Numerical assessment of the impact of a PCM thermal conductivity on a storage system's performance

The thermophysical properties of phase change materials (PCM) are central to their selection as part of a thermal storage system (TES) and the design of the heat exchange system within the TES. The thermal conductivity is typically fairly low for most commonly used PCMs (from 0.2 to 0.4 W/m center dot K), which is an important consideration when designing latent heat energy storage systems (LHESS). Therefore, material scientists have been asking the question: by how much does the thermal conductivity of a PCM need to be increased to positively impact the design and performance of a TES? An answer to this question is not straightforward as it depends partly on other PCM thermophysical properties, on the type of heat exchange system geometry, on the mode of operation and on the targeted power/energy storage of the TES. This paper starts providing an answer to that question through a numerical study based on a simplified model of an experimental setup studied previously in the authors' laboratory. A model was created in COMSOL Multiphysics, initially validated against experimental results for various conditions, and used to study the impact of changing the thermal conductivity of the PCM (dodecanoic acid) on discharging power of the TES. The results show that even increasing the thermal conductivity of the PCM by a factor of 50 only leads to a maximum instantaneous power increase by a factor of 2 or 3 depending on the LHESS configurations.