Enhanced critical heat flux with single-walled carbon nanotubes bonded on metal surfaces

This study investigates a novel and practical technique to improve the critical heat flux (CHF) of thermal devices by bonding a film of single-walled carbon nanotubes (SWCNTs) to metal surfaces. Various SWCNT film layers in thicknesses of 296, 613, 845, and 1432 nm were fabricated by vacuum filtration. Experimental work of surface characterization and pool boiling heat transfer was conducted with bare stainless steel grade 316 heaters and SWCNT-coated heaters in the deionized water under atmospheric pressure. Surface characterization of the CNT adhesion showed that SWCNT adhesion to the metal surface exhibited properties of a smooth porous medium with smaller roughness compared to the bare SS316 substrate. Wall superheat and applied heat flux were measured and high speed images of boiling process were captured at a rate of 1500 frames/s during respective tests. The CHF with the random SWCNT network-coated heater was observed to increase by up to 55% compared to the bare SS316 heater. The increased porosity with the adhesion of a random SWCNT network is believed responsible for the enhanced CHF. However, nucleate boiling heat transfer coefficient with SWCNT-coated heaters was reduced compared to the bare heaters due to the lower surface roughness.