Numerical analyses on heat transfer characteristics of ultra-thin heat pipes: Fundamental studies with a three-dimensional thermal-fluid model

Abstract Three-dimensional numerical analyses were conducted on the vapor flow and the heat transfer characteristics of the ultra-thin heat pipes. Recently, the ultra-thin heat pipes with a thickness below 1.0 mm have been used for thermal management of thin electronic devices such as smartphones. Different from a conventional capillary-driven heat pipe, the idea of centered wick structure is adopted for the ultra-thin heat pipes. The thermal-fluid model of the ultra-thin heat pipe was made. The heat pipe model was composed of the vapor and the liquid-wick region. The velocity, the pressure and the temperature distributions of the heat pipe model were obtained numerically by changing the height of the vapor region between 0.2 mm and 0.8 mm. Due to the vapor flow friction, the relatively large temperature difference was found inside the vapor region when the height was 0.2 mm. The effect of the vapor flow friction cannot be neglected in the thermal design of the ultra-thin heat pipes. Moreover, the conduction-based mathematical model of the ultra-thin heat pipe was also made, and the validity of the present numerical analyses was confirmed by comparing the numerical results with experimental data in literature.