Amelioration of the pool boiling heat transfer performance by colloidal dispersions of carbon black

Recently, carbon-based colloid materials gained popularity in boiling heat transfer (BHT) research. Among them, carbon nanotubes (CNT), functionalized CNT, graphene, graphene oxide, reduced graphene oxide, and nanodiamonds have been investigated in the literature. Most of the studies reported enhanced BHT performance. This study aimed to investigate the BHT performance of the colloidal dispersions of carbon black (CB), which has favorable intrinsic properties but it has not yet been studied in BHT research. Experimentally, stable dispersions of CB colloids were prepared in deionized water at three different weight concentrations: 0.001%, 0.005% and 0.01%. A custom-built experimental pool boiling setup with a flat copper heating surface was used to investigate the BHT performance of the CB colloids. The heat transfer coefficient (HTC) and critical heat flux (CHF) enhancements of the nanofluids increased with the increasing CB concentration and reached 190.5% and 67.8%, respectively at 0.01 wt% CB. The CHF enhancement was attributed to the decent lateral heat conduction of the CB microlayer. It prevented localized heating by spreading the surface heat in lateral directions and delayed the formation of hot/dry spots to higher heat fluxes. The HTC enhancement was due to the densely distributed small cavities on the coating layer, which increased the surface roughness by similar to 9-fold. This provided a larger effective surface area for heat transfer, and a greater active bubble nucleation site density. The more hydrophobic surface rendered higher bubble departure frequency that effectively transferred the heat from the heating surface to the bulk fluid. (C) 2019 Elsevier Ltd. All rights reserved.