2.3.7. Thickness over Boiling Time

This subtopic has already been discussed throughout the current work, but nevertheless, and concerning the thickness of the deposition layer, it is worth mentioning the experimental work performed by the authors Park et al. [67] who evaluated the effects of the pool-boiling-induced nanoparticle deposition on the CHF improvement. With this purpose, boiling experiments were conducted to evaluate the impact of the thickness of the deposited nanoparticle layer on the CHF using a 0.01 vol. % alumina nanofluid with a Ni–Cr wire as the heating surface. The thickness of the nanoparticle-deposited layer was managed by different boiling times for pre-coating and the CHF evolution curve was acquired in function of the time of the pre-coating process. The authors found that the CHF remain unaltered regardless of the boiling time over a critical pre-coating time, whereas the CHF was dramatically increased during a relatively short pre-coating time. Moreover, the CHF occurrence was moderately decreased after the critical time region. It was also

stated that the porosity decreased as the pre-boiling time increased since a denser layer was produced when the boiling time was extended. Moreover, the reduced number of pores affected the CHF decrement after that alteration. This fact denotes that the fluid fraction closely linked with the phase change diminished and this decrease would be promoted when employing a high concentration nanofluid during sufficient pool-boiling time. However, an excessive deposited layer thickness may result in a negative impact on the CHF. Overall, the authors concluded the following:

