NUCLEATION LABORATORY

THE FLOW DIFFUSION NUCLEATION CHAMBER:

A QUANTITATIVE TOOL FOR NUCLEATION RESEARCH

J. Chem. Phys. 104 , 382 (1996)

 Vivek Vohra and Richard H. Heist  

RESEARCH SUMMARY

We report the design and testing of a flow nucleation chamber that allows critical supersaturation measurements using a variety of background gases at ambient pressure and a conveniently accessible range of temperatures.  We have developed a model for the mass and energy transport processes occurring within the nucleation chamber.  Although this model works well for the conditions used during these experiments, our analysis suggests that improvement can be realized by incorporating second-order, axial dispersion effects into the analysis.  This will be done in a subsequent refinement of the model description.  The limited ranges of pressure and temperature accessible to this particular device result only from our desire to first carefully study and quantify the operation of this device in order that extending these operating ranges can be accomplished in an orderly and well-defined manner.

      Critical supersaturation data obtained with this flow nucleation chamber accurately reproduce thermal diffusion cloud chamber data.  While critical supersaturation measurements were the objective of this investigation, nucleation rate measurements are also desirable.  This nucleation chamber was designed to allow convenient optical access to the nucleation zone, which will facilitate quantitative nucleation rate measurements. 

      We report results of preliminary measurements of nucleation in the presence of a variety of different background gases and discuss these results in the context of data in the literature obtained using other nucleation measurement devices.  Results of these preliminary measurements of nucleation at ambient pressure in the presence of different background gases, shown below in the accompanying figure, suggest that the nature of the background gas may influence nucleation at ambient pressure.  These data, while still of a preliminary nature, are consistent with data already published obtained at elevated pressures using a specially designed high pressure cloud chamber also in our laboratory.  The ability to investigate nucleation irrespective of the density of the background gas overcomes a major operational limitation of the upward thermal diffusion cloud chamber.  

    The figure shows results of Scrit measurements using the Flow Diffusion Nucleation Chamber employing four different background gases at a variety of temperatures and a comparison with Scrit data obtained using a thermal diffusion cloud chamber.  The Scrit data obtained using hydrogen and helium as background gases compare well with similar data obtained from the diffusion cloud chamber.  The Scrit data obtained using nitrogen and argon strongly suggest a possible background gas effect.  For specific details concerning these results, consult the original paper.

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