# On the Use of Infrared Thermography for the Estimation of Melting Enthalpy
## 3 Results  
As each sample studied with the IRT-based method is represented by an important number of pixels, different approaches may be considered for the calculation of the enthalpy. The first approach (Case 1) would be to consider the signal of the sample, as the average signal of all the pixels constituting the sample, as seen in Figure 2a. The second method (Case 2) would be to treat the signal of each pixel independently and consider the melting enthalpy of the sample as the average enthalpy obtained for all the pixels. Figure 2b shows that all pixels do not have the same signal trend. If we take a look at Figure 2c illustrating the average distribution of the signal inside a sample of Myristic acid, one can notice that the outer rim of the sample is characterized by significant deviations in comparison with the rest of the sample. This deviation may be due to geometrical aberrations from extreme viewing angles, to misinterpretation of the sample contour during image treatment process (associating the crucible or the support plate to the sample) or to the effect of a reflection of the environment (crucible or support plate) on the sample. This observation can be made for all samples, and therefore, we considered a third case (Case 3) identical to Case 2 but without taking into account pixels in the outer rim. As reliably knowing which pixels belong to the sample is not conceivable, about 15% of the pixels whose signal deviate the most from the mean were deleted. This percentage was chosen to be sure to include erroneous pixels while limiting the amount of useful data lost. As seen in Figure 2d, the signals of the remaining pixels are more uniform and closer to the average signal. The melting enthalpies obtained with the IRT-based method in the three cases, with DSC measurements and as stated in the literature [23; 33; 35; 37; 42; 43; 44; 45], are reported in Table 2.  
In the first case, significant errors were obtained with the IRT methods by considering the average signal of the pixels in the sample. The calculated melting enthalpy appears to be acceptable for the LA+MA and PA+SA eutectic mixtures, but relative deviations as high as \(\Delta H_{m}\) (\(\
icefrac{{\text{V/g}}}{{\text{V/g}}}\)) are not significant. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Literature**[23; 33; 35; 37; 42; 43; 44; 45]} & \multicolumn{2}{c}{**DSC (This Work)**} & \multicolumn{2}{c}{**IRT (This Work)**} \\ \cline{2-9}  & \(\mathbf{T}_{m}\) (\(\
icefrac{{\text{{}^{\circ}}}}{\text{C}}\)) & \(\mathbf{\Delta H}_{m}\) (\(\
icefrac{{\text{{}^{\  
as 50% can be obtained for the MA+SA eutectic sample. Although the signal appears to remain rather linear between the solid and liquid state, the average signal is characterized by a rather important noise level. This noise may induce errors during the interpolation of the sample temperature during phase change. Treating the signal of each pixel individually seems to considerably improve the accuracy of the melting enthalpy calculation. For the LA+SA eutectic blend, for example, the relative deviation went down from 32.2% to only 2.1%. For the LA+PA eutectic sample, the relative deviation becomes 0.1% instead of 18.6%. Although the estimation for the MA+SA and MA+SA samples is still rather high, we are now limited to an 18.0% relative deviation, which is acceptable for a first estimation. This gain in performance is likely due to the fact that by making the calculation on each pixel individually, we can consider each pixel as a sample within the sample, with its own dynamic and temperature dependence of the emissivity. This consideration allows accounting for temperature inertia within the sample and compensates for the non-uniformity in temperature in the sample. Figure 2c illustrates this aspect well and shows an infrared signal distribution matching the shape of the sample, therefore suggesting a possible temperature gradient. The effect of omitting outer rim pixels is not very pronounced.