A compact setup to study homogeneous nucleation and condensation

Abstract

An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 10(6) Pa resulting from mass flow rates of up to 600 l(N) min(-1) and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD.

Development of an EAM potential for zinc and its application to the growth of nanoparticles

“…As a result it was found that at the global minimum, corresponding to zero Kelvin, the structure is qualitative different to the bulk structure; it is based on distorted oblate Marks decahedra. It is also clear that the c/a ratio in a small cluster is not equal to The (blue) circles are from cooling simulations starting at 298 K, the (green) triangles-up are for cooling simulations starting at 400 K. The solid curve is the correlation with eqn (12).…”

“…9 The interest in zinc nanoparticles and small clusters is twofold: first the formation of zinc clusters starting with homogeneous nucleation 10 followed by growth and structure formation, as well as their properties, are of interest in a solar process for hydrogen formation. 11,12 Under certain conditions the reoxidation of zinc can be suppressed to a large extent, leading to zinc clusters. Secondly zinc is a hcp metal with a strong deviation of the lattice constant ratio c/a = 1.856 from the ideal value c/a = 1.63 corresponding to the close packing fraction 0.74.…”

Modeling of H2O/D2O Condensation in Supersonic Nozzles

“…Alternatively, the depletion of vapor from the gas phase, or the appearance of the condensate has been directly measured using spectroscopy (Tanimura et al 1995;Paci et al 2004;Tanimura et al 2005;Tanimura et al 2007). Finally, visible light scattering has been used to detect the appearance of the aerosol, and follow, at least qualitatively, its continued growth (Stein and Wegener 1967;Streletzky et al 2002;Karlsson et al 2007). Despite this extensive experimental work, none of these measurements provides detailed quantitative information on the aerosol itself, i.e., the size distribution of the particles formed during condensation.…”