6. Discussion

Some applications mainly based on Rayleigh and Marangoni thermal convection were briefly presented. These technologies were developed by researchers working on the frontier of various subjects which, from the authors point of view, is the perfect spot for human advances. Several complicated theories have a similar way finding unexpected common technological applications for most humans.

Thermal convection in its general sense has found practical applications in a number of other fields. For example, geology and volcanology use the theory of Rayleigh convection in fluids confined between insulating walls and many industrial equipments for heat transfer use the theory of convection too. On the other hand and to the best knowledge of the authors there are very few new technologies using Rayleigh or Marangoni convection as the ones presented here. It is remarkable that the physical mechanisms of these phenomena are at the core of the above presented technologies and what makes them work is the vast results reported since several decades.

Hopefully, researchers working on interdisciplinary projects could take advantage of the large amount of reported results on Rayleigh and Marangoni convection.

### 7. Conclusions

Here, an interesting connection between rheology and thermal hydrodynamics is presented through some applications. The theoretical approach is linked to an experimental setup by using dimensionless parameters like the Rayleigh number and the wavenumber. Already existent applications are then presented as the result a strong understanding of the physics involved. It can be concluded that for applications involving viscoelastic fluids rheology is intrinsically related to the thermal hydrodynamics. This is, pattern formation and heat transfer cannot be controlled if adequate constitutive model are not used. The rheological behavior of the fluid is key for these applications since relaxation time actually favors the heat transfer. It can be also concluded that robust control strategies, on the fluid rheology and heat transfer, may be needed for some applications as such is the fabrication of corrugated surfaces case. In this case the solvent is evaporated, so that viscoelasticity and then heat transfer change, which is not taken into account. Finally, it is shown that further investigation in this branch of rheology is needed.

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