Liquid flow over laser-patterned superhydrophobic surfaces
Notice bibliographique
Résumé
Drag reduction is beneficial in most fluid flow applications. In this thesis, the drag reduction potential of superhydrophobic surfaces fabricated by femtosecond (fs) laser micromachining is investigated under both internal and external flows. As fs laser material interaction is not well understood, its application for the fabrication of textured surface is studied in detail. New surface structures were fabricated on titanium, stainless steel, aluminum, and copper samples. The resulting structures were characterized, and the evolution of structure formation was mapped with two irradiation models, namely the fluence and pulse-per-spot (F-PPS) model and the accumulated fluence profile (AFP) model, consisting of two parameters each. Moreover, the effect of material properties, such as the electron-phonon coupling strength and thermal conductivity, on microstructure formation were identified. The insight, gained through the investigation of fs laser surface texturing, was used to fabricate different hierarchically patterned superhydrophobic surfaces. Hierarchical laser-inscribed regularly patterned surfaces offered greater drag reduction in micro-scale fluid flow compared to the similarly patterned non-hierarchical surfaces. Three different patterns, such as rectangular pillars in a square lattice, grates in the direction of flow, and rhombic pillars in a hexagonal lattice, were compared for their relative drag reduction abilities. While the latter exhibits a more stable Cassie wetting state, it nevertheless results in a lower normalized slip length compared to the other two patterns at a fixed solid fraction. The effect of surface chemistry was studied by coating the patterned samples with a hydrophobic fluoroalkylsilane. The silanized samples provided increased drag reduction compared to the non-silanized samples even though there was no noticeable difference in their dynamic contact angles. Furthermore, measurements of the water penetration depth showed that contact angle measurements are not sufficient to judge the role that surface chemistry plays on drag reduction.In addition to the study of drag reduction over the regularly patterned surfaces, drag on a randomly patterned polytetrafluoroethylene (PTFE) surface was studied for both internal and external flows. The superhydrophobic PTFE reduced drag in both micro-scale and macro-scale internal flows. Slip length on this surface was measured with two different measurement methods, namely through rheometry and pressure differentials. These slip length measurements were further verified by using a semi-analytical model. Terminal velocities of similarly patterned PTFE spheres were measured in three different liquids to study their drag reduction potential in external flow. Unlike the internal flow experiments, however, the superhydrophobic spheres increased drag in external flow both in the viscous and inertial regimes.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».