The following study investigated the melting behavior of coconut oil as a phase-change material in shell-and-tube and shell-and-coil thermal energy storage systems. The primary objective was to deepen the understanding of PCM melting dynamics under varying boundary conditions, aiming to optimize TES designs for renewable energy applications. This research addresses a gap in understanding how different heat-transfer configurations and boundary conditions affect melting efficiency. Experimental setups included two distinct heat-transfer surfaces in a cylindrical shell—a copper tube and a copper coil—tested under constant wall temperatures (34 °C for the tube, 33 °C for the coil) and constant heat flux (597 W/m² for the coil). Findings reveal that melting under constant heat flux takes approximately twice as long as under constant wall temperatures, underscoring the critical role of heat-transfer conditions in TES performance. The liquid fraction was estimated using two approaches: image-based analysis and the volume-averaged temperature method. The former proved less reliable due to geometric limitations, particularly when the heat-transfer surface was distant from the shell wall. Conversely, the latter yielded higher accuracy, especially in the shell-and-tube setup. Due to the scarcity of correlations for constant heat-flux conditions, the novel contribution of this work is the development of a modified semi-empirical correlation for the shell-and-coil TES system. For this purpose, an existing model, which demonstrated strong alignment with experimental data, was adapted. The findings suggest that slower melting under constant heat flux could benefit applications needing sustained heat release, like solar energy systems. Future work could investigate additional PCMs or novel geometries to further improve TES efficiency and scalability.

Various types of heat pipes are available to purchase off the shelf, from various manufacturers, but most of them have strictly defined geometry and technical parameters. However, when there is a need to use a heat pipe (HP) with an unusual size and shape or working conditions other than the standard ones, it becomes very costly to order them from manufacturers, especially in small quantities, and only a few producers are willing to fulfill such an order. This paper presents a detailed description and step-by-step method of manufacturing and testing a low-cost HP with specific properties and geometry, cooperating with a modular heat recovery system based on the use of phase change materials (PCM) for electromobility applications. The presented heat pipes were made entirely by hand, primarily with the use of basic workshop tools, without the use of specialized and automated CNC machines. Utensils used during the process were either made by hand or using desktop FDM 3D printers. During the evaluation of heat pipes’ performance within PCM (coconut oil), simple statistical functions were used. One-dimensional and two-dimensional histograms were used to visualize data obtained during this research. The presented method allows the manufacturing of heat pipes that are, on average, able to melt about 35% more PCM than an empty copper pipe with the exact same geometry. The HPs’ performance in coconut oil was evaluated on the basis of their future applications.