and uniform heat flux at two walls and uniform temperature at other walls (case B). The rarefaction effects are treated using the firstorder slip boundary conditions. By means of finite Fourier transform method, analytical solutions are obtained for the velocity and temperature distributions as well as the Poiseuille number. Furthermore, the threshold value of the mixed convection...
Gaseous slip flow forced convection in microducts of arbitrary but constant cross section
, Article Nanoscale and Microscale Thermophysical Engineering ; Vol. 18, issue. 4 , 2014 , p. 354-372 ; Sadeghi, A ; Sharif University of Technology
Abstract
This is a theoretical study that extends a classical method of treating the convection heat transfer in complex geometries to gaseous slip flow forced convection in microchannels with H1 thermal boundary condition. Through this line, the momentum and energy equations in cylindrical coordinates are made dimensionless. Afterward, solutions are presented that exactly satisfy the dimensionless differential equations along with the symmetry condition and finiteness of the flow parameter at the origin. The first-order slip boundary conditions are then applied to the solution utilizing the least squares matching method. Though the method is general enough to be applied to almost any arbitrary cross...
Mixed pressure and AC electroosmotically driven flow with asymmetric wall zeta potential and hydrophobic surfaces
, Article ASME 2013 Heat Transfer Summer Conf. Collocated with the ASME 2013 7th Int. Conf. on Energy Sustainability and the ASME 2013 11th Int. Conf. on Fuel Cell Science, Engineering and Technology, HT 2013 ; Volume 1 , 2013 ; 9780791855478 (ISBN) ; Sharif University of Technology
2013
Abstract
The present study examines Alternating Current (AC) electroosmotic flows in a parallel plate microchannel subject to constant wall temperature. Numerical method consists of a central finite difference scheme for spatial terms and a forward difference scheme for the temporal term. Asymmetric boundary conditions are assumed for Poison-Boltzmann equation for determining the electric double layer (EDL) potential distribution. The potential distribution is then used to evaluate the velocity distribution. The velocity distribution is obtained by applying slip boundary conditions on the walls which accounts for probable hydrophobicity of surfaces. After determining the velocity distribution...
Gaseous slip flow forced convection through ordered microcylinders
, Article Microfluidics and Nanofluidics ; Volume 15, Issue 1 , 2013 , Pages 73-85 ; 16134982 (ISSN) ; Baghani, M ; Saidi, M. H ; Sharif University of Technology
2013
Abstract
This is a theoretical study dealing with longitudinal gaseous slip flow forced convection between a periodic bunch of microcylinders arranged in regular array. The selected geometry has applications in microscale pin fin heat sinks used for cooling of microchips. The flow is considered to be hydrodynamically and thermally fully developed. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The velocity and temperature discontinuities at the boundary are incorporated into the solutions using the first order slip boundary conditions. The method considered is mainly analytical in which the governing equations and three of the boundary conditions...
Boundary drag force acting on an impenetrable nano-particle
, Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010, Istanbul ; Volume 3 , 2010 , Pages 469-473 ; 9780791849170 (ISBN) ; Kebriai, M. H ; Meigounpoury, M. R ; Sharif University of Technology
2010
Abstract
Flow over nano spheres is a fundamental problem encountered in many engineering technical problems and the motion of nano-particles is important in many technical areas, for example nano-organizms motion in aqueous media, super hydrophobic spray for coating materials, nano-capsules for detecting cancer, and additive nano-particles in oil and fuel for automotive engines. In this paper computations are performed to determine the steady flow forces acting on the stationary nano-tube for Reynolds numbers in the range of 0.1
Effect of liquid viscosity on instability of high-spinning partially-filled shell rotors
, Article International Journal of Structural Stability and Dynamics ; Volume 13, Issue 6 , 2013 ; 02194554 (ISSN) ; Permoon, M. R ; Sharif University of Technology
2013
Abstract
In this study, the instability of spinning cylindrical shells partially filled with viscous liquid is investigated. Based on the Navier-Stokes equations for the incompressible flow, a 2D model is developed for liquid motion at each section of the cylinder. The governing equations of the cylinder vibrations are obtained based on the first-order shear deformable shell theory. The nonpenetration and no-slip boundary conditions of the flow on the wetted surface of the cylinder relate the liquid motion to the shell vibrations. Also the liquid pressure exerted on the cylinder wall combines the vibrations of the rotary cylinder to the liquid motion. By using the obtained coupled liquid-structure...
Coarsening dynamics of nanodroplets on topographically structured substrates
, Article Journal of Physics Condensed Matter ; Volume 25, Issue 4 , 2013 ; 09538984 (ISSN) ; Moosavi, A ; Sharif University of Technology
2013
Abstract
Employing a biharmonic boundary integral method with linear elements, coarsening dynamics of nanodroplets on topographical step heterogeneity is investigated. It is shown that the step height and droplet configuration have an influential effect on the dynamics. Increasing the step height slows down the process while locating the droplets close to the step boosts the coarsening rate. Considering a slip boundary condition enhances the dynamics and reveals a transition in the droplet migration direction. Our results reveal that increasing the surface wettability weakens the dynamics. Various types of the disjoining pressure over the step are also considered and their effects on the coarsening...
A modified SPH method for simulating motion of rigid bodies in Newtonian fluid flows
, Article International Journal of Non-Linear Mechanics ; Volume 47, Issue 6 , 2012 , Pages 626-638 ; 00207462 (ISSN) ; Fatehi, R ; Manzari, M. T ; Sharif University of Technology
2012
Abstract
A weakly compressible smoothed particle hydrodynamics (WCSPH) method is used along with a new no-slip boundary condition to simulate movement of rigid bodies in incompressible Newtonian fluid flows. It is shown that the new boundary treatment method helps to efficiently calculate the hydrodynamic interaction forces acting on moving bodies. To compensate the effect of truncated compact support near solid boundaries, the method needs specific consistent renormalized schemes for the first and second-order spatial derivatives. In order to resolve the problem of spurious pressure oscillations in the WCSPH method, a modification to the continuity equation is used which improves the stability of...
A systematic method for the complex walls no-slip boundary condition modeling in dissipative particle dynamics
, Article Scientia Iranica ; Volume 18, Issue 6 , December , 2011 , Pages 1253-1260 ; 10263098 (ISSN) ; Saidi, M. S ; Sharif University of Technology
2011
Abstract
The dissipative particle dynamics method is an efficient method for studying the hydrodynamics of complex fluids. One of the most challenging aspects of this method appears when the solid walls exist. The solid walls disturb the homogeneity of the fluid near the wall and cause some spurious fluctuations. Thus, in recent years a large amount of effort has been devoted to solve this shortcoming. Fortunately the mentioned problem has almost been solved for the simple walls such as flat walls, circular cylinders, spheres, etc. However no systematic model has addressed the complex walls. It should be noted that almost all of the walls we deal with in practical problems such as MEMS devices,...
Effects of corrugated roughness on gaseous slip flow forced convection in microtubes
, Article Journal of Thermophysics and Heat Transfer ; Volume 25, Issue 2 , 2011 , Pages 262-271 ; 08878722 (ISSN) ; Salarieh, H ; Saidi, M. H ; Mozafari, A. A ; Sharif University of Technology
Abstract
Because of technological restrictions, it is actually impossible to fabricate smooth microchannels. Therefore, exploring the roughness effects on the flow characteristics at microscale is of great importance for scientific communities. The present investigation deals with the effects of corrugated roughness on the fully developed slip flow forced convection in micropipes. The governing equations subject to first-order slip boundary conditions are solved by means of the straightforward perturbation method. Closed-form expressions are obtained for the dimensionless velocity and temperature distributions, for the friction coefficient and pressure drop, and finally for the Nusselt number. The...
Study of subsonic-supersonic gas flow through micro/nanoscale nozzles using unstructured DSMC solver
, Article Microfluidics and Nanofluidics ; Volume 10, Issue 2 , February , 2011 , Pages 321-335 ; 16134982 (ISSN) ; Roohi, E ; Sharif University of Technology
2011
Abstract
We use an extended direct simulation Monte Carlo (DSMC) method, applicable to unstructured meshes, to numerically simulate a wide range of rarefaction regimes from subsonic to supersonic flows through micro/nanoscale converging-diverging nozzles. Our unstructured DSMC method considers a uniform distribution of particles, employs proper subcell geometry, and follows an appropriate particle tracking algorithm. Using the unstructured DSMC, we study the effects of back pressure, gas/surface interactions (diffuse/specular reflections), and Knudsen number on the flow field in micro/nanoscale nozzles. If we apply the back pressure at the nozzle outlet, a boundary layer separation occurs before the...
Oscillatory response of charged droplets in hydrogels
, Article Journal of Non-Newtonian Fluid Mechanics ; Volume 234 , 2016 , Pages 215-235 ; 03770257 (ISSN) ; Sharif University of Technology
Elsevier
2016
Abstract
Characterization of droplet-hydrogel interfaces is of crucial importance to engineer droplet-hydrogel composites for a variety of applications. In order to develop electrokinetic diagnostic tools for probing droplet-hydrogel interfaces, the displacement of a charged droplet embedded in a polyelectrolyte hydrogel exposed to an oscillating electric field is determined theoretically. The polyelectrolyte hydrogel is modeled as an incompressible, charged, porous, and elastic solid saturated with a salted Newtonian fluid. The droplet is considered an incompressible Newtonian fluid with no charges within the droplet. The droplet-hydrogel interface is modeled as a surface with the thickness of zero...
Three-dimensional numerical simulation of rising bubbles in the presence of cylindrical obstacles, using lattice boltzmann method
, Article Journal of Molecular Liquids ; Volume 236 , 2017 , Pages 151-161 ; 01677322 (ISSN) ; Seyyedi, S. M ; Taeibi Rahni, M ; Ganji, D. D ; Sharif University of Technology
Abstract
A typical process in many industrial applications is rising bubble dynamic in viscous liquids like two-phase reactors. Examining the physical behavior of bubbles may improve the understanding of systems regarding design and operation. This study focused on the splitting of bubbles resulting from their impact on solid obstacles. Fragmentation of the bubbles appears in many applications such as lab on a chip in small scale or slug bubbly flow moving upward in a tube in large scales. Using a new index-function model in Lattice Boltzmann technique proposed by “He”, we simulated the deformation and motion of a bubble in different regimes, through which, we accurately captured a sharp interface...
Transient analysis of falling cylinder in non-Newtonian fluids: further opportunity to employ the benefits of SPH method in fluid-structure problems
, Article Chemical Product and Process Modeling ; Volume 12, Issue 1 , 2017 ; 21946159 (ISSN) ; Ramazani Saadat Abadi, A ; Kamyabi, A ; Sharif University of Technology
Walter de Gruyter GmbH
2017
Abstract
Smoothed particle hydrodynamics (SPH) was applied to simulate the free falling of cylindrical bodies in three types of fluids including Newtonian, generalized-Newtonian and viscoelastic fluids. Renormalized derivation schemes were used because of their consistency in combination with the latest version of no slip boundary condition to improve the handling of moving fluid-structure interactions (FSIs). Verification of the method was performed through comparing the results of some benchmark examples for both single and two phase flows with the literature. The effects of some parameters such as the viscosity of the Newtonian fluid, the n index of the power-law fluid and the relaxation time of...
Magneto-mechanical stability of axially functionally graded supported nanotubes
, Article Materials Research Express ; Volume 6, Issue 12 , 2019 ; 20531591 (ISSN) ; Mirtalebi, H ; Ahmadian, M. T ; Sharif University of Technology
Institute of Physics Publishing
2019
Abstract
In this paper, size-dependent vibration analysis of axially functionally graded (AFG) supported nanotubes conveying nanoflow under longitudinal magnetic fields are performed, aiming at performance improvement of fluid-interaction nanosystems. Either the density or the elastic modulus of the AFG nanotube varies linearly or exponentially along the axial direction. Based on the nonlocal continuum theory, the higher-order dynamical equation of motion of the system is derived considering no-slip boundary condition. Galerkin discretization technique and eigenvalue analysis are implemented to solve the modeled equation. The validity of the simplified model is justified by comparing the results with...
Magneto-mechanical stability of axially functionally graded supported nanotubes
, Article Materials Research Express ; Volume 6, Issue 12 , 2019 ; 20531591 (ISSN) ; Mirtalebi, H ; Ahmadian, M. T ; Sharif University of Technology
Institute of Physics Publishing
2019
Abstract
In this paper, size-dependent vibration analysis of axially functionally graded (AFG) supported nanotubes conveying nanoflow under longitudinal magnetic fields are performed, aiming at performance improvement of fluid-interaction nanosystems. Either the density or the elastic modulus of the AFG nanotube varies linearly or exponentially along the axial direction. Based on the nonlocal continuum theory, the higher-order dynamical equation of motion of the system is derived considering no-slip boundary condition. Galerkin discretization technique and eigenvalue analysis are implemented to solve the modeled equation. The validity of the simplified model is justified by comparing the results with...