Study of copper chemical-plating modified polyacrylonitrile-based carbon fiber wick applied to compact loop heat pipe

Abstract

This paper reports on the working characteristics of a flat plate loop heat pipe (LHP) with a thin polyacrylonitrile-based carbon fiber felt as a porous medium structure. To improve the hydrophilic properties of carbon fiber, a chemical-plating process is used to coat the carbon fiber surface with copper. The surface characteristics and pumping characteristics of modified capillary wicks are characterized using an electron microscope, scanning electron microscope, infrared radiation camera, and high-speed photography. The results show that the flat plate LHP with the modified thin carbon fiber felt as the capillary wick can start successfully and maintain stable operation in the range of 15–75 W (heat flux of 12 W/cm2). The total thermal resistance varies from 1.1 to 0.45 °C/W at heat loads ranging from 15 to 75 W. As a flexible and soft material, carbon fiber has the advantages of good matching with the evaporator, and resistance to mechanical damage. After it is modified by copper plating on its surface, it becomes a kind of hydrophilic material with an excellent capillary force. Furthermore, the copper plating layer increases the surface thermal conductivity and is beneficial to the uniform heating of the working fluid in the evaporating chamber. The fabrication of carbon fiber capillary wick is not limited to its volume.