# Edible Oils as Practical Phase Change Materials for Thermal Energy Storage
## 3 Results and Discussion
### Thermal Properties of Coconut Oil
There was no significant difference between the average value of \(T_{\text{mpt}}\) determined from 20 heating curves at 10 K/min and the values determined at 2 K/min, and all values are within the uncertainty of \(T_{\text{mpt}}\) (\(\pm\) 1.5 \({}^{\circ}\)C) and in good agreement with the peak melting temperatures reported for coconut oil in the literature [25; 26; 31; 32; 33; 36]. Table 2 lists the values of \(\Delta_{\text{fus}}H\) and \(T_{\text{mpt}}\) of coconut oil determined in the present work and values reported in the literature. The DSC results for R-CNO and V-CNO show that coconut oil is potentially suitable as a PCM for thermal energy storage given its large latent heat of fusion (\(\geq\)100 J g\({}^{-1}\)) and its thermal stability after 200 melt-freeze cycles, contrasting with the results for margarine and shortening. The coconut oil \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference** & **Measurement Method** & \(\Delta_{\text{fus}}H\)/(J g\({}^{-1}\)) & \(T_{\text{mpt}}\)\({}^{f}\)C \\ \hline This work–refined coconut oil & DSC & \(105\pm 11\) & \(24.5\pm 1.5\) \\ (R-CNO) & & & \\ \hline This work–virgin coconut oil & DSC & \(106\pm 11\) & \(23.9\pm 1.5\) \\ (V-CNO) & & & \\ \hline
[25] & DSC & \(72.01\pm 0.21\) & \(24.73\pm 0.12\) \\ \hline
[26] & DSC & \(120.6\pm 2.0\) & \(21.05\) \\ \hline
[29] & T-history & \(249\) & not reported \\ \hline
[33] & DSC & \(97\) - \(102\) & \(26.2\)–\(26.7\) \\ \hline
[34] & DSC & \(103\pm 1\) & \(24\pm 1\) \\ \hline
[35] & DSC & \(115.3\) & \(23.9\) \\ \hline
[36] & DSC & \(110.4\) & \(26.78\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Values of the latent heat of fusion, \(\Delta_{\text{fus}}H\), and melting temperature, \(T_{\text{mpt}}\), of coconut oil determined in this work and as reported in the literature. Figure 3: DSC thermograms of (**a**) refined coconut oil (R-CNO) and (**b**) virgin coconut oil (V-CNO) measured at 10 K/min for Cycle 1 (first melt of a fresh sample) and after 5, 100, and 200 melt-freeze cycles. For both R-CNO and V-CNO, the widths of the endothermic (melting) and the shapes of the exothermic (solidification) peaks changed slightly after cycling but values of \(\Delta_{\text{fus}}H\) and \(T_{\text{mpt}}\) derived from the endothermic peaks of all cycles remain within the uncertainty of the measurements. (**c**) Regardless of the number of thermal cycles, the first melt DSC curve for each coconut oil sample featured a main peak and a shoulder peak that merged into a single peak in the subsequent melting curves (see also Figure S5 of Supplementary Materials). results are not surprising given that, unlike margarine and vegetable shortening, coconut oil is not a blend of oils with other additives. Coconut oil consists mostly of fatty acids, dominated by 47%-51% dodecanoic acid (aka lauric acid, [CH\({}_{3}\)(CH\({}_{2}\))\({}_{10}\)COOH]) [14; 15; 23], which are all very good PCMs [44; 45]. It is important to note that, of the pure saturated unbranched fatty acids, there are none with melting temperatures between 17 and 28 \({}^{\circ}\)C, and often eutectic mixtures of two or more fatty acids are prepared in order to obtain a PCM with \(T_{\text{mpt}}\) within this range [13; 21; 22; 44; 45]. This temperature range is particularly useful for thermal energy storage applications in buildings [3; 12; 46; 47; 48]. Conveniently, the melting point of coconut oil (24.5 \({}^{\circ}\)C) falls within this temperature range. The DSC results showed that there are only slight differences between the thermal properties of refined and virgin coconut oil: although there was an observable difference for their solidification behavior, their melting was almost the same, even after 200 thermal cycles (Figure 5). Therefore, in this work, we focus on further characterization of refined coconut oil because its retail cost is about half that of virgin coconut oil (Table 1), although the difference in price is less for bulk quantities and as commodities.