Enhanced heat transfer in copper heat pipes using hybrid nanofluids: experimental and RSM analysis

Hybrid nanofluids have emerged as promising candidates for improving thermal performance in heat transfer systems. This study investigates the effects of heat input, inclination angle, and filling ratio on the Overall Heat Transfer Coefficient (OHTC) and Thermal resistance (TR) using mono and hybrid nanofluids, emphasizing particle size and composition. A Response Surface Methodology (RSM) approach was employed to model interactions and optimize operating conditions. Four nanofluids—SiC-L, SiC-S, Al₂O₃/SiCL, and Al₂O₃/SiC-S—were tested in a copper heat pipe with heat inputs ranging from 40– 70 W, inclination angles of 0°–90°, and filling ratios of 60%–90%. The results demonstrate that Al₂O₃/SiC-S achieved the highest U (540 W/m²K) and the lowest R (0.30 K/W) at optimal conditions (70 W heat input, 60° inclination, and 80% filling ratio). Smaller nanoparticles (SiC-S and Al₂O₃/SiC-S) consistently outperformed larger ones due to enhanced surface area and Brownian motion, improving Thermal Conductivity (TC) by up to 48%. These findings highlight the potential of hybrid nanofluids for advanced cooling technologies and suggest future research into long-term stability and cost-effective synthesis for industrial applications.