Experimental Characterization of Capillary-Fed Carbon Nanotube Vapor Chamber Wicks

Abstract

The thermal performance of passive vapor chamber heat spreaders can be improved by enhancing evaporation from the internal wick structure. A wick structure that integrates conventional copper screen mesh and carbon nanotubes (CNTs) is developed and characterized for increased heat transport capability and reduced thermal resistance. The high-permeability mesh provides for a low-resistance liquid flow path while the carbon nanotubes, with their high thermal conductivity and large surface area, help reduce conduction and phase-change resistances. The wicks are fabricated by sintering a copper mesh on a multilayer substrate consisting of copper and molybdenum. CNTs are grown on to this mesh and a submicron layer of copper is evaporated on to the CNTs to improve wettability with water and wicking. Samples grown under varying degrees of positive bias voltage and varying thicknesses of post-CNT-growth copper evaporation are fabricated to investigate the effect of surface morphology variations. The resultant boiling curves indicate that micro/nano-integrated wicks fabricated with higher positive bias voltages during CNT synthesis coupled with thicker copper coatings produce lower wick thermal resistances. Notably, heat fluxes at the heater surface of greater than 500 W/cm2 were supported without a critical heat flux condition being reached.