No abstract

This paper investigates numerically the melting of n-eicosane inside horizontal cylinders. The cylinders are embedded in a storage tank where hot air flows parallel to the cylinders during the charging process. The 2D mathematical model is based on the enthalpy-porosity method. To solve the conservation equations (continuity, momentum and energy), a CFD commercial software is employed. Numerical predictions are validated by comparison with benchmark results available in the literature. The melting characteristics of n-eicosane in horizontal cylinders are presented. The phase change dynamics, temperature distributions and melt flow patterns are analyzed. The effect of heating rate is investigated. Results show that after certain time natural heat convective currents have not the same positive effect on the melting rate due to the continuous heating of the upper melt in the enclosure; which contributes to lower the thermal charging time. Low heating rate (h=25 W m-2 K) intensifies this negative effect.

Encapsulation of Phase Change Materials (PCM) for energy storage, thermal comfort and many other energy applications is receiving much attention due to the fact that material, physical characteristics and geometry of the container can affect drastically the thermal performance of the PCM. Phase change materials have usually low thermal conductivity which impairs their thermal charging and discharging characteristics. Different geometries were investigated including rectangular, cylindrical and spherical with and without extended surfaces to investigate the heat charge processes. Cylindrical geometries of circular sections were intensively investigated while cylinders and tubes with elliptic and elongated cross section received less attention, although they may have better thermal performance for thermal storage. The present numerical investigation is aimed at contributing to better understand the effects of the elliptic geometry and how the different geometrical and operational parameters can affect the thermal performance of the enclosed PCM. The present investigation reports the results of a numerical study on elliptic cylinders containing PCM under melting conditions. The 2D inward melting problem is modeled by using a CFD code. The numerical model is based upon the enthalpy-porosity method along with the finite control volume techniques. The numerical predictions are validated against available experimental results. The inward melting process is analyzed for two orientations of the elliptic enclosures. Due to the flow field effect namely the Rayleigh-Bénard convection, the numerical results showed that the horizontal elliptic enclosure have higher melting rate and hence lower total melting time compared to those of the vertical elliptic enclosure.