Veröffentlichungen

Thermal energy storage systems contribute, among other things, to increasing the security of supply in the district heating system and to improving the efficiency of the district heating system (e.g., increasing the flexibility of the heat generator units, waste heat utilization better hydraulic operation). Pressure vessels, so called slim hot water storage tanks (storage type b1, [1]) are suitable for this purpose. The above mentioned advantages require efficient storage operation (low internal and external storage losses). This paper deals with the minimization of internal losses by improving the thermal stratification behavior. Thermal stratification with a thermocline between hot and cold zone as narrow as possible is an indicator of low mixing processes during loading. Minimizing these mixing processes during loading takes a key role in minimizing internal storage losses. Lohse [2] and Brähmer [3] investigated loading with conventional radial diffuser in slim hot water storage tanks with numerical flow simulation. The work identifies adverse flow effects due to the slim tank shape, such as a wall jet. This wall jet stimulates mixing processes and thus increases the internal storage losses. To overcome this flow problem, Findeisen et al. [4] proposes swirl loading. The investigations of Oestreich et al. [6] showed the flow behavior in the diffuser and in the storage, the effects on the thermal stratification as well as the advantageousness. This paper aims to provide a more detailed description of the flow processes. This knowledge is essential to better understanding the causes and effects of swirl loading and the structure of thermal stratification. Modeling and simulation of the diffuser and storage, respectively, are performed using Ansys CFX [6] Large eddy simulation is applied to resolve turbulent structures. This paper presents for the first time the vortex structures in the diffuser with internal elements for swirl generation. The storage flow exhibits similar behavior to known density flows (e.g., head and nose formation , instabilities in the free shear layers), which was previously unknown. High Peclet numbers (high advection currents) in the storage model lead to numerical instability of the simulation and therefore require increased discretization efforts.

Schlagwörter: thermal energy storage, charging, radial diffuser, swirl, large eddy simulation