Enhancing thermal performance of two-phase closed thermosyphons by inhibiting geyser boiling: Synergistic effects of carbon nanotube nanofluids

Abstract

Two-phase closed thermosyphons (TPCTs) are passive heat transfer devices utilized in various applications owing to their simple, effective heat transfer ability. However, their thermal performance and structural integrity are undermined by aspects such as temperature fluctuations associated with geyser boiling. To resolve these issues, the present study was aimed at exploring the potential of carbon nanotube (CNT) nanofluids to enhance thermal conductivity and alter the surface wettability between the CNT nanofluid and the inner surface of the evaporation section, thus suppressing temperature fluctuations and improving the thermal performance of the TPCT. Specifically, the addition of 0.5 wt% CNTs to distilled water (DW) led to an approximately 3.35 % enhancement in thermal conductivity in the temperature range of 293.15–313.15 K. In terms of wettability, the addition of 0.5 wt% CNTs to DW increased the contact angle on a homogeneous glass surface while decreasing it by 13.37 % on an inhomogeneous surface with randomly deposited CNTs, achieving greater hydrophilicity. In the TPCT operation experiments, DW exhibited aperiodic and drastic temperature fluctuations at inclination angles of 90°, 60°, and 30°; in contrast, the 0.5 wt% CNT nanofluid showed stable temperature profiles, significantly reducing the maximum and average temperature differences between the bottom and top of the evaporation section. Even with temperature fluctuations, the overall thermal resistance reduced by up to 9.48 %, whereas the heat transfer coefficient increased by up to 19.66 %. These results confirm that the addition of 0.5 wt% CNTs to DW drastically improved the thermal performance of the TPCT. © 2025 The Authors