Experimental Study on Non-Phase Change Heat Pipe and its Mechanism Analysis

ABSTRACT

A novel concept of Non-Phase Change Heat Pipe (NPC-HP) is firstly proposed in this paper. With the successful development of NPC-HP, a great deal of experimental studies on NPC-HP and a preliminary exploration on its working mechanism has been done. The heat transfer in NPC-HP is not dependent on the phase change, but on its pressure response to the temperature change, and thus many deficiencies and limitations of conventional heat pipes are overcome, such as the dry-up phenomenon, the gravitational effect etc. With both high heat transfer rate and high heat flux (of the order of magnitude of 10⁴ W/cm²), it would become a new type of heat transfer components. The experimental study on the factors affecting the heat transfer in NPC-HP, such as: the working medium property and its total filling rate, the shape of NPC-HP, and the methods of heating and cooling from the surrounding, etc. exposes the unique mechanism of NPC-HP: With the outside heat source as the driving force, the heat transfer is dependent on the system pressure response to the temperature change, rather than the volume response to the temperature change as in conventional heat pipes. At both appropriate filling rate and appropriate temperature of the working medium, a remarkable pressure rise of the medium inside the pipe resulting from the outer heat input effectively restrains the phase change characterized by liquid phase expansion and vapor phase contraction and leads to a special mode of heat transfer with phase change suppressed. The complete evolving process from convective heat transfer, heat transfer with phase change to a mode of phase change suppressed has repeatedly been captured in a series of experiments on a NPC-HP. Especially, a wavy pattern of temperature distribution along the loop pipe is found at the phase change suppressed state.

Keywords: NPC-HP, Heat transfer rate, Pressure response, Wavy distribution of temperature.

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