AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Exploring the Phase Transitions of Highly Supersaturated Vapors and Supercooled Nanodroplets of Short-Chain (C5-C7) Alkanes in a Supersonic Laval Nozzle
KEHINDE OGUNRONBI, Barbara Wyslouzil, The Ohio State University
Abstract Number: 188 Working Group: Aerosol Physics
Abstract The phase behavior of simple molecules in high speed flows has proven to be an interesting area of research both in basic science and applied science. Of particular importance is the phase behavior of chain molecules - normal alkanes – because condensation in high speed flows is one way to remove them from raw natural gas. In addition to the studies of vapor to liquid phase transitions of n-alkanes been done, a few researchers have also investigated the crystallization of supercooled n-alkane liquid droplets. Recently, it was shown that surface and bulk freezing could be observed in supercooled nanodroplets of n-octane and n-nonane in a supersonic flow (Modak et al., 2013). This contrasts with other reports in the literature (Wu et al., 1993) that concluded the surface freezing phenomenon was restricted to alkanes containing at least 14 carbon atoms. For these longer chained alkanes, surface-freezing at the vapor-liquid interface occurs at temperatures above the bulk melting temperature, Tm.
We have begun to study phase transitions of n-alkanes with 5<n<7 using three experimental techniques: pressure trace measurements (PTMs), Fourier Transform Infrared (FTIR) spectroscopy, and Small Angle X-ray Scattering (SAXS). The PTMs characterize the expanding gas mixture flow, the SAXS experiments characterize the aerosols generated in the nozzle, and data from the FTIR experiments are used to determine the distribution of the condensible in the three phases. For these relatively short-chain alkanes, we observe evidence for freezing in heptane and hexane, but for n-pentane freezing is not observed in spite of sub-cooling the liquid by ~33 K.