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Furukawa Review No.27

Steady and Transient Heat Transfer Characteristics of Flat Micro Heatpipe

Yuichi Kimura, Yoshio Nakamura, Junji Sotani and Masafumi Katsuta

Abstract

Recently, a flat micro heatpipe of slim-profile for use in electronic equipment like personal computers is drawing attention because of its ease of mounting and attachment to heat sources. In this paper steady-state heat transfer characteristics of this heatpipe have been experimentally confirmed in detail, and a prediction method for its maximum heat transfer rate is proposed. Moreover in performance measurement, transient heat transfer characteristics due to step input have also been evaluated since actual operation of the heatpipe itself normally starts from room temperature.
In the steady-state measurement, evaluation was carried out while the temperature of adiabatic section of the heatpipe was maintained at 50<C by adjusting the cooling capacity of a fan, and the amount of working fluid and the lengths of evaporating and condensing sections were taken as parameters. As the result, it has been confirmed that the maximum heat transfer rate increases as the amount of working fluid increases, and that the longer the lengths of evaporating and condensing sections, the greater the maximum heat transfer rate. In view of these results, the equation of pressure balance has been reexamined in order to predict the maximum heat transfer rate more accurately.
In the transient-state measurement, temperature rise due to step input was held constant by adjusting the cooling capacity of Peltier elements mounted on the condensing section of the heatpipe, and the amount of working fluid, the temperature of heatsink and the time interval of step input were taken as parameters. As the result, it has been confirmed that the maximum heat transfer rate measured using a step input becomes smaller than that of the steady state due to the lowered working temperature.

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