Latent heat thermal energy storage system with pillow-plate heat exchangers topology – Assessment of thermo-fluid dynamic performance and application potential

This research investigates the novel concept of pillow plate latent heat thermal energy storage (PP-LHTES) for storing process heat and/or waste heat at medium temperature, up to around 200 °C, and with a focus on mobile TES applications, such those in the maritime sector. The work introduces a novel methodology that combines computational fluid dynamics (CFD) with reduced-order modelling (ROM) techniques to evaluate the thermo-economic performance of PP-LHTES at the prototype scale (∼102 kWh) and predict its potential at full scale (∼MWh). These are the key aspects of novelty of the research. The study focuses on the impact of key technical factors, including the selection and thermophysical properties of the phase change material (PCM), its melting temperature and latent heat of fusion, the operating temperature, and the flow rate of the heat transfer fluid. Furthermore, the cost-effectiveness of PP-LHTES was examined by evaluating nine design parameters, such as the number of pillow plates and the cost per unit of PCM. Findings indicate that PP-LHTES appear to have a competitive advantage in volumetric energy storage density at the system level (∼89 kWh/m³), making it more compact than other LHTES solutions (∼53 kWh/m³) with a similar specific capital cost (∼200 €/kWh). The PP-LHTES module weighs 500 kg, occupies 0.25 m³, and provides an energy storage capacity of 17 to 22 kWh. The scalability of the design is investigated and results emphasize the its versatility. The mass-averaged volumetric energy storage density is comparable to existing LHTES systems (∼50 kWh/t). This is due to the distinctive design of pillow plate heat exchangers, which integrate heat transfer fluid channels and extended heat transfer surfaces into a compact structure. This design increases energy density at the system level, reduces the overall footprint, and enhances the feasibility of deploying TES devices in end-user applications.