# Numerical Investigation of Latent Thermal Storage in a Compact Heat Exchanger Using Mini-Channels
## 4 Conclusions  
This incorporation of rectangular mini-channels with internal air passages into an LTES component was studied, considering two types of configurations. Three-dimensional phase change simulations of RT22 in a cuboid of 0.15 \(\times\) 0.15 \(\times\) 0.1 m\({}^{3}\), with vertically oriented channels, were carried out. The channels have different hydraulic diameters and aspect ratios of the internal flow passages while having almost similar volume and external heat transfer surfaces. In channel-2, fins were also investigated to enhance thermal performance. The simulation results show that the thermal performance of the system is enhanced as the number of channels increases in both the channel-1 and channel-2 cases. The mean UA value increases as the number of channels increases and the PCM packing factor decreases. The enhancement is majorly attributed to the increase in the external surface area with a higher number of channels, while the air flow rate per channel decreases given a constant total air flow rate entering the cuboid. Increasing the flow rate improves the mean UA value in both melting and solidification. For instance, for channel-1 with PF = 82.4%, channel-2 with PF = 82% and finned channel-2 with PF = 80.2%, the mean UA value of melting increases by 30%, 35% and 44% as the total flow rate of the HTF increases from 7 L/s to 24 L/s, respectively. The comparison of channel-1 and channel-2 with similar packing factors shows that the difference in the air heat transfer coefficient has an insignificant effect on the mean phase change powers and the mean UA values. For instance, the air heat transfer coefficients of channel-2 with PF = 82.0% are about 30-40% higher than those of channel-1 with PF = 82.4%, for the simulated total flow rate of 7-24 L/s. However, the enhancement in the mean UA values of the former lies within 1-5%, as compared to the latter, credited to its minor higher external surface area. Adding fins to the channel-2 cases, doubling the heat transfer area on the PCM side, can increase the mean UA values by 15-31% for the entire ranges of simulated flow rates and packing factors. Another benefit with channel-2 is the considerably lower pressure drop as compared to channel-1. This is due to its higher hydraulic diameter, particularly with high total flow rates and high packing factors. Given a constant flow rate, the channel-2 configurations have higher PEC than the channel-1 configurations, achieving a higher gain in stored/extracted thermal energy in exchange for the used fan power. Figure 13: PEC of the compact component as a function of total air flow rate: (**a**) melting—Tin = 30 \({}^{\circ}\)C, (**b**) solidification—Tin = 15 \({}^{\circ}\)C.  
The results show that the mini-channels could be optimized to have a higher performance in heat transfer with a lower pressure drop. The metal 3D printing method, as an alternative method in manufacturing conceptual designs, could be used in implementing innovative features. This includes optimization of the hydraulic diameter and the aspect ratio of the HTF passages, maximizing the area-to-volume ratio of the channels and manufacturing innovative fin configurations to enhance the heat transfer on the PCM side. Finally, optimization, manufacturing and experimental testing of the mini-channels under laboratory conditions could be the next steps paving the commercialization of such products and their usage on a large scale. Conceptualization, A.A.; methodology, A.A.; software, A.A.; investigation, A.A.; data curation, A.A.; writing--original draft preparation, A.A.; writing--review and editing, J.N.C. and V.M. ; visualization, A.A.; supervision, J.N.C. and V.M. ; project administration, V.M. ; funding acquisition, V.M. All authors have read and agreed to the published version of the manuscript. This work was supported and funded by the Swedish Energy Agency (P48283-1). Not applicable. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.