Fundamental Investigations on Sability and Structure of Flow and Heat Transfer in Cyclone Cooling Chambers

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The research project Wärmeübertragung in einer Zyklonkühlkammer has been designed for 4 years. The present proposal is now for the second phase (3rd and 4th year) of the project. In the first 2 years, the axial- and circumferential velocity field was experimentally studied via Particle Image Velocimetry (PIV) and the heat transfer in the cyclone cooling chamber was measured by a transient technique using thermochromic liquid crystals (TLCs). The flow and the heat transfer were additional simulated with the open source program OpenFOAM. The attention was on the investigation of different outlet geometries. Therefore, a 180° tube bend and a tangential outlet were investigated in detail. It turned out that a change of this sort of outlet geometry has no significant influence on the flow field in the swirl tube. This is a very important result concerning a future application of the swirl tube into a cooling channel in a gas turbine blade. The flow independence for outlet geometries with deflection shows, that swirl cooling can be well applied in technical applications in the future.The complex flow field and the heat transfer in cyclone cooling chambers are strongly affected by stability effects. Here the swirl number plays an important role for the flow field stability and the occurrence of a backflow region in the tube center. The previous investigations dealt only with high swirl numbers, so a backflow region occurred in all cases. Thus, detailed investigation on the generation of a backflow region with low swirl numbers is missing.Because of this the objective of the second phase of the project is to understand and describe the fundamentals of the backflow in the tube core and the influence on the heat transfer. Especially the effect of the vortex breakdown and its transition region shall be investigated in detail. Here, it is very interesting for which swirl number a backflow region in the core develops and how it influences the cooling capability of the cyclone cooling chamber.Furthermore the previous investigations show the formation of a stable helical vortex structure. These secondary vortices have a big influence on the heat transfer in the swirl tube. So a further objective of the project is to extent the knowledge of the energy transfer between the main and the secondary vortices. Therefore a water injection into the swirl tube shall be investigated in detail. Due to the water injection additional energy will be added to the system. The idea is to manipulate the angular velocity of the solid body vortex in the tube core with the evaporation heat. Thus, the influence on the solid body vortex and on the heat transfer shall be studied in detail.