The Properties of Small Water Clusters from Isothermal Nucleation Rate Measurements
We have made direct measurements of the stationary, homogeneous nucleation rates, J=N/Δt, in supersonic Laval nozzles. The number densities, N, of droplets formed are measured using small angle neutron scattering (SANS) experiments and the time intervals during which nucleation occurs, Δt <10 μs, are derived from static pressure measurements along the axis of the nozzle. By using nozzles with different expansion rates, we obtain the first isothermal nucleation rate measurements as a function of supersaturation for these devices with a relatively small error margin in J of +/-50%. At temperatures T of 210, 220, and 230 K, the maximum nucleation rates for D 2O range between 4- 1016< J /cm -3s-1 < 3- 1017 for supersaturations S ranging from 46 to 143. Applying the first and second nucleation theorems to isothermal nucleation rate data directly yields estimates for the number of molecules in the critical cluster n* and the excess internal energy E x(n*), respectively. The agreement between these values and the classical values predicted assuming the critical cluster is a compact spherical object are really quite good even though under our conditions n* is less than 10 and the water is highly supercooled.
B. E. Wyslouzil et al., "The Properties of Small Water Clusters from Isothermal Nucleation Rate Measurements," Proceedings of the AIChE Annual Meeting and Fall Showcase (2005, Cincinnati, OH), American Institute of Chemical Engineers (AIChE), Oct 2005.
AIChE Annual Meeting and Fall Showcase (2005: Oct. 30-Nov. 4, Cincinnati, OH)
Keywords and Phrases
Isotherms; Neutron scattering; Pressure effects; Supersaturation; Theorem proving; Thermal effects; Angle neutron scattering (SANS); Isothermal nucleation; Nucleation theorems; Water clusters; Nucleation
Article - Conference proceedings
© 2005 American Institute of Chemical Engineers (AIChE), All rights reserved.