共查询到20条相似文献，搜索用时 46 毫秒
1.
A focusing-based microfluidic mixer was studied. The micromixer utilizes the focusing process required for cytometry to reduce the diffusion distance of molecules to be mixed in order to facilitate the passive diffusion-controlled mixing process. It was found that both the high flow rate ratio of the sheath flow to the flows to be mixed and the low flow rate of the mixing fluids resulted in the short mixing length required within the microfluidic channel. It was shown that a complete mixing was achieved within a distance of 4 mm in the micromixer for the focused mixing fluids at a flow rate of 2 μl∕min and a flow rate ratio of the sheath flow to the flows to be mixed at 4:1. The mixer described here is simple and can be easily fabricated and controlled. 相似文献
2.
Shilpa Sivashankar Sumeyra Agambayev Yousof Mashraei Er Qiang Li Sigurdur T. Thoroddsen Khaled Nabil Salama 《Biomicrofluidics》2016,10(3)
This paper proposes a new “twisted” 3D microfluidic mixer fabricated by a laser writing/microfabrication technique. Effective and efficient mixing using the twisted micromixers can be obtained by combining two general chaotic mixing mechanisms: splitting/recombining and chaotic advection. The lamination of mixer units provides the splitting and recombination mechanism when the quadrant of circles is arranged in a two-layered serial arrangement of mixing units. The overall 3D path of the microchannel introduces the advection. An experimental investigation using chemical solutions revealed that these novel 3D passive microfluidic mixers were stable and could be operated at a wide range of flow rates. This micromixer finds application in the manipulation of tiny volumes of liquids that are crucial in diagnostics. The mixing performance was evaluated by dye visualization, and using a pH test that determined the chemical reaction of the solutions. A comparison of the tornado-mixer with this twisted micromixer was made to evaluate the efficiency of mixing. The efficiency of mixing was calculated within the channel by acquiring intensities using ImageJ software. Results suggested that efficient mixing can be obtained when more than 3 units were consecutively placed. The geometry of the device, which has a length of 30 mm, enables the device to be integrated with micro total analysis systems and other lab-on-chip devices. 相似文献
3.
This work is concerned with the investigation of the concentration fields in an electrokinetic micromixer and its optimization in order to achieve high mixing rates. The mixing concept is based on the combination of an alternating electrical excitation applied to a pressure-driven base flow in a meandering microchannel geometry. The electrical excitation induces a secondary electrokinetic velocity component, which results in a complex flow field within the meander bends. A mathematical model describing the physicochemical phenomena present within the micromixer is implemented in an in-house finite-element-method code. We first perform simulations comparable to experiments concerned with the investigation of the flow field in the bends. The comparison of the complex flow topology found in simulation and experiment reveals excellent agreement. Hence, the validated model and numerical schemes are employed for a numerical optimization of the micromixer performance. In detail, we optimize the secondary electrokinetic flow by finding the best electrical excitation parameters, i.e., frequency and amplitude, for a given waveform. Two optimized electrical excitations featuring a discrete and a continuous waveform are discussed with respect to characteristic time scales of our mixing problem. The results demonstrate that the micromixer is able to achieve high mixing degrees very rapidly. 相似文献
4.
Electroconvection is known to cause strong convective mixing in a microchannel near a nanoporous membrane or a nanochannel in contact with an electrolyte solution due to the external electric field. This study addresses micromixer behavior subject to electroconvection occurring near a nanoporous membrane in-situ fabricated by a laser polymerization technique on a microfluidic chip. We found that the micromixer behavior can be categorized into three regimes. Briefly, the weak electroconvection regime is characterized by weak mixing performance at a low applied voltage and KCl concentration, whereas the strong electroconvection regime has a high mixing performance when the applied voltage and KCl concentration are moderately high. Finally, the incomplete electroconvection regime has an incomplete electric double-layer overlap in the nanopores of the membrane when the electrolyte concentration is very high. The mixing index reached 0.92 in the strong electroconvection regime. The detailed fabrication methods for the micromixer and characterization results are discussed in this paper. 相似文献
5.
We demonstrated a simple method for the device design of a staggered herringbone micromixer (SHM) using numerical simulation. By correlating the simulated concentrations with channel length, we obtained a series of concentration versus channel length profiles, and used mixing completion length Lm as the only parameter to evaluate the performance of device structure on mixing. Fluorescence quenching experiments were subsequently conducted to verify the optimized SHM structure for a specific application. Good agreement was found between the optimization and the experimental data. Since Lm is straightforward, easily defined and calculated parameter for characterization of mixing performance, this method for designing micromixers is simple and effective for practical applications. 相似文献
6.
Buchegger W Haller A van den Driesche S Kraft M Lendl B Vellekoop M 《Biomicrofluidics》2012,6(1):12803-128039
In this study, the pre-steady state development of enzymatic bioreactions using a microfluidic mixer is presented. To follow such reactions fast mixing of reagents (enzyme and substrate) is crucial. By using a highly efficient passive micromixer based on multilaminar flow, mixing times in the low millisecond range are reached. Four lamination layers in a shallow channel reduce the diffusion lengths to a few micrometers only, enabling very fast mixing. This was proven by confocal fluorescence measurements in the channel’s cross sectional area. Adjusting the overall flow rate in the 200 μm wide and 900 μm long mixing and observation channel makes it possible to investigate enzyme reactions over several seconds. Further, the device enables changing the enzyme/substrate ratio from 1:1 up to 3:1, while still providing high mixing efficiency, as shown for the enzymatic hydrolysis using β-galactosidase. This way, the early kinetics of the enzyme reaction at multiple enzyme/substrate concentrations can be collected in a very short time (minutes). The fast and easy handling of the mixing device makes it a very powerful and convenient instrument for millisecond temporal analysis of bioreactions. 相似文献
7.
The most basic micromixer is a T- or Y-mixer, where two confluent streams mix due to transverse diffusion. To enhance micromixing, various modifications of T-mixers are reported such as heterogeneously charged walls, grooves on the channel base, geometric variations by introducing physical constrictions, etc. The performance of these reported designs is evaluated against the T-mixer in terms of the deviation from perfectly mixed state and mixing length (device length required to achieve perfect mixing). Although many studies have noticed the reduced flow rates for improved mixer designs, the residence time is not taken into consideration for micromixing performance evaluation. In this work, we propose a novel index, based on residence time, for micromixing characterization and comparative analysis. For any given mixer, the proposed index identifies the nondiffusive mixing enhancement with respect to the T-mixer. Various micromixers are evaluated using the proposed index to demonstrate the usefulness of the index. It is also shown that physical constriction mixer types are equivalent to T-mixers. The proposed index is found to be insightful and could be used as a benchmark for comparing different mixing strategies. 相似文献
8.
An integrated microfluidic chip is proposed for rapid DNA digestion and time-resolved capillary electrophoresis (CE) analysis. The chip comprises two gel-filled chambers for DNA enrichment and purification, respectively, a T-form micromixer for DNA/restriction enzyme mixing, a serpentine channel for DNA digestion reaction, and a CE channel for on-line capillary electrophoresis analysis. The DNA and restriction enzyme are mixed electroomostically using a pinched-switching DC field. The experimental and numerical results show that a mixing performance of 97% is achieved within a distance of 1 mm from the T-junction when a driving voltage of 90 V/cm and a switching frequency of 4 Hz are applied. Successive mixing digestion and capillary electrophoresis operation clearly present the changes on digesting φx-174 DNA in different CE runs. The time-resolved electropherograms show that the proposed device enables a φx-174 DNA sample comprising 11 fragments to be concentrated and analyzed within 24 min. Overall, the results presented in this study show that the proposed microfluidic chip provides a rapid and effective tool for DNA digestion and CE analysis applications. 相似文献
9.
Inertial microfluidics has brought enormous changes in the conventional cell/particle detection process and now become the main trend of sample pretreatment with outstanding throughput, low cost, and simple control method. However, inertial microfluidics in a straight microchannel is not enough to provide high efficiency and satisfying performance for cell/particle separation. A contraction–expansion microchannel is a widely used and multifunctional channel pattern involving inertial microfluidics, secondary flow, and the vortex in the chamber. The strengthened inertial microfluidics can help us to focus particles with a shorter channel length and less processing time. Both the vortex in the chamber and the secondary flow in the main channel can trap the target particles or separate particles based on their sizes more precisely. The contraction–expansion microchannels are also capable of combining with a curved, spiral, or serpentine channel to further improve the separation performance. Some recent studies have focused on the viscoelastic fluid that utilizes both elastic forces and inertial forces to separate different size particles precisely with a relatively low flow rate for the vulnerable cells. This article comprehensively reviews various contraction–expansion microchannels with Newtonian and viscoelastic fluids for particle focusing, separation, and microfluid mixing and provides particle manipulation performance data analysis for the contraction–expansion microchannel design. 相似文献
10.
11.
李中明 《中国科学院研究生院学报》1983,21(2):153-160
The genus Palaeosmunda was established by R. E. Gould in 1970 based upon some
Late Permian Osmundaceous trunks with well-developed leaf gaps and rhomboidal
sclerotic ring within petiolar base seen in cross section. As he thinks that the latter
character is more important than the former, this genus could not be assigned to any
subfamily of Osmundaceae.
However, the leaf gap is one of the most important characters in the structure of the fern stem, so the author suggests that this genus should be assigned to subfamily
Osmundoideae and its diagnosis must be emended as follows:
The genus Palaeosmunda is represented by some rhizomes (or trunks), roots and
leaf bases of ferns which structurally are preserved, resembling Osmundacaulis but
which can’t be assigned to any group of this genus.
Stem containing an ectophloic dictyoxylic siphonostele; if tracheids present in
the pith, they being multiseriate scalariform pitted; pith or cortex sometimes contain-
ing groups of secretory cells or sclerenchyma; number of leaf traces seen in a tran-
sverse section of cortex more than 30; leaf traces adaxially curvature, rarely oblong-
shaped; petiolar bases with or without stipular expansion, containing a C-shaped
vascular strand; root diarch.
Type species——Palaeosmunda williamsii.
According to this diagnosis some primitive osmundaceous species with the leaf
gaps, which have already found in Upper Permian and Lower Triassic, could be assigned
to this genus. Two of them are P. williamsii Gould and P. playfordii Gould, and
Osmundacaulis beardmorensis, which was from Lower Triassic of Antarctica in 1978,
should be assigned to the genus Palaeosmunda.
In this paper two osmundaceous new species: P. primitiva and P. plenasioides were
found in the coal balls of Upper Permian age from Wangjiazhai of Shuicheng of
Guizhou Province, China.
P. primitiva is represented by two trunks; stem about 4 cm in diameter; stele
actophloic dictyoxylic siphonostele; pith cavity about 3—4 mm in diameter, contianing
parenchyma and tracheids; xylem cylinder thin, less than 10 tracheids in radial thick-
ness, dissected by leaf gaps. Inner cortex about 1.5 cm thick, mainly parenchymatous,
but sometimes containing a few sclerenchymatous; number of leaf traces seen in a
transverse section about 50—60; leaf traces departing at 35—45º,open C-shaped at
point of departure, gradually becoming shallow C-shaped or V-shaped in different
parts; protoxylem in base of leaf traces single, endarch; when leaf traces pass through
inner cortex, protoxylem biturcating. Petiole bases without stipular expansion, probablyloosely embracing the stem; xylem strand of potiole trace shallow C-shaped, surrounded by selerenchyma; sclerotic ring round, connected with single sclerenchyma mass in the concavity of the petiole trace. Root arising singly from leaf trace, diarch, with inner and outer cortex.
P. plenasioides is represented by a rhizome; stem more than 4 cm in diameter;
stele actophloic dictyoxylic siphonostele; xylem cylider with about 20 tracheids in
radial thickness, dissected by leaf gaps; xylem bundle U-, O-, or crosier- (i.e. query-)
shaped; pith and inner cortex parenchymatous, with many groups of secretory cells;
leaf trace C-shaped, its base containing two endarch protoxylem groups; root diareh,with inner and outer cortex, arising singly from leaf trace or its base. 相似文献
12.
对压力驱动微通道弯道部分流场的扩散进行了数值模拟，说明了由弯道引起的二次流对流体沿径向的扩散起着重要的作用，而对沿周向的扩散则影响甚微。流体在弯道中的扩散程度和弯道曲率、Re数之间并非单凋变化的关系，对应最大扩散程度的无量纲弯道曲率约为0．42，而最小扩散程度所对应的Re数则为0．5。本文结论对手微通道的优化设计有参考价值。 相似文献
13.
Efficient mixing is difficult to achieve in miniaturized devices due to the nature of low Reynolds number flow. Mixing can be intentionally induced, however, if conducting or nonconducting obstacles are embedded within the microchannel. In the case of conducting obstacles, vortices can be generated in the vicinity of the obstacle due to induced charge electro-osmosis (ICEO) which enhances mixing of different streams: the obstacle shape affects the induced zeta potential on the conducting surface, which in turn influences the flow profile near the obstacle. This study deals with optimization of the geometric shape of a conducting obstacle for the purpose of micromixing. The obstacle boundary is parametrically represented by nonuniform rational B-spline curves. The optimal obstacle shape, which maximizes the mixing for given operating conditions, is found using genetic algorithms. Various case studies at different operating conditions demonstrated that the near right triangle shape provides optimal mixing in the ICEO flow dominant regime, whereas rectangular shape is the optimal shape in diffusion dominant regime. The tradeoff between mixing and transport is examined for symmetric and nonsymmetric obstacle shapes. 相似文献
14.
Paul D Saias L Pedinotti JC Chabert M Magnifico S Pallandre A De Lambert B Houdayer C Brugg B Peyrin JM Viovy JL 《Biomicrofluidics》2011,5(2):24102
A broad range of microfluidic applications, ranging from cell culture to protein crystallization, requires multilevel devices with different heights and feature sizes (from micrometers to millimeters). While state-of-the-art direct-writing techniques have been developed for creating complex three-dimensional shapes, replication molding from a multilevel template is still the preferred method for fast prototyping of microfluidic devices in the laboratory. Here, we report on a "dry and wet hybrid" technique to fabricate multilevel replication molds by combining SU-8 lithography with a dry film resist (Ordyl). We show that the two lithography protocols are chemically compatible with each other. Finally, we demonstrate the hybrid technique in two different microfluidic applications: (1) a neuron culture device with compartmentalization of different elements of a neuron and (2) a two-phase (gas-liquid) global micromixer for fast mixing of a small amount of a viscous liquid into a larger volume of a less viscous liquid. 相似文献
15.
Yu Chen 《Journal of The Franklin Institute》1975,300(3):185-191
The dynamic radial stress distribution in a circular hollow cylinder, bonded to a rigid core at its inner surface and prevented from outward displacement by a smooth rigid cylindrical wall, due to a rotational motion with a variable angular velocity, is analyzed.The stress as a function of radial distance and time is determined. A sample calculation shows that the stress changes from tension at the inner surface to compression at the outer surface, as would be expected. The variation of stress vs radial distance is plotted for several instants of time. Also, the stress vs time for various radial positions is plotted. 相似文献
16.
This study reports an integrated microfluidic system capable of isolation, counting, and sorting of hematopoietic stem cells (HSCs) from cord blood in an automatic format by utilizing a magnetic-bead-based immunoassay. Three functional modules, including cell isolation, cell counting, and cell sorting modules are integrated on a single chip by using microfluidic technology. The cell isolation module is comprised of a four-membrane-type micromixer for binding of target stem cells and magnetic beads, two pneumatic micropumps for sample transport, and an S-shaped channel for isolation of HSCs using a permanent magnet underneath. The counting and sorting of HSCs are performed by utilizing the cell counting and sorting modules. Experimental results show that a separation efficiency as high as 88% for HSCs from cord blood is achieved within 40 min for a sample volume of 100 μl. Therefore, the development of this integrated microfluidic system may be promising for various applications such as stem cell research and cell therapy. 相似文献
17.
In this paper, thermal mixing characteristics of two miscible fluids in a T-shaped microchannel are investigated theoretically, experimentally, and numerically. Thermal mixing processes in a T-shaped microchannel are divided into two zones, consisting of a T-junction and a mixing channel. An analytical two-dimensional model was first built to describe the heat transfer processes in the mixing channel. In the experiments, de-ionized water was employed as the working fluid. Laser induced fluorescence method was used to measure the fluid temperature field in the microchannel. Different combinations of flow rate ratios were studied to investigate the thermal mixing characteristics in the microchannel. At the T-junction, thermal diffusion is found to be dominant in this area due to the striation in the temperature contours. In the mixing channel, heat transfer processes are found to be controlled by thermal diffusion and convection. Measured temperature profiles at the T-junction and mixing channel are compared with analytical model and numerical simulation, respectively. 相似文献
18.
Micromixers with floor-grooved microfluidic channels have been successfully demonstrated in experiment. In this work, we numerically simulated the mixing within the devices and used the obtained concentration versus channel length profiles to quantitatively characterize the process. It was found that the concentration at any given cross-section location of the microfluidic channel periodically oscillates along the channel length, in coordination with the groove-caused helical flow during the mixing, and eventually converges to the neutral concentration value of two the mixing fluids. With these data, the specific channel length required for each helical flow to complete, the mixing efficiency of the devices, and the total channel length required to complete a mixing were easily defined and quantified, and were used to directly and comprehensively characterize the micromixing. This concentration versus channel length profile-based characterization method was also demonstrated in quantitatively analyzing the micromixing within a classic T mixer. It has clear advantages over the traditional concentration image-based characterization method that is only able to provide qualitative or semiquantitative information about a micromixing, and is expected to find an increasing use in studying mixing and optimizing device structure through numerical simulations. 相似文献
19.
Harisha Ramachandraiah Sahar Ardabili Asim M. Faridi Jesper Gantelius Jacob M. Kowalewski Gustaf M?rtensson Aman Russom 《Biomicrofluidics》2014,8(3)
Passive particle focusing based on inertial microfluidics was recently introduced as a
high-throughput alternative to active focusing methods that require an external force field to
manipulate particles. In inertial microfluidics, dominant inertial forces cause particles to move
across streamlines and occupy equilibrium positions along the faces of walls in flows through
straight micro channels. In this study, we systematically analyzed the addition of secondary Dean
forces by introducing curvature and show how randomly distributed particles entering a simple
u-shaped curved channel are focused to a fixed lateral position exiting the curvature. We found the
lateral particle focusing position to be fixed and largely independent of radius of curvature and
whether particles entering the curvature are pre-focused (at equilibrium) or randomly distributed.
Unlike focusing in straight channels, where focusing typically is limited to channel cross-sections
in the range of particle size to create single focusing point, we report here particle focusing in a
large cross-section area (channel aspect ratio 1:10). Furthermore, we describe a simple u-shaped
curved channel, with single inlet and four outlets, for filtration applications. We demonstrate
continuous focusing and filtration of 10 μm particles (with >90% filtration
efficiency) from a suspension mixture at throughputs several orders of magnitude higher than flow
through straight channels (volume flow rate of 4.25 ml/min). Finally, as an example of high
throughput cell processing application, white blood cells were continuously processed with a
filtration efficiency of 78% with maintained high viability. We expect the study will aid in the
fundamental understanding of flow through curved channels and open the door for the development of a
whole set of bio-analytical applications. 相似文献