# Numerical Design and Laboratory Testing of Encapsulated PCM Panels for PCM-Air Heat Exchangers
## 3 Results and Analysis
### Laboratory Test
#### 3.2.2 Thermal Enhancement Factor (TEF)  
The pressure drop increase presented in the previous section was expected due to the introduction of ridges. However, to evaluate if the pressure drop increases effectively, or in other words, if the pressure drop increased in a lower rate than the heat transfer, both existing and new panel were compared with the flat panel using Equation (8). These results are presented in Figure 16; showing that the new panel with 8 mm gap presented the best performance with a TEF higher above 1.8 for the three Reynolds numbers tested with an average of 1.89. At low Reynolds number, (Re = 1954) the existing panel performed better than at higher airflows (Re = 4067 and 6061). However, the higher TEF is not higher than the new panel with 8 mm gap. The effectiveness of the new panel is shown more clearly according to the increase of the Reynolds number while the existing panel reduces to an average of 1.20. It is interesting to notice that the existing panel has a lower TEF (1.08 on average) when Re = 4067 and 6061 at 8 and 9 mm gaps. This result indicates the inefficiency of the existing panel at higher airflows where the introduction of bulges in the flat panel results in an increase of heat transfer at the same cost of an increase in pressure drop. Conversely, the highest TEF was found at Re = 6061 with 10 mm gap and represented an increase of 49.9% when compared to the existing panel (Table 8). Table 8 also shows that the highest increase in percentile when compared to the existing panel occurred at 8 mm gap and Re = 6061 and represented an increase of 84.4%. Furthermore, Table 8 also shows that improvements at any Reynolds number was found with a gap of 8 mm. Figure 16: Thermal Enhancement Factor of the existing and new panel with error bar showing the uncertainty of 8.6%. Figure 15: Nusselt number ratio between existing and new panel with flat panel with error bar showing the uncertainty of 7.9%. As a result, after heat transfer, pressure drop and TEF analysis, the new panel with a gap of 8 mm presented the best choice as it has the highest TEF on average (1.88) and the highest increase in heat transfer (20%, 94% and 124%, respectively, for Re = 1954, 4067 and 6061). The increase in pressure drop was expected due to ridges inclusions and corresponded to 44.7%, 65.7%, and 95.1%, respectively, for Re = 1954, 4067 and 6061. As the pressure drop is an important consideration the capability of the existing fan to provide the necessary airflow when the new panels are stacked in one, two or three TB was investigated. The results are presented in Figure 17.  
The results show a considerable increase in pressure drop. Table 9 shows an average increase of 345%, 258% and 380% when the pressure drop of the new and existing thermal batteries are compared. However, the higher heat transfer of the new panel will reduce the fan operation time at higher airflows. The results can also be seen in Figure 18 where the head curve of the fan is plotted with the results obtained from the laboratory tests and the simulations of shapes 11, 24 and 26. Figure 18 shows that the fan is capable to provide the airflow required when one, two or three TB are used. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Averaged Reynolds Number** & **8 mm** & **9 mm** & **10 mm** \\ \hline
1954 & 5.9\% & \(-\)15.1\% & \(-\)29.8\% \\
4067 & 66.7\% & 22.0\% & \(-\)8.9\% \\
6061 & 84.4\% & 48.9\% & 49.9\% \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Percentile increase in TEF from the existing to the new panel.