Experimental investigation of dynamic mass transfer during droplet formation using micro-LIF in a coaxial microchannel
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Coaxial
Microchannel
Mass transfer coefficient
Mass fraction
Microchannel is not only a channel for fluid flowing,but also a tool for microfluid flow control. By incorporating the characteristics and feature of the microchannel,microfluid driving,sampling,mixing, separating droplets formatting and controlling have been realized.In recent years,most studies have been focused on the application of surface effects to achieve microfluid control,as the surface-to-volume ratio is nearly millionfold increased in microchannel relative to that in macrochannel and the surface effects are greatly increased in microfluidic flows.However,only a few studies were carried out on controlling microfluid flows by using microchannel structural characteristics.In order to illuminate the fact that the microchannel configuration is also an effective way to control microfluid flow behavior,this paper discusses two aspects of flow control based on microchannel configuration.One is a special configuration of microchanels to be used as microvalve,the other is a special microchannel configuration to be used for formatting and controlling tiny droplets.And thus microchannel configuration is shown to be able to play an important part in microfluidic control.
Microchannel
Flow Control
Disk formatting
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Microchannel
Microreactor
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Abstract This paper reports a computational and theoretical investigation of pressure-flow characteristics of a microchannel having a superhydrophobic bottom wall with embedded air-cavities and, thin deformable membrane as the top wall. Two-way fluid-structure interaction (FSI) and unsteady volume of fluid (VOF) methods are employed for fluid-solid boundary and liquid-air interface at ridge-cavity, respectively. A novel theoretical model has been developed for the pressure-flow characteristics of microchannel with deformable top and superhydrophobic bottom wall. The theoretical and numerical results for pressure drop across the microchannel have shown a good agreement with a maximum deviation of 6.69%. Four distinct types of microchannels viz, smooth (S) (rigid non-textured), smooth with deformable top (SDT), smooth with superhydrophobic bottom (SSB) and, smooth with superhydrophobic bottom and deformable top wall (SSBT) have been investigated for the comparison of their pressure-flow characteristics. The Poiseuille Numbers (fRe) for SSBDT microchannel is found to be lowest with an average of 18.7% and maximum of 23.5% lower than S microchannel at 𝑅𝑒 = 60. Up to 48.59% of reduction in pressure drop was observed for the SSBDT microchannel as compared to smooth (S) microchannel of same dimensions. Further, critical Reynolds Number (Re critical ) (at which the air-water interface breaks and super-hydrophobicity vanishes) was found to be ∼ 20% higher for SSBDT microchannel compared to SSB microchannel. Thus, the wall compliance in SSBDT microchannel is found to increase the capability to sustain the super-hydrophobicity at higher Re numbers.
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Heating of fluid in microchannels is an important process in many micro fluidic devices (microreactors, microsensors and microthrusters). A microchannel with heater grooves was fabricated using DRIE method. A nickel wire is fixed in the groove which was formed perpendicularly to the microchannel. After the microchannel and the wire were assembled. FeCl_3 solution was pumped through the channel in order to etch the wire. The exposed part of nickel wire was etched locally in the microchannel. The fabrication is simple but this heater is expected to work effectively for microchannel fluid.
Microchannel
Microreactor
Fluidics
Groove (engineering)
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A model of non-uniform cross-section microchannels for realizing flow uniformity is developed in this work. For easy fabrication of microchannels, only the microchannel widths are changed while the thicknesses remain unchangeable in this model, and the relation of the widths of two adjacent microchannels has been established. A specific case is illustrated to study the influence of structural parameters on the microchannel widths. Result indicates that almost all the microchannel widths have symmetrical distribution. The maximum value appears near the edge while the minimum value in the middle microchannel. For all the structural parameters, the rake angle of manifold has a considerable effect on the microchannel width, and the preset value of microchannel width shows a slight influence.
Microchannel
Rake
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Microchannel
Hydraulic diameter
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Using a standing wave field of ultrasound, it is possible to trap and manipulate small objects at nodes of a sound pressure distribution. In the present paper, a sound wave was generated by a transducer far from a microchannel, and propagated into a microchannel on a glass plate, where it generated a standing wave field. When the liquid water containing alumina particles was injected into the microchannel, the particles flowed along several layers in the flat microchannel. It was shown that the traveling wave was transmitted into the microchannel and the standing wave field was formed in the microchannel. When a half circular space and a branched microchannel were added in the center of the microchannel and the frequency of the ultrasound swept, the exit channel of the particle flow can be selected.
Microchannel
Microchannel plate detector
Standing wave
Particle (ecology)
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Preconcentration microfluidic devices are fabricated incorporating straight or convergent–divergent microchannels and hydrogel or N afion membranes. Sample preconcentration is achieved utilizing concentration–polarization effects. The effects of the microchannel geometry on the preconcentration intensity are systematically examined. It is shown that for the preconcentrator with the straight microchannel, the time required to achieve a satisfactory preconcentration intensity increases with an increasing channel depth. For the convergent–divergent microchannel, the preconcentration intensity increases with a reducing convergent channel width. Comparing the preconcentration performance of the two different microchannel configurations, it is found that for an equivalent width of the main microchannel, the concentration effect in the convergent–divergent microchannel is faster than that in the straight microchannel.
Microchannel
Microchannel plate detector
Concentration polarization
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Cylindrical droplet formation in a W/O (water in oil) system of microchannel was analyzed experimentally and theoretically. The microchannel shape was modified to generate smaller droplet based on theoretical model. Numerical and experimental investigations were carried out with the novel microchannel. It is found that generated droplet was almost the spherical shape, since the diameter was smaller enough than the depth of microchannel. The results indicated that 3-dimensional and more precise theoretical model should be applied to realize the smaller droplet generation.
Microchannel
Oil droplet
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This article investigates fluid distribution in multichannel microfluidic devices with U-shaped manifolds. The parameters investigated include Reynolds number, microchannel width, microchannel spacing width, and microchannel length. The study is carried out using a microfluidic device having 50 microchannels employing water as the working fluid. The flow distribution in the microfluidic device is investigated for microchannel widths between 100 µm to 500 µm and for Reynolds number ranging between 0.04 to 100. The effect of channel spacing width on flow distribution is investigated for microchannel spacing widths between 100 µm to 500 µm. The increase in Reynolds number affects the flow distribution by increasing the non-uniformity of the flow. It is found that increasing the microchannel width causes more non-uniformity in the flow. It is also found that increasing the microchannel spacing width decreased the non-uniformity of the flow distribution. It is found that increasing the channel width from 100 µm to 300 µm increased the flow maldistribution by 83%, and increasing the microchannel spacing width from 100 µm to 300 µm decreased the flow maldistribution by 42%. It is observed that the microchannel width has a stronger influence on the flow distribution compared with microchannel spacing width. The study is useful for examining the flow maldistribution in microfluidic devices as their performance is dependent on flow rate.
Microchannel
Hydraulic diameter
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