Enhanced pool boiling heat transfer by metallic nanoporous surfaces under low pressure

• Published in: International journal of heat and mass transfer 2022-03, Vol.184, p.122382, Article 122382
• Main Authors: Huang, Guanghan, Tang, Kairui, Yu, Shudong, Tang, Yong, Zhang, Shiwei
• Format: Article
• Language: English
• Subjects: Atmospheric models; Boiling; Bubble dynamics; Dynamic structural analysis; Enhanced pool boiling; Heat transfer; Heat transfer coefficients; Hot dip galvanizing; Low pressure; Nanoporous surface; Optimization
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2021.122382

•This enhanced pool boiling by nano-structure is firstly investigated at low pressure in this study.•The enhanced nanoporous copper surface (NCS) is fabricated by the hot-dip galvanizing & dealloying and the galvanization time is optimized.•The low pressure significantly affects the boiling behaviors and bubble dynamics, such as increasing bubble departure diameter and decreasing departure frequency.•The heat transfer coefficient enhancement of the NCS ranges from 71.6% (at 65 kPa) to 139% (at 25 kPa) compared to the plain wall. The nano-structure enhanced pooling boiling at standard atmosphere has been fully studied in literature but it is rarely investigated under low pressure. However, the boiling behaviors and bubble dynamics of nano-structures highly depend on the working pressure. This study investigated the enhanced pool boiling (under low pressure) of a nanoporous copper surface (NCS) fabricated by the hot-dip galvanizing & dealloying. The boiling curves and bubble characteristics of the NCS under low-pressure boiling conditions (25 kPa and 65 kPa) were evaluated by a test set up with high-speed visualization. To validate the present experimental plain-wall HTC under low pressure, three predicted models (Labuntsov, modified Rohsenow, and Stephan-Abdelsalam) were applied to obtain the theoretical HTCs for comparison. Besides, the optimization of the galvanization time has been conducted. Experimental results showed that the NCS significantly improved the pool boiling heat transfer and mitigated the negative influence of sub-atmospheric conditions. The enhanced mechanisms are the augmented nucleate site density, decreased bubble departure diameter, and increased bubbles generation frequency induced by the promoted hydrophilicity and rough morphology of the NCS. Among the three analyzed samples, the NCS-500 °C-3 min surface yielded the lowest wall superheat at the onset of boiling (ONB) and the highest heat transfer coefficient (HTC). In addition, the nanoporous surface leads to higher HTC enhancement upon the plain surface at a lower pressure. Specifically, the HTC enhancement percentage was increased from 71.6% (at 65 kPa) to 139% (at 25 kPa) as the pressure decreased. [Display omitted] .