POOL BOILING HEAT TRANSFER CHARACTERISTICS OF POROUS NICKEL MICROSTRUCTURE SURFACES

Pool boiling is an effective heat dissipation approach in electronic cooling, battery thermal management, etc. This study used the electrochemical deposition method to fabricate one smooth nickel specimen (named Ni-smooth) and three specimens with a porous nickel-stacked structure. The three porous specimens were created with deposition current densities of 0.5 A·cm^-2 (named Ni-0.5), 2.0 A·cm^-2 (names Ni-2.0), and 5.0 A·cm^-2 (named Ni-5.0), respectively. The four samples underwent microstructural characterization via scanning electron microscopy. The increasing current density led to the porous nickel surface exhibiting a more distinct pore structure, and the nickel sphere grains became more refined, developing a loose "mound-like" structure. A marked increase in the nickel film thickness was also observed. Through visual experiments, we evaluated their wettability, and through pool-boiling experiments, we tested their boiling heat-transfer properties. Our findings suggest that samples incorporating a porous nickel structure consistently outperform unmodified samples regarding heat-transfer efficiency. Specifically, sample Ni-0.5A demonstrated the most optimal boiling heat-transfer performance, evidenced by a 32.2% reduction in temperature at the onset of boiling, a 19.9% increase in critical heat flux density, and a 78.6% larger maximum heat-transfer coefficient compared to the smooth nickel sample. These marked improvements are intrinsically linked to the specific characteristics of the porous nickel structure. The higher performance of samples Ni-0.5 can be attributed to the presence of additional nucleation sites within the porous structure and the formation of smaller micro-crystalline dendritic constructs due to the specific current density applied during electrodeposition. Understanding this relationship between surface characteristics and electrodeposition is essential in maximizing heat-transfer efficiency.