Multi-Scale Modelling of a Large Scale Shell-and-Tube Latent Heat Storage System for Direct Steam Generation Power Plants

The ability of Phase-Change Materials (PCM) to store steam at a constant or almost constant temperature makes them attractive for the heat storage systems of Direct Steam Generation (DSG) solar plants. The design of a shell-and-tube PCM storage module requires to know the influence on heat transfer of the natural convection movements in the liquid PCM. This work presents a multi-scale modelling approach of a storage module taking into account the effects of these small-scale movements in a module-scale design model. A lute 3D model of the PCM fusion during steam charge is used to establish a local 1D correlation for the heat transferred between the liquid water / steam heat transfer fluid (HTF) inside the tubes, and the PCM outside the tubes. A generic design model is then built using this correlation. The methodology was tested on the case of a prototype scale storage module available at CEA Grenoble. The design model reproduces the heat transfer rate predicted by the CFD model, and measured experimentally during a test charge, while allowing 10 to 90 times shorter computational tunes than the CFD model.