Thermal energy storage with zonal fixed beds of phase change material: a simulative and experimental investigation

Abstract

The high energy demand, especially in thermal energy sector, is in the need for more efficient solutions. A hybrid thermal energy storage offers the possibility to enhance the thermal power per volume of storage, by combining the concept of stratification and phase change within a desired temperature range. A concept design of such a hybrid thermal energy storage is made by introducing numerical flow simulation into the design process. An analysis of differently encapsulated phase change materials set the base to be able to profoundly compare experimental and numerical data. Hence, an experimental setup to study various shapes of encapsulated phase change material is developed in the present work. The resulting comparison of the single encapsulation validates the numerical model introduced to calculate phase change. High numerical effort of the phase change process Leads to a new approach of numerically portraying the phase change process. The enthalpy-conductivity approach is developed and validated through a single encapsulation, but offers the possibility to study phase change processes in the interacting thermal processes of a realistic sized 2m3 thermal energy storage. This work offers this new enthalpy-conductivity approach, a modeling method to implement a packed bed into a thermal energy storage and a combined numerical flow model to simulate the hybrid thermal energy storage in CFD. An experimental test facility of such a hybrid thermal energy storage is designed within the present work, as well. lt offers a comparison between experimental data and the numerical analyses and, additionally, provides a baseline for future hybrid thermal energy storage studies. The proposed combining storage of the packed bed of phase change material and the stratification of the heat transfer fluid, result in an enhancement of the thermal power of the storage volume by more than 140 %. The results lead to an adaptable approach to use numerical flow simulations as part of the design process to further increase the thermal power and efficiency of thermal energy storages.