Thermal diffusion cloud chamber: New criteria for proper operation

Document Type


Publication Date

Winter 2003

Publication Title

Atmospheric Research


We report results of new nucleation experiments involving 1-pentanol with hydrogen as the background gas obtained from constant temperature critical supersaturation experiments utilizing the high-pressure diffusion cloud chamber. We have observed significant background gas effects on vapor nucleation that differ somewhat from that we have reported previously. In this paper, we discuss the important issue of stability (the absence of buoyancy-driven convective motion of the gas–vapor mixture) and cloud chamber operation; and we focus now on the lower total pressure limit required for stable chamber operation. We describe how violating this limit is manifested by the experimental data, and we show actual results for the nucleation of 1-pentanol with hydrogen as a background gas which illustrates the importance of considering these stability issues. For the first time, we identify three regions of operation for the diffusion cloud chamber. Region I corresponds to the range of total pressures below this lower total pressure limit; Region III corresponds to the range of total pressures above the upper total pressure limit (described earlier); and, Region II corresponds to the range of total pressures that permit “proper” operation of the diffusion cloud chamber. Here we define proper operation as operation under conditions that are believed to be well represented by a one-dimensional model of diffusion in a stagnant gas. We provide, for the first time, an empirical procedure for determining the lower total pressure limit. We also argue against the commonly used pressure ratio as a predictor for “proper” cloud chamber operation.


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