Three-wavelength extinction technique for characterizing aerosols under industrial conditionsA new developed in-situ and on-line measuring device has been adapted to the conditions of industrial gas cleaning equipment in order to realize measurements of particle sizes and concentrations of aerosols. It has been used to characterize hydrochloric acid, sulphuric acid and salt solution droplets. The measuring method is based on the three-wavelength extinction technique. The results, which have been achieved with this method, have been compared with measurements of a particle sampler for silizium dust and oil droplets and with chemical analysis for acid aerosols. There has been good agreement between the different measuring techniques. The method has successfully been tested in particular for liquid aerosols with high particle concentrations up to 10 9 particles/ cm 3 .

The formation of argon clusters by homogeneous nucleation of pure argon diluted in helium was investigated in the supersonic outflow of a shock tube, where the clusters were detected by laser light scattering from the particles in supersaturated states. The thermodynamic states for the onset of homogeneous nucleation varied between 48 and 85 K with corresponding argon partial pressures in the range 2–850 Torr. Values of adiabatic supercooling with respect to the argon phase equilibrium ranged between 3 and 10 K. The experiments are in agreement with previous investigations in subsonic shock tube and supersonic Ludwieg tube expansions but disagree with previous investigations in steady supersonic nozzle expansions. It is possible to explain qualitatively the observed differences in argon nucleation behavior on the basis of a thermodynamic and kinetic concept independent of the basic assumptions of existing nucleation theories.

Low temperature Raman spectra of hydrogen in simple and binary clathrate hydratesThe onset of homogeneous condensation of binary vapors in the supersaturated state is studied by means of the unsteady expansion in a shock tube. The experiments are concerned with low temperatures down to 220 K which are of particular interest for atmospheric conditions. Two representative systems, ethanol/n-propanol and water/ethanol, are investigated since they allow a sufficient theoretical description. The first system forms a nearly ideal solution, whereas the latter one is an example of a strongly nonideal mixture. For either system vapor mixtures of various compositions are diluted in dry air at small mole fractions and expanded in the driver section from room temperature. The onset of homogeneous condensation is detected optically and the corresponding thermodynamic state is evaluated. The experimental results are compared with the binary nucleation theory and the particular problems of the theoretical evaluation at the low temperatures are discussed. The use of surface tension values derived for small binary droplets in the nucleation theory is mandatory to restore agreement between theory and experiment for the surface active system water/ethanol.

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The vapor nucleation of argon was investigated in shock tube expansions starting from room temperature. The cooling from the superheated initial state to nucleation onset was attained in unsteady flow fields at high Mach numbers M=5. Thermodynamic states for homogeneous nucleation were observed between 30 and 180 Torr at corresponding temperatures in the range of 50–70 K. The high starting temperatures do not affect the nucleation onset states compared to previous experiments on the subject, where the expansions started from much lower temperatures. The slight differences in the onset states to previous experiments employing cryogenic shock and Ludwieg tubes may be attributed to the higher cooling rates and to nonisentropic expansion effects.