A review on container geometry and orientations of phase change materials for solar thermal systems

•Effect of container geometries and orientations on PCM melting are reviewed.•Stainless steel and aluminum are selective PCM container materials.•Fins provide a significant melting enhancement of PCM than nanoparticles.•Vertical PCM containers produce effective melting than horizontal orientation.•Thermal energy storage improves the productivity of solar collectors. Phase change materials (PCM) are employed to store thermal energy in solar collectors, heat pumps, heat recovery, hot and cold storage. PCMs are encapsulated primarily in shell-and-tube, cylindrical, triplex-tube, spherical, rectangular, and trapezoidal containers. This review focuses on PCM's melting and solidification in different container geometries and their orientations for heat storage in solar thermal systems. The thermal storage performance of PCM depends upon fins, nanoparticle addition, container geometry, and orientations. The operating parameters such as heat transfer fluid temperature, flow rate, and initial temperature of storage material play a dominant role in PCM melting. The use of fins and nanoparticles in the shell-and-tube containers increase the melting rate to 71 and 62.6%, whereas the change in container orientation improved the melting rate up to 47.5%. The addition of fins increases the melting rate significantly, followed by nanoparticles and the container's orientation. The variation of the container's geometry and its orientation improves PCM melting passively. Container materials are preferably stainless steel and aluminum for organic and inorganic PCMs to avoid corrosion. PCM container geometry and orientations are practical passive heat transfer enhancement techniques in the long-term compared to adding nanoparticles and attaching fins. This review focuses on significant aspects of PCM container designs for practical solar thermal storage.