Micro/Nano-Scale Fluid Flows on Structured Surfaces

2008 ◽  
Author(s):  
Min Chen ◽  
Bing-Yang Cao ◽  
Zeng-Yuan Guo
Keyword(s):  
Surface Structure ◽  
Knudsen Number ◽  
Liquid Flow ◽  
Slip Length ◽  
Velocity Slip ◽  
Maxwell Model ◽  
Boundary Slip ◽  
Structured Surfaces ◽  
Surface Nanostructures ◽  
Surface Nanostructure

Understanding the effects of surface nanostructures on fluid flow in micro- and nano-channels is highly desirable for micro/nano-electro-mechanical systems. By way of equilibrium and non-equilibrium molecular dynamics simulations, wetting on nano-structured surfaces and liquid flow in nano-channels with structured surfaces are simulated. The surfaces show dual effects on the boundary slip and friction of the liquid flow in nano-channels. Generally, the nanostructures enhance the surface hydrophilicity for a hydrophilic liquid-solid interaction, and increase the hydrophobicity for a hydrophobic interaction. Simultaneously, the nanostructures distort the nanoscale streamlines of the liquid flow near the channel surface and block the flow, which decreases the apparent slip length. The twofold effects of the nanostructures on the surface wettability and the hydrodynamic disturbance result in a non-monotonic dependence of the slip length on the structure’s size. However, the surface structure may lead to a very high contact angle of about 170° in some cases, which cause the surface show super-hydrophobicity and lead to a remarkable velocity slip. The surface nanostructures can thus be applied to control the friction of micro- and nano-flows. In addition, the gaseous flows in micro- and nano-channels with structured surfaces are simulated. The geometry of the surface is modeled by triangular, rectangular, sinusoidal and randomly triangular nanostructures respectively. The results show that the velocity slips, including negative slip, depend not only on the Knudsen number but also the surface structure. The impacts of the surface nanostructure and the gas rarefaction are strongly coupled. In general, the slip length of a gaseous flow over a structured surface is less than what predicted by the Maxwell model, and depends not only on the Knudsen number but also the size of the surface nanostructures.

scholarly journals Role of Solid Wall Properties in the Interface Slip of Liquid in Nanochannels

Micromachines ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 663 ◽  
Author(s):  
Wei Gao ◽  
Xuan Zhang ◽  
Xiaotian Han ◽  
Chaoqun Shen
Keyword(s):  
Liquid Flow ◽  
Coupling Strength ◽  
Solid Wall ◽  
Slip Length ◽  
Boundary Slip ◽  
Near Surface ◽  
Wall Properties ◽  
Fluid Coupling ◽  
Interface Slip

A two-dimensional molecular dynamics model of the liquid flow inside rough nanochannels is developed to investigate the effect of a solid wall on the interface slip of liquid in nanochannels with a surface roughness constructed by rectangular protrusions. The liquid structure, velocity profile, and confined scale on the boundary slip in a rough nanochannel are investigated, and the comparison of those with a smooth nanochannel are presented. The influence of solid wall properties, including the solid wall density, wall-fluid coupling strength, roughness height and spacing, on the interfacial velocity slip are all analyzed and discussed. It is indicated that the rough surface induces a smaller magnitude of the density oscillations and extra energy losses compared with the smooth solid surface, which reduce the interfacial slip of liquid in a nanochannel. In addition, once the roughness spacing is very small, the near-surface liquid flow dominates the momentum transfer at the interface between liquid and solid wall, causing the role of both the corrugation of wall potential and wall-fluid coupling strength to be less obvious. In particular, the slip length increases with increasing confined scales and shows no dependence on the confined scale once the confined scale reaches a critical value. The critical confined scale for the rough channel is larger than that of the smooth scale.

scholarly journals The study of surface wetting, nanobubbles and boundary slip with an applied voltage: A review

2014 ◽  
Vol 5 ◽  
pp. 1042-1065 ◽  
Author(s):  
Yunlu Pan ◽  
Bharat Bhushan ◽  
Xuezeng Zhao
Keyword(s):  
Contact Angle ◽  
Fluid Flow ◽  
Charge Density ◽  
Surface Charge ◽  
Liquid Flow ◽  
Applied Voltage ◽  
Surface Charge Density ◽  
Slip Length ◽  
Surface Wetting ◽  
Boundary Slip

The drag of fluid flow at the solid–liquid interface in the micro/nanoscale is an important issue in micro/nanofluidic systems. Drag depends on the surface wetting, nanobubbles, surface charge and boundary slip. Some researchers have focused on the relationship between these interface properties. In this review, the influence of an applied voltage on the surface wettability, nanobubbles, surface charge density and slip length are discussed. The contact angle (CA) and contact angle hysteresis (CAH) of a droplet of deionized (DI) water on a hydrophobic polystyrene (PS) surface were measured with applied direct current (DC) and alternating current (AC) voltages. The nanobubbles in DI water and three kinds of saline solution on a PS surface were imaged when a voltage was applied. The influence of the surface charge density on the nanobubbles was analyzed. Then the slip length and the electrostatic force on the probe were measured on an octadecyltrichlorosilane (OTS) surface with applied voltage. The influence of the surface charge on the boundary slip and drag of fluid flow has been discussed. Finally, the influence of the applied voltage on the surface wetting, nanobubbles, surface charge, boundary slip and the drag of liquid flow are summarized. With a smaller surface charge density which could be achieved by applying a voltage on the surface, larger and fewer nanobubbles, a larger slip length and a smaller drag of liquid flow could be found.

scholarly journals Impact of chosen force fields and applied load on thin film lubrication

Friction ◽  
2021 ◽  
Author(s):  
Thi D. Ta ◽  
Hien D. Ta ◽  
Kiet A. Tieu ◽  
Bach H. Tran
Keyword(s):  
Thin Film ◽  
Shear Stress ◽  
Surface Structure ◽  
Rheological Properties ◽  
Surface Potential ◽  
Applied Load ◽  
Velocity Slip ◽  
Thin Film Lubrication ◽  
Lubrication Performance ◽  
Film Lubrication

AbstractThe rapid development of molecular dynamics (MD) simulations, as well as classical and reactive atomic potentials, has enabled tribologists to gain new insights into lubrication performance at the fundamental level. However, the impact of adopted potentials on the rheological properties and tribological performance of hydrocarbons has not been researched adequately. This extensive study analyzed the effects of surface structure, applied load, and force field (FF) on the thin film lubrication of hexadecane. The lubricant film became more solid-like as the applied load increased. In particular, with increasing applied load, there was an increase in the velocity slip, shear viscosity, and friction. The degree of ordering structure also changed with the applied load but rather insignificantly. It was also significantly dependent on the surface structure. The chosen FFs significantly influenced the lubrication performance, rheological properties, and molecular structure. The adaptive intermolecular reactive empirical bond order (AIREBO) potential resulted in more significant liquid-like behaviors, and the smallest velocity slip, degree of ordering structure, and shear stress were compared using the optimized potential for liquid simulations of united atoms (OPLS-UAs), condensed-phase optimized molecular potential for atomic simulation studies (COMPASS), and ReaxFF. Generally, classical potentials, such as OPLS-UA and COMPASS, exhibit more solid-like behavior than reactive potentials do. Furthermore, owing to the solid-like behavior, the lubricant temperatures obtained from OPLS-UA and COMPASS were much lower than those obtained from AIREBO and ReaxFF. The increase in shear stress, as well as the decrease in velocity slip with an increase in the surface potential parameter ζ, remained conserved for all chosen FFs, thus indicating that the proposed surface potential parameter ζ for the COMPASS FF can be verified for a wide range of atomic models.

Hierarchical Nano/Micro-structured Surfaces with High Surface Area/Volume Ratios

2021 ◽  
pp. 1-36
Author(s):  
Ketki Lichade ◽  
Yizhou Jiang ◽  
Yayue Pan
Keyword(s):  
Surface Structure ◽  
Surface Area ◽  
Light Trapping ◽  
High Surface ◽  
High Surface Area ◽  
Three Dimensional ◽  
Structure Design ◽  
Surface Structures ◽  
Structured Surfaces ◽  
Design And Manufacture

Abstract Recently, many studies have investigated additive manufacturing of hierarchical surfaces with high surface area/volume (SA/V) ratios, and their performance has been characterized for applications in next-generation functional devices. Despite recent advances, it remains challenging to design and manufacture high SA/V ratio structures with desired functionalities. In this study, we established the complex correlations among the SA/V ratio, surface structure geometry, functionality, and manufacturability in the Two-Photon Polymerization (TPP) process. Inspired by numerous natural structures, we proposed a 3-level hierarchical structure design along with the mathematical modeling of the SA/V ratio. Geometric and manufacturing constraints were modeled to create well-defined three-dimensional hierarchically structured surfaces with a high accuracy. A process flowchart was developed to design the proposed surface structures to achieve the target functionality, SA/V ratio, and geometric accuracy. Surfaces with varied SA/V ratios and hierarchy levels were designed and printed. The wettability and antireflection properties of the fabricated surfaces were characterized. It was observed that the wetting and antireflection properties of the 3-level design could be easily tailored by adjusting the design parameter settings and hierarchy levels. Furthermore, the proposed surface structure could change a naturally-hydrophilic surface to near-superhydrophobic. Geometrical light trapping effects were enabled and the antireflection property could be significantly enhanced (>80% less reflection) by the proposed hierarchical surface structures. Experimental results implied the great potential of the proposed surface structures for various applications such as microfluidics, optics, energy, and interfaces.

Transport Behavior of Liquid Hydrocarbon in Shale Matrix with Mixed Wettability Nanopores

2021 ◽  
Author(s):  
Guoxiang Zhao ◽  
Yuedong Yao ◽  
Caspar Daniel Adenutsi ◽  
Lian Wang ◽  
Fengrui Sun
Keyword(s):  
Organic Matter ◽  
Slip Length ◽  
Flow Behavior ◽  
Darcy Law ◽  
Transport Capacity ◽  
Boundary Slip ◽  
Permeability Model ◽  
Oil Transport ◽  
Transport Behavior ◽  
Mixed Wettability

Abstract Shale oil is an unconventional petroleum resource which has high total organic carbon (TOC) content and abundant nanopores. The transport behavior of oil through organic rich shales cannot be described by the classical Darcy law due to its complex pore structure and the complicated distribution of organic matter, which results in nanoconfined effects. In this work, on the basis of the boundary slip phenomenon and the fractal scaling theory, a model for oil transport in shale matrix is established considering nanoconfined effects and adsorbed organic matter. The results show that it is necessary to make correction of viscosity and the boundary slip length in order to accurately describe the flow behavior of oil in shale matrix with mixed wettability nanopores. Long chain molecules are more sensitive to nanoconfined effects, especially when adsorbed organic matter is considered. Also, the oil transport capacity in organic shale matrix is greatly enhanced compared to the classical no-slip permeability model. Meanwhile is the oil transport capacity is significantly reduced in inorganic shale matrix. This work shows that the identification of higher TOC region and considering the nanoconfined effects are necessary from the concept of oil transport in shale matrix.

scholarly journals A novel physical mechanism of liquid flow slippage on a solid surface

2020 ◽  
Vol 6 (13) ◽  
pp. eaaz0504 ◽  
Author(s):  
Yuji Kurotani ◽  
Hajime Tanaka
Keyword(s):  
Liquid Flow ◽  
Density Fluctuation ◽  
Physical Mechanism ◽  
Slip Length ◽  
Quiescent State ◽  
Physical Explanation ◽  
Liquid Transport ◽  
Viscous Liquids ◽  
Gas Layer ◽  
Solid Walls

Viscous liquids often exhibit flow slippage on solid walls. The occurrence of flow slippage has a large impact on the liquid transport and the resulting energy dissipation, which are crucial for many applications. It is natural to expect that slippage takes place to reduce the dissipation. However, (i) how the density fluctuation is affected by the presence of the wall and (ii) how slippage takes place through forming a gas layer remained elusive. Here, we report possible answers to these fundamental questions: (i) Density fluctuation is intrinsically enhanced near the wall even in a quiescent state irrespective of the property of wall, and (ii) it is the density dependence of the viscosity that destabilizes the system toward gas-layer formation under shear flow. Our scenario of shear-induced gas-phase formation provides a natural physical explanation for wall slippage of liquid flow, covering the slip length ranging from a microscopic (nanometers) to macroscopic (micrometers) scale.

Entrapment of interfacial nanobubbles on nano-structured surfaces

Soft Matter ◽  
2017 ◽  
Vol 13 (32) ◽  
pp. 5381-5388 ◽  
Author(s):  
Yuliang Wang ◽  
Xiaolai Li ◽  
Shuai Ren ◽  
Hadush Tedros Alem ◽  
Lijun Yang ◽  
...  
Keyword(s):  
Nucleation Mechanism ◽  
Hydrophobic Surfaces ◽  
Structured Surfaces ◽  
Surface Nanostructures

The nucleation mechanism of interfacial nanobubbles is revealed on immersed nanostructured hydrophobic surfaces. The result shows that surface nanostructures play a key role in controlling nanobubbles' size, position, and even morphology.

Investigation of Heat Transfer Over a Rotating Disk in Case of Temperature and Velocity Jump Conditions by Using Differential Transform Method

2010 ◽  
Author(s):  
A. Y. Gunes ◽  
G. Komurgoz ◽  
A. Arikoglu ◽  
I. Ozkol
Keyword(s):  
Heat Transfer ◽  
Knudsen Number ◽  
Temperature Jump ◽  
Velocity Slip ◽  
Rotating Disk ◽  
Jump Conditions ◽  
Governing Equations ◽  
Transform Method ◽  
Differential Transform ◽  
Velocity Jump

The energy crisis in the last two decades has turned the attention of scientific and engineering communities to redesigned and developed heat-fluid interaction systems. All of the details in analyses are reconsidered to reduce energy consumption. The present work examines the effects of temperature and velocity jump conditions on heat transfer, fluid flow over a single rotating disk. The flow due to rotating disks is of great interest in thermal engineering as it appears in many industrial and engineering applications such as gas turbine engines and micropumps. The related equation of flow, which is nonlinear and coupled, and heat transfer governing equations are reduced to ordinary differential equations by applying the so-called classical approach which was first introduced by Von Karman. Instead of this approach, a pure numerical one, the recently developed popular semi numerical analytical technique differential transform method (DTM), with Benton transformation, is employed to solve the reduced governing equations under the assumptions of velocity-slip and temperature jump conditions on the disk surface. The solution is valid for continuum and slip-flow regime which has a Knudsen number smaller than 0.1. The results attained for various physical cases are interpreted by using non-dimensional parameters related to flow and temperature fields. Velocity and temperature profiles are presented graphically. The effect of various parameters such as the Knudsen Number (Kn), Reynolds Number (Re) and Nusselt Numbers (Nu) are examined. The observed physical consequences are the velocity slip and temperature jump at the wall becoming strongly dependant on the Knudsen number. It is also observed that the temperature jump and velocity jump conditions have nonlinear effects on slip; these effects are investigated with great details and presented graphically.

HYDRAULIC AND THERMAL PERFORMANCES OF LAMINAR FLOW IN FRACTAL TREELIKE BRANCHING MICROCHANNEL NETWORK WITH WALL VELOCITY SLIP

Fractals ◽  
2020 ◽  
Vol 28 (02) ◽  
pp. 2050022 ◽  
Author(s):  
DALEI JING ◽  
JIAN SONG ◽  
YI SUI
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Convective Heat Transfer ◽  
Hydraulic Resistance ◽  
Convective Heat ◽  
Slip Length ◽  
Velocity Slip ◽  
Diameter Ratio ◽  
Slip Condition ◽  
Wall Velocity

This work theoretically studies the effects of wall velocity slip on the hydraulic resistance and convective heat transfer of laminar flow in a microchannel network with symmetric fractal treelike branching layout. It is found that the slip can reduce the hydraulic resistance and enhance the Nusselt number of laminar flow in the network; furthermore, the slip can also affect the optimal structure of the fractal treelike microchannel network with minimum hydraulic resistance and maximum convective heat transfer. Under the size constraint of constant total channel surface area, the optimal diameter ratio of microchannels at two successive branching levels of the symmetric fractal treelike microchannel network with a minimized hydraulic resistance is only dependent on branching number [Formula: see text] in the manner of [Formula: see text] for no slip condition, but decreases with the increasing slip length, the increasing branching number and the increasing length ratio of microchannels at two successive branching levels for slip condition. The convective heat transfer of the treelike microchannel network is independent on the diameter ratio for no slip condition, but displays an increasing after decreasing trend with the increasing diameter ratio for slip condition. The symmetric treelike microchannel network with the worst convective heat transfer performance is the network with diameter ratio equaling one for slip condition.

Analysis and Simulation of Heat Transfer in a Superhydrophobic Microchannel

2010 ◽  
Author(s):  
Ryan Enright ◽  
Marc Hodes ◽  
Todd R. Salamon ◽  
Yuri Muzychka
Keyword(s):  
Thermal Behavior ◽  
Slip Length ◽  
Velocity Slip ◽  
Constant Heat Flux ◽  
Concentration Limit ◽  
Scaling Analysis ◽  
Channel Temperature ◽  
Geometric Scaling ◽  
Flux Boundary Conditions ◽  
Trapped Gas

The transport behavior of a superhydrophobic Hele-Shaw channel subject to arbitrary velocity slip, temperature slip, and constant heat flux boundary conditions is analyzed, resulting in a general expression for the Nusselt number. The results of a scaling analysis and numerical simulation are then presented characterizing the thermal behavior of an idealized pillar-structured superhydrophobic surface in the low pillar concentration limit that treats the trapped gas phase as adiabatic. When thermal behavior is uncoupled from the flow, the temperature slip length is shown to follow the same φs−1/2 dependency on pillar solid fraction as the velocity slip length. Further analysis and simulation including the effects of Marangoni stress, so that the thermal and flow fields are no longer decoupled, yields a further geometric scaling parameter. It is demonstrated that the apparent slip length may be increased against an adverse channel temperature gradient due to the local non-equilibrium of temperature in the vicinity of each pillar.

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