Modifying the Heat Transfer and Capillary Pressure of Loop Heat Pipe Wicks with Carbon Nanotubes.

Porous material is a critical component in the loop heat pipe (LHP) device, the efficiency of which depends on the thermal conductivity of the wick and its capillary capacity. A new bilayer wick based on ceramic material and carbon nanotubes in the outer surface has been designed. The thermal conductivity and capillary pressure of the surface of a ceramic LHP wick prototype have been modified by growing multiwalled carbon nanotubes (MWCNTs). The presence of a thin layer of MWCNTs increased the thermal conductivity of wick specimens between 18.87 and 26.42% for temperatures ranging from -50 to 50 degrees C. The thermal conductivity of the grown MWCNTs calculated considering a mean layer thickness of 5 mu m was 59 W/mK. The effective pore diameter of zircon ceramic wicks decreased from 0.54 to 0.31 mu m leading to an important increase in capillary pressure. The maximum heat transfer capacity and thermal resistance of the designed by-layer wick have been determined. The presence of carbon nanotubes decreases the thermal resistance and enabled the enhancement of the thermal and porous characteristics of the wicks in a promising way so as to optimize their performance as LHPs wicks.