Stress analysis and thermal performance of ultra-thin heat pipes for compact electronics

The ultra-thin heat pipe (UTHP) has been established as a highly effective thermal control component for cooling electronics with large heat generation rate and limited space for cooling. However, UTHP has been severely limited in application because of buckling or breaking on the shell of UTHP during the flattening process. In this study, a series of high-accuracy UTHPs with a thickness of 0.38–0.47 mm were fabricated by the phase-change flattening process. An internal vapor pressure model of the heat pipe during flattening was constructed and the heat transfer performances of UTHPs under different working conditions were experimentally investigated. According to the internal vapor pressure model, the pipe wall stress after flattening was the first to reach the yield strength of the material, and the upper limit heating temperature of UTHPs decreased with the decrease of flattened thickness. The maximum heat transfer capacity decreased with the decreased flattened thickness. UTHP with a thickness of 0.47 mm has a maximum heat transfer capacity of 4.5 W and a minimum thermal resistance of 0.64 °C/W. Moreover, gravity appeared to impose minimal effects on the heat transfer performance of UTHPs and the heat transfer capabilities of the UTHPs fluctuated within ±0.5 W for different gravity orientations.