# Edible Oils as Practical Phase Change Materials for Thermal Energy Storage
## 2 Materials and Methods
### Experimental Methods  
The melting temperatures, \(T_{\text{mpt}}\), and latent heats of fusion, \(\Delta_{\text{fus}}H\), of the edible oils were determined with a TA Instruments Q200 differential scanning calorimeter (DSC, TA Instruments, New Castle, DE, USA). Analysis of DSC data was performed using Universal Analysis 2000 computer software (version 4.5A, TA Instruments-Waters LLC 1998-2007, New Castle, DE, USA). The DSC was calibrated prior to each set of experiments by measuring \(\Delta_{\text{fus}}H\) and \(T_{\text{mpt}}\) of a high-purity indium standard (\(\Delta_{\text{fus}}H\) = 28.7J g\({}^{-1}\) and \(T_{\text{mpt}}\) = 156.6 \({}^{\circ}\)C [40]). For each DSC measurement, a sample of mass between 10 and 15 mg was hermetically sealed in a standard DSC aluminum pan and measured in a He gas atmosphere, at a gas flow rate of 25 mL min\({}^{-1}\). The latent heat of fusion was determined from \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Product** & **Abbreviation** & **Cost (US \$/kg)** & **Main Composition** \\ \hline Parkay@Margarine & M1 & 2 & \begin{tabular}{c} Non-hydrogenated oil blend (68\%), \\ modified milk ingredients (18\%) and \\ water (12\%) \\ \end{tabular} \\ \hline Imperial@Margarine & M2 & 2 & \
\begin{tabular}{c} Non-hydrogenated oil blend (60\%), milk \\ ingredients and water \\ (unspecified amounts) \\ \end{tabular} \\ \hline Crisco@Vegetable Shortening & VS & 4 &
\begin{tabular}{c} Fully and partially hydrogenated soybean \\ and palm oils, mono and diglycerides \\ \end{tabular} \\ \hline Refined Coconut Oil (Suraj@brand) & R-CNO & 6 & Coconut oil \\ \hline Virgin Coconut Oil (Our & V-CNO & 11 & 100\% virgin coconut oil \\ Finest@brand) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Edible fats and oils tested in this study. The abbreviation is the sample name used in the text. The cost is the approximate average retail cost of the brands tested in this study and the composition is from the ingredients specified on the product label. measurements performed at heating rates of 10 K/min and the melting temperature was determined from measurements at rates of 2 K/min, as recommended for high accuracy [41]. Typical uncertainties for this DSC system are \(\pm\) 10 % for \(\Delta_{\text{fus}}H\) and \(\pm\) 1.5 \({}^{\circ}\)C for \(T_{\text{mpt}}\) and at least 3 samples from each PCM were measured, and their values of \(\Delta_{\text{fus}}H\) and \(T_{\text{mpt}}\) were within these uncertainties. The melting temperature of a material from a DSC experiment corresponds to the onset of the melting peak, \(T_{\text{onset}}\)[41]. However, due to the large number of components in the edible oils which broaden melting, the onset of melting was not well defined. For all samples here, the peak temperature will be reported as \(T_{\text{mpt}}\), as is conventional for a blend PCM [42]. Moreover, it is important to note that the melting and crystallization behavior of fats and oils can be complex, with a strong dependence on the heating rate and maximum heating temperature [26]. However, our DSC measurements and analysis focused on the determination of \(\Delta_{\text{fus}}H\) and \(T_{\text{mpt}}\) from experimental conditions as close as possible to real-life solar thermal applications. The stabilities of \(\Delta_{\text{fus}}H\) and \(T_{\text{mpt}}\) of virgin coconut oil (V-CNO) and refined coconut oil (R-CNO) after repeated melt-freeze cycles were determined from cycling experiments conducted on bulk samples. About 3 g of each type of coconut oil was placed in a screw-cap glass vial and heated in an oven to 50 \({}^{\circ}\)C until melted and then cooled to 0 \({}^{\circ}\)C in an ice-water bath until solidified. No attempt was made to exclude air from contact with the samples. In total, 200 melt-freeze cycles were carried out for each type of coconut oil, where one cycle consisted of a heating step from 0 to 50 \({}^{\circ}\)C (completely liquid) followed immediately by a cooling step from 50 to 0 \({}^{\circ}\)C (completely solid).