Effects of surface characteristics of oxidized Zircaloy-4 on Pool boiling heat transfer

초록

Specimens of Zircaloy-4 were oxidized at 600 °C, 700 °C, and 800 °C for various time durations. Pool boiling experiments were conducted on these specimens to investigate the effects of oxidation on boiling heat transfer, which is essential for understanding cooling operations in nuclear reactors. Oxidation creates microstructural defects on the specimen surface, which enhances the surface wettability crucial for boiling heat transfer enhancement. However, the experimental results show that the critical heat flux (CHF) and heat transfer coefficient (HTC) values peaked at the specimens with oxide layer thickness between 20 and 30 μm, where the CHF increased by up to 147% for 600 °C, 168% for 700 °C, and 191% for 800 °C oxidized specimens compared to the bare specimen. This implies that surface wettability greatly affected heat transfer in specimens with oxide layer thicknesses below 30 μm, but not for higher thicknesses. The structural orientation of the cracks within the oxide layer have adverse effects on boiling heat transfer enhancement, where vertical cracks increase the surface wettability, but the horizontal cracks complicate bubble escape and obstruct the replenishment of the cooling fluid. The CHF ratio of specimens with oxide layer thicknesses exceeding 30 μm exhibited decreasing trend with decreasing thermal conductivity. As such, this study investigated the factors of the boiling heat transfer of oxidized Zircaloy-4, which are closely associated with thermal-hydraulic safety, therefore contributing to enhancement of the safety and efficiency of nuclear reactors. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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