NUCLEATION LABORATORY
VAPOR TRANSPORT WITHIN THE THERMAL DIFFUSION CLOUD CHAMBER
J. Chem. Phys. 113(17), 7398 (2000)
F.T.
Ferguson, R.H. Heist and J.A. Nuth III
RESEARCH
SUMMARY
In this paper we present a review of two different, one-dimensional models of
the vapor transport within the thermal diffusion cloud chamber (TDCC).
In the first case the assumption is made that there are no convective
fluxes within the chamber and that heat and mass transport occur by diffusion
only. Although in this model there
are no restrictions on the transport of the two components within the chamber,
the assumption of zero velocities within the chamber results in an incorrect
flux boundary condition for the background gas.
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| A comparison between nonane experimental data and CNT predictions. The supersaturation prediction based on the zero velocity assumption indicates a pressure effect while the typical equations used to calculate the supersaturation profile in the TDCC do not show this effect. |
In the second case, the model for vapor transport is based on the typical,
stagnant background gas assumption and the equations for this model are similar
to those describing operation of the classic Stefan tube in which there is
transport of a volatile species through a noncondensible background gas.
Unfortunately, this model of vapor transport within the TDCC also suffers
from the same inconsistencies noted for the Stefan tube problem.
In this stagnant background gas model, when the convective contributions
to the flux are small, the two models give reasonably close result.
For larger convective contributions, predicted values for the
supersaturation in the nucleation region of the TDCC can differ by more than 50%
for the two models. This behavior is
evident in the included figure.
One interesting feature of the zero velocity model is that it predicts a change in the supersaturation profile within the TDCC with changing total pressure, whereas no pressure dependence is predicted using the stagnant background gas model. Unfortunately, the direction of this pressure change is opposite to that seen in experimental observations.
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