Nanoturf Surfaces for Reduction of Liquid Flow Drag in Microchannels

2004 ◽  
Author(s):  
Chang-Hwan Choi ◽  
Joonwon Kim ◽  
Chang-Jin Kim
Keyword(s):  
Drag Reduction ◽  
Liquid Flow ◽  
Continuous Flow ◽  
Good Control ◽  
Black Silicon ◽  
Parallel Plates ◽  
Fluidic Devices ◽  
Engineered Surfaces ◽  
Flow Drag ◽  
Liquid Flows

We report nano-engineered surfaces (NanoTurf), designed to make various micro- and nano-fluidic devices and systems less frictional for liquid flows, and describe microchannels made with such a surface. While our group has reported a dramatic (> 95%) drag reduction of discrete droplets flowing in a space between two parallel-plates covered with “random” nano-posts created by the “black silicon method” [1], this paper describes various nanofabrication techniques, including those capable of “designing” nanostructures with not only a good control of pattern sizes and periods but also practical manufacturability to be embedded in various micro- and nano-fluidic devices and systems. Microchannels are developed using the designed nanostructure surfaces and used for continuous flow tests.

scholarly journals Velocity bias in intrusive gas-liquid flow measurements

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
B. Hohermuth ◽  
M. Kramer ◽  
S. Felder ◽  
D. Valero
Keyword(s):  
Liquid Flow ◽  
Breaking Waves ◽  
Correction Method ◽  
Force Balance ◽  
Bubble Velocity ◽  
Natural Environments ◽  
Flow Measurements ◽  
Gas Liquid Flow ◽  
Liquid Flows ◽  
Velocity Bias

AbstractGas–liquid flows occur in many natural environments such as breaking waves, river rapids and human-made systems, including nuclear reactors and water treatment or conveyance infrastructure. Such two-phase flows are commonly investigated using phase-detection intrusive probes, yielding velocities that are considered to be directly representative of bubble velocities. Using different state-of-the-art instruments and analysis algorithms, we show that bubble–probe interactions lead to an underestimation of the real bubble velocity due to surface tension. To overcome this velocity bias, a correction method is formulated based on a force balance on the bubble. The proposed methodology allows to assess the bubble–probe interaction bias for various types of gas-liquid flows and to recover the undisturbed real bubble velocity. We show that the velocity bias is strong in laboratory scale investigations and therefore may affect the extrapolation of results to full scale. The correction method increases the accuracy of bubble velocity estimations, thereby enabling a deeper understanding of fundamental gas-liquid flow processes.

CFD Modelling for Gas-Liquid and Liquid-Liquid Taylor Flows in the Entrance Region of Microchannels

2021 ◽  
Author(s):  
Amin Etminan ◽  
Yuri S. Muzychka ◽  
Kevin Pope
Keyword(s):  
Liquid Flow ◽  
Continuous Flow ◽  
Velocity Ratio ◽  
Time History ◽  
Simulation Method ◽  
Cfd Modelling ◽  
Cross Sectional ◽  
Systematic Analysis ◽  
Gas Liquid Flow ◽  
The Moment

Abstract This paper presents a CFD-based simulation method for air/water and water/dodecane Taylor flows through an axisymmetric microchannel with a circular cross-sectional area. A systematic analysis is conducted by exploring the effects of different superficial velocities and apparent viscosities on the hydrodynamics of a slug flow regime. A concentric junction is employed to make bubbles of air in a continuous flow of water and slugs of water in a continuous flow of dodecane oil. A time-history study is conducted to predict the air-bubble and water-slug evolution processes, in particular at the moment of slug breakup. The results show that the larger apparent viscosity ratio of phases involved in the liquid-liquid flow generates a more stable interface. However, the liquid slug length is less and film thickness is slightly larger in liquid-liquid compared to gas-liquid flow. Furthermore, variations in gas and liquid holdups are correlated by the superficial velocity ratio. The numerical analysis developed in this paper is in good agreement with the correlations and data in the literature.

scholarly journals Effects of Side Walls on Pipe Inlet Flow (Drag Reduction by Separated Flow Control Using Ring Shaped Small Obstacle)

2009 ◽  
Vol 4 (2) ◽  
pp. 468-478 ◽  
Author(s):  
Toshitake ANDO ◽  
Toshihiko SHAKOUCHI ◽  
Hiroyuki YAMAMOTO ◽  
Koichi TSUJIMOTO
Keyword(s):  
Drag Reduction ◽  
Flow Control ◽  
Separated Flow ◽  
Inlet Flow ◽  
Side Walls ◽  
Flow Drag ◽  
Small Obstacle ◽  
Pipe Inlet

Convective flow in methanogenic granules

1997 ◽  
Vol 36 (6-7) ◽  
pp. 311-316 ◽  
Author(s):  
J. C. Van den Heuvel ◽  
E. E. Beuling ◽  
D. Van Dusschoten ◽  
O. L. Roosenschoon ◽  
P. G. Verschuren
Keyword(s):  
Liquid Flow ◽  
Atmospheric Conditions ◽  
Pressure Oscillations ◽  
Activity Increase ◽  
Pressure Cycling ◽  
Internal Ph ◽  
Flow Through ◽  
Liquid Flows ◽  
Diffusive Relaxation ◽  
Enhance Mass

Gas bubbles entrapped in biocatalyst particles subjected to hydrostatic pressure oscillations, e.g. during recirculation in loop reactors, will induce intraparticle liquid flows, and thereby enhance mass transfer in excess of diffusion. This ‘breathing particle’ mechanism was already demonstrated in methanogenic granules from an IC reactor, and led to an average macroscopic activity increase of 13%. The existence of the alternating convective liquid flow responsible for this higher activity has now been established independently with pulsed field gradient NMR, as the intraparticle water mobility during pressure oscillations was found 16.5% larger. Micro-electrode measurements of the internal pH of a granule revealed the occurrence of a fast liquid flow through a channel between a central cavity and the periphery during pressure cycling, and the subsequent diffusive relaxation under atmospheric conditions.

Fluid Mechanics of Flow Through Rectangular Hydrophobic Microchannels

2011 ◽  
Author(s):  
Navid Kashaninejad ◽  
Weng Kong Chan ◽  
Nam-Trung Nguyen
Keyword(s):  
Aspect Ratio ◽  
Rectangular Cross Section ◽  
Expansion Method ◽  
Channel Height ◽  
Parallel Plates ◽  
Laminar Regime ◽  
Dimensional Solution ◽  
Eigenfunction Expansion Method ◽  
Flow Through ◽  
Liquid Flows

In this study, the effect of two important parameters have been evaluated for pressure driven liquid flows in microchannel in laminar regime by analytical modeling, followed by experimental measurement. These parameters are wettability conditions of microchannel surfaces and aspect ratio of rectangular microchannels. For small values of aspect ratio, the channel was considered to have a rectangular cross-section, instead of being two parallel plates. Novel expressions for these kinds of channels were derived using eigenfunction expansion method. The obtained two-dimensional solutions based on dual finite series were then extended to the case of a constant slip velocity at the bottom wall. In addition, for large values of aspect ratio, a general equation was obtained which is capable of accounting for different values of slip lengths for both upper and lower channel walls. Firstly, it was found out that for low aspect ratio microchannels, the results obtained by analytical rectangular 2-D model agree well with the experimental measurements as compared to one dimensional solution. For high aspect ratio microchannels, both models predict the same trend. This finding indicates that using the conventional 1-D solution may not be accurate for the channels where the width is of the same order as the height. Secondly, experimental results showed that up to 2.5% and 16% drag reduction can be achieved for 1000 and 250 micron channel height, respectively. It can be concluded that increasing the surface wettability can reduce the pressure drop in laminar regime and the effect is more pronounced by decreasing the channel height.

Experimental Evaluation of the Nukiyama-Tanasawa Equation for Pneumatically Generated Aerosols Used in Flame Atomic Spectrometry

1992 ◽  
Vol 46 (4) ◽  
pp. 669-676 ◽  
Author(s):  
Coral Robles ◽  
Juan Mora ◽  
Antonio Canals
Keyword(s):  
Organic Solvents ◽  
Liquid Flow ◽  
Experimental Evaluation ◽  
Gas Flow ◽  
Droplet Size Distribution ◽  
Atomic Spectrometry ◽  
Fraunhofer Diffraction ◽  
Sauter Mean Diameter ◽  
Mean Diameter ◽  
Liquid Flows

The Nukiyama-Tanasawa equation has been checked for its applicability to predict the Sauter mean diameter of aerosols generated pneumatically under the conditions usually employed in FAAS. The measurements of droplet-size distribution have been carried out by means of a laser Fraunhofer diffraction system. The effects of both gas and liquid flows, and solvent physical properties, on experimental and calculated Sauter mean diameters of the aerosols have been studied. The results show that this equation, under normal conditions used in FAAS, correctly describes the trends of Sauter mean diameter variation of aerosols generated pneumatically with respect to the flows of nebulizing gas and liquid. Increases in liquid flow or decreases in gas flow give rise to increases in Sauter mean diameters of the aerosols. However, the absolute values predicted according to the equation far exceed the experimental Sauter mean diameters obtained, the divergences being larger at higher liquid flow/nebulizing gas flow ratios. The overestimation for water ranged from 1.8- to 8.1-fold, and for organic solvents and methanol+water mixtures from 3.6- to 13.3-fold. Under the conditions studied, experimental Sauter mean diameter values for the organic solvents and methanol+water mixtures studied were well below those found for water, under comparable conditions. This result contradicts the predictions of the Nukiyama-Tanasawa equation mainly at high liquid flow/nebulizing gas flow ratios. The main reason for this divergence is the overweighting assigned to the second term of the equation.

scholarly journals High-performance monoliths in heterogeneous catalysis with single-phase liquid flow

2017 ◽  
Vol 2 (4) ◽  
pp. 498-511 ◽  
Author(s):  
Christian P. Haas ◽  
Tibor Müllner ◽  
Richard Kohns ◽  
Dirk Enke ◽  
Ulrich Tallarek
Keyword(s):  
Heterogeneous Catalysis ◽  
Liquid Flow ◽  
Continuous Flow ◽  
High Performance ◽  
Single Phase ◽  
Rapid Screening ◽  
Flow Mode ◽  
Reaction Parameters ◽  
On Line ◽  
Phase Liquid

On-line control and monitoring in heterogeneous catalysis utilizing high-performance supports allows rapid screening of intrinsic reaction parameters in continuous-flow mode.

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