Abstract View
Investigating Homogeneous Nucleation of Propane and N-Butane in Supersonic Nozzle Expansions
JIAQI LUO, Barbara Wyslouzil, The Ohio State University
Abstract Number: 423
Working Group: Aerosol Physics
Abstract
Supersonic separators have been proposed as an environmentally friendly way to remove heavier alkanes from natural gas. Understanding the non-equilibrium vapor-liquid phase transitions of n-alkanes is therefore essential to the development of these devices. Homogeneous nucleation rates have been measured in supersonic Laval nozzles for n-alkanes down to n-pentane, and, thus, n-butane and propane are the next logical candidates from both the experimental and theoretical points of view. A second goal of our research is to determine the critical cluster sizes from isothermal nucleation rate measurements. Working with these short-chain alkanes should then let us compare our nucleation results to those determined via direct mass spectrometric sampling in post-nozzle flows carried out at ETH Zürich. In particular, we can follow the nucleation process as it changes from one controlled by a free energy barrier to the barrier-free, collisional limit. All experiments use argon as the carrier gas. Pressure Trace Measurements (PTMs) provide estimates of the temperature, pressure, mass fraction of condensate, flow velocity, and area ratio of flow. The conditions corresponding to the onset of condensation and the characteristic times required by the phase transition are presented and discussed for n-butane and propane. Classical Nucleation Theory (CNT) fails to describe the particle formation process under our conditions because of its incorrect description of the smallest clusters. The determination of experimental nucleation rates requires the combination of PTMs results and number densities measured by Small Angle X-ray Scattering (SAXS) experiments. Correlation functions between number densities and initial partial pressure of n-pentane and n-hexane were used to estimate the number densities of propane and n-butane. Further SAXS experiments will be conducted once the Advanced Photon Source is again available for outside researchers.