Simulative Analyse zum Hystereseverhalten von Phasenwechselmedien in Latentwärmespeichern anhand des thermischen Leistungsverlaufs
Latent heat storages based on phase change materials (PCM) are able to store thermal energy almost isothermally, i.e. in a narrow temperature interval. This enables efficient use of low-exergy heat sources with low temperature levels. By using the solid-liquid phase change for energy storage, latent heat storages can be realized more compact with regard to small temperature strokes than with sensible storage media. PCMs are available for many temperature ranges. For successful system integration of PCM storages, the potential and limitations of this technology must be correctly taken into account already in the design and thus in the modeling stage. A special property of PCM is the hysteresis, which describes the phenomenon that the crystallization process takes place at a lower temperature than the melting process. The model-based consideration of the hysteresis behavior requires a high implementation effort, since it is necessary to toggle between two valid h(T)-curves with the aid of an additional hysteresis model. In model-based studies of PCM storage systems, the hysteresis is often neglected by assuming an averaged h(T)-curve. Since the neglect of the hysteresis does not follow any systematic process, verifiability of the correctness of this decision is limited. In the present work, a model of a PCM storage was built and validated using experimental data. The model was then used to compare and evaluate the calculated performance curves of 120PCMs each with and without the use of the averaged h(T)-curve. Finally, potential ordering criteria were investigated that can qualitatively account for the hysteresis behavior and correlate with the calculated deviations. The difference between the mean temperatures of the melting and solidification processes was found to be a reliable criterion.
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