# Melting of Paraffin Waves Embedded in a Porous Matrix Made by Additive Manufacturing
## 1 Introduction
[PERSON] and [PERSON] [7] presented an experimental study on the phase change process of paraffin, as well as of calcium chloride hexahydrate, as PCMs embedded in metal foams and in expanded graphite. Experimental results revealed that the addition of a porous insert, either metal foam or expanded graphite, can enhance the heat transfer rate of the PCM. Other works related to the melting of PCM embedded in metal foams can be found in [8; 9; 10; 11; 12]. Instead of random structures, which are typical of metal foams, periodic structures can be generated by means of additive manufacturing technology, allowing the choice of every single detail of the sample to be printed. Different structures, such as Kelvin cells, Weaire-Phelan cells, or body-centered or face-centered cubic (BCC or FCC) cells, were reported in the literature to simulate the random structure of foams. Most of these studies were numerically carried out. [PERSON] et al. [13] carried out CFD simulations of conjugate heat transfer considering five periodic foams represented by Kelvin cell-lattice structures to be used as catalyst carrier, and they found that the strut diameter and the solid thermal conductivity were the key parameters to improve heat transfer and to reduce hot spots. [PERSON] et al. [14] compared CFD results of pressure drop and mass transfer coefficient of structures made by Kelvin cells and by micro-computed tomography scans of open-cell foams. Based on the numerical results, the authors demonstrated that Kelvin cells were a valid model to study real foams for porosities higher than 80%; in addition, Kelvin cells had clearly more favorable mass transfer to pressure drop trade-off. Other numerical studies of Kelvin cell structures can be found in [15; 16; 17]. The Weaire-Phelan model was considered by [PERSON] et al. [18], who numerically investigated non-isothermal solid-gas flows through an idealized metal foam heat exchanger, proving that the Weaire-Phelan model can be used as an alternative to the real metal foam sample. The Weaire-Phelan model was implemented by [PERSON] and [PERSON] [19] to simulate the melting phase change of paraffins at the pore-scale with volume change in high porosity open-cell foams. BCC based structures were initially studied by [PERSON] et al. [20], who computed the fluid and heat flow in BCC periodic structures, obtaining the effective thermal conductivity, pressure drop, and heat transfer coefficient. The numerical results were compared against existing experimental measurements and semiempirical models based on data related to metal foams. Later on, the same authors [21] extended the study to other structures, such as FCC and A15 structures. A numerical study aimed at investigating the melting of paraffins inside a BCC structure was carried out by [PERSON] et al. [22]. The numerical model was validated with experimental values from the literature. The results indicated that the decrease in the porosity resulted in an increase in the effective thermal conductivity of the metal foam, which makes the heat diffusion in the composite material faster than that in pure paraffin. Furthermore, a small pore diameter well uniformed the melting front and the temperature inside the composite structure. As it can be noticed from this introduction, many of the works related to periodic structures are numerically conducted, and no experimental work on periodic structures similar to those previously reported can be found in the open literature. However, the recent developments in additive manufacturing (AM) technology permit the creation of periodic structures from CAD models, making possible experimental tests besides numerical simulations. This paper reports some experimental results on the melting of three different paraffin waxes, namely RT42, RT55, and RT64 HC, inside a modified BCC structure with a base cell having an edge of 5 mm. The entire periodic structure has a square edge of 100 mm, and a thickness of 20 mm, and it is tested in an upright position.