UNS: Heterogeneous Nucleation on Nanoparticles

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#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.