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

罗德尼·奥Fox 0730250在湍流状态下操作的微型反应器用于"快速纳米沉淀”，以实现生产疏水有机化合物的均匀尺寸的纳米颗粒所需的混合时间。由于整个过程由混合和动力学控制，而不是热力学，因此可以在连续过程中以工业规模快速制造大量精确控制的纳米颗粒，而不需要长批次时间和处理大量溶剂。然而，设计一个微型反应器所需的快速沉淀的理解，需要详细了解宏观，中观和微观混合的发展过饱和的作用。更一般地说，在开发用于快速纳米沉淀的微型反应器中的一些关键问题是：（i）微型反应器在不同流速和流比下的操作效率如何？(ii)多喷射器微型反应器与双撞击流反应器相比如何？(iii)在微型反应器中观察到的流动状态是什么？如何优化它们以实现快速混合？为了回答这些问题，可以采用计算流体动力学（CFD），前提是它已经根据设计所关注的操作条件范围内的实验数据进行了充分验证。目前，微尺度反应器的设计是通过试验和错误来完成的;因此，预测计算工具的可用性将改变这一领域的研究方式。爱荷华州开发了基于低雷诺数湍流模型的CFD模型，并使用在普林斯顿收集的受限撞击射流（CIJ）和多入口涡流混合器（MIMV）微尺度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是非常有前途的，并表明，计算流体动力学确实将是一个变革性的工具，微型反应器的流场的细节，在微型反应器的出口转换数据的间接依赖留下了许多悬而未决的问题，真正的预测能力的计算流体动力学模型。这种不令人满意的情况提供了动力，开发直接数值模拟（DNS）和微尺度实验工具，可以提供本地数据的瞬时速度和标量场的微尺度反应器，需要严格的CFD模型验证。为了满足这一需求，这两个PI正在合作开发微尺度粒子图像测速仪（microPIV），用于测量在湍流状态下运行的微尺度反应器中的瞬时速度场。最近microPIV测量的湍流在一个微型CIJ反应器已经证明了这种测量的可行性，使用国家的最先进的设备在他们的实验室。此外，他们最近已经证明了控制实验不确定性的能力，需要与CFD预测定量比较的水平。该项目的主要目的是继续改进这项有前途的工作，使实验数据能够为微尺度反应器的CFD模型提供明确的验证。第二个目标是进行选定的DNS的基本控制方程的流体速度在微尺度反应器，以补充实验microPIV数据。这些数据将用于系统的验证研究，以改进CFD模型，并确定其对微尺度反应器设计的有效性范围。智力优点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，在微尺度流的需要，图像小域和非定常速度场的定量准确测量的愿望导致非常严格的实验要求相比，宏观流动。同样，微型反应堆预测计算模型的开发和验证推动了现有知识的极限。例如，在低雷诺数、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，但这是微尺度反应器设计的核心问题。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。其动机是纳米颗粒在药物递送中的使用和潜在用途，特别是水溶性差的药物、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快速纳米沉淀。该项目开发的工具将促进Flash NanoPrecipitation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的影响可能是改变微型反应器设计领域。

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.