Transport in the static diffusion cloud chamber revisited

The static diffusion chamber (SDC) allows the measurement of critical supersaturation and of nucleation rates and it is a powerful instrument for the vapor nucleation study. Earlier, within the scope of the International Nucleation Workshop Group, nucleation rates of the n-pentanol-helium system have been measured using different experimental techniques. Disagreement of experimental data obtained using the static diffusion chamber and data obtained using other methods, particularly the laminar flow diffusion chamber, can be explained by re-examining the mass and energy transport analysis used to describe static diffusion chamber operation. In the present research we describe the mass and energy transport in the SDC modeled as an effectively open system with mass and energy transport in one direction with a nonzero diffusion flux at the system boundaries. Calculated values for vapor supersaturation are compared with the n-pentanol nucleation rate experimental results of the American-Czech group [M. Rudek, J. L. Katz, I. Y. Vidensky , J. Chem. Phys. 111, 3623 (1999)] and with a nucleation rate Reference Equation obtained from an earlier investigation involving the n-pentanol-helium system. From our results one can see that there is a significant difference in the calculated supersaturation for all of the data. The magnitude of this difference is quite large even for the relatively small vapor mass fractions at a nucleation temperature of 260 K. We also note that the calculated nucleation temperatures from our analysis are slightly larger than those reported in the work of Rudek 4 We performed our calculations with and without the thermal diffusion term. We observed that the effect of thermal diffusion on the transport process is relativelly small and is not particularly essential to include in this comparison that we are making the effects of the different flux boundary conditions. (C) 2001 American Institute of Physics.