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discovered 02_2012

FOCUS// The HZDR Research Magazine WWW.Hzdr.DE 30 31 which numerical codes could be compared and at the same time used as input and improved. Until very recently CFD- programs could not predict when exactly there would be a blockage of the back-flow water through the steam and when there would be a partial limitation. New data from Christophe Vallée’s experiments have been able to help in this way improve the computer models that Thomas Höhne had also been working on meticulously in the ”CFD“ Division at the HZDR headed by Dirk Lucas. “We have developed a new model‚ the Algebraic Interfacial Area Density Model, that can be used to determine the interaction of phases with different density at their interfacial layers much more accurately than before“, says Thomas Höhne. To simulate the experiment on the computer, a computer cluster comprising of several processors worked on this for around three months. In particular, the accurately simulated interactions at interfacial layers between water and steam were a significant factor. To convert the results into practice, the researchers are working closely with the CFD-developer ANSYS Germany, with whom the HZDR has a strategic partnership. “We were particularly happy about the support from our Indonesian colleague Deendarlianto from the Gadjah-Mada University in Yogyakarta, who received a Humboldt scholarship to work with us on this project for two years. Together we developed the simulations and we were overjoyed when the results turned out to be a really good match with the experimental data. In the meantime our simulation that is close to reality has been put into practice for counter-current flow limitations and can be implemented by companies“, reports Dirk Lucas. The Institute of Fluid Dynamics at the HZDR is a long-term partner in the German CFD-network. It also has a special partnership with the Institute for Nuclear Safety Systems Tsuruga and the University of Kobe in Japan. Scientists there have used the experimental data from Christophe Vallée to validate a simplified model and they have also made their own simulations and experimental data available to test the HZDR- model. The authorization for the operation of the Japanese nuclear power plants depends among other things on the verification procedure also for the extreme case of counter- current flow limitation. This was tested for a maintenance phase when there is a lower pressure than under normal operation in the reactor vessel. Says Dirk Lucas: “True to the theory that only a validated code is a good code, our new CFD-model has already been tried and proven in practice. In the next step we want to calculate other liquids and heat loss. In the future we will then hopefully have a universal code for counter-current flow limitations.“ Simulation tool for crude oil and vapor A great advantage of the CFD-programs is that they are extremely relevant for practical applications, as they can be used in a wide range of fields such as safety analyses for nuclear power plants and production processes in the chemical industry to the construction of fuel cells. If one considers the production of substances in the chemical industry, then cases of counter-current flow limitations are also possible there. The vapor in a separating column could press against the liquid crude petroleum, restricting its flow. Because we now understand this special flow formation as a result of the Rossendorf experiments and simulation calculations, we now have a lever for preventing this undesired phenomenon in the chemical industry. Further, this is an important step along the way to greater energy efficiency in the day-to-day running of industry. Literature Deendarlianto, T. Höhne, D. Lucas, C. Vallée, G. A. Zabala et al.: “CFD studies on the phenomena around counter-current flow limitations of gas/liquid two-phase flow in a model of a PWR hot leg”, in Nuclear Engineering and Design, vol. 241 (2011), p. 5138-5148 (DOI 10.1016/j.nucengdes.2011.08.071) EXPERIMENT AND SIMULATION: Qualitative comparison of the experiment’s stream structures (left) with the CFD simulation (right). In both instances, a large wave develops, which is broken by the steam flow. Contact _Institute of Fluid Dynamics at HZDR AREVA Endowed Chair for Imaging Techniques in Energy and Process Engineering at the TU Dresden Prof. Uwe Hampel Dr. Dirk Lucas