# Melting of Paraffin Waves Embedded in a Porous Matrix Made by Additive Manufacturing
## 3 Test Module and Paraffin Waves  
The structure was experimentally tested in an upright position. The module was laterally heated by means of an electrical heater, which is a copper plate inside which a nickel-chrome wire resistance was inserted. This heater is placed in contact with one of the two plates of the structure, and a thermal paste was used between the heater and the plate. The heater is connected to a DC power supplier. Three different heat fluxes are supplied: 10, 15, and 20 kW m\({}^{-2}\), to which heat flow rates of 100, 150, and 200 W correspond. The supplied heat flow rate is calculated as the product between the electrical differential potential (EDP) across the heater and the current flowing into the heater. The EDP is directly measured, whereas the current is measured by means of a reference electrical resistance (shunt). The shunt is in series with the heater, and the measurement of the EDP across the shunt (whose resistance is known) permits the calculation of the current flowing in the electrical circuit. The supplied electrical power can be measured with such a technique with an uncertainty of \(\pm\)0.13%.  
Two bakelite plates were glued to the structure, one to the bottom side and one to the rear side, and they act both as an insulating material and as containment for the paraffin. A glass window is glued to the front side, acting as containment and as a window to observe the melting front during the experimental tests. A schematic is reported in Figure 2(a).  
Figure 3: (**a**) Structure with bakelite plates and glass window; (**b**) entire module inside the Teflon case.  
Figure 2: Porous matrix made by modified BCC cells between the two plates.  
The entire module with the heater is placed inside a Teflon case (see Figure 3b) to limit as much as possible the heat losses to the external ambient. The top part is not covered to permit the filling procedure of the paraffin.  
Three holes were drilled in the right plate, and thus also in the Teflon case, as reported in Figure 3b: these holes permit us to host three T-type thermocouples that measure the temperature of the paraffin inside the structure. The tips of these thermocouples reach the centerline in the middle of the porous matrix at 25, 50, and 75 mm from the bottom side of the structure. These thermocouples have an uncertainty of \(\pm\)0.5 K. All the implemented thermocouples are connected to a Kaye 170 ice point temperature. All the signals, i.e., of the thermocouples and of the two EDP measurements, are connected to the data acquisition system (DAQ).  
Three different paraffins were implemented for the experimental tests as phase change material. These paraffins have different melting temperatures, allowing us to understand the effect of this parameter on the thermal performance during the heating process. The paraffins have melting temperatures of 42, 55, and 64 \({}^{\circ}\)C, whose values are compatible with electronics cooling applications. The paraffins are named RT42, RT55, and RT6 HC, and the number that appears in each name represents the correspondent melting temperature, even if it would be better to consider a melting temperature range instead of a specific melting temperature. These paraffins, supplied by Rubitherm GmbH, are chemically inert and stable after multiple cycles of melting and solidification. Some of the main thermophysical properties are reported in Table 1.