**6. Conclusions**

The thermal-flow processes taking place in the low-temperature phase-change material, which was a mixture of paraffin wax that was capsuled in a melamine-formaldehyde membrane and water, were presented and analysed in the article. The experimental and numerical investigations during transient processes were carried out for the copper modules filled with a PCM for three different outer diameters (15, 22, and 28 mm) and a fixed height of 250 mm. A total of four cases i.e., for stagnant condition (0.0 m/s) and for three different mean velocity values of 0.92, 2.27, and 3.18 m/s for each module were tested. The experiment was performed in a wind tunnel, especially designed for this purpose. In addition, the internal structure of the tested PCMs was also analysed while using a SEM. The following conclusions can be drawn from the research carried out:


**Author Contributions:** Conceptualisation, A.O., W.-Q.C., P.B., M.P. and S.P.; methodology, A.O., W.-Q.C., P.B. and S.P.; software, W.-Q.C. and P.B.; validation, A.O., W.-Q.C., P.B. and S.P.; formal analysis, A.O., W.-Q.C., P.B., M.P. and S.P.; investigation, A.O. and W.-Q.C.; resources, S.P.; writing— original draft preparation, A.O., W.-Q.C., P.B., M.P. and S.P.; writing—review and editing, A.O., W.-Q.C., P.B., M.P. and S.P.; visualisation, A.O., W.-Q.C., P.B. and S.P.; supervision, S.P.; project administration, S.P., funding acquisition, S.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was partly funded by National Centre for Research and Development of Poland gran<sup>t</sup> number POIR.04.01.04-00-0037/15 and partly supported by the internal research funds of the Department of Thermodynamics and Renewable Energy Sources at Wrocław University of Science and Technology, Poland, No. 8201003902 (MPK 9090750000). Calculations have been carried out using resources provided by Wrocław Center for Networking and Supercomputing (http://wcss.pl), gran<sup>t</sup> Nos. 202 and 309.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank Halina Pawlak-Kruczek and Michał Czerep from Wrocław University of Science and Technology for providing and assistance in conducting tests using a Scanning Electron Microscope (SEM) for PCM analysis.

**Conflicts of Interest:** The authors declare no conflict of interest.
