Enhanced electronics cooling via carbon nanotube-coated micro heat pipes: comparative performance of water and ethanol

This study experimentally investigates the thermal performance of carbon nanotube (CNT)-coated micro heat pipes (MHPs), focusing on the coupled effects of nanostructured surface functionalization and working fluid selection. Oxygenated CNT coatings are applied to microchannel surfaces to induce superhydrophilicity and enhance capillary transport. The performance of CNT-coated MHPs charged with deionized (DI) water and ethanol is systematically compared with uncoated counterparts. The CNT-DI configuration demonstrates the best performance, achieving a maximum effective thermal conductivity of 2830 W/m·K (over seven times that of copper), with a peak enhancement of 258% at 1.63 W. Under high heat loads, it reduces heater temperature by more than 10 °C compared to the uncoated DI case. Thermal resistance analysis reveals that interfacial phase-change resistances, particularly at the evaporator, dominate overall performance. The CNT coating significantly reduces these resistances for water by enabling ultrafast capillary wicking and efficient vapor desorption. In contrast, CNT-ethanol systems are inferred to exhibit increased interfacial resistance, which is consistent with stronger molecular adsorption and possible molecular trapping that suppresses vapor release, and degraded heat transfer. These findings demonstrate that wettability alone is insufficient to ensure performance enhancement. Instead, fluid-surface compatibility and desorption kinetics govern the phase-change efficiency. The study provides practical design guidance for CNT-enhanced MHPs and indicates that CNT-DI systems are promising candidates for high heat flux electronics and AI-driven thermal management applications.