排序方式: 共有28条查询结果,搜索用时 10 毫秒
11.
Chien-Hsiung Tsai Han-Taw Chen Yao-Nan Wang Che-Hsin Lin Lung-Ming Fu 《Microfluidics and nanofluidics》2007,3(1):13-18
This paper deals with computational and experimental investigations into pressure-driven flow in sudden expansion microfluidic
channels. Improving the design and operation of microfluidic systems requires that the capabilities and limitations of 2-dimensional
(2-D) and 3-dimensional (3-D) numerical methods in simulating the flow field in a sudden expansion microchannel be well understood.
The present 2-D simulation results indicate that a flow separation vortex forms in the corner behind the sudden expansion
microchannel when the Reynolds number is very low (Re∼0.1). However, the experimental results indicate that this prediction is valid only in the case of a sudden expansion microchannel
with a high aspect ratio (aspect ratio >> 1). 3-D computational fluid dynamics simulations are performed to predict the critical
value of Re at which the flow separation vortex phenomenon is induced in sudden expansion microchannels of different aspect ratios. The
experimental flow visualization results are found to be in good agreement with the 3-D numerical predictions. The present
results provide designers with a valuable guideline when choosing between 2-D or 3-D numerical simulations as a means of improving
the design and operation of microfluidic devices. 相似文献
12.
This paper presents an experimental and numerical investigation into electrokinetic focusing injection on microfluidic chips. The valving characteristics on microfluidic devices are controlled through appropriate manipulations of the electric potential strengths during the sample loading and dispensing steps. The present study also addresses the design and testing of various injection systems used to deliver a sample plug. A novel double-cross injection microfluidic chip is fabricated, which employs electrokinetic focusing to deliver sample plugs of variable volume. The proposed design combines several functions of traditional sample plug injection systems on a single microfluidic chip. The injection technique uses an unique sequence of loading steps with different electric potential distributions and magnitudes within the various channels to effectuate a virtual valve. 相似文献
13.
This paper presents a microfluidic T-form mixer utilizing alternatively switching electroosmotic flow. The microfluidic device is fabricated on low-cost glass slides using a simple and reliable fabrication process. A switching DC field is used to generate an electroosmotic force which simultaneously drives and mixes the fluid samples. The proposed design eliminates the requirements for moving parts within the microfluidic device and delicate external control systems. Two operation modes, namely, a conventional switching mode and a novel pinched switching mode, are presented. Computer simulation is employed to predict the mixing performance attainable in both operation modes. The simulation results are then compared to those obtained experimentally. It is shown that a mixing performance as high as 97% can be achieved within a mixing distance of 1 mm downstream from the T-junction when a 60 V/cm driving voltage and a 2-Hz switching frequency are applied in the pinched switching operation mode. This study demonstrates how the driving voltage and switching frequency can be optimized to yield an enhanced mixing performance. The novel methods presented in this study provide a simple solution to mixing problems in the micro-total-analysis-systems field. 相似文献
14.
提出一种广泛使用的CO2激光法,以直接读写烧蚀的方式,进行快速的聚甲基丙烯酸甲酯(PMMA)基材的微流控分析芯片的制造.利用此方法所制造的微流道,将以扫描电子显微镜(SEM)、原子力显微镜(AFM)及表面轮廓仪进行各项表面性质的分析.本文所发展的CO2激光烧蚀法,提供了一个可广泛使用及具有经济效应的PMMA基材的微流控分析芯片的制造方法.在此激光制程法中,微流控分析芯片的制造图案可由商业的套装软件绘制而成,再传输至激光系统中进行烧蚀微管道,结果显示利用离焦法的激光制程技术,在没有退火处理的情况下,就可以获得表面相当平滑的微流道,表面粗糙度小于4nm. 相似文献
15.
Chia-Yen Lee Chih-Yung Wen Hui-Hsiung Hou Ruey-Jen Yang Chien-Hsiung Tsai Lung-Ming Fu 《Microfluidics and nanofluidics》2009,6(3):363-371
This study designs and characterizes a novel MEMS-based flow-rate micro-sensor consisting of a platinum resistor deposited
on a silicon nitride-coated silicon cantilever beam. Due to the difference between the thermal conductivities of the silicon
nitride film and the silicon beam, the tip of the cantilever structure bends slightly in the upward direction. As air travels
across the upper surface of the sensor, it interferes with the curved tip and displaces the beam in either the upward or the
downward direction. The resulting change in the resistor signal is then used to calculate the velocity of the air. A flow-direction
micro-sensor is constructed by arranging eight cantilever structures on an octagonal platform. Each cantilever is separated
from its neighbors by a tapered baffle plate connected to a central octagonal pillar designed to attenuate the aerodynamic
force acting on the cantilever beams. By measuring the resistor signals of each of the cantilever beams, the micro-sensor
is capable of measuring both the flow rate and the flow direction of the air passing over the sensor. A numerical investigation
is performed to examine the effects of the pillar height and pillar-to-tip gap on the airflow distribution, the pressure distribution,
the bending moment acting on each beam, and the sensor sensitivity. The results show that the optimum sensor performance is
obtained using a pillar height of 0.75 mm and a pillar-to-tip gap of 5 mm. Moreover, the sensitivity of the octagonal sensing
platform is found to be approximately 90% that of a single cantilever beam. 相似文献
16.
Rong-Hua Ma Po-Cheng Chou Yu-Hsiang Wang Tzu-Han Hsueh Lung-Ming Fu Chia-Yen Lee 《Microsystem Technologies》2009,15(8):1201-1205
Utilizing conventional micro-electro-mechanical systems techniques, this study fabricates and characterizes a novel micro
gas flow sensor comprising four silicon nitride/silicon wafer cantilever beams arranged in a cross-form configuration. The
residual stresses induced within the beams during their fabrication cause the tip of each beam to curve slightly in the upward
direction. However, as air travels over the surface of the sensor, the upstream cantilevers are deflected in the downward
direction, while the downstream cantilevers are deflected in the upward direction. The velocity of the air flow is then determined
by measuring the corresponding change in resistance of the piezoresistors patterned on the upper surface of each cantilever
beam. It is shown that by measuring the change in resistance of all four cantilever beams, the proposed sensor can detect
not only the velocity of the air flow, but also its direction. 相似文献
17.
This paper proposes a simple method for enhancing the separation efficiency of DNA biosamples in a capillary electrophoresis
(CE) microchip by using high-voltage pulsed DC electric fields. A high-voltage amplifier is used to establish electric fields
of up to 1 kHz to carry out CE separation; electrophoresis and electroosmotic effects are then pulsely induced. The experimental
and numerical investigations commence by separating a mixed sample comprising two fluoresceins with virtually identical physical
properties, namely Rhodamine B and Rhodamine 6G. It is found that the level of separation is approximately 2.1 times higher
than that achieved using a conventional DC electric field of the same intensity. The performance of the proposed method is
further evaluated by separating a DNA sample of HaeIII digested ΦX-174 ladder. The experimental results indicate that the separation level of the neighboring peaks 5a and 5b
in the DNA marker is approximately 1.2, which is significantly higher than the value of 0.8 obtained using a CE scheme with
a conventional DC electric field. The improved separation performance of the proposed pulsed DC electric field approach is
attributed to a lower Joule heating effect as a result of a lower average power input and the opportunity for heat dissipation
during the zero-voltage stage of the pulse cycle. Overall, the results demonstrate that the method proposed in this study
provides a simple, low-cost technique for achieving a high separation performance in CE microchips. 相似文献
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Microfluidic mixing: a review 总被引:2,自引:0,他引:2
The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either "active", where an external energy force is applied to perturb the sample species, or "passive", where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers. 相似文献