Experimental Study on Counter-Gravity Effect of Non-Phase Change Heat Pipes

An innovative concept of Non-Phase Change Heat Pipe (NPC-HP) was recently proposed by the present authors. Different shapes of NPC-HP with different structures have been successfully developed in our laboratory. The heat transfer in NPC-HP is not dependent on phase change, but on pressure response to temperature change. With the external heat source as the driving force, the remarkable pressure rise of the working medium inside NPC-HP resulting from the heat input precedes the rise of the saturated vapor pressure, thus effectively restrains the phase change in the loop pipe and finally results in a special heat transfer mode with phase change suppressed. NPC-HP has much higher heat flux (as high as 10⁴ W/cm²) and much higher heat transfer rate compared to traditional heat transfer components. Besides, NPC-HP overcomes the deficiencies or limitations of conventional heat pipes, such as the dry-up phenomenon, the difficulty of heat transfer in counter-gravitational direction, etc. It is, in fact, a new generation of heat transfer components with a completely new mechanism. In order to testify the counter-gravity effect of NPC-HP, an experiment for downward heat transmission in NPC-HP is arranged. The test result demonstrates the superior capability of downward heat transfer of NPC-HP. For heating power of 275W, heat effectively transmits downwards to the cooling end of the pipe at the vertical distance of 1.68m from the heating position. The temperature difference is about 7°C from the top to the bottom of the pipe. This result is hardly realizable in conventional heat pipes. A preliminary analysis on the mechanism of downward heat transfer is then made. For an effective downward heat transfer, it is essential for NPC-HP to keep phase change effectively and opportunely suppressed in the loop pipe as well as to further keep natural convection restrained. Because of its superior performance, NPC-HP will undoubtedly become a new generation of heat transfer components, and have wide applications in different industries.