UNS: Heterogeneous Nucleation on Nanoparticles

#1511498 Wyslouzil，Barbara E.飞机起飞或着陆时机翼附近的蒸汽流尾迹说明了由异质成核引发的高速流中的冷凝。空气在经过机翼时冷却，其相对湿度开始超过100%。这种不稳定的情况促使水凝结在颗粒上形成云。同样的现象可以在许多其他工程应用中发挥重要作用，包括从低压汽轮机中提取能量，天然气中的脱水和重烃去除，以及高超音速风洞的开发。不幸的是，有一些实验数据来测试在这些设备的极端条件下的非均质成核理论。该项目将使用超音速喷嘴装置来测量异质成核速率、颗粒生长速率以及最终液滴的尺寸和结构。 所有这些对于开发工业过程中的非均相冷凝的精确模型至关重要。本项目探讨在超音速流中发生的高度非平衡条件下的非均相成核，并研究由此产生的颗粒生长和结构。 含有两种可冷凝物质的蒸气载气混合物将流过超音速喷嘴。种子气溶胶将通过在较高蒸气压可冷凝物不饱和的条件下较低蒸气压可冷凝物的均匀成核和生长来产生。 随着流动继续冷却，较高蒸气压的材料将变得过饱和并且将在预先存在的气溶胶上成核。静态压力测量将表征流动，空间分辨的小角度和广角X射线散射将表征气溶胶，红外光谱将量化蒸汽，液体和固体状态之间的可冷凝物的分布。一个一维的流动模型，结合异质成核和生长将被调整，以匹配实验观察，以产生估计的异质成核率。

#1511498Wyslouzil, Barbara E.The streaming vapor trail near an airplane's wing during takeoff or landing illustrates condensation in a high-speed flow initiated by heterogeneous nucleation. The air cools as it passes over the wing, and its relative humidity starts to exceed 100%. This unstable situation drives water condensation on particles forming a cloud. The same phenomenon can play an important role in many other engineering applications including energy extraction from low pressure steam turbines, dehydration and heavy hydrocarbon removal from natural gas, and development of hypersonic wind tunnels. Unfortunately, there are few experimental data to test theories of heterogeneous nucleation at the extreme conditions in these devices. This project will use a supersonic nozzle apparatus to measure rates of heterogeneous nucleation, rates at which particles grow, and the size and structure of the final droplets. All of these are crucial for developing accurate models of heterogeneous condensation in industrial processes.This project explores heterogeneous nucleation under highly non-equilibrium conditions that occur in supersonic flows and investigates the resulting particle growth and structure. Vapor-carrier gas mixtures containing two condensable species will flow through a supersonic nozzle. The seed aerosol will be produced by homogeneous nucleation and growth of the lower vapor pressure condensable under conditions where the higher vapor pressure condensable is subsaturated. As the flow continues to cool, the higher vapor pressure material will become supersaturated and will nucleate on the preexisting aerosol. Static pressure measurements will characterize the flow, spatially resolved small and wide angle X-ray scattering will characterize the aerosol, and infrared spectroscopy will quantify the distribution of the condensable between the vapor, liquid and solid states. A one-dimensional flow model that incorporates heterogeneous nucleation and growth will be tuned to match experimental observations to yield estimates for the heterogeneous nucleation rates.