Pool boiling performance enhancement of micro/nanoporous coated surfaces fabricated through novel hybrid method

An experimental study of nucleate pool boiling is conducted on the GNP/Ni-Al2O3 (GNP-graphene nano particle) nano-composite coated copper surfaces at atmospheric pressure using distilled water (DI) as boiling fluid. The microporous coated surfaces are fabricated using hybrid method (electrochemical deposition of GNP and nano-composite coating of Ni-Al2O3). A modified surface structure is generated as a result of this deposition, and different surface morphological parameters of this modified structure, such as surface structure, roughness and wettability, are investigated. Results show the enhancement in boiling heat transfer coefficient (BHTC) and critical heat flux (CHF) in nano-composite coated surfaces compared to the bare Cu surface. The improvement in boiling performance is mostly attributable to the enhancement of roughness and wettability as well as the higher thermal conductivity of the GNP/Ni-Al2O3 nano-coating. The highest CHF of 2217 (kW/m2) and BHTC of 112.83 (kW/m2K) is found in case of composite nano-coated superhydrophilic (CNCS) surfaces, which are 104% and 123% more than the bare Cu surface. High-speed visualization is used to conduct a quantitative investigation of the dynamics of bubble, including active bubble site density, emission frequency of the bubble, bubble departure diameter and their impact on the performance of pool boiling heat transfer.