面向电磁MEMS的微流通道流体运动特性的数值模拟研究

基于正交磁场和速度场的弱耦合作用,建立微流孔通道内导电流体的二维直流磁流体动力学模型,采用数值模拟方法研究电磁MEMS微流道内的导电流体运动特性。数值模拟基于Galerkin有限元方法,采用SIMPLE压力修正算法,求解瞬态不可压层流运动。模拟结果表明微流道内上游抛物线型速度分布的流体加速明显,并在控制段形成M型速度分布,当Hartmann数增大到一定数值后,并不能显著增加系统压力降,反而可能在电极区形成回流涡。

基于光波导微环谐振器的IgG非标记检测微流体分析系统

设计开发了与微环谐振器集成的微流体通道系统,不仅避免了敞开环境中由于液体挥发造成的微环谐振器表面盐分的聚结,屏蔽空气中的各种杂质,而且只需要30μL反应溶液,减少了药品用量,大大节约了实验成本。同时,采用绝缘体硅(SOI)材料,利用光刻技术设计和制作了波导宽度为450 nm,半径为5μm,品质因子(Q值)为20000的光波导微环谐振器。集成的微环谐振器传感系统具有低成本、免标记、能实时监测生化反应过程等特点。以不同浓度的酒精溶液为测试对象,研究了微环谐振器对均质溶液的传感性能,传感芯片对溶液折射率的探测灵敏度为76.09 nm/RIU,探测极限为5.25×10^(-4)RIU,验证了此微环谐振器对均质溶液进行浓度检测的可行性。利用此传感系统对人免疫球蛋白IgG进行了非标记免疫检测。在测试中,采用微流体通道系统将相应抗体修饰到微环谐振器表面,利用光谱仪对修饰过程以及抗原抗体特异性结合过程中的共振谱线漂移情况进行了监测。结果表明,光波导微环谐振器可以对生物分子进行实时监测。

基于双LPFGs传感器的混泥土氯离子浓度激光测量

氯离子渗透腐蚀是主要钢筋混凝土结构中损伤之一,极大降低混凝土结构的耐久性。为了检测混凝土中氯离子浓度,本文提出了一种简单、灵敏、可用于混凝土氯离子浓度检测的双长周期光纤光栅传感器及其检测方法。基于新的理论模型,通过测量经过双长周期光纤光栅的传输光功率,可以很容易地计算出溶液中氯离子浓度,测量范围可达5g/L^35g/L,误差范围为0.18%,同时克服测量过程中温度变化的影响。设计了一种微流体通道,可以克服弯曲和应变的影响。因此,本文所报道的双长周期光学光栅传感器有助于混凝土氯离子浓度的长期精确监测。

Computational analysis of the flow of pseudoplastic power-law fluids in a microchannel plate

The flow of pseudoplastic power-law fluids with different flow indexes at a microchannel plate was studied using computational fluid dynamic simulation.The velocity distribution along the microchannel plate and especially in the microchannel slits,flow pattern along the outlet arc and the pressure drop through the whole of microchannel plate were investigated at different power-law flow indexes.The results showed that the velocity profile in the microchannel slits for low flow index fluids was similar to the plug flow and had uniform pattern.Also the power-law fluids with lower flow indexes had lower stagnation zones near the outlet of the microchannel plate.The pressure drop through the microchannel plate showed huge differences between the fluids.The most interesting result was that the pressure drops for power-law fluids were very smaller than that of Newtonian fluids.In addition,the heat transfer of the fluids through the microchannel with different channel numbers in a wide range of Reynolds number was investigated.For power-law fluid with flow index(n=0.4),the Nusselt number increases continuously as the number of channels increases.The results highlight the potential use of using pseudoplastic fluids in the microheat exchangers which can lower the pressure drop and increase the heat transfer efficiency.

Enhanced single-nanoparticle collisions for the hydrogen evolution reaction in a confined microchannel

Single nanoparticle(NP)collisions technique has been widely employed in electrocatalysis.However,the short collision duration of single NPs hinders the further improvement in their electrocatalytic performance.Here,to increase the dynamic collision duration of single NPs in the electron tunneling region,enhanced near-wall hindered diffusion is introduced in the stochastic collision process by coupling a Au ultramicroelectrode(UME)with a confined microchannel.In the case of single palladium nanoparticle(Pd NP)collisions for the hydrogen evolution reaction(HER),the hydrodynamic trapping confined in the microchannel effectively permits the activation of the HER on the single Pd NPs.The microchannel-based Au UME is promising in the application of single-NP collisions to energy conversion.

Numerical simulation of immiscible liquid-liquid flow in microchannels using lattice Boltzmann method

Immiscible kerosene-water two-phase flows in microchannels connected by a T-junction were numerically studied by a Lattice Boltzmann (LB) method based on field mediators.The two-phase flow lattice Boltzmann model was first validated and improved by several test cases of a still droplet.The five distinct flow regimes of the kerosene-water system,previously identified in the experiments from Zhao et al.,were reproduced.The quantitative and qualitative agreement between the simulations and the experimental data show the effectiveness of the numerical method.The roles of the interfacial tension and contact angle on the flow patterns and shapes of droplets were discussed and highlighted according to the numerical results based on the improved two-phase LB model.This work demonstrated that the developed LBM simulator is a viable tool to study immiscible two-phase flows in microchannels,and such a tool could provide tangible guidance for the design of various microfluidic devices that involve immiscible multi-phase flows.

An on-chip electroosmotic micropump with a light-addressable potentiometric sensor

An on-chip electroosmotic(EO) micropump(EOP) was integrated in a microfluidic channel combined with a light-addressable potentiometric sensor(LAPS). The movement of EO flow towards right and left directions can be clearly observed in the microfluidic channel. The characteristics of photocurrent-time and photocurrent-bias voltage are obtained when buffer solution passes through the sensing region. The results demonstrate that the combination of an on-chip EOP with an LAPS is feasible.

Dielectrophoresis Flow Control of Volatile Fluids in Microchannels

In recent years the microchannel heat exchangers have been applied in a great variety of technical areas. One of the problems, which exist in the microcharmel technology is the flow instabilities, including fluid maldistribution in the microcharmels array for the case of two-phase flow especially in micro-evaporators. One of the ways to solve this problem is flow rate control at the microcharmel inlet. However, due to very small inlet to the array of microchannels the classic flow restriction device （with moving mechanical parts） will be difficult to apply. The new device for the flow rate control based on the dielectrophoresis force was presented in the paper. Experimet^tal research results of using this device for refrigerant flow control was presented in the paper. The experimentally obtained relationships between applied voltages and frequencies and flow rates were presented showing opportunity for applying such method for refrigerants and other volatile fluids.

Bubble breakup in a microfluidic T-junction

We conduct a computational fluid dynamics simulation to investigate the behaviors of bubble breakup in a microfluidic T-junction using volume-of-fluid method to represent the interface. The evolution of bubble mor- phology and the distributions of velocity and pressure in flow field are analyzed, and the effect of width ratio between main channel and branch on the bubble mor- phology are evaluated. The results indicate that, the ＂tun- nel＂ breakup, obstructed breakup, combined breakup and non-breakup are observed during the bubble flows through the T-junctions under different condition. The whole bub- ble breakup process undergoes the extension, squeeze and pinch-off stages, while the non-breakup process experi- ences extension and pushing stages. We find that, in the squeeze stage, a local vortex flow forms at the front edge of the bubble for the ＂tunnel＂ breakup while the velocity inside the bubble is of a parabolic distribution for the obstructed breakup. Irrespective of non-breakup regimes, there is a sudden pressure drop occurring at the gas-liquid interface of the bubble in the squeeze stage, and the pres- sure drop at the front interface is far larger than that at the depression region. The transition of the bubble breakup regime through the T-junction occurs with an increase in width ratio of main channel to the branch, which sequen- tially experiences the non-breakup regime, ＂tunnel＂ breakup regime and obstructed breakup regime. The flow regime diagrams are plotted with a power-law correlation to distinguish the bubble/droplet breakup and non-breakup regimes, which also characterize the difference between bubble and droplet breakup through a T-junction.