Experimental and theoretical determination of pool boiling heat transfer on nano structured surfaces

• Mechanisms of boiling performance on nano structured surfaces are clarified. • Impacts brought by nanoarray inter-unit spacing, coverage area ratio, and structural configurations are assessed. • Optimal structures need to make a balance between vapor escape pathways and liquid replenishment capabilities. • An improved theoretical model for predicting CHF by accounting for capillary wicking is built up. This study investigates the enhancing mechanisms of nano structures in pool boiling performance systematically through a comprehensive analysis of three key parameters: inter-unit spacing in nanoarrays, coverage area ratio, and structural configurations. Results show that while super-hydrophilic nano structured surfaces significantly improve critical heat flux (CHF), they reduce heat transfer coefficient (HTC) simultaneously. The parameter optimization demonstrates that varying the spacing between nano array units under constant coverage area ratio shows limited boiling enhancement, whereas increasing the coverage area ratio substantially boosts CHF. The maximum CHF (with correspondingly lowest HTC) is achieved at a full surface nano structure coverage. Through comparative bubble dynamics analysis, this study also identifies nano stripe configurations as particularly effective in manipulating vapor bubble behavior. These aligned structures promote liquid rewetting, achieving an optimal CHF at an 80 % coverage ratio while maintaining competitive HTC levels. This configuration makes a favorable balance between vapor escape pathways and liquid replenishment capabilities. Finally, this study further advances theoretical understanding through an improved predictive model for CHF on the nano structured surfaces by accounting for capillary wicking based on bubble force balance, demonstrating high accuracy within the super-hydrophilic regime. These insights can provide valuable guidelines for designing surface nano structures to optimize both thermal safety and operational efficiency in boiling applications.