The temperature and size distribution of large water clusters from a non-equilibrium model.

A hybrid Lagrangian-Eulerian approach is used to examine the properties of water clusters formed in neon-water vapor mixtures expanding through microscale conical nozzles. Experimental size distributions were reliably determined by the sodium doping technique in a molecular beam machine. The comparison of computed size distributions and experimental data shows satisfactory agreement, especially for (H2O)n clusters with n larger than 50. Thus validated simulations provide size selected cluster temperature profiles in and outside the nozzle. This information is used for an in-depth analysis of the crystallization and water cluster aggregation dynamics of recently reported supersonic jet expansion experiments.

Area and edge effects in radiometric forces.

The radiometric force on several configurations of heated plates placed in a stagnant gas is examined experimentally, with a high-resolution thrust stand, and numerically using the direct simulation Monte Carlo method and a discrete ordinate solution of a model kinetic equation. A wide range of pressures from 0.006 to 6 Pa was examined, corresponding to Knudsen numbers from 20 to 0.02, in argon and helium test gases. The radiometric force, important in a number of emerging micro- and nanoscale applications, is shown to be mostly area dependent in the transitional regime where it reaches its maximum at Kn approximately 0.1.