Eiji Yazaki, Asami Hatamoto, Koji Fumoto
Abstract: The increasing heat generation density of modern electronic devices necessitates advanced cooling technologies to maintain reliability and prevent performance degradation. A recently developed thermal device, the Meander-shaped Low-Fill Heat Pipe (MLFHP), features a meandering open-loop channel and operates effectively at extremely low filling ratios below 10 vol.%, unlike conventional pulsating heat pipes. While previous studies have demonstrated its superior temperature uniformity under natural air cooling, its performance under high heat flux conditions and different cooling environments has not been fully clarified. In this study, the heat transport characteristics of an MLFHP were experimentally investigated under three cooling conditions: natural air cooling, forced air cooling, and water cooling. The effects of filling ratio, air velocity, and cooling water flow rate on thermal performance were examined. Thermal resistance and heat transfer coefficients were evaluated using measured temperature distributions and heat input data. The results showed that the MLFHP at a filling ratio of 10 vol.% achieved significantly lower thermal resistance than at 50 vol.% under natural air cooling, with a minimum value of 0.16 K/W—approximately 80% lower than that of the conventional case. Under forced air cooling, increased air velocity enhanced tolerance to high heat flux but induced temperature oscillations in the heating section due to excessive condensation and liquid retention in the cooling section. Similarly, under water cooling, higher flow rates raised the maximum allowable heat flux by about 19%, although pronounced temperature fluctuations appeared at elevated heat inputs. These findings indicate that excessive cooling can destabilize liquid circulation within the channel despite improving heat flux tolerance. Overall, this study demonstrates that the MLFHP exhibits excellent heat transport capability at low filling ratios, making it a promising thermal management solution for compact, high-power electronic devices. The results also highlight the importance of optimizing cooling conditions to balance effective heat removal and stable operation.
Keywords: Heat pipe, Low fill, Cooling conditions.
Date Published: December 30, 2025 DOI: 10.11159/jffhmt.2025.051
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