A study on the effect of working fluid filling ratio and inclination for cryogenic heat pipes.

In this study, the thermal behavior of a cryogenic heat pipe was experimentally investigated. The cryogenic heat pipe is a conventional type of a heat pipe (wicked heat pipe). The heat pipe studied here utilizes a cryogenic fluid as its working fluid and operates at low temperatures. To carry out the experiments, commercially available heat pipes that use water as the working fluid and are typically intended for use at room temperature were utilized. This study replaced the working fluid with either N₂ or Ar. The heat pipe consists of copper and has a diameter of 6 mm, a length of 200 mm, and a thickness of 1 mm. The wick structure comprises sintered powder copper and grooves. The study investigated the impact of the filling ratio of the working fluid and the inclination angle of the cryogenic heat pipe. The N₂− and Ar-heat pipes both exhibited an overall thermal resistance (R_th) value of 0.20 and 0.25 K/W, respectively, during normal heat pipe operation mode. It was found that the filling ratio of the working fluid had a significant impact on both the maximum heat transport capability, Q_max, and the overall thermal resistance of the heat pipe. Moreover, the inclination angle also had an effect on Q_max, with an angle greater than 10 ˚ when the evaporator section is positioned below the condenser section being found to notably increase the value of Q_max. [ABSTRACT FROM AUTHOR]