Comparison of RC-model and FEM-model for a PCM-plate storage including free convection

Latent heat storage is one option to increase the efficiency and reduce CO2-emissions of process heat applications in the temperature range between 100 °C and 250 °C. In the present study a latent heat storage system based on flown through heat exchanger plates according to the FracTherm®-design is examined. The sugar alcohol d-mannitol is used as PCM. A simplified capacity resistor (RC) simulation model is developed. In contrast to common RC-models, this model can simulate free convection of the storage material in liquid phase during charging. Additionally, a detailed physical simulation model based on the Finite-Element-Method is developed and validated with measured data. A verification of the new RC-model and the FEM-model is carried out. The mean deviation of the outlet fluid temperature between both models is 0.62 K. The mean deviation of the PCM-temperature is 0.85 K. Due to the 20 to 30 times shorter simulation time, the RC-model is well suited for dimensioning and optimizing plate type heat exchangers for latent heat storages.