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91.
Mubashshir Ahmad Ansari Kwang-Yong Kim 《American Institute of Chemical Engineers》2009,55(9):2217-2225
The mixing of fluids in a microchannel is numerically investigated using three-dimensional Navier–Stokes equations. The microchannel has circular mixing chambers that are designed to create a self-circulating flow that operates at low Reynolds numbers. The investigations have been performed on a design that comprises of four circular mixing chambers that are joined together with constriction channels. The study has been carried out in two parts. Firstly, the mixing and the flow field are analyzed for a wide range (1–250) of the Reynolds number. Secondly, the effects of two design parameters, namely, the ratio, w/d, of the width of the constriction channel to the diameter of the circular chamber, and the angle, θ, between the outer walls of the chamber and the connection channel, on the mixing and the flow field have been evaluated. The mixing has been evaluated using a parameter, called mixing index, which is based on the variance of the mass fraction. The mixing index at the end of the device increases rapidly with the Reynolds number. The presence of a flow recirculation zone in the circular chamber is found to be effective in enhancing mixing, especially for larger Reynolds numbers. The mixing performance improves with an increase in θ, and with a decrease in w/d. The characteristics of the pressure drop have also been investigated as a function of the Reynolds number and geometric parameters. © 2009 American Institute of Chemical Engineers AIChE J, 2009 相似文献
92.
Heat transfer and hydrodynamic performances for nanofluids, Al2O3‐water and SiO2‐water, are numerically investigated with different nanoparticles’ volume fractions and the initial velocities in a fractal microchannel heat sink. The fractal microchannel is 100 μm × 100 μm in the inlet cross‐section, and the length at the 0th level is 2000 μm. A constant heat flux of 500 kW/m2 was applied to the bottom wall of the fractal microchannel heat sink. The heat transfer and hydrodynamic performances of different cases are discussed in terms of the mean heat transfer coefficient, mean base temperature, pressure loss, thermal resistance, friction factor f/f0, and COP/COP0. Results indicate that increasing the initial velocity and nanoparticles’ volume fraction lead to an enhanced heat transfer at the expense of pressure loss. Al2O3‐water has a higher mean heat transfer coefficient and pressure drop than that of SiO2‐water, a lower f/f0, mean base temperature, thermal resistance, and COP/COP0. Ultimately, as compared to pure water, the heat transfer coefficients of 4% Al2O3‐water increased by 7.53%, 7.80%, 8.00%, 8.14%, 8.16%, and 8.30%, and the pressure drops increased by 32.09%, 31.41%, 30.81%, 30.05%, 29.21%, and 28.58%, respectively, corresponding to the initial velocities by 4, 5, 6, 7, 8 and 9 m/s. 相似文献
93.
研究了3种微通道板基底羟基化的方法,测量了羟基化处理后微通道板基底表面水接触角及通道端面的形貌变化,分析了各种方法中微通道板基底的亲水性和腐蚀情况。实验结果表明:氨水双氧水溶液对基体表面的亲水性能提升不大,NaOH溶液对基体有腐蚀作用,经食人鱼溶液处理的基体表面亲水性明显提高且无腐蚀作用。研究了微通道板在食人鱼溶液中的浸泡时间和浸泡温度对表面亲水性的影响。结果表明:随着浸泡温度的增加,微通道板表面水接触角先减小后增大,当温度为80℃时达到极小值,浸泡时间对微通道板表面的亲水性影响不大。最终确定了微通道板表面羟基化工艺:浸泡温度为80℃,静置时间为20~60 min。 相似文献
94.
Microchannel two‐phase flow is an effective cooling method used in microelectronics, in which the heat flux density is unevenly distributed usually. The paper is focused on numerical study the effect of aspect ratio on the flow boiling of microchannels with nonuniform heat flux. The heat source is a three‐dimensional (3D) integrated circuit. 3D microchannel model and volume of fluid method are coupled in numerical simulation. The results show that the aspect ratio has no relationship with the two‐phase pressure drop of the microchannel. It has a certain influence on the distribution of bubble shape. In terms of the heat transfer coefficient, the aspect ratio has a certain influence on a section of the inlet. Due to the nucleate boiling, the convective heat transfer in the remaining areas is the dominant factor and the average heat transfer coefficient is mainly determined by the heat flux at the bottom of the channel. 相似文献
95.
Boilingofliquidsinmicrochannelsand/ormicrostructures,asoneoftheveryimportanttopicsinthisarea,hasuniquesignificanceinthedevelopmentofnewtechnologiesanddevicesforcontrolofenergytransferandotheradvancedapplicationsrequiringverycompactandextremelylargehea… 相似文献
96.
Christian Lutz Uwe Bog Tobias Loritz Julia Syurik Sharali Malik Chethala Neelakandhan Shyam Kumar Christian Kübel Michael Bruns Christian Greiner Michael Hirtz Hendrik Hlscher 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(7)
The locally defined growth of carbon nanofibers with lambda shape in an open flame process is demonstrated. Via the growth time, the geometry of the structures can be tailored to a Λ‐ or λ‐type shape. Microchannel cantilever spotting and dip‐pen nanolithography are utilized for the deposition of catalytic salt NiCl2 · 6H2O for locally controlled growth of lambda‐shaped carbon nanofibers. Rigorous downscaling reveals a critical catalytic salt volume of 0.033 µm³, resulting in exactly one lambda‐shaped carbon nanofiber at a highly predefined position. An empirical model explains the observed growth process. 相似文献
97.
In the present study, the investigation on photochemical machining (PCM) of stainless steel (SS-304) by ferric chloride as etchant is reported. SS-304 is machined by PCM process to obtain accurate dimensions and better geometrical features. Weighted grey relational analysis (WGRA) technique is used in optimization of PCM process parameters. DoE (L27) orthogonal array is applied to evaluate machining parameters, such as concentration of etchant, etching time, and temperature of etchant. The multiobjective optimization technique is used to optimize material removal rate (MRR), surface roughness (Ra), undercut (Uc) and etch factor (EF). Weighted grey relational grade is calculated to minimize Uc and surface roughness and to maximize MRR and EF. The quality characteristics MRR, EF, Uc, and Ra are reporting the improvement after the confirmatory test. The optimum machining parameters are processed to manufacture the microfluidic channel used in biomedical applications. The microfluidic channels and its assembly with Y-type for mixing of fluid with a size of 100 µm, 200 µm, and 300 µm are developed and investigated. 相似文献
98.
由于传统加工方法不能解决PMMA微流道的加工质量不好和效率低的问题,本文对超快激光直写PMMA制备微流道的烧蚀机理和工艺参数进行了研究。根据实验分析不同的激光功率、加工速度和加工次数对微流道的宽度和横截面的影响规律,利用超快激光加工系统制备微流道,并采用超景深三维显微镜观测微流道的表面形貌。实验结果表明,当超快激光的加工速度为20 mm/s时,激光功率为1.5 W时,制备的微流道的宽度较小、宽度趋势比较平稳;当超快激光作用PMMA的次数一样,由于加工速度逐渐增加,制备的微流道其宽度和激光的加工速度保持线性增加。当加工速度越大时,微流道的宽度较小、且壁面趋势相对平缓,而当加工速度一定,超快激光的输出功率在1.5 W时,微流道内壁区域不易出现残渣堆积和气泡隆起现象。本文通过优化超快激光加工系统的工艺参数,从而加工出尺寸精度高、表面光滑、宽度为20~90 μm的微流道芯片。 相似文献
99.
100.
建立了多孔侧肋双层微通道复合热沉模型,选取最大热阻最小化为优化目标、热沉单元端面纵横比为优化变量,在热沉总体积和流体区域体积占比给定的条件下,对复合热沉进行了构形优化,并分析了冷却剂入口速度、多孔材料孔隙率、上下通道高度比、流体区域体积占比、肋厚比等参数对热沉最优构形的影响.结果表明:给定初始条件,优化热沉单元端面纵横比,可使最大热阻减小21.19%;在热沉单元端面纵横比较小时,减小孔隙率有利于降低最大热阻,而在热沉单元端面纵横比较大时,存在最优的孔隙率使得最大热阻最小;上下通道高度比和肋厚比的改变均未影响热沉最优构形. 相似文献