Special cloud chambers for investigations into the time-behaviour of homogeneously nucleated spontaneous condensation

Abstract

Spontaneous condensation is induced by nucleation in supersaturated, i.e. in metastable vapour states of very short life-time. The rate of change of the thermal variables thus affects the so-called critical supersaturation, where the incipient condensation becomes observable. Consequently, a complete phenomenological description of spontaneous condensation requires the consideration of rate- or timevariables such as, e.g., a cooling- or an expansion-rate. Since comparatively few experimental results on the influence of these parameters are published and virtually all of them were attained in supersonic nozzle flow, i.e. at relative high expansion rate (P=1000–200000 s⁻¹), two special cloud chambers were designed for low (0.5–130 s⁻¹) and medium (100–500 s⁻¹) expansion rate, respectively, with the intention to correlate critical supersaturation S _W with P and temperature T in a wide range of vapour density — up to the critical point. The two cloud chambers are presented together with the relevant experimental procedures. First experimental results, obtained in both chambers with the pure vapours of carbon dioxide and ammonia, could be correlated with the respective data sets previously registered during Laval-nozzle experiments.