<p>This study explores the thermal performance of hybrid nanofluids consisting of silver (Ag), aluminum oxide (Al₂O₃), and multi-walled carbon nanotubes (MWCNTs) as additives in copper heat pipes. The primary aim is to assess the efficiency of these nanofluids in enhancing heat transfer under various experimental conditions, including nanoparticle concentrations (0.10%, 0.25%, 0.50%), heat inputs (ranging from 40 to 70&#xa0;W), and inclination angles (0° to 90°). Deionized water served as the base fluid, and surfactants such as sodium dodecyl sulfate and cetyltrimethylammonium bromide (CTAB) were used to stabilize the nanoparticles. The hybrid nanofluids demonstrated superior thermal conductivity compared to deionized water, with Ag/MWCNT nanofluids reaching up to 1.6 W m⁻¹ K⁻¹ and Al₂O₃/MWCNT achieving 1.5 W m⁻¹ K⁻¹, as opposed to 0.607 W m⁻¹ K⁻¹ for pure water. While thermal conductivity is a critical parameter influencing heat transfer performance, it is not the sole determinant. This study also evaluated other factors, such as viscosity, density, and overall heat transfer coefficient, to comprehensively assess nanofluid performance. For instance, the heat transfer coefficient integrates thermal conductivity with convective effects, influenced by nanoparticle concentration and flow dynamics. The reduction in thermal resistance, achieved through enhanced convection and improved fluid mixing due to Brownian motion, highlights the importance of multiple interconnected properties. Additionally, factors like inclination angle and filling ratio were shown to impact fluid flow and phase change efficiency within the heat pipe, underscoring the multifaceted nature of performance metrics beyond thermal conductivity alone. Viscosity measurements indicated a slight increase, contributing to improved heat transfer properties but necessitating additional energy for fluid flow. The study revealed that the optimal nanoparticle concentration was 0.50%, which reduced thermal resistance by 51% and significantly increased the overall heat transfer coefficient by over 100% relative to deionized water. The results underscore the potential of hybrid nanofluids, particularly in applications requiring efficient thermal management, such as electronics cooling and renewable energy systems. These findings provide a foundation for further research into optimizing nanofluid formulations and their integration into high-performance heat transfer systems.</p>