广域克努增数下纳流控通道型流导元件气体传输多重机理

Vacuum conductance elements are the standard tool for the measurement of gas microflow. It is widely used in vacuum calibration，leak detection, gas sampling for analysis and flow control. Currently, an empirical conversion formula for describing transport properties of fluids is not easy to achieve due to the complicated path for gas flow in the conductance element. Numerical experiments have to be carried out to obtain a large database for the predictability of different gas species. Such element is an urgent obstacle remaining unsolved for the calibration of gas flow, due to lack of fully understanding the gas flow through the complicated nano/microchannels. The structure of the nanofluidic channel is an excellent candidate for the conductance element because its structure is simple and well controlled，and it is therefore easy to predict the gas flow conductance and rate of specific gases by empirical conversion formulas.. In this proposal, the gas transport mechanisms considering the real gas effect through the nanofluidic channels is investigated, in order to improve the knowledge of gas flow through nanochannels in terms of predictability for the gas molecular flow behavior in the conductance elements. The gas-transfer mechanism includes bulk-gas transfer and adsorption-gas surface diffusion exist during the gas flowing through the nanochannels, where the bulk-gas-transfer mechanism includes slip flow and Knudsen diffusion. Langmuir isotherm having monolayer gas adsorption is held, and dynamic equilibrium between the bulk gas and the adsorbed gas can be achieved. The model of surface diffusion for adsorbed gas is established, which is based on popping model derived under low pressure. the bulk-gas-transfer model is also developed considering the slip boundary condition. To depict the multiple transport mechanisms, an unified model is developed by coupling the bulk gas transport model and the surface diffusion model in a wide range of Knudsen numbers. The nanofluidic channels are fabricated using dry etching and fusion bonding based on the silicon wafer, and then bonded with CF flanges. The property of gas transport through the nanochannels is systematically investigated using mass spectrometer method and flow method, respectively. The multiple transport mechanism could be revealed according to the channel dimensions, pressure conditions and different gas spices based on the experiments and numerical simulations. The gas transfer behavior could be predicted and controlled by varying above parameters in terms of the gas transfer mechanism. . This proposal should provide fundamental contributions to predict and control the gas flow through the conductance elements. It should also find broad applications in the vacuum calibration，leak detection, gas sampling for analysis and flow control.

真空流导元件是气体微流量计量测试的标准器具，广泛应用于真空计量、泄漏检测、气体采样分析和流量控制等方面。传统真空流导元件传输路径复杂，无法建立准确的传输模型对气体流动特性进行调控和预测，成为制约真空计量检测发展的瓶颈。纳流控通道结构简单，尺寸可控，作为流导元件可以有效解决这一问题。纳流控通道中的气体传输包括滑移流、分子流和表面扩散。本项目基于气-固表面吸附气体扩散概念推导低压条件下的表面扩散解析模型，结合通用滑移边界建立压差流动方程，构建广域克努增数下气态工质在纳流控流导元件内的统一流动模型；发展硅纳流控流导组件的制造及其封装方法；利用质谱法和流量法测试气体流动特性，结合数值模拟，揭示通道结构、不同压强和气体种类等因素对气体多重传输的影响规律，以实现新型流导元件内气体流导行为的调控和预测。研究结果将为真空流导元件传输特性的调控和预测以及气体微流量计量技术的发展提供理论依据和新方法。

真空流导元件是气体微流量计量测试的标准器具,目前传统流导元件难以获得气体传输路径的结构尺寸，无法建立准确气体传输模型，难以调控和预测元件内气体流动特性，而纳流控通道流导元件可以解决这一瓶颈问题，本项目研究气体在纳流控通道内气体传输行为，分别建立粗糙壁面和光滑壁面的表面扩散模型和考虑通用滑移边界的体相流动模型，构建广域克努增数下气态工质在通道内的统一传输流态方程；发展硅和石墨烯纳流控流导组件的微纳制造及其封装方法；结合数值仿真和气体传输实验，揭示纳流控真空流导元件与气体传输相关的尺度效应、稀薄效应以及流态演化机制，达到调控和预测气体流动行为的目的。主要工作和成果综述如下：.1、针对粗糙表面纳流控通道内的气体输运现象，利用分子间碰撞频率和壁面-分子碰撞频率加权耦合滑移流、克努森扩散和体扩散并考虑吸附气体表面扩散，建立了气体传输的统一模型，结合实验验证了表面扩散的存在。.2、运用通量相关函数计算了气体在表面光滑的纳流控通道内的输运扩散系数，构建了气体在纳米通道内的扩散模型，结果表明气体在通道内吸附分子的表面扩散是气体快速输运的原因，表面扩散系数随表面覆盖度的增大而增大。.3、优化基于多孔氧化铝和硅-硅的纳流控通道型流导元件制作工艺，研究通道尺寸与密度、镀膜面积、刻蚀和SDB工艺参数等因素对通道封闭的影响，成功实现作出纳米尺度流控通道可控制作；.4、提出Leak-on-tube新流导元件结构形式，采用熔融键合技术解决硅流控芯片与金属热膨胀系数不匹配的问题，获得了极低流导的纳流控通道和金属封接结构；.5、提出利用石墨烯缺陷作为气体传输通道的新方法，基于无转移转移技术，获得了极低流导的纳流控通道和金属封接结构及可靠的金属封接；.6、以纳流控通道流导元件为核心集成极小气体流量供给系统，应用于吸气剂和真空泵性能测试、国防真空检漏计量方面；发展的基于微纳流控的混合微透镜阵列-光栅的制造技术，有效提高集成光学系统的光谱分辨率。