# Numerical Design and Laboratory Testing of Encapsulated PCM Panels for PCM-Air Heat Exchangers
## 4 Conclusions  
Researchers have focused their attention to develop new PCMs or assess existing PCM encapsulations in different climates and environmental conditions. However, few of them focused their attention on the heat transfer between panel and air. This is essential to provide a ventilation system which takes advantage of the PCM-air heat transfer to increase its responsiveness. Focused on five KPIs, those of ease to manufacture, cost of production, rigidity, pressure drop and heat transfer, the present study performed a parametric analysis via CFD simulation. A set of 12 different geometries were analyzed using 3D CFD models to design a panel for a PCM-Air heat exchanger. One geometry and shape was selected as the most effective as it can double the heat transfer of the PCM-air side and holds 13.7% more PCM material when compared to an existing commercial panel. A further 12 variations and nine configurations were tested using 2D CFD models. The pressure \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**1 Thermal Battery**} & \multicolumn{4}{c}{**2 Thermal Batteries**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Melting**} & \multicolumn{2}{c}{**Solidifying**} & \multicolumn{2}{c}{**Melting**} & \multicolumn{2}{c}{**Solidifying**} & \multicolumn{2}{c}{**Solidifying**} & \\ \cline{2-9}  & **EP** & **NP** & **EP** & **NP** & **EP** & **NP** & **EP** & **NP** & **Average** (\(\sigma\))** \\ \hline Laboratory test (Wh) & 831.8 & 1015.8 & \(-\)725.6 & \(-\)1066.0 & 1472.3 & 2029.1 & \(-\)1508.6 & \(-\)2336.0 & \\ \hline
3 LC (Wh) & 817.5 & 1059.7 & 828.8 & 1074.3 & 1635.0 & 2119.4 & 1657.5 & 2148.6 & \\ \hline Difference (Wh) & \(-\)14.3 & 43.9 & 103.2 & 8.4 & 162.7 & 90.4 & 148.9 & \(-\)187.4 & \(\begin{array}{c}105.4\\ (\pm\)44.5 \\ \end{array}\) \\ \hline Difference & \(-\)1.7\% & 4.3\% & 14.2\% & 0.8\% & 11.1\% & 4.5\% & 9.9\% & \(-\)8.0\% & \(\begin{array}{c}9.4\%\\ (\pm\)6.7\%) \\ \end{array} \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Thermal load for melting and solidifying. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **Time (h)** & **Increase (in\%)** \\ \hline \multirow{3}{*}{1 TB} & \multirow{3}{*}{Melting} & EP 1 TB & 3.5 & \multirow{3}{*}{86\%} \\  & & NP 1 TB & 6.5 & & \\  & & EP 1 TB & 4.0 & & \\  & & NP 1 TB & 5.5 & & \\ \hline \multirow{3}{*}{2 TB} & \multirow{3}{*}{Melting} & EP 2 TB & 4.5 & \multirow{3}{*}{100\%} \\  & & NP 2 TB & 9.0 & & \\ \cline{1-1}  & & EP 2 TB & 5.0 & & \\ \cline{1-1}  & & NP 2 TB & 8.5 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Melting and solidifying times for one and two thermal batteries. drop increased 3.3 times and therefore more power will be necessary to provide the same airflow. However, the heat transfer increase on the PCM-Air side can lead to a reduction in the required airflow. The selected panel was fabricated and three laboratory tests validated the simulations. The first laboratory test analyzed the heat transfer with different gaps between the panels and Reynolds numbers. For the highest Reynolds number tested (6061), the Nusselt number increased by 124, 72 and 77%, when compared to the existing panel. For Re = 4067, 94, 36 and 5% were found and the most interesting was at a lower Reynolds number (1954). This lower number made the existing panel more efficient when a gap of 9 and 10 mm was used. A reasonable explanation is that at lower airflows, the protrusions now contribute to increase the heat transfer. When the new and existing panels are compared in terms of the thermal enhancement factor, an increase of 84.4% was found for an 8 mm gap and a Reynolds number of 6061 while at 10 mm and a Reynolds number equals to 1954, the existing panel performs 29.8% better than the new panel. The pressure drop was also tested to evaluate if the small fan is capable to provide the same airflow despite the increase in pressure drop. The results were positive with the fan being able to provide the same airflow as the existing panel.