**4. Conclusions**

The numerical model using CFD of a helical tube-in-tube heat exchanger with and without passive techniques was successfully carried out. The main contributions of the present research are the following:


In this work the numerical results, analysis, and discussion were presented; if more information is needed for future research lines, the corresponding author can provide it upon request.

**Author Contributions:** The authors contribute equally to this manuscript. Investigation, D.C.; Methodology, M.V.; Software, J.G.A.; Writing—review and editing, B.A.E-T.

**Funding:** This research received no external funding.

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