Über die Kondensation verschiedener Dämpfe bei adiabatischer Expansion

Summary

In accordance withKöhler's theory, considerable supersaturation is needed to get the entire body of condensation nuclei to grow into droplets; the degree of saturation is determined by the size of the individual nuclei and their solubility in the condensed liquid. Since it is known that in expansion meters all the atmospheric particles which count as condensation nuclei do in fact grow into droplets, it may be assumed that the designated supersaturation in the expansion chambers is achieved for at least a short space of time. The formation of the theoretically correct degree of supersaturation requires, however, that once the moisture saturation has been exceeded condensation should markedly lag behind pressure variation, in order to allow time for the requisite supersaturation to develop.

Experiments designed to test this question have established that condensation follows extraordinarily quickly on variation of pressure after moisture saturation has been exceeded. Condensation is also virtually uninfluenced by the choice of vapour used. At very high expansion speeds the condensation process is governed by the operative laws of diffusion. Measurements indicate that the degrees of supersaturation occurring in the expansion chambers lie considerably below the level of critical saturation even for the smallest nuclei.