Modal heat transfer dynamics during flow boiling of dielectric fluids on laser-textured conical microcavities

Fontanarosa, Donato (author), Vodopivec, Matevž (author), Castagne, Sylvie (author), Zupančič, Matevž (author), Vetrano, Maria Rosaria (author)

The present work investigates flow boiling heat transfer enhancement on functionalised surfaces featuring arrays of femtosecond-laser-textured microcavities manufactured on 100 µm thick stainless steel foils. The influence of cavity aspect ratio and cavity pitch is examined using a novel diagnostic approach that integrates high-speed infrared thermography of transient surface temperature fields with high-speed video imaging of the boiling process. A global analysis of heat transfer performance is followed by an analysis of the heat transfer dynamics via multiscale Proper Orthogonal Decomposition. The test matrix includes three cavity pitches (100 µm, 200 µm and 500 µm), two aspect ratios (2.5 and 7.5) and two channel orientations (i.e., horizontal and vertical). Global results show that, in horizontal orientation and high-aspect-ratio cavities, the 100 µm pitch yields the lowest wall superheat and highest heat transfer coefficient, while in the vertical channel, the best performance is achieved with 200 µm pitch cavities. The dynamic analysis reveals that enhancement arises from heat transfer dynamics occurring at smaller spatial scales and higher spatial densities, while not necessarily at higher frequencies. On the best-performing surfaces, the dominant frequencies are found to be low, as densely distributed vapour clusters from multiple smaller bubbles travel across the surface at a slower rate. Moreover, the observed performance of 200 µm pitch cavities in the vertical channel indicates that, in vertical upward flow, larger pitches are more effective under the combined influence of geometry and gravity. Together, the results offer design guidelines for optimising micro-textured surfaces for specific flow orientations and operating conditions.

• Language: English
• Keywords: artificial nucleation sites, conical cavities, flow boiling, femtosecond laser texturing, heat transfer dynamics
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Author Accepted Manuscript
• Year: 2026
• Number of pages: 1-15 str.
• Numbering: Vol. 302, Part 2, art. 131822
• PID: 20.500.12556/RUL-184171
• UDC: 536.2:66.046.7:535
• ISSN on article: 1873-5606
• DOI: 10.1016/j.applthermaleng.2026.131822
• COBISS.SI-ID: 282908419
• Publication date in RUL: 01.07.2026

Record is a part of a journal

• Title: Applied thermal engineering
• Publisher: Elsevier
• ISSN: 1873-5606
• COBISS.SI-ID: 23195397

Licences

• License: CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
• Link: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Description: The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.

Secondary language

• Language: Slovenian
• Keywords: nukleacijska mesta, konične jamice, prisilno konvektivno vrenje, strukturiranje s femtosekundnim laserjem, dinamika prenosa toplote