Phase Change Materials (PCMs) are characterized by large thermal energy storage densities. However, their low thermal conductivity hinders the heat diffusion during the phase change process, increasing the charge and discharge times of the energy storage. Among the methods studied in the literature to enhance the PCM thermal response, the coupling of porous metallic media is one of the most promising. According to previous numerical and scale studies available in the literature, the heat transfer into the matrices can be dominated either by conduction or convection. In the literature, experiments on melting fronts are mainly conducted by imposing a constant heat flux. The novelty of this work is to perform tests at constant wall temperatures to detect the melting front propagation. The first type boundary condition allows to track the PCM surface temperature distribution temporal evolution at fixed Rayleigh numbers
The experimental facility consists of a polycarbonate cubic box containing the composite matrix. A mica heater provides the heat load on one side of the test cell. A PID controller keeps the wall temperature constant during the experiment. Three thermocouples acquire the temperature at different locations in the matrix bulk. A Zinc-Selenide window (transparent to the long wave infra-red spectrum) allows acquiring the evolution of the foam/PCM temperature distribution at the matrix side with a Long Wave InfraRed camera. By changing the imposed temperatures at the wall, the PCM melting and solidification front at known Rayleigh numbers is dynamically recorded. An in-house MATLAB^® algorithm analyses the infrared images and traces the evolution of the melting front position.
The experimental observations quantify, in relationship with the Rayleigh number, the role of the natural convection among the heat transfer mechanisms involved in the melting process within the composite matrices and provide data to be compared with theoretical and numerical models.