Thermal and hydrodynamic characteristics of an ultra-thin flattened centered-wick heat pipe: Experiments and numerical analyses

Abstract

An ultra-thin flattened heat pipe with a centered-wick structure is a promising option for the thermal management of ultra-slim electronic devices. However, while experimental studies are being actively conducted, the thermal and hydrodynamic characteristics of the ultra-thin flattened centered-wick heat pipe have not been deeply analyzed. In the present study, therefore, experiments and three-dimensional numerical analyses were conducted to clarify the characteristics specific to this type of heat pipe. Because a semi-transparent flat-plate centered-wick heat pipe with inner height of 0.5 mm was fabricated in the authors’ previous study, the present study was performed based on this semi-transparent heat pipe. The experiments were conducted to obtain experimental results for comparison with numerical results. In the numerical analyses, the heat pipe was represented by a model comprising vapor, liquid–wick, upper wall, and lower wall regions; the numerical results were obtained for the velocity, pressure, and temperature distributions within the heat pipe. The experimental and numerical results confirmed that their good agreement was obtained within ± 6 % when a condensation end position was set 20 mm from the inlet of the condenser section. In contrast to conventional heat pipes, the present centered-wick heat pipe contains vapor-wick-wall contact lines, which causes the concentration of heat flux. The numerical results clarified that the concentration of heat flux occurred in the wick structure within the range of 0.2 mm from the bottom. This range needs to be considered to improve the wick structure of the centered-wick heat pipe. Simple one-dimensional equations were derived to discuss the vapor pressure difference within the heat pipe. Agreement was obtained within ± 10 % between the vapor pressure differences from one- and three-dimensional calculations.