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Salt templated and graphene nanoplatelets draped copper (GNP-draped-Cu) composites for dramatic improvements in pool boiling heat transfer.

ABSTRACT: We demonstrate a novel technique to achieve highly surface active, functional, and tunable hierarchical porous coated surfaces with high wickability using a combination of ball milling, salt-templating, and sintering techniques. Specifically, using ball-milling to obtain graphene nanoplatelets (GNP) draped copper particles followed by salt templated sintering to induce the strength and cohesiveness to the particles. The salt-templating method was specifically used to promote porosity on the coatings. A systematic study was conducted by varying size of the copper particles, ratio of GNP to copper particles, and process parameters to generate a variety of microporous coatings possessing interconnected pores and tunnels that were observed using electron microscopy. Pool boiling tests exhibited a very high critical heat flux of 289 W/cm² at a wall superheat of just 2.2 °C for the salt templated 3 wt% GNP draped 20 µm diameter copper particles with exceedingly high wicking rates compared to non-salt-templated sintered coatings. The dramatic improvement in the pool boiling performance occurring at a very low surface temperature due to tunable surface properties is highly desirable in heat transfer and many other engineering applications.

SUBMITTER: Rishi AM

PROVIDER: S-EPMC7371685 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Salt templated and graphene nanoplatelets draped copper (GNP-draped-Cu) composites for dramatic improvements in pool boiling heat transfer.

Rishi Aniket M AM Kandlikar Satish G SG Gupta Anju A

Scientific reports 20200720 1

We demonstrate a novel technique to achieve highly surface active, functional, and tunable hierarchical porous coated surfaces with high wickability using a combination of ball milling, salt-templating, and sintering techniques. Specifically, using ball-milling to obtain graphene nanoplatelets (GNP) draped copper particles followed by salt templated sintering to induce the strength and cohesiveness to the particles. The salt-templating method was specifically used to promote porosity on the coat ...[more]

PMID: 32686716

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Project description:This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results.

Dataset Information

Salt templated and graphene nanoplatelets draped copper (GNP-draped-Cu) composites for dramatic improvements in pool boiling heat transfer.

Publications

Salt templated and graphene nanoplatelets draped copper (GNP-draped-Cu) composites for dramatic improvements in pool boiling heat transfer.

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