Boiling flow of graphene nanoplatelets nano-suspension on a small copper disk

In the present work, an attempt was made to experimentally quantify the boiling heat transfer coefficient (BHTC) of graphene oxide-water nano-suspension (NS) inflow boiling heat transfer regime. The NS was prepared at weight fractions of 0.025, 0.05, and 0.1% using the two-step method and further stabilized for 17 days (at wt% = 0.1). Results showed that the presence of graphene oxide nanoplatelets (GNPs) imposed an extreme fouling thermal resistance (FTR) to the surface, which caused a reduction in the BHTC over 1000 min of continuous operation after the CHF point. This was mainly due to the presence of the graphene oxide on the surface, which created a surficial fouling layer and heat accumulation on the surface. Instead, the sedimentation layer promoted the critical heat flux (CHF) point such that the point for water was 1370 kW/m(2) reaching 1640 kW/m(2) for NS at wt% = 0.1. Likewise, the highest BHTC of 17.4 kW/(m(2)K) at Re = 10,950 was obtained. Also, with increasing the heat flux and flow rate, the BHTC increased. The same trend was also identified with a mass fraction of GNPs up to CHF point. The increase in the BHTC was attributed to the intensification of the Brownian motion and thermophoresis effect in the boiling micro-layer close to the surface. (C) 2020 Elsevier B.V. All rights reserved. (AU)