Direct Measurement of Liquid Fraction in Ice Melting

Nowadays, Phase Change Materials (PCMs) have become more and more interesting. The number of articles on PCMs is rising quickly: looking at Scopus, in the 90s less than 1k papers were published, while from 2010 to 2019 you can find around 13k papers and only in the last two years more than 6k papers have been published. This popularity is due to their upsides, for example, the possibility to reuse wasted heat, leading to a more environmental-friendly use of thermal energy, and counteracting climate changes and global warming. In this wave of new studies on PCMs, it is important to have effective tools to design proper Latent Thermal Energy Storage (LTES) systems and diagnose their operation. Computational Fluid Dynamics (CFD) can be one of these tools: the enthalpy-porosity method for liquid-solid phase change modelling has been validated many times against temperature and liquid fraction data. The experimental liquid fractions used for the validations is a difficult parameter to measure properly, especially for geometrically complex systems. In the present study, a novel methodology is proposed to analyse PCMs with a CFD approach, validated against time-resolved liquid fraction data from a X-ray computed tomography measurement system. This new methodology has been tested here, by melting the most common PCM in nature: ice/water system, and it showed a good agreement between numerical and experimental liquid fractions: the difference between the two is lower than 1 % in the middle of the melting process, i.e. when the algorithm to extract volume fractions from CT images works best because there is nearly the same amount of liquid and solid phases.