DENSITY OSCILLATION FROM NANOSCALE TO MACROSCALE

2008 ◽  
Vol 22 (27) ◽  
pp. 2649-2658 ◽  
Author(s):  
X. Y. CHEN ◽  
Y. LIU ◽  
J. M. YANG
Keyword(s):  
Molecular Dynamics ◽  
Channel Flow ◽  
Channel Width ◽  
Density Structure ◽  
Flux Rate ◽  
Confined Fluid ◽  
Threshold Channel ◽  
Micro Channels ◽  
Confined Flow ◽  
Density Oscillation

The effect of channel width on the density structure of confined fluid in the nano-/micro-channels is examined by equilibrium molecular dynamics (EMD) simulation. It was found that the density oscillation occurs near the wall in both cases of the macroscale or nanoscale confined flow. There exists a threshold channel width L threshold , when channel width H<L threshold , density oscillates throughout the channel. When H>L threshold , L threshold is constant and about 5–6 molecular diameter long, and the density becomes uniform beyond this threshold layer. A newly defined ch number may serve to be the parameter to compare similarity in the micro-/nano-scale channel flow. Moreover, the effect of the density oscillation on fluid mass flux rate is examined quantitatively. The result shows that the effect should be considered when the channel width is below 5 molecular diameter.

Effects of Real Surface Roughness on Fluid Flow in Nanochannels

2010 ◽  
Author(s):  
Ali Kharazmi ◽  
Reza Kamali
Keyword(s):  
Molecular Dynamics ◽  
Surface Roughness ◽  
Fluid Flow ◽  
Computer Program ◽  
Md Simulation ◽  
Real Surface ◽  
Micro Channels

In the present study, a computer program based on a molecular dynamics scheme has been developed for simulating fluid flow in nano- and micro-channels with roughness. According to the previous studies of nanochannels flows, surface roughness has a great effect on the rheology of the flow. Therefore a more realistic surface roughness has been developed and its influence on the fluid flow has been investigated using Molecular Dynamics (MD) Simulation.

Effect of Electrical Double Layer on Electrical Conductivity and Pressure Drop in Pressure-Driven Micro-Channel Flow

2006 ◽  
Author(s):  
Bochuan Lin ◽  
Heng Ban
Keyword(s):  
Electrical Conductivity ◽  
Pressure Drop ◽  
Channel Flow ◽  
Double Layer ◽  
Electrical Double Layer ◽  
Debye Length ◽  
Channel Width ◽  
Micro Channel ◽  
Order Of Magnitude ◽  
Pressure Driven

The effect of electrical double layer (EDL) on micro-channel flow has been studied widely. Most research focused on flows with typical channel width or pipe diameter much greater than the thickness of EDL (Debye length). In such cases, the influence of EDL on the overall electrical conductivity is small, and a constant bulk electrical conductivity is often used in calculations. In our study of pressure-driven micropipette injection flow, the pipe size is on the same order of magnitude as the Debye length. To elucidate the effect of overlapping EDL the flow inside a micro-channel was analyzed. The governing equations for the flow, the Poisson equation for the electric potential, and the charge continuity equation for the net charge were solved analytically. The effect of overlapping EDL on the electrical conductivity and velocity distribution in the micro-channel and the pressure drop were quantified. The results showed that, the average conductivity of electrolyte solution inside the channel increased significantly, dependent on the channel width. With the modified mean electrical conductivity, the pressure drop for the pressure-driven flow was smaller than that without considering the influence of EDL on conductivity.

Micro Cryogenic Coolers With Mixed Refrigerants

2013 ◽  
Author(s):  
Ryan Lewis ◽  
Yunda Wang ◽  
Paul Schroeder ◽  
Collin Coolidge ◽  
Ray Radebaugh ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Channel Flow ◽  
Pressure Ratio ◽  
Maximum Flow ◽  
Cooling Power ◽  
Micro Channel ◽  
Standard Ml ◽  
Micro Channels ◽  
Flow Through ◽  
Cryogenic Cooler

A number of small electronic devices benefit from micro-scale low temperature operation. Recently we have developed micro cryogenic coolers (MCCs) using a low-pressure, mixed-refrigerant Joule-Thomson cycle. The cryocoolers utilizes a MEMS-enabled gas compressor coupled to a micro cold stage. Two cold stages have been developed: one which uses a fiber-enabled heat exchanger assembled to a micro-machined throttling valve, and another which uses a MEMS-based heat exchanger. A microcompressor has been developed which uses MEMS-based check valves coupled to a membrane, which is actuated with a mechanically amplified piezoelectric amplifier. The compressor measures a volume 15 mL, can generate a pressure ratio of 6:1 and a maximum flow-rate of 60 standard mL/min. The complete cryocooler has reached low temperatures of 177 K, although temperature instability has been an issue, due to 2-phase flow through the micro-channels. This paper will cover the development and testing of the micro cryogenic cooler, as well as an analysis of the micro channel flow. A proper understanding of the micro-channel flow allows us to design refrigerant mixtures to improve the cooling power, and modify the cooler to eliminate temperature instabilities.

Ranking migration cue contributions to guiding individual fibroblasts faced with a directional decision in simple microfluidic bifurcations

2019 ◽  
Vol 11 (5) ◽  
pp. 208-220
Author(s):  
Quang Long Pham ◽  
Anh Tong ◽  
Lydia N Rodrigues ◽  
Yang Zhao ◽  
Migle Surblyte ◽  
...  
Keyword(s):  
Decision Making ◽  
Tissue Growth ◽  
Channel Width ◽  
Contact Guidance ◽  
Diffusion Modeling ◽  
Directed Cell Migration ◽  
Micro Channels ◽  
Artificial Tissue ◽  
Directional Decisions

Abstract Directed cell migration in complex micro-environments, such as in vivo pores, is important for predicting locations of artificial tissue growth and optimizing scaffold architectures. Yet, the directional decisions of cells facing multiple physiochemical cues have not been characterized. Hence, we aim to provide a ranking of the relative importance of the following cues to the decision-making of individual fibroblast cells: chemoattractant concentration gradient, channel width, mitosis, and contact-guidance. In this study, bifurcated micro-channels with branches of different widths were created. Fibroblasts were then allowed to travel across these geometries by following a gradient of platelet-derived growth factor-BB (PDGF-BB) established inside the channels. Subsequently, a combination of statistical analysis and image-based diffusion modeling was used to report how the presence of multiple complex migration cues, including cell-cell influences, affect the fibroblast decision-making. It was found that the cells prefer wider channels over a higher chemoattractant gradient when choosing between asymmetric bifurcated branches. Only when the branches were symmetric in width did the gradient become predominant in directing which path the cell will take. Furthermore, when both the gradient and the channels were symmetric, contact guidance became important for guiding the cells in making directional choices. Based on these results we were able to rank these directional cues from most influential to the least as follows: mitosis > channel width asymmetry > chemoattractant gradient difference > and contact-guidance. It is expected that these results will benefit the fields of regenerative medicine, wound healing and developmental biology.

scholarly journals Elastic Turbulence of Aqueous Polymer Solution in Multi-Stream Micro-Channel Flow

Micromachines ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 110 ◽  
Author(s):  
Jiayan Tai ◽  
Yee Cheong Lam
Keyword(s):  
Flow Field ◽  
Channel Flow ◽  
Flow Instability ◽  
Flow Behavior ◽  
Power Spectra ◽  
Micro Channel ◽  
Polymer Molecules ◽  
Aqueous Solvent ◽  
Micro Channels ◽  
Flow Field Characteristics

Viscous liquid flow in micro-channels is typically laminar because of the low Reynolds number constraint. However, by introducing elasticity into the fluids, the flow behavior could change drastically to become turbulent; this elasticity can be realized by dissolving small quantities of polymer molecules into an aqueous solvent. Our recent investigation has directly visualized the extension and relaxation of these polymer molecules in an aqueous solution. This elastic-driven phenomenon is known as ‘elastic turbulence’. Hitherto, existing studies on elastic flow instability are mostly limited to single-stream flows, and a comprehensive statistical analysis of a multi-stream elastic turbulent micro-channel flow is needed to provide additional physical understanding. Here, we investigate the flow field characteristics of elastic turbulence in a 3-stream contraction-expansion micro-channel flow. By applying statistical analyses and flow visualization tools, we show that the flow field bares many similarities to that of inertia-driven turbulence. More interestingly, we observed regions with two different types of power-law dependence in the velocity power spectra at high frequencies. This is a typical characteristic of two-dimensional turbulence and has hitherto not been reported for elastic turbulent micro-channel flows.

Multiscale MD/LBM Simulations of Flow in Complex Nano/Micro Channels

2010 ◽  
Author(s):  
D. D. Marsh ◽  
S. P. Vanka
Keyword(s):  
Molecular Dynamics ◽  
Lattice Boltzmann ◽  
Stokes Equations ◽  
Velocity Slip ◽  
Navier Stokes ◽  
Graphics Processor ◽  
Micro Channels ◽  
Hybrid Code ◽  
Hybrid Solver ◽  
Complex Boundaries

This paper examines the fluid behavior in micro and nano sized channels by using a coupled Molecular Dynamics and Lattice Boltzmann solution method, implemented in a novel fashion on a Graphics Processor. Molecular Dynamics is well known for its ability to resolve phenomena in the near wall regions, where continuum assumptions are no longer valid, at the expense of computational power. Lattice Boltzmann is a mesoscale continuum-description solver that is very efficient and reduces to the Navier-Stokes equations, thereby being a logical choice to solve regions further from the wall. This method is parallelized to be run on the Graphics Processor, using NVIDIA’s CUDA programming language. Individually, Lattice Boltzmann methods are approximately 70× faster on the GPU than a modern CPU, Molecular Dynamics is about 5× faster. Higher resolutions are able to be simulated than previously performed due to the efficiency of this implementation. We analyze the results of straight channel Poiseuille flow using the hybrid solver and note the continuum breakdown is successfully predicted by the hybrid code in the form of density oscillations near the wall along with velocity slip conditions. Streamlines, contours and velocity profiles are utilized to illustrate these points. Future work includes expanding this solver’s capability to handle complex boundaries.

scholarly journals Optimization of Biporous Micropillar Array for Enhanced Heat Transfer Performance

2015 ◽  
Author(s):  
Mengyao Wei ◽  
Sivanand Somasundaram ◽  
Bin He ◽  
Qian Liang ◽  
Rishi Raj ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Aspect Ratio ◽  
Capillary Pressure ◽  
Heat Transfer Performance ◽  
Channel Width ◽  
Viscous Drag ◽  
Transfer Performance ◽  
Micro Channels ◽  
Pitch Ratio

Biporous evaporator wicks for heat pipe and vapor chambers can perform superiorly by reducing the viscous drag with larger pores or channels and simultaneously generate higher capillary pressure with smaller pores radius. Unlike conventional sintered metal biporous wicks, cylindrical silicon micropillar based evaporator with microchannels, possess the following advantages: mature and easily controllable fabrication process, possibility of direct integration with semiconductor devices and no risk of thermal expansion mismatch. In this work, we investigated a biporous wick for the evaporator design, which consists of micro pillar arrays interspersed within micro channels. This design was systematically studied by constructing a mathematical model, by coupling Brinkman’s equation with mass and energy conservation equations, to predict the biporous wicks’ heat transfer performance. In order to find the best combination of geometric factors that give the highest heat flux at a certain superheat value, optimization in Matlab was done. The effect of diameter to pitch ratio, aspect ratio, channel width and contact angle on wick’s permeability, capillary pressure and evaporative heat flux were also investigated. Conclusion was drawn that a higher diameter to pitch ratio of 0.57, reasonable aspect ratio of 1.75∼3.22, island to channel width ratio of around 1.96 are preferred in this kind of biporous wick’s design. Biporous wick show potential to dissipate heat flux of 515.7 W/cm2 at superheat of 40 °C, which is 134 % higher compared to monoporous wick.

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