Interface tracking and numerical simulation of micro-bubble controlled growth in micro restrained space

通过对微机电系统微流体器件中气泡生长实验结果的分析,考虑加热元表面液体微层的作用,将微气泡生长分为晶核形成、球形气泡、受侧壁挤压的气泡、沿微通道生长的气泡4个阶段,建立了矩形微通道内微气泡控制生长物理模型;采用Level Set Method模拟了矩形微通道内微气泡控制生长过程,获得了微气泡生长特性。数值模拟结果表明:微气泡初期生长速率较快,后期由于凝结率增大使生长速率减缓;液体温度、微通道宽度、微加热元宽度、加热电压等均对气泡生长始点和生长速率有显著影响。Based on the experimental results of micro-bubble controlled growth in MEMS(micro-electro-mechanical system)devices,the bubble growth process could be divided into four stages,namely,nucleating,spherical bubble,bubble restrained by lateral wall,bubble elongating along the channel.A physical model of micro-bubble growth in the rectangular microchannel was established by considering the micro layer of liquid in the heater.Numerical simulation of micro-bubble growth in the micro restrained space was performed by the Level Set Method and the characteristics of micro-bubble growth were obtained and analyzed.The simulated data showed that micro-bubble grew rapidly in the early stage but grew slowly in the late stage due to the increasing condensation rate on the interface.The results also indicated that the initial temperature of liquid,width of the microchannel,width of the microheater,and the heating voltage had remarkable effects on the bubble inception and bubble growth rate.国家自然科学基金项目(50406019);; 中国博士后科学基金项目(2004035669);; 江苏省博士后科学研究资助计划项目(苏人通2004[计]300号)~

Micro-bubble controlled growth in rectangular microchannel of micro-electro-mechanical systems

采用微机电系统(MEMS)硅加工工艺,设计、加工出了6种不同规格的实验用微气泡控制生长MEMS器件;构建了MEMS器件中微气泡控制生长实验系统并完成了实验,讨论了热负荷、微加热元宽度、微通道截面参数、工质流速及物性参数等对微气泡生长的影响。结果表明:同等实验条件下,加热电压幅值越高,微气泡生长速率越快;加热脉冲宽度仅对微气泡形成后的进一步生长有影响;加热条件相同的前提下,微加热元宽度越大,气泡成核所需的时间越短、微气泡生长速率越快;微通道宽度一定且高宽比大于1的条件下,高宽比越小,后期微气泡生长速率越慢;微流体的流速越高,微气泡生长始点越晚、生长速率也越低。相同实验条件下,R113、FC-72、去离子水三者中,R113中微气泡生长始点最靠前、生长速率最快,去离子水中微气泡生长最靠后、生长速率最慢。With the silicon microfabrication process,six micro-electro-mechanical systems(MEMS) devices for exploring micro-bubble growth were designed and fabricated.Experimental investigations of micro-bubble growth in micro restrained space were performed.The results showed that the micro-bubble growth rate was influenced by heat power,dimensions of microheater,microchannel section,microfluidic velocity,and materials of the fluid.A higher heating voltage resulted in faster bubble growth.The width of heating pulse took effect during the latter period of bubble growth.Under the same heating voltage and pulse width,a larger width of the microheater led to faster bubble growth.When the aspect ratio of the microchannel section was over 1.0,a smaller aspect ratio brought on slower bubble growth during the latter period.The larger the microfluidic velocity,the later the bubble growth start point,and the slower the bubble growth.Under the same test condition,the bubble growth rate of R113 was the largest among the three working fluids,followed by FC-72 and deionized water,due to the effect of thermophysical parameters of the fluids.国家自然科学基金项目(50406019);; 中国博士后科学基金项目(2004035669);; 江苏省博士后科学研究资助计划项目(苏人通2004[计]300号)~