Boiling performance on surfaces with capillary-length-spaced one- and two-dimensional laser-textured patterns

• Published in: International journal of heat and mass transfer 2018-12, Vol.127, p.1188-1196
• Main Authors: Voglar, Jure, Gregorčič, Peter, Zupančič, Matevž, Golobič, Iztok
• Format: Article
• Language: English
• Subjects: Boiling; Capillary length; Fiber lasers; Foils; Heat flux; Heat transfer coefficients; Heating; Laser beam texturing; Laser surface engineering; Lasers; Micro cavities; Microstructure; Nucleation sites; Pool boiling; Surface chemistry; Texturing; Working fluids
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2018.07.056

•This study involves water pool boiling on laser-induced multi-scale micro-cavities.•Different 1D and 2D arrangements of boiling patterns were made on heater foils.•The two-dimensional designs did not perform better than the one-dimensional ones.•Capillary length was found to be optimal spacing between laser textured regions.•Fully treated sample expressed the highest (1200 kW/m2) heat flux prior to burnout. This investigation used laser-processed 25-μm-thick stainless steel foils as heaters in pool boiling experiments under subcooled and saturated conditions at atmospheric pressure. Boling surfaces were modified by a nanosecond fiber laser. In most cases, laser-textured parts on boiling surfaces were spaced apart by a capillary length of water (2.5 mm) and had different shapes and arrangements. Multi-scale micro-cavities (with diameters ranging from 0.2 to 10 μm) on the laser-textured areas of the surfaces provided potential active nucleation sites. The highest heat flux measured before the burnout was observed on the fully treated sample; this heat flux was a factor of 3.7 greater than that of the untreated sample. The sample with hexagonally arranged textured circular shapes with a diameter of 2.0 mm provided a more than 4-fold higher heat transfer coefficient compared to the untreated sample. All of the laser-textured boiling surfaces showed enhanced pool boiling heat transfer performance in comparison to the untreated surface. The optimal spacing between the laser-textured regions was experimentally found to be equal to the capillary length of the working fluid. Our results demonstrate that laser texturing has strong potential for producing patterned surfaces for engineering applications of boiling heat transfer.