Optimizing CTAB–Al2O3/DI nanofluid concentration enhances the maximum thermal power of FMHPs

With the rapid rise of 5G communications and artificial intelligence, thermal management for high-power-density electronics is facing growing demands. The flat micro heat pipe (FMHP) represents an attractive passive cooling solution; however, conventional working fluids often fall short in meeting demanding heat-transport limits. Although nanofluid modification has been extensively investigated, the synergistic mechanism between surfactant concentration and nanoparticles remains insufficiently understood, impeding quantitative design guidelines for practical engineering applications. In this study, we develop an FMHP modified with a CTAB–Al 2 O 3 /deionized-water (DI) nanofluid and identify 0.07 wt% as the comprehensive optimum concentration by jointly considering maximum thermal power, thermal-resistance level, and capillary transport performance. By employing a stepwise heat-loading testbed, we systematically evaluated the FMHP performance across a concentration gradient ranging from 0.03–0.20 wt%. Experimental results indicate that CTAB effectively reduces the contact angle. At this comprehensive optimum concentration, CA07 attains the highest maximum thermal power of 58.5 W (a 31.23% improvement over the unmodified device) while maintaining a low minimum overall thermal resistance of 0.14 °C/W, corresponding to a 44.2% reduction relative to the unmodified A07 case. These results demonstrate a significant enhancement in heat transport capability, offering a practical strategy for thermal management of high-power electronics and establishing a quantitative design framework for surfactant–nanoparticle synergy in nanofluid-enhanced FMHPs. The present conclusions are based on experiments conducted under horizontal orientation and fixed cooling-water and ambient-temperature conditions, and their applicability to other operating configurations requires further verification.