80 research outputs found
On the effect of surfactant adsorption and viscosity change on apparent slip in hydrophobic microchannels
Substantial experimental, theoretical, as well as numerical effort has been
invested to understand the effect of boundary slippage in microfluidic devices.
However, even though such devices are becoming increasingly important in
scientific, medical, and industrial applications, a satisfactory understanding
of the phenomenon is still lacking. This is due to the extremely precise
experiments needed to study the problem and the large number of tunable
parameters in such systems.
In this paper we apply a recently introduced algorithm to implement
hydrophobic fluid-wall interactions in the lattice Boltzmann method. We find a
possible explanation for some experiments observing a slip length depending on
the flow velocity which is contradictory to many theoretical results and
simulations. Our explanation is that a velocity dependent slip can be detected
if the flow profile is not fully developed within the channel, but in a
transient state.
Further, we show a decrease of the measured slip length with increasing
viscosity and demonstrate the effect of adding surfactant to a fluid flow in a
hydrophobic microchannel. The addition of surfactant can shield the repulsive
potential of hydrophobic walls, thus lowering the amount of slip with
increasing surfactant concentration.Comment: 9 pages, 6 figure
Roughness induced boundary slip in microchannel flows
Surface roughness becomes relevant if typical length scales of the system are
comparable to the scale of the variations as it is the case in microfluidic
setups. Here, an apparent boundary slip is often detected which can have its
origin in the assumption of perfectly smooth boundaries. We investigate the
problem by means of lattice Boltzmann (LB) simulations and introduce an
``effective no-slip plane'' at an intermediate position between peaks and
valleys of the surface. Our simulations show good agreement with analytical
results for sinusoidal boundaries, but can be extended to arbitrary geometries
and experimentally obtained surface data. We find that the detected apparent
slip is independent of the detailed boundary shape, but only given by the
distribution of surface heights. Further, we show that the slip diverges as the
amplitude of the roughness increases.Comment: 4 pages, 6 figure
Random-roughness hydrodynamic boundary conditions
We report results of lattice Boltzmann simulations of a high-speed drainage
of liquid films squeezed between a smooth sphere and a randomly rough plane. A
significant decrease in the hydrodynamic resistance force as compared with that
predicted for two smooth surfaces is observed. However, this force reduction
does not represent slippage. The computed force is exactly the same as that
between equivalent smooth surfaces obeying no-slip boundary conditions, but
located at an intermediate position between peaks and valleys of asperities.
The shift in hydrodynamic thickness is shown to depend on the height and
density of roughness elements. Our results do not support some previous
experimental conclusions on very large and shear-dependent boundary slip for
similar systems.Comment: 4 pages, 4 figure
Simulation of fluid flow in hydrophobic rough microchannels
Surface effects become important in microfluidic setups because the surface
to volume ratio becomes large. In such setups the surface roughness is not any
longer small compared to the length scale of the system and the wetting
properties of the wall have an important influence on the flow. However, the
knowledge about the interplay of surface roughness and hydrophobic
fluid-surface interaction is still very limited because these properties cannot
be decoupled easily in experiments.
We investigate the problem by means of lattice Boltzmann (LB) simulations of
rough microchannels with a tunable fluid-wall interaction. We introduce an
``effective no-slip plane'' at an intermediate position between peaks and
valleys of the surface and observe how the position of the wall may change due
to surface roughness and hydrophobic interactions.
We find that the position of the effective wall, in the case of a Gaussian
distributed roughness depends linearly on the width of the distribution.
Further we are able to show that roughness creates a non-linear effect on the
slip length for hydrophobic boundaries.Comment: 10 pages, 5 figure
Autoantibodies to granulocytes in chronic inflammatory bowel disease are not correlated with antibodies to intestinal goblet cells in ulcerative colitis and to pancreatic juice in Crohn`s disease
Умная теплица
Цель работы – проектирование автоматизированной системы полива растений и проветривания помещения внутри теплицы. Благодаря этому создаются благоприятные условия для произрастания растений. Регулируется влажность и температура окружающей среды.
В процессе исследования проводилось создание структурной схемы и проектирование системы автополива и проветривания. В результате исследования была спроектирована система капельного автополива. Для вентиляции выбрана гидравлическая система проветривания
Основные конструктивные, технологические и технико-эксплуатационные характеристики: влажность воздуха, влажность почвы, температура воздуха. Область применения: создание простой и удобной системы автополива и проветривания.The aim of this work is designing an automated system of irrigation and ventilation inside the greenhouse. This creates favorable conditions for the growth of plants. Adjustable humidity and temperature of the environment.
In the process of investigation the creation of block diagrams and system design automatic irrigation and ventilation. The study was designed a system of drip-irrigation. For ventilation of the selected hydraulic system of ventilation
The basic constructive, technological and technical-operational characteristics: humidity, soil moisture, air temperature. Scope: create a simple and convenient system of auto-irrigation and ventilation
Heterogeneous integration on silicon photonics
To enhance the functionality of the standard silicon photonics platform and to overcome its limitations, in particular for light emission, ultrafast modulation, and nonlinear applications, integration with novel materials is being investigated by several groups. In this paper, we will discuss, among others, the integration of silicon waveguides with ferroelectric materials such as lead zirconate titanate (PZT) and barium titanate (BTO), with electro-optically active polymers, with 2-D materials such as graphene and with III-V semiconductors through epitaxy. We discuss both the technology and design aspects
Genotype of CHO host cell line has higher impact on mAb production and quality than process strategy or cell culture medium
Chinese hamster ovary (CHO) cells comprise a variety of lineages, including CHO-DXB11, CHO-K1, CHO-DG44 and CHO-S. Despite the fact that CHO cell lines share a common ancestor, extensive mutagenesis and clonal selection have resulted in substantial genetic heterogeneity among them. Data from sequencing shows that different genes are lacking from individual CHO cell lines and that each cell line harbors a unique set of mutations that are relevant to the bioprocess. However, literature outlining how the observed genetic differences affect CHO cell performance during bioprocess operations remains scarce. In this study, we examined host cell-specific differences among three widely used CHO cell lines (CHO-K1, CHO-S and CHO-DG44) and recombinantly expressed the same monoclonal antibody (mAb) in an isogenic format in all cell lines by using bacterial artificial chromosomes (BACs) as transfer vector. Cell-specific growth, product formation and heavy and light chain mRNA levels were studied in batch, fed-batch and perfusion cultures. Furthermore, two different cell culture media were investigated. Product quality was studied through glycoprofiling, and the thermal denaturation was analyzed using differential scanning calorimetry (DSC). We found CHO cell line-specific preferences for mAb production or biomass synthesis that were determined by the host cell line rather than product-specific mRNA levels. Additionally, quality attributes of the expressed mAb were influenced by the host cell line and medium used
Influence of Slim Rod Material Properties to the Siemens Feed Rod and the Float Zone Process
AbstractThe identification and understanding of material properties influencing the float zone process is important to crystallize high purity silicon for high efficiency solar cells. Also the knowledge of minimal requirements to crystallize monocrystalline silicon with the float zone process is of interest from an economic point of view. In the present study, feed rods for the float zone process composed of a central slim rod and the deposited silicon from the Siemens process are investigated. Previous studies have shown that the slim rod has a significant impact on the purity and suitability for further crystallization processes. In particular, contaminations like substitutional carbon and the presence of precipitates as well as the formation of oxide layers play an important role and are investigated in detail. For this purpose different slim rod materials were used in deposition and float zone crystallization experiments. Samples were prepared by cross sectioning and core drilling of Siemens rods, which were recrystallized with the float zone process. Recrystallized drilled cores are analyzed with FT-IR spectrometry concerning the carbon and oxygen content. To estimate the grain growth behavior on the slim rod surface in dependence of the used slim rod material, EBSD mappings inside a SEM are performed on squared and circular slim rods. TEM analysis was used to investigate the presence of an oxide layer at the interface between slim rod and deposited polycrystalline silicon. Additionally the influence of a nitrogen-containing gas atmosphere during the slim rod pulling is investigated by IR microscopy and ToF-SIMS regarding Si3N4 precipitation
Lattice Boltzmann simulations in microfluidics: probing the no-slip boundary condition in hydrophobic, rough, and surface nanobubble laden microchannels
In this contribution we review recent efforts on investigations of the effect
of (apparent) boundary slip by utilizing lattice Boltzmann simulations. We
demonstrate the applicability of the method to treat fundamental questions in
microfluidics by investigating fluid flow in hydrophobic and rough
microchannels as well as over surfaces covered by nano- or microscale gas
bubbles.Comment: 11 pages, 6 figure
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