Definition of a new set of parameters for the dynamic thermal characterization of PCM layers in the presence of one or more liquid-solid interfaces

The objective of the research is the definition of a new set of parameters to evaluate the effective dynamic thermal behavior of a layer subject to phase change (PCM) that, for the effect of non-sinusoidal periodic boundary conditions, characterizing the external walls of air-conditioned buildings, give rise to the formation of one or more melting or solidification bi-phase interfaces. Such bi-phase interfaces originate on the boundary surfaces, or are always present and fluctuate within the layer. Defined parameters are to be used for the thermal design of innovative walls containing a PCM layer, targeting the reduction of power peaks entering the environment, in order to reduce the energy requirements and even to improve the indoor thermal comfort. The study has been developed by a finite difference numeric calculation model, which explicitly determines, the number and the position of the bi-phase interfaces that originate in the layer and the temperature and the heat flux fields. The methodology developed allowed us to determine the dynamic characteristics, for each month of the year, of PCM layers with different melting temperatures and thermophysical properties and subject to climatic conditions of two locations, one with a continental climate and the second one with a Mediterranean climate. In particular, it was found that all defined dynamic parameters, irrespective of locality and of PCM type, are related to the latent storage efficiency and, furthermore, some calculation correlations between the dynamic parameters were obtained. Finally, the results show that it was sufficient to reach the phase change in a portion of the layer of about 35% to obtain excellent dynamic thermal performance