Droplet boiling on two-tier hierarchical micro-pillar array surface – Nucleate boiling regime

• Published in: International journal of multiphase flow 2025-01, Vol.182, p.104950, Article 104950
• Main Authors: Wang, Tianjiao, Hu, Zhenhang, Zheng, Yi, Shen, Shengqiang, Liang, Gangtao
• Format: Article
• Language: English
• Subjects: Bubble nucleation; Droplet boiling; Hierarchical micro-pillar array; Nucleate boiling; Vapor expansion
• ISSN: 0301-9322
• DOI: 10.1016/j.ijmultiphaseflow.2024.104950

•Bubble dynamics inside droplet in the nucleate boiling regime on two-tier hierarchical micro-pillar array surfaces are systematically studied.•Secondary pillars are most effective at improving heat transfer performance when configured on side of primary pillars and least effective when configured on top of primary pillars.•Configuration of secondary pillars on side of primary pillars enhances heat transfer significantly when triple-phase contact line on pillars dominates evaporation.•Droplet evaporation rate decreases anomalously because evaporation is hindered near primary pillars by wrapping of droplet when secondary pillars are configured on substrate.•Geometrical effects of primary pillar including pillar side length, spacing and height and mechanisms are analyzed. Although hierarchical structured surfaces have shown great potential in improving heat transfer performance of boiling, the mechanisms associated with structure configuration and structure size remain elusive. In this work, the nucleate boiling regime of droplet on single-tier micro-pillar array (SM) surfaces and three types of two-tier hierarchical micro-pillar array (THM) surfaces is investigated comprehensively using the lattice Boltzmann model. Effects brought by the primary pillar size and the secondary pillar configuration on the development of vapor confined in pillar gaps are emphatically discussed from bubble nucleation through vapor coalescence to vapor expansion. Boiling dynamic characteristics concerning droplet morphological evolution, liquid-vapor interfacial deformation and triple-phase contact line (TPCL) motion are elucidated by the distributions of vapor pressure, fluid temperature and substrate heat flux. It is most efficient for the secondary pillar to enhance boiling heat transfer performance when configured on the side of primary pillar and least efficient when configured on the top of primary pillar. [Display omitted]