Enhanced pool boiling critical heat flux of water using carbon nanotubes adhesion on stainless steel heaters

This study investigates a novel and practical technique to improve the thermal safety margin of the thermal devices by introducing the Single-Walled Carbon Nanotubes (SWCNTs) adhesion on metal surfaces. As a quantitative measure of the thermal safety margin, critical heat flux is introduced and relevant experimental work has been conducted with bare stainless steel grade 316 heaters and CNT-coated heaters. CNTs were adhered to the metal substrate of SS316, whose dimension is 16×4×2 mm³ in length, width, and thickness, respectively. Various CNTs layer thicknesses of 280, 569, 960, and 1400 nm were fabricated. Bare and CNT-coated SS316 heaters were electrically heated via Joule heating using 12 kW DC power supply of 1200A-10V in the pool of deionized water at atmospheric pressure. After fabricating the CNT adhesion, surface characterization of SEM, AFM, roughness, contact angle measurement was conducted. This clearly shows that CNT adhesion to the metal surface exhibits smooth porous media but with smaller roughness compared to bare SS316 substrate. Wall superheat and applied heat flux were measured for bare and CNT-coated heaters. High speed images of boiling process were captured during respective tests at a rate of 1500 frames/sec. It is observed that CHF with CNT-coated heater increases by up to 55% as compared to the bare SS316 heater, which suggests that safety margin is improved significantly using the CNT adhesion on the metal surfaces. However, nucleate boiling heat transfer coefficient is reduced due to the lower surface roughness.