ChemEng.Upatras Seminars 2022 - Stylianos Varoutis, Karlsruhe Institute of Technology (KIT)
Abstract
During the last decade research in the field of rarefied gas dynamics has attracted a lot of attention. This refreshed interest is due to applications in the emerging field of nano- and micro-fluidics, as well as to the more traditional fields of vacuum technology and high altitude aerodynamics. Some of these applications may include important phenomena such as those related to polyatomic gases, chemical reactions, evaporation, and condensation. Representative examples include gas flows in mass flow controllers, micro propulsion nozzles in high altitude and space gas dynamics, pipe networks, pumps and distillation towers in vacuum systems, membranes and porous media in filtering, fabrication processes in microelectronics and gaseous devices in micro-electromechanical systems (MEMS). The gas rarefaction is specified by the Knudsen number (Kn), which is defined as the ratio of the mean free path over a characteristic macroscopic length of the problem. In general, when the flow is considered as far from local equilibrium, then the well-known hydrodynamic equations cannot be applied since the continuum assumption and the associated constitutive laws are not valid anymore. In these cases two main numerical approaches can be implemented in order to address problems in the whole range of the Knudsen number.
The first approach is based on the kinetic theory of gases as expressed by the integro-differential Boltzmann equation or its associated kinetic models, in which a deterministic numerical solution of the corresponding kinetic equation is performed. Typical examples are the BGK and Shakhov kinetic models. The second approach is the particle based Direct Simulation Monte Carlo (DSMC) method. The DSMC is a probabilistic numerical scheme, in which a large number of statistically representative particles are modelled. Particle motion is modeled deterministically, while the collisions are treated stochastically.
Within the above framework, the aim of this talk is twofold. The first part will be devoted to the presentation of the above numerical approaches and how these are applicable in other fundamental or engineering areas (chemical reacting flows, combustion, etc). Moreover, the corresponding experimental techniques will be discussed. The second part will be devoted to the presentation of illustrative examples in which the kinetic equations or DSMC have been applied, as for instance, the vacuum system of the nuclear fusion reactor ITER and the numerical modelling of a cryopump.
Speakers Short CV
Dr. Stylianos Varoutis was born in Athens, Greece, in 1980. He received his diploma from the Department of Mechanical Engineering, University of Thessaly, Greece, in 2004, and his M.Sc. and Ph.D. degrees in Rarefied Gas Dynamics from University of Thessaly, in 2006 and 2009, respectively. He moved to the Institute for Technical Physics at Karlsruhe Institute of Technology (KIT), in 2009, as an EFDA Fusion Researcher Fellow. Since then, he has been working at KIT as a Senior Research Scientist. Dr. Varoutis’ research is focused on computational and experimental studies of rarefied gas flow phenomena in various scientific and technological fields including high-altitude aerothermodynamics, gaseous microfluidics and vacuum manufacturing processes. Broadening applications of rarefied gas dynamics is one of his long-term research goals. Dr. Varoutis is coordininating a small team of researchers at Karlsruhe Institute of Technology (KIT). The research team has developed accelerated computational algorithms and solvers for the deterministic as well as the stochastic DSMC particle methods, which both solve the Boltzmann and model kinetic equations. Such new techniques are especially useful in studying low-speed and/or unsteady flows and have allowed to address several challenging problems in vacuum science and technology as well as in nuclear fusion fields.