Parasitic heat transport in thermal energy storage for Carnot batteries

对于卡诺电池的效率，热能存储（TES）是一个关键组成部分。它应该以低成本长时间储存大量热能。通常使用液体材料，如水或熔融盐。该存储器可以应用为双罐系统，其中冷流体在一个罐中，热流体在另一个罐中，或者应用为分层存储器，其中热流体直接存储在冷流体上方。然而，即使在最初温度均匀的单个储罐中，由于热损失到周围环境，也会产生热分层。由于壁材料通常具有比存储介质更大的热导率，因此热量从热区域经由壁传递到较冷区域，反之亦然。这驱动靠近壁的热对流，这强制混合，从而破坏火用。这种影响不仅可以在小型系统中看到，也可以在工业规模的大型系统中看到。这些寄生对流的理解是在自然界和工程中的许多流体力学和传热问题的根本利益。更重要的是，它将有助于提高整体效率方面的能源和有效能的热电联产的卡诺电池，但也为热电联产一般用于其他加热应用。因此，该项目也旨在为实现“Wärmewende”做出宝贵贡献。

For the efficiency of Carnot-Batteries, the thermal energy storage (TES) is a key component. It should store large amounts of thermal energy over a long time at low cost. Often liquid materials like water or molten salt are used. The storage can be applied as a two-tank system with cold fluid in one tank and the hot fluid in the other tank, or as a stratified storage, where hot fluid is stored directly above the cold fluid. However, even in single storage tanks with initially uniform temperature, thermal stratification develops due to heat losses to the surrounding. Since the wall material typically has a larger thermal conductivity than the storage medium, heat is transferred from the hot region via the wall to colder regions an vice versa. This drives thermal convection close to the wall, which enforces mixing and thus destroys exergy. The effect can be seen in small systems, but also in larger systems in industrial scale. The understanding of these parasitic convective flows is of fundamental interest for many fluid mechanical and heat transfer problems in nature and engineering. More important, it will help to improve the overall efficiency in terms of energy and exergy of TES for Carnot-Batteries, but also for TES in general for other heating applications. Thus, the project aims also to be a valuable contribution to achieve the 'Wärmewende'.