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

Einer ZykLonkühlkammer的研究项目Wärmeüberggung已经设计了4年。目前的提案是该项目的第二阶段(第3年和第4年)。在前两年，用粒子图像测速仪(PIV)对轴向和周向的速度场进行了实验研究，并用热致变色液晶(TLC)的瞬变技术测量了旋风冷却室内的换热。利用开源程序OpenFOAM对流动和换热进行了数值模拟。重点考察了不同出水口的几何形状。为此，对180°弯管和切向出口进行了详细的研究。结果表明，这种出口几何形状的改变对旋流管内的流场没有明显影响。这是一个关于涡流管在燃气轮机叶片冷却通道中的应用的非常重要的结果。考虑偏转的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有很好的应用前景。旋风冷却室内复杂的流场和换热受稳定性影响很大。在这里，涡流数对流场的稳定性和管内回流区的出现起着重要作用。以前的研究只涉及高旋流数，因此所有情况下都会出现回流区。因此，缺乏对低旋流数回流区产生的详细研究。因此，该项目第二阶段的目标是了解和描述管芯中回流的基本原理及其对换热的影响。特别是对涡破裂及其过渡区的影响进行了详细的研究。在这里，核心回流区的涡流数目以及它如何影响旋风冷却室的冷却能力是非常有趣的。此外，以前的研究表明形成了稳定的螺旋涡结构。这些二次涡对旋流管内的换热有很大的影响。因此，该项目的另一个目标是扩大对主旋涡和次级旋涡之间能量传递的了解。因此，应对旋流管中的注水进行详细的研究。由于注水，系统将增加额外的能量。这个想法是用蒸发热来控制管芯中固体旋涡的角速度。因此，应详细研究其对固体涡和换热的影响。

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.