# Numerical Investigation of Latent Thermal Storage in a Compact Heat Exchanger Using Mini-Channels
## 2 Materials and Methods
### PCM Thermos-Physical Properties  
Material properties of the investigated PCM and RT22 are missing in the literature. RT22 is an organic commercial PCM provided by RUBITHERM undergoing the solid-liquid phase change around 22 \({}^{\circ}\)C. The thermo-physical properties, including density in the liquid phase, enthalpy and isobaric specific heat capacity, thermal conductivity and viscosity, were measured experimentally. The liquid density was measured using two pyknometers of 50 and 100 mL, enthalpy and specific heat via a \(\mu\)DSC evo 7 from the Setaram instrument, thermal conductivity via a Hot Disk TPS-2500 and viscosity via a rotational Brookfield viscometer. The linear correlation of the measured stress with the strain rate in the liquid phase, obtained in the viscosity measurement procedure, shows that RT22 has a Newtonian behavior. The measured properties are shown in Figure 3 as functions of temperature and summarized in Table 3. The measurement methodology via the aforementioned instruments used to measure the thermo-physical properties of RT22 in this paper was explained in detail by [PERSON] et al. (2018) for two other organic PCMs.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Channel-1** & **Channel-2** \\  & **(Extrusion-Al3003)** & **(DMLS-AlSi\({}_{10}\)Mg)** \\ \hline Area to volume ratio \(\left[\frac{\text{A}_{\text{n}}}{\text{Vol}}\left(\frac{\text{m}^{3}}{\text{m} ^{2}}\right)\right]\) & 943 & 987 \\ Hydraulic diameter \(\left[\text{d}_{\text{h}}\left(\text{mm}\right)\right]\) & 1.63 & 2.27 \\ Density \(\left(\frac{\text{kg}}{\text{m}^{3}}\right)\) & 2730 & 2620 \\ Specific heat capacity \(\left(\frac{\text{M}}{\text{Ke}_{\text{R}}}\right)\) & 892 & 846 \\ Thermal conductivity \(\left(\frac{\text{W}}{\text{m}\cdot\text{K}}\right)\) & 162 & 111 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Geometrical characteristics and material properties of the channels.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Number of Channels** & **PF (\%)** \\ \hline  & 5 \(\times\) 12 & 86.8 \\ Channel-1 & 5 \(\times\) 16 & 82.4 \\  & 5 \(\times\) 20 & 78 \\ \hline  & 6 \(\times\) 12 & 84.6 \\ Channel-2 & 6 \(\times\) 14 & 82 \\  & 6 \(\times\) 16 & 79.4 \\ \hline  & 6 \(\times\) 12 & 83 \\ Channel-2-finned & 6 \(\times\) 14 & 80.2 \\  & 6 \(\times\) 16 & 77.4 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Investigated configurations.  
Figure 3: Temperature-dependent thermo-physical properties of RT22: (**a**) liquid density, (**b**) heat flows upon melting/solidification, (**c**) thermal conductivity and (**d**) dynamic viscosity.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Density (\(\frac{\text{kg}}{\text{m}}\))** & **778 (20 \({}^{\circ}\)C)** \\ \hline Specific heat capacity (\(\frac{\text{k}}{\text{kg}^{\text{-}}\text{K}}\)) & 4.6 (15 \({}^{\circ}\)C)–2.4 (30 \({}^{\circ}\)C) \\ Latent heat of phase change (\(\frac{\text{k}}{\text{kg}}\)) & 163.8 \\ \(\Delta\text{T}_{\text{m}}\) (\({}^{\circ}\)C) & 20.4–23.7 \\ \(\Delta\text{T}_{\text{f}}\) (\({}^{\circ}\)C) & 20.1–22.8 \\ Thermal conductivity (\(\frac{W}{\text{m}^{\text{-}}\text{K}}\)) & 0.14 (15, 30 \({}^{\circ}\)C) \\ Viscosity (Pa-s) & 0.00407 (25 \({}^{\circ}\)C) \\ Thermal expansion coefficient (\(\frac{1}{\text{k}}\)) & 0.00084 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Measured thermo-physical properties of RT22.