Nonane and Deutirium Oxide Droplet Growth in a Supersonic Nozzle

HARSHAD PATHAK (1), Dirk Bergmann (2), Barbara Wyslouzil (1), Judith Wolk (2), Reinhard Strey (2)

(1) The Ohio state University, Columbus (2) Universtat zu Koln, Germany

     Abstract Number: 360
     Last modified: May 10, 2010

Abstract
Dehydration is an important purification step in natural gas processing that prevents the formation of methane hydrates inside pipelines. Conventional methods for dehydration like pressure swing absorption and glycol dehydration require the use of chemicals and bulky equipment. An alternate method is to use supersonic separators which cool the gas adiabatically, induce droplet formation, and remove the condensate by cyclonic separation. Various models of multicomponent condensation are used to design these separators. These models need to be compared with experimental data to test their applicability for experimental conditions inside the supersonic separators- namely, low droplet sizes and high cooling rates. We use a supersonic nozzle to produce a binary aerosol of nonane (a representative higher alkane) and D$_2O (for experimental convenience). Condensation and droplet growth of the aerosol inside the nozzle is studied using Pressure Trace Measurements (PTM), Fourier-Transform Infrared Spectroscopy (FTIR) and Small angle X-Ray Scattering (SAXS). We use the equations of mass, momentum and energy conservation and continuity to determine the unknown variables of temperature, density, area ratio, velocity and mass fraction condensed in our PTM experiments. For quantitative FTIR analysis, we measure the absorption spectra for the flow inside the nozzle at a spatial resolution of c.a. 3-4 mm and assume that our absorption spectrum is a linear combination of a well characterized vapor phase spectrum and a well characterized liquid phase spectrum. Using Beer-Lamberts law that absorbance is proportional to concentration, mass fraction condensed is calculated. For SAXS experiments, we assume that our droplets are polydisperse spheres following a Schultz distribution and measure the droplet size distribution at a spatial resolution of 2 mm and calculate the number densities and volume fractions. Finally, the results from the three experimental techniques are compared with one another.