John L. Schmitt

The homogeneous nucleation of nonane

The homogeneous nucleation rate of n‐nonane has been measured as a function of temperature and supersaturation ratio in a precision fast‐expansion chamber. The measured nucleation rate ranges from 102 to 105 drops/cm3 over the temperature range 215–270 K. The results have been compared to the classical theory and to the classical theory with the RKC replacement factor. The RKC theory functional form is the basis for an empirical rate equation to fit the data. A full listing of the thermodynamic constants used for the reduction of the data is given.

Homogeneous nucleation of ethanol

The authors have used an expansion cloud chamber to measure homogeneous nucleation rate as a function of temperature and supersaturation in ethanol. Nucleation rates from 102 to 105 drops/cm3 sec were measured in the temperature range 252–272 °K. An empirical functional fit to the data is used to extrapolate for comparison with other data in the literature at a nucleation rate of 1 drop/cm3 sec and to compare with the predictions of the classical Becker–Doring homogeneous nucleation theory. A full listing of the data and thermodynamics constants used in the reduction of the data is given in an appendix.The authors have used an expansion cloud chamber to measure homogeneous nucleation rate as a function of temperature and supersaturation in ethanol. Nucleation rates from 102 to 105 drops/cm3 sec were measured in the temperature range 252–272 °K. An empirical functional fit to the data is used to extrapolate for comparison with other data in the literature at a nucleation rate of 1 drop/cm3 sec and to compare with the predictions of the classical Becker–Doring homogeneous nucleation theory. A full listing of the data and thermodynamics constants used in the reduction of the data is given in an appendix.

Homogeneous nucleation of toluene

The authors have used a fast expansion chamber to measure the homogeneous nucleation rate of toluene as a function of temperature and supersaturation. The measured nucleation rate ranges from 102 to 105 drops/cm3 s over a temperature range of 215–267 K. The measurements are compared with the ‘‘classical’’ nucleation theory and with the RKC theory. The inclusion of the RKC replacement factor brings the data into good agreement with theory using physically realistic values of the surface tension and the sticking coefficient. An empirical curve fit to the data is presented as well as a full listing of the thermodynamic constants used for the calculations.

Condensation Coefficient Measurement for Water in the UMR Cloud Simulation Chamber

Abstract A systematic series of condensation coefficient measurements of water have been made using the University of Missouri—Rolla cooled-wall expansion chamber which simulates the thermodynamics of cloud. This coefficient is seen to decrease from a value near unity, at the outset of simulation, to a value in the neighborhood of 0.01 toward the end of a simulation. Final values of this coefficient are sufficiently low as to contribute significantly to the broadening of the drop-size distribution in cloud.

Precision expansion cloud chamber for homogeneous nucleation studies

The author describes an expansion cloud chamber for the study of the nucleation of a single component vapor (homogeneous nucleation). The design draws on the many years of experience in this Center in construction of chambers for homogeneous nucleation of water. Design features of the chamber are: exact control of temperature (±0.03 ° C), pressure (±0.5 mm Hg), and automatic control of cycling. Construction features are: all construction materials are stainless steel, glass, or fluorocarbon plastics; the piston seal is a very flexible welded stainless steel bellows; the chamber can be made very clean by heating under vacuum and it is compatible with many substances, e.g., ethanol, nonane, and toluene. Performance features are: excellent repeatability of the expansion cycle over a temperature range of 45° to —15 °C and in day to day operation. Safety features are: automatic detection and warning and inerting against fire and explosion from combustible vapor in the chamber enclosure. The determination of th...

Binary nucleation of ethanol and water

The authors have used a fast expansion cloud chamber to measure binary homogeneous nucleation rates in several ethanol–water mixtures as a function of temperature, ethanol and water activities and nucleation rate. Data (ethanol and water activities) are presented for a range in nucleation rate from 103 to 105 drops/cm3 s from 263 to 293 K for mixtures having mole ratios (ethanol/water) of 10, 4, 0.1, 0.01, and 0.001. A comparison of the extensive data set to other data in the literature shows good agreement. We find current theory, as expected, is unable to accurately predict the data at low ethanol concentrations.

Homogeneous nucleation of n-pentanol measured in an expansion cloud chamber

An expansion cloud chamber was used to measure homogeneous nucleation rates for n-pentanol in argon carrier gas at four nucleation temperatures 292, 282, 272, and 252 K. The nucleation rates range from about 15000 to 400 drops/cm3 s. The data exhibits changes with time that are attributed to the removal of trace impurities by self-cleaning action in the cloud chamber. Data at the highest supersaturation ratio for a given number of drops observed is considered to be closest to true homogeneous nucleation. A comparison of these measurements with data in the literature at similar temperatures and nucleation rates shows the data from this study to be approximately three orders of magnitude lower in nucleation rate at a given supersaturation ratio.

Binary nucleation of n-octane and i-octane

The authors used a Wilson expansion cloud chamber to measure binary homogeneous nucleation rates for pure n-octane, pure i-octane, and 3:1, 1:1, 1:3 (mole ratio) mixtures in a temperature range from 215 to 260 K. The nucleation rates range from approximately 100 to 50 000 drops/cm3 s. Current binary nucleation theory is unable to predict the data for this nearly ideal system.

A study of vapor phase self-initiated thermal polymerization of styrene with an expansion chamber

Studies of the self-initiated polymerization of styrene have been performed in the uniform environment of an expansion cloud chamber, using nucleation of liquid monomer drops for detection. These studies are the first of this kind in an expansion chamber and, although preliminary and designed to explore feasibility, have yielded many interesting results. The occurrence of the self-initiated nonterminated gas phase processes, previously observed in a diffusion cloud chamber, has now been confirmed in an expansion chamber. At 15 °C the initiation rate is measured to be 2 to 6 radicals cm−3 s−1 and the propagation constant is approximately 6×10−21 cm3 molecule−1 s−1. Additional studies in the presence of oxygen indicate the (expected) formation of polystyrene peroxide as well as its cleavage into additional radicals at 25 °C.

University of Missouri–Rolla cloud simulation facility: Proto II chamber

The Graduate Center for Cloud Physics Research at UMR has developed a cloud simulation facility to study phenomena occurring in terrestrial clouds and fogs. The facility consists of a pair of precision cooled‐wall expansion chambers along with extensive supporting equipment. The smaller of these chambers, described in this article, is fully operational, and is capable of simulating a broad range of in‐cloud thermodynamic conditions. It is currently being used to study water drop growth and evaporation for drops nucleated (activated) on well‐characterized aerosol particles. Measurements have been made not only for continuous expansions (simulated updraft) but also for cyclic conditions, i.e., sequences of expansion‐compression cycles resulting in alternating drop growth and evaporation. The larger of the two cloud chambers is nearing completion and will provide a broader range of conditions than the smaller chamber. The facility is supported by a fully implemented aerosol laboratory which routinely produce...