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Critical heat flux enhancement in pool boiling through increased rewetting on nanopillar array surfaces.

ABSTRACT: Boiling is a key heat transfer process for a variety of power generation and thermal management technologies. We show that nanopillar arrays fabricated on a substrate enhance both the critical heat flux (CHF) and the critical temperature at CHF of the substrate and thus, effectively increase the limit of boiling before the boiling crisis is triggered. We reveal that the enhancement in both the CHF and the critical temperature results from an intensified rewetting process which increases with the height of nanopillars. We develop a predictive model based on experimental measurements of rewetting velocity to predict the enhancement in CHF and critical temperature of the nanopillar substrates. This model is critical for understanding how to control boiling enhancement and designing various nanostructured surfaces into specific applications.

SUBMITTER: Nguyen TB

PROVIDER: S-EPMC5859279 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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Critical heat flux enhancement in pool boiling through increased rewetting on nanopillar array surfaces.

Nguyen Thien-Binh TB Liu Dongdong D Kayes Md Imrul MI Wang Baomin B Rashin Nabeel N Leu Paul W PW Tran Tuan T

Scientific reports 20180319 1

Boiling is a key heat transfer process for a variety of power generation and thermal management technologies. We show that nanopillar arrays fabricated on a substrate enhance both the critical heat flux (CHF) and the critical temperature at CHF of the substrate and thus, effectively increase the limit of boiling before the boiling crisis is triggered. We reveal that the enhancement in both the CHF and the critical temperature results from an intensified rewetting process which increases with the ...[more]

PMID: 29555913

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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

Critical heat flux enhancement in pool boiling through increased rewetting on nanopillar array surfaces.

Publications

Critical heat flux enhancement in pool boiling through increased rewetting on nanopillar array surfaces.

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