Characteristics of volume expansion during solidification in water-based phase change materials through capillary adsorption shaping

The practical application of naturally occurring water-based phase change materials (PCMs) for cold energy storage is hindered by the risk of structural cracking and potential leakage caused by volume expansion, particularly when deployed in confined spaces. In this study, cellulose sponges were employed to absorb the water-based PCMs, forming shaped composite PCM pieces through capillary action. Each shaped piece was encapsulated in a polymer plastic film bag to prevent leakage during the phase change process. The volume expansion coefficient of phase change (ξ) was experimentally evaluated. The results demonstrate that the composite PCMs containing pure water and NaCl solution exhibit maximum ξ values of 1.99 % and 2.4 %, respectively, which are substantially lower than that of pure water (9 %). A fractal model was developed to predict the effective thermal conductivity (ETC) of the composite module and validated against experimental results. The findings reveal that the ETC exceeds 0.2 W/(m·K) when the liquid saturation is higher than 52.87 %. At a given saturation level, the porosity and thermal conductivity of the sponge were found to be the dominant factors influencing the ETC of the composite PCM. This study facilitates the modular application of water-based PCMs in cold energy storage systems.