# Edible Oils as Practical Phase Change Materials for Thermal Energy Storage
## 3 Results and Discussion
### Thermal Properties of Coconut Oil
Moreover, compared to V-CNO which has a strong coconut odor, especially when heated above its melting point, molten R-CNO has only a very subtle coconut odor. Figure 4: Latent heats of fusion, \(\Delta_{\text{fus}}H\), (in blue) and melting temperatures, \(T_{\text{mpt}}\), (in red) of (**a**) refined coconut oil (R-CNO) and (**b**) virgin coconut oil (V-CNO) as functions of thermal cycle. Although a small change was observed after the first cycle, all values were within the uncertainties of the measurements over the 200 melt-freeze cycles. The solid lines correspond to the average values of \(\Delta_{\text{fus}}H\) and \(T_{\text{mpt}}\) (calculated from the first 20 heating curves of a fresh sample) and the dashed lines show the range of their uncertainties: \(\pm\) 10% for \(\Delta_{\text{fus}}H\) and \(\pm\) 1.5 \({}^{\circ}\)C for \(T_{\text{mpt}}\). Figure 5: DSC thermograms of R-CNO and V-CNO after 5 and 200 melt-freeze cycles show similar changes in melting (endothermic) peaks in response to thermal cycling and similar melting behavior for a given cycle but different solidification (exothermic) behavior for the two types of coconut oil. The cooling curves of Figure 3a and Figure S5 in Supplementary Materials show that R-CNO supercools in the DSC, with a significant difference between the peak melting and the peak solidification temperatures, up to 19 K for the sample measured at a rate of 10 K/min (Figure 3a). This difference became less (\(\sim\)10 K) when the sample was cooled at a slower rate (i.e., 0.5 K/min, Figure S5c,d in Supplementary Materials) or when comparing the onset of the melting with the onset of the solidification temperatures. Nevertheless, the supercooling measured by DSC is significant and could be detrimental for R-CNO as a TES material given that the enthalpy stored upon melting at 24.5 \({}^{\circ}\)C would not be fully recovered at these cooling rates with this sample size unless R-CNO was cooled to below 10 \({}^{\circ}\)C.  
However, supercooling can be influenced by sample size, so to further investigate the supercooling of R-CNO, we measured the heating and cooling curve of a large sample (15 mL) of R-CNO as described in Section 2.2. Prior to these measurements, we melted (by hot air) and solidified (by cold water bath) the sample of R-CNO a total of 10 times. For the heating curve measurement, the sample was heated from 18 to 28 \({}^{\circ}\)C and the range of the solid-liquid transition was determined by visual inspection (appearance of liquid in the test tube) and from changes in the slope of the temperature-versus-time curve (Figure S6 in Supplementary Materials). For the cooling curve measurement, the solid sample was heated from its equilibrium temperature (room temperature, \(\sim\) 21.5 \({}^{\circ}\)C) to 40 \({}^{\circ}\)C by hot air and then left to cool by ambient air (Figure 6). The temperature-versus-time curve measured on heating (Figure S6 in Supplementary Materials) showed that the melting temperature range of the 15 mL R-CNO sample was 21-27 \({}^{\circ}\)C. The sample started to melt as its temperature reached \(\sim\)21 \({}^{\circ}\)C, as recorded by the probe placed at the middle of the sample (the ambient temperature measured close to the sample was 28 \({}^{\circ}\)C). When the temperature of R-CNO reached 24.7 \({}^{\circ}\)C, all the sample had melted and appeared as viscous, opaque liquid. At \(T\) = 27.2 \({}^{\circ}\)C, the melted R-CNO sample became a transparent liquid. This melting point range agrees well with the DSC results (Figure S5a-c in Supplementary Materials), indicating that melting is not so prone to sample size influence. The cooling curve of the R-CNO sample (Figure 6) showed that the temperature decreased to \(\sim\)22.5 \({}^{\circ}\)C then increased to 23.4 \({}^{\circ}\)C. This increase in temperature started as the liquid sample became more opaque and viscous, indicating the start of the solidification, with corresponding exothermicity and increase in temperature.