Abstract
Phase change materials are used in latent heat thermal energy storages to store a high amount of energy during phase change. A hybrid storage concept was developed with the aim of utilizing this high storage capacity in combination with Ruths steam storages. In the concept, a container filled with phase change material is placed at the shell surface of the Ruths steam storage. This container can be divided into several chambers filled with different phase change materials. An arrangement of electrical heating elements or heat exchangers at the internal side of these chambers is also provided. In this paper, a model of the hybrid storage concept is developed. The model consists of different sub-models, which are connected to each other. The simulation results of a hybrid storage show how important the model is for the analysis of the concept. Furthermore, the validation of the Ruths steam storage sub-model with operational measurement data of a storage line is presented. A maximum deviation between the operational measurement data and the simulation results of 6.43% occurs in terms of pressure at the internal side of the pressure vessel. In addition, the latent heat thermal energy storage sub-model was checked with the analytic solution.
Highlights
The optimal use of energy resources, especially renewable energy, requires a certain level of flexibility in an industrial production system
The hybrid storage concept presented in this paper proposes the installation of the latent heat thermal energy storage (LHTES) at the cylindrical shell surface only
The pressure inside the vessel can sometimes become higher than the pressure of the charging steam during the simulation, because the measured pressure of the charging steam is used to determine the specific enthalpy of the charging and the charging mass flow is given
Summary
The optimal use of energy resources, especially renewable energy, requires a certain level of flexibility in an industrial production system. This model, which is an extension of the model presented by Dusek and Hofmann [10,11], can be used to study the interaction between the different storage parts This extension applies different heat transfer coefficients for each water phase inside the RSS vessel. One way is to assume that the two-phase fluid at the internal side of the vessel is in a thermodynamic equilibrium at all times which means that liquid and steam have the same temperature [7,8,12] Another approach is presented by Stevanovic et al [13,14], in which no equilibrium is assumed to model the RSS. Zauner et al [23] tested two approaches for modeling a hybrid sensible-latent heat storage where the PCM is placed inside tubes of a shell-and-tube arrangement and the heat transfer fluid (thermal oil) flows around these tubes. The presented model allows a first estimation of the interaction of the two combined storage types, which is illustrated by the simulation results of a hybrid storage example
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