Microscale Reactor CFD Model Validation Using Direct Numerical Simulations, High-Speed MicroPIV, and Reactive Laser-Induced Fluorescence

Rodney O.Fox 0730250在湍流状态下运行的微型反应器用于闪光纳米沉淀，以达到生产疏水有机化合物的均匀尺寸纳米颗粒所需的混合时间。由于整个过程是由混合和动力学控制的，而不是热力学，因此可以在工业规模的连续过程中快速制造大量精确控制的纳米颗粒，而不需要长时间的批次和处理大量的溶剂。然而，为了理解设计微型反应器所需的快速沉淀，需要详细了解宏观、中观和微观混合在过饱和发展中的作用。更广泛地说，开发用于闪光纳米沉淀的微型反应器的一些关键问题是：(I)在不同的流速和流量比下，微型反应器的运行效率如何？(2)多喷嘴微型反应堆与具有两个撞击流的反应堆相比如何？(3)在微型反应器中观察到的流态是什么？如何优化它们以实现快速混合？为了回答这些问题，可以使用计算流体力学(CFD)，前提是它已经在设计所需的操作条件范围内与实验数据进行了充分的验证。目前，微型反应堆的设计是通过实验试验和错误进行的；因此，预测计算工具的可用性将改变这一领域的研究方式。爱荷华州立大学建立了一个基于低雷诺数湍流模型的CFD模型，并利用普林斯顿大学收集的受限冲击射流(CIJ)和多入口涡流混合器(MIMV)微型反应器的出口转换数据进行了部分验证。虽然这些验证研究的结果非常有希望，并表明CFD确实将成为微型反应器设计的变革性工具，但出口转化数据对微型反应器内流场细节的间接依赖留下了许多关于CFD模型真实预测能力的悬而未决的问题。这种不令人满意的情况促使人们开发直接数值模拟和微尺度实验工具，以提供严格的CFD模型验证所需的微尺度反应器内瞬时速度场和标量场的局部数据。为了满足这一需求，两个PI正在合作开发微尺度粒子图像测速仪(MicroPIV)，用于测量在湍流区运行的微尺度反应器中的瞬时速度场。最近对微型CIJ反应器中湍流的MicroPIV测量已经证明了使用其实验室中最先进的设备进行此类测量的可行性。此外，他们最近展示了将实验不确定性控制到与CFD预测进行定量比较所需的水平的能力。该项目的主要目的是继续改进这项有希望的工作，使实验数据能够为微型反应堆的CFD模型提供最终的验证。第二个目标是对微尺度反应器中流体速度的基本控制方程进行精选的解析，以补充实验的microPIV数据。这些数据将被用于系统的验证研究，以改进CFD模型，并确定其对微型反应堆设计的有效性范围。开发用于测量微尺度装置中的流量的实验工具是一项重要的技术和智力挑战。事实上，在微尺度流动中，需要对小区域成像，以及对非定常速度场的定量准确测量的渴望，导致了与宏观尺度流动相比非常严格的实验要求。同样，微型反应堆预测计算模型的开发和验证也突破了现有知识的极限。例如，低雷诺数、高施密特数流动中标量耗散率的预测仍然是一个悬而未决的问题，但这是微型反应堆设计的核心。更广泛的影响通过经济、可扩展的工艺生产均匀尺寸的疏水有机化合物纳米颗粒是一个相当大的挑战。它的动机是纳米颗粒在药物输送中的使用和潜在用途，特别是难于溶解的药物、化妆品、染料、医学成像和诊断以及杀虫剂。生产这种纳米颗粒的最先进的工艺之一是闪光纳米沉淀。该项目开发的工具将促进闪光纳米沉淀所需的微型反应器的设计和优化，并将补充其他NSF资助项目中正在开发的纳米颗粒形成的详细动力学模型。因此，该项目的潜在更广泛影响可能是改变微型反应堆设计领域。

Rodney O. Fox 0730250Microscale reactors operating in the turbulent flow regime are used in Flash NanoPrecipitation" to achieve the required mixing times for the production of uniform-sized nanoparticles of hydrophobic organic compounds. Because the overall process is controlled by mixing and kinetics, as opposed to thermodynamics, significant quantities of precisely controlled nanoparticles can be rapidly manufactured at the industrial scale in a continuous process without the need for long batch times and handling large quantities of solvents. However, the understanding of rapid precipitation needed to design a microscale reactor requires a detailed understanding of the role of macro-, meso- and micromixing on the development of supersaturation. More generally, some of the key questions in developing microscale reactors for Flash NanoPrecipitation are: (i) How efficiently will the microscale reactor operate at different flow velocities and stream ratios? (ii) How do multi-injector microscale reactors compare to reactors with two impinging streams? (iii) What are the flow regimes observed in microscale reactors and how can they be optimized for rapid mixing? To answer these questions, computational fluid dynamics (CFD) can be employed, provided that it has been adequately validated against experimental data over the range of operating conditions of interest for design. Currently, microscale reactor design is done by experimental trial and error; hence the availability of a predictive computational tool would transform how research is done in this field. A CFD model based on low-Reynolds-number turbulence models has been developed at Iowa State and partially validated using outlet conversion data collected at Princeton for confined impinging jet (CIJ) and multi-inlet vortex mixer (MIMV) microscale reactors. While the results of these validation studies are extremely promising and suggest that CFD will indeed be a transformative tool for microscale reactor design, the indirect dependence of the outlet conversion data on the details of the flow field in the microscale reactor leaves many open questions concerning the true predictive capability of the CFD model. This unsatisfactory situation provides the motivation for developing direct numerical simulation (DNS) and microscale experimental tools that can provide the local data for instantaneous velocity and scalar fields in microscale reactors that are required for rigorous CFD model validation. To meet this need, the two PIs are collaborating on the development of microscale particle image velocimetry (microPIV) for measuring the instantaneous velocity field in microscale reactors operating in the turbulent flow regime. Recent microPIV measurements of turbulent flow in a microscale CIJ reactor have demonstrated the feasibility of such measurements using the state-of-the-art equipment in their laboratory. Moreover, they have recently demonstrated the ability to control experimental uncertainty to the level required for quantitative comparisons with CFD predictions. The primary purpose of this project is to continue to improve this promising work to the point where the experimental data can provide for definitive validation of CFD models for microscale reactors. The second goal is to perform selected DNS of the fundamental governing equations for the fluid velocity in microscale reactors to complement the experimental microPIV data. These data will be employed in a systematic validation study to improve the CFD model, and to determine its range of validity for microscale reactor design. Intellectual Merit The development of experimental tools for the measurement of flow in microscale devices is an important technical and intellectual challenge. Indeed, in microscale flows the need to image small domains and the desire for quantitatively accurate measurements of unsteady velocity fields leads to very stringent experimental requirements as compared to macroscale flows. Likewise, the development and validation of predictive computational models for microscale reactors pushes the limits of current knowledge. For example, the prediction of the scalar dissipation rate in low-Reynolds-number, high-Schmidt-number flows is still an open problem, but one which lies at the heart of microscale reactor design. Broader Impact The production of uniform-sized nanoparticles of hydrophobic organic compounds by an economical, scalable process is a considerable challenge. It is motivated by the use and potential use of nanoparticles in drug delivery, especially poorly water soluble drugs, cosmetics, dyes, medical imaging and diagnostic, and pesticides. One of the most advanced processes to produce such nanoparticles is Flash NanoPrecipitation. The tools developed in this project will facilitate the design and optimization of the microscale reactors needed for Flash NanoPrecipitation, and will complement the detailed kinetic models for nanoparticles formation under development in other NSF-funded projects. The potential broader impact of this project could thus be to transform the field of microscale reactor design.