**5. Conclusions**

The paper has reported on the results of the numerical investigation of laminar free convection heat transfer from various tube configurations. The single cylinder and the tube arrays of 4 × 1 and 4 × 2 arrangements at *Ra* = 10<sup>3</sup> and 10<sup>4</sup> were used for computational model verification. The main part of the research focused on the tube arrays in the configuration of 4 × 4 (base, concave, convex) at *Ra* in the range of 1.3 × 10<sup>4</sup> to 3.7 × 104. From the obtained local and average Nusselt numbers and temperature fields, the following conclusions can be drawn:


**Author Contributions:** Writing—original draft preparation; Conceptualization; Methodology and Validation, Z.B., S.K.; Software; Data Curation and Validation, S.K.; Formal analysis; Resources and Supervision, Z.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** The paper was created within the project VEGA 1/0086/18 The Research of Temperature Fields in the System of Shaped Heat Transfer Surfaces, funded by the Ministry of Education, Science, Research, and Sport of the Slovak Republic.

**Acknowledgments:** The authors thanks to the very competent reviewers for the valuable comments and suggestions.

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