Simultaneous Analysis of the Dispersed Liquid and the Bulk Gas Phase of Water Sprays Using Raman Spectroscopy.

Currently, a comprehensive physical description of sprays is not possible, as the involved heat- and mass-transport mechanisms have not yet been understood completely. Therefore, we here show and apply a straightforward Raman evaluation technique which simultaneously probes spatially resolved (i) droplet temperature, (ii) evaporation progress and (iii) entrainment of air into the spray. First, the working principle of the Raman technique and the calibration of the sensor are described. Then, the applicability of the Raman technique is demonstrated showing example measurement results obtained from a superheated water spray. The plausibility of the obtained measurement results is demonstrated comparing them with computations for thermodynamic equilibrium conditions. Information about the droplet temperature, the evaporation progress and the entrainment of air might complement the insights into heat- and mass-transport mechanisms which can already be provided applying other existing optical spray diagnostic techniques.

Attractive particle interaction forces and packing density of fine glass powders.

We study the packing of fine glass powders of mean particle diameter in the range (4-52) µm both experimentally and by numerical DEM simulations. We obtain quantitative agreement between the experimental and numerical results, if both types of attractive forces of particle interaction, adhesion and non-bonded van der Waals forces are taken into account. Our results suggest that considering only viscoelastic and adhesive forces in DEM simulations may lead to incorrect numerical predictions of the behavior of fine powders. Based on the results from simulations and experiments, we propose a mathematical expression to estimate the packing fraction of fine polydisperse powders as a function of the average particle size.

Liquid phase temperature determination in dense water sprays using linear Raman scattering.

Linear Raman scattering has been applied for the determination of the temperature of the liquid phase in water sprays under normal and superheated conditions. The envelope of the Raman OH-stretching vibration band of water is deconvoluted into five Gaussian peaks which can be assigned to five different intermolecular interactions (hydrogen bonding). The intensity of each of the peaks is a function of the temperature and the phase of the water under investigation. The interference of the Raman signals originating from the water vapor is eliminated from the Raman signals originating from the liquid water. Consequently the temperature of the liquid water droplets surrounded by water vapor is accessible which is favorable for the investigation of non-equilibrium sprays where the droplet temperature is different to the vapor temperature.