Prof. Günter Brenn
Institute of Fluid Mechanics and Heat Transfer
Graz University of Technology, Graz, Austria
Dr. Günter Brenn received his Aerospace Engineering degree from the University of Stuttgart in Germany in 1985. He received his Ph.D. from the same university in 1990. His doctoral research on drop shape oscillations was supervised by Professor A. Frohn (Institute of Aerospace Thermodynamics, University of Stuttgart, Germany).
After a two-year post-doctoral stay in Japan, he joined Professor F. Durst’s Chair of Fluid Mechanics (LSTM) at the University of Erlangen-Nürnberg (Germany) in 1992. Here, Dr. Brenn completed his habilitation in fluid mechanics in 1999.
In 2002, he took his present full professor position at the University of Technology in Graz, Austria. He teaches fluid mechanics, heat and mass transfer. His research interests are spray flows, the rheology and rheometry of complex liquids, heat and mass transfer in disperse systems, the stability of free-surface flows, and optical flow measuring techniques. He published more than 130 peer-reviewed papers in scientific journals, the monograph “Analytical Solutions for Transport Processes” (Springer, 2017), and more than 160 contributions to scientific conferences. He is the European Editor-in-Chief of the journal Atomization and Sprays and a member of the editorial advisory board of Experiments in Fluids.
He received the 1994 award from the Visualisation Society of Japan, the Norman-Chigier Award for Excellence in Reviewing 2016, and two awards for developments from science to business. He was nominated for the Balzan Award for Fluid Dynamics in 2018.
Title: Self-similar pressure-atomized sprays with heat and mass transfer
Abstract: Sprays are produced by atomization of a liquid in an ambient gaseous medium. The properties of the two-phase flow fields of sprays cannot be described in a universal manner for all kinds of sprays. Axisymmetric free spray flow fields, however, exhibit self-similar properties, so that they can be described in an elegant way using the concept of self-similarity. This applies to air-assisted atomization as well as to pressure-atomized Diesel sprays and sprays from liquid-liquid coaxial swirl atomizers.
The present keynote lecture develops the self-similar equations of motion of disperse two-phase flow fields and applies them to pressure-atomized free sprays. Parameters in the self-similar equations are obtained from detailed phase-Doppler experiments, varying the Weber and Ohnesorge numbers of the nozzle flows independently. The experiments for use with self-similar spray characterisation must ensure high statistical reliability of the drop data, even at the edges of the spectra of drop properties. The experiments show that both the liquid drop and the gas flow fields of pressure-atomized sprays may be self-similar.
The work published earlier by the present authors is advanced by modeling heat and mass transfer between the drops and the gas based on the self-similar spray description, thus accounting for spray evaporation. Both the gas-phase temperature and the concentration of the vapour phase are determined by well-known transport equations in their self-similar forms. The self-similar transform of the effect of drop evaporation is compared against results obtained using the Frössling correlation for the Sherwood number. A modified drag law for single droplets is proposed for providing the drop velocity relative to the gas phase. The vapour concentration at the drop surface is obtained from a droplet vaporization model based on a mass and energy balance of a moving droplet in a non-saturated atmosphere. The vapour concentration determined from the self-similar analysis and the respective mass source remain to be validated against experiments or results from numerical simulations.