Development of Surrogate Models for Latent Thermal Energy Storage Systems with Macro-encapsulated Phase Change Material

• Applicant: Dr.-Ing. Andreas König-Haagen
• Subject Area: Technical Thermodynamics
• Term: from 2020 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 444616738

So far, only highly simplified models are available for the simulation of a complete latent thermal energy storage with macro-encapsulated phase change material (PCM). However, extensive preliminary work has shown that single capsules of these storage units can already be described satisfactorily with the aid of CFD simulations. But the CFD simulation of a complete storage unit cannot be realized due to the required computing and storage capacity. The aim of this project is therefore to derive surrogate models based on CFD models which precisely predict the phase change processes in latent thermal energy storage systems with macro-encapsulated PCM, but require only a small fraction of the computational effort of a complete CFD simulation. The surrogate models to be developed are divided into two groups. The first group consists of data-fit surrogate models which can be subdivided into CFD surrogate models and real-time surrogate models. In the CFD surrogate models, the heat transfer fluid is explicitly simulated, whereas the capsules are considered with the help of boundary conditions and the data-fits coupled to them. The real-time surrogate models, on the other hand, approximate the behavior of the entire storage unit using data-fits. The second group of surrogate models is based on a projection of a high-resolution model onto a subspace, which greatly reduces the number of equations to be solved. This method is first applied to Stefan problems in MATLAB and then transferred to CFD simulations of latent thermal energy storage units with macro-encapsulated PCM. In the context of this project the following questions are to be answered:1. To what extent are adjustments to existing CFD models necessary in order to be able to derive surrogate models for latent thermal energy storage units with macro-encapsulated PCM?2. How large are the deviations between surrogate models and CFD models for the simulation of a single capsule?3. Are projection-based surrogate models suitable for application to latent thermal energy storage units with macro-encapsulated PCM and latent thermal energy storage devices in general?4. How close is the agreement between surrogate models and test results for a complete storage system?5. Are the deviations from simplified to detailed surrogate models significant in relation to the deviations to the experiments?6. How do the boundary and initial conditions affect the three points mentioned above?7. What influence does the choice of the transferred parameters have on the effort involved in creating the surrogate models and the computational effort as well as accuracy of the simulations performed with the surrogate models?

• DFG Programme: WBP Fellowship
• International Connection: Spain
• Host: Professor Koldobika Martin Escudero