Thermal-transport mechanisms and application trends in micro heat pipes: A quantitative review

Micro heat pipes (MHPs) are compact, passive, two-phase thermal management devices that enable high heat transport capability through capillary-driven phase change. Their small footprint, low thermal resistance, and rapid thermal response make them increasingly relevant for modern systems experiencing escalating heat fluxes due to miniaturization. This review synthesizes recent advancements in MHP design, fabrication, working fluid optimization, and application-specific performance. Key application domains electronic cooling, renewable and solar energy systems, biomedical instruments, battery thermal management, and emerging nuclear and aerospace platforms are critically examined with emphasis on quantitative performance indicators such as maximum heat flux, temperature uniformity, and thermal resistance. Geometric innovations (micro-grooves, star-shaped channels, hybrid structures), nanofluid-enhanced working media, and integration with PCMs are highlighted as major breakthroughs that continue to expand the operational envelope of MHPs. Despite wide applicability, several challenges remain, including orientation sensitivity, fill-ratio selection, material compatibility, nanofluid stability, and limited long-term reliability data. Comparative insights reveal that well-optimized MHPs outperform conventional heat spreaders and certain two-phase cooling devices in high-power, space-constrained environments. This review identifies critical research gaps and outlines opportunities for next-generation thermal management in areas such as EV batteries, 5G/6G electronics, micro-reactors, and space systems. The article consolidates fragmented existing knowledge to support future design and deployment of MHP-based technologies.