discovered_01_2016

WWW.HZDR.DE 30 31 RESEARCH // THE HZDR RESEARCH MAGAZINE mathematically to be scalable to larger applications. This is the only way to model complex heat transfer processes in fuel elements under all conceivable circumstances. New experiments are then conducted to validate the findings. "At HZDR, I can combine research and technical applications," the 27-year-old is happy to report. Better understanding of evaporation processes Debasish Sarker has a Master’s degree in Mechanical Engineering and Energy Systems. Following his studies in Bangladesh and South Korea, he came to HZDR two years ago to pursue his Ph.D. He investigates single steam bubbles, at a scale of less than a millimeter. At his test facility, a high- speed camera provides him with high-resolution images of the evaporation surface and bubble formation. They allow Sarker to observe how steam bubbles form and glide along the wall, as well as to measure their flow speed. He also simulates the bubble formation on the computer. "I want to contribute to a better understanding of evaporation," the 33-year-old says. He is particularly interested in finding out how to optimize heat transfer at slow flow velocities in small spaces, as is the case, for instance, in tight bundle heat exchangers. This is fundamental knowledge of great importance for passive cooling systems. He is convinced that "if we can make progress here, it will impact the energy efficiency of a lot of large industrial facilities." Debasish Sarker’s research is also of interest to his two colleagues. He examines the evaporation processes on Sebastian Unger’s coated samples. And for Thomas Geißler, it is vital to understand what is happening when a steam bubble grows and becomes detached. Greater safety and energy efficiency Even though all German nuclear reactors will be off the grid by 2022, research in nuclear power plant safety and safe storage of fuel elements is still needed. Germany will only be able to have a say in future debates about global safety standards and participate in international research projects if it continues to cultivate its own expertise in the field. The three Ph.D. projects under the supervision of Uwe Hampel are partly funded by the Federal Ministry for Economic Affairs and Energy. Their research outcomes, however, can be applied in many fields. Insight into the boiling crisis is vital to any situation in which vast amounts of heat must be cooled in a small space, which is the case, for example, in certain computer components. Hydrophobic coating, on the other hand, could have an impact in the field of renewable energies. If small differences in temperature can be exploited better using such coatings, it would be possible to increase the efficiency of biogas, geothermal, solar and heat recovery systems. HAND IN HAND: Basic experiment, simulation and technology development – the three doctoral candidates Debasish Sarker, Sebastian Unger and Thomas Geißler (from left to right) share ideas in front of the steam drum at the TOPFLOW facility. Photo: Oliver Killig _Institute of Fluid Dynamics at HZDR _AREVA Endowed Chair of Imaging Techniques in Energy and Process Engineering at TU Dresden Prof. Uwe Hampel u.hampel@hzdr.de _TU Dresden Thomas Geißler and Sebastian Unger _Institute of Fluid Dynamics at HZDR Debasish Sarker CONTACT

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