•Visual experimental system is built to study the orientations effect on phase change.•The melting interface is observed in the experiment.•Inclination angle significantly affects heat transfer in pure phase change material.•Heat sink is designed using composite PCM without considering installation angle. Using paraffin as phase change material, the melting behaviors of pure phase change material and phase change material embedded in open-cell metal foams (composite phase change material) at different inclination angles are studied. Experimental system enabling continuous rotating is designed and built to explore the influence of inclination angles on phase interface evolution and temperature responses inside pure and composite phase change materials. Constant wall temperature is applied on one surface while others are thermally insulated. Experiments are carried out at angles of 0°, 30°, 60°, and 90° respectively. The effects of inclination on the melting behavior of phase change materials are analyzed by visualizing the solid-liquid interface and analyzing the temperature responses. Results demonstrate that the inclination angle has a great influence on the formation and development of natural convection during melting of pure phase change material, affecting the solid-liquid interface propagation and heat transfer rate. Compared with the case at 90°, the full melting time is reduced by 12.28%, 22.81% and 34.21% at 0°, 30° and 60°, respectively. However, when phase change material is melted in open-cell metal foam, heat conduction dominates, and inclination angle has little influence. Melting fractions at different inclination angles are the same and temperature curves at given points overlaps with each other.