## 3 Results and Discussion
### Specific Heat Capacity, Thermal Diffusivity, and Thermal Conductivity
The EG's effect in increasing thermal conductivity is predominant in the cases of MPA and RT44 (more than 15 times), while, for RT35, is slightly higher than 8 times, as clear in Figure 10b. In any case, the thermal conductivities are in the range 0.25-0.45 W/m\(\cdot\)K for all of the neat PCMs, and they are increased above 4 W/m\(\cdot\)K in the composites. Errors in these measurements can arise from different applied pressures during specimen preparation or from improper EG impregnation, which strongly affects not only the bulk density but also the thermal diffusivity; a higher void fraction will reflect a lower thermal diffusivity because voids are excellent thermal insulators [39]. These obtained thermal conductivity values are compared in Table 4 with those obtained in representative studies in which EG was used to increase the PCM thermal conductivity. Both fatty acids and paraffins were considered with melting temperatures in the ranges 18-69 \({}^{\circ}\)C and 36-64 \({}^{\circ}\)C, respectively. Table 4 evidences the large amount of data related to the thermal conductivity of various PCM/EG composites with melting temperatures in the range 18 \({}^{\circ}\)C and 69 \({}^{\circ}\)C. The higher the EG content, the higher the thermal conductivity. The highest values of thermal conductivity, 8-24 W/mK, were obtained with the composition with 25% EG in stearic acid for applications at a high temperature (Tm 69 \({}^{\circ}\)C). Moreover, as is clear from Table 4, our vacuum impregnation and compaction process permits a thermal conductivity enhancement in the range 4-6 W/m\(\cdot\)K, higher than the majority of works in which the main production strategies consist of melt PCM mixing with EG. \begin{table}
\begin{tabular}{c c c c} \hline
**PCM Type** & **T\({}_{m}\)** & _EG Content_ & \(\lambda\) & _Year_ \\  & [\({}^{\circ}\)C] & **[wt.\%]** & **[W/m\(\cdot\)K]** & **[Reference]** \\ \hline Fatty acid (PA) & 68 & 8.0 & 0.8 & 2009 [51] \\ Fatty acid (CA-LA-PA) & 18 & n.a. & 0.7 & 2012 [52] \\ Fatty acid (LA-MA-PA) & 31 & 5.3 & 1.7 & 2013 [53] \\ Fatty acid (PA-SA) & 54 & 7.1 & 2.5 & 2014 [54] \\ Fatty acid (SA) & 69 & 15.0–30.0 & 7.5–23.3 & 2016 [55] \\ Fatty acid (SA base) & 53 & 5.0–20.0 & 1.5–3.2 & 2018 [56] \\ Fatty acid (SA base) & 53 & 2.0–10.0 & 0.8–3.6 & 2019 [57] \\ Fatty acid (MA) & 53 & 6.5 & 2.1 & 2020 [58] \\ Fatty acid (CA-SA) & 25 & 10.0–12.0 & 0.5–0.6 & 2021 [59] \\ Fatty acid (LA-SA) & 31 & 10.0–15.0 & 0.6 & 2022 [60] \\ Fatty acid (SA) & 68 & 8.0–12.0 & 3.3–6.5 & 2022 [28] \\ Fatty acid (SA) & 69 & 5.0–25.0 & 0.7–7.7 & 2022 [61] \\ Fatty acid (MA) & 54 & 4.0–6.0 & 2.3 & 2023 [62] \\ Fatty acid (CA-MA) & 19 & 5.0–20.0 & 0.3–1.2 & 2024 [63] \\ Fatty acid (PA) & 61 & 16.0 & 4.9 & 2024 [64] \\ Fatty acid (PA-SA) & 53 & 9.0–12.3 & 4.0–10.3 & 2024 [39] \\ Fatty acids & 62–66 & 2.0–6.0 & 0.3–0.5 & 2024 [65] \\ Fatty acid (MA-PA) & 48 & 12.3 & 4.7 & 2025 Present study \\ Paraffin & 64 & 2.0–6.0 & 0.3–0.5 & 2024 [65] \\ Paraffin & 53–57 & 6.0 & 1.0–1.3 & 2019 [66] \\ Paraffin & 50 & 8.0 & 0.8 & 2022 [30] \\ Paraffin & 36 & 10.0–30.0 & 5.3–6.0 & 2024 [67] \\ Paraffin & 37 & 12.3 & 4.0 & 2025 Present study \\ Paraffin & 45 & 12.3 & 6.0 & 2025 Present study \\ \hline \end{tabular} \(T_{m}\) = melting temperatures; \(\lambda\) = thermal conductivity value at room temperature (mainly 20–30 \({}^{\circ}\)C). CA capric acid; LA laurric acid; PA palmitic acid; MA myristic acid; SA stearic acid.  
\end{table} 
Table 4: Comparative thermal conductivity (\(\lambda\)) of PCM/EG composite based on fatty acid and paraffins at selected different melting temperatures.