Confined and unconfined nucleate boiling of HFE7100 in the presence of nanostructured surfaces

Abstract

A B S T R A C TThis article presents experimental results for the confined and unconfined nucleate boiling of saturated HFE7100 (C 4 F 9 OCH 3 ) at atmospheric pressure and using nanostructured copper discs as heating surfaces. The nanostructures studied consisted of nanoparticles of maghemite (Fe 2 O 3 ) on the heating surface, comprised of a copper disc. Different values for the diameter (10 and 80 nm) and roughness (R a = 0.02 µm and 0.16 µm) were studied. The nanoparticle adhesion on the heating surface plays a more important role in the confined boiling process than the surface roughness. As an original result, it was demonstrated that for a confinement with a gap length of 0.1 mm and heat flux of 40 kW/m 2 the heat transfer coefficient (HTC) increased by 31% and 100% for the cases with the deposition of nanoparticles of 10 nm and 80 nm, respectively. However, without the nanoparticles the HTC decreased by 21% when compared with the reference case, that is, a smooth plate (R a = 0.02 µm) and unconfined boiling.

Influence of coated surfaces and gap size on boiling heat transfer of deionized water

“…In summary, both studies performed by Souza et al [12,13] showed that HTC degradation for coated surfaces depends on the original surface roughness and the nanoparticle diameter ratio. The authors showed that surfaces with high roughness (R a = 0.160 µm) coated with larger nanoparticles diameters (80 nm) have a decrease in the thermal performance in the same way as those surfaces with low roughness (R a = 0.020 µm) coated with smaller nanoparticles diameters (10 nm).…”

“…The nucleate boiling regime is one of the most important heat transfer mechanisms even before the pioneering research of Ishibashi and Nishikawa [10] about confined nucleate boiling up to recent studies related to confined boiling and modified surfaces [11][12][13]. The gap size effect can be characterized by a dimensionless number known as the Bond number, Bo, defined as the ratio of the characteristic length to the confined space, s, and the capillary length, L b , proportional to the detachment diameter of the vapor bubble [14].…”

“…Moreover, Souza et al [13] presented results for confined boiling on a smooth heating surface (R a = 0.020 µm) in which HTC increased by 100% for heat flux values close to 40 kW/ m 2 and for surfaces with deposition of maghemite nanoparticles of 80 nm diameter. However, for heat flux values higher than 40 kW/m 2 , a decrease in HTC was identified.…”

Enhanced Nucleate Boiling of Novec 649 on Thin Metal Foils Via Laser-Induced Periodic Surface Structures

“…Several pool-boiling experimental studies [21] (most commonly performed on functionalized copper surfaces and with FC-72 as the working fluid) showed an enhancement of CHF up to 60 % on micro-/ nanostructured surfaces in comparison with bare samples, while extended (finned) surfaces [30] with or without additional micro-/ nanostructures were able to increase the CHF even above 1000 kW/m 2 . In terms HTC values on copper, silicon, stainless steel and aluminum, different experiments on surfaces with significantly increased micro-/ nanoscale roughness demonstrated enhancements of 50-250 % [31][32][33][34][35], highly porous surfaces demonstrated enhancements of 400-500 % [36,37], while up to 8-fold improvements were observed on finned surfaces [38]. It can be summarized that increased surface roughness with appropriate micro-/nanofeatures (including porosity) increases active nucleation site density, bubble frequency and capillary effects (delaying the surface dryout).…”

Gasoline surrogates in nucleate boiling heat transfer

“…In recent decades, nucleate boiling with pure components and mixtures has been widely investigated and discussed in the literature, both in textbooks [13,15] and scientific papers. There are many works that discuss the mechanisms and characteristics of nucleate boiling [20,29,39,42,45,46] and correlations for predicting the heat transfer coefficient (HTC), either for pure components [14,21,33,34,40] or mixtures [18,41,48,49]. This substantial research effort is justified by the many applications where nucleate boiling is found, such as refrigeration, nuclear energy and space engineering.…”