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 °C. The thermal conductivity of the grown MWCNTs calculated considering a mean layer thickness of 5 µm was 59 W/mK. The effective pore diameter of zircon ceramic wicks decreased from 0.54 to 0.31 µm 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.