Anwendung von CFD Simulationen dichter Partikelströmungen bei der Konstruktion eines thermischen Energiespeichers

Abstract

Aufgrund des steigenden Anteils von regenerativen, fluktuierenden Energiequellen an der Energieversorgung ist die Bereitstellung elektrischer Energie eine immer größer werdende Herausforderung für die Netzbetreiber. Um die Versorgungssicherheit und die Stabilität des Netzes garantieren zu können, wird es künftig immer wichtiger werden, Energiespeicher großen Maßstabs zu entwickeln. In der vorliegenden Arbeit wir ein solcher Energiespeicher vorgestellt und einige zentrale Problemstellungen mit Hilfe einer CFD Software beleuchtet. Außerdem wird der Algorithmus des verwendeten CFD Softwarepakets Barracuda genauer betrachtet und zusammengefasst.

Due to the increasing amount of energy produced by fluctuating, renewable sources, i.e. wind and solar power, providing electricity at all times has become a challenge for network operators. One key piece of the puzzle to sustain service security will be the development of high capacity energy storage to provide these fluctuating with more flexibility. Such an energy technology was presented in recent publications. The sandTES system, as it is described in several publications, contains a fluidized bed heat exchanger to store waste heat as sensible heat in sand. In this thesis the system of a sandTES prototype and the expected problems occurring will be simulated with Barracuda, a CFD software package, that is designed especially for particle flows. The computational calculation of such flows is a challenge, which has yet to be mastered in different kinds of flow regimes. While the algorithms for simulating problems of one-phase fluid dynamics have matured over the last decades, the calculation of momentum exchange between particles in a fluid flow is still problematic. The reason is, that the interaction strongly depends on the particles form and surface. These two factor have either to be involved directly to the algorithm or to be modelled by a correlation. The algorithm of Barracuda uses a model to calculate the interaction between the particles based on the fluid volume fraction in the cell. This approach eliminates the dependency of the momentum calculation on speed and form of the particles by reducing them to a continuous phase while calculating the interaction. Part of the thesis will be the evaluation of the algorithm with experiments made within sandTES project and furthermore the support in designing a sandTES pilot plant.