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

研究项目Wärmeübertragung in einer Zyklonkühlkammer已经设计了4年。目前的提案是项目第二阶段（第三和第四年）的提案。在前2年中，轴向和周向速度场的实验研究，通过粒子图像测速（PIV）和在旋风冷却室的传热测量的瞬态技术，使用热致变色液晶（TLC）。流动和传热的额外模拟与开源程序OpenFOAM。注意力集中在不同出口几何形状的研究上。因此，详细研究了180°管弯曲和切向出口。结果表明，这种出口几何形状的变化对旋流管内的流场没有明显的影响。这是一个非常重要的结果，涉及涡流管在燃气涡轮机叶片冷却通道中的未来应用。具有偏转出口几何形状的流动独立性表明，旋流冷却在未来的技术应用中具有良好的应用前景。稳定性效应对旋流冷却室中复杂的流场和传热有很大的影响。旋流数对流场的稳定性和管中心回流区的出现起着重要的作用。以前的研究只涉及高涡流数，因此在所有情况下都会出现回流区。因此，缺少对低涡流数回流区产生的详细研究。因此，项目第二阶段的目标是了解和描述管芯内回流的基本原理及其对传热的影响。特别是涡破裂及其过渡区的影响应详细研究。在这里，这是非常有趣的旋流数的回流区的核心发展和它如何影响旋风冷却室的冷却能力。此外，以前的研究表明，一个稳定的螺旋涡结构的形成。这些二次涡对旋流管内的换热有很大的影响。因此，该项目的进一步目标是扩大主涡和次涡之间的能量传递的知识。因此，应详细研究向旋流管中注水。由于水的注入，额外的能量将被添加到系统。其思想是利用蒸发热来操纵管芯内固体涡的角速度。因此，应详细研究对固体涡流和传热的影响。

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.