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. 2018 Jul:122:10.1016/j.ijheatmasstransfer.2018.01.141.
doi: 10.1016/j.ijheatmasstransfer.2018.01.141.

Effect of surfactants on the stability and solar thermal absorption characteristics of water-based nanofluids with multi-walled carbon nanotubes

Tae Jong Choi  1 , Seok Pil Jang  1   2 , M A Kedzierski  2
Affiliations

Effect of surfactants on the stability and solar thermal absorption characteristics of water-based nanofluids with multi-walled carbon nanotubes

Tae Jong Choi et al. Sol Energy. 2018 Jul.

Abstract

This paper reports the effect of various surfactants on the suspension stability and the solar thermal absorption characteristics of water-based nanofluids containing multi-walled carbon nanotubes (MWCNTs) that can be used as working fluids for volumetric solar thermal receivers. The water-based MWCNT nanofluids were prepared using a two-step method with four commonly used surfactants: sodium dodecylbenzenesulfonate (SDBS), cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Triton X-100 (TX-100). The stability of the four surfactant-treated nanofluids was analyzed for over a month with an in-house developed laser transmission system. The effect of temperature on the stability of the nanofluid/surfactant mixtures was also examined. In addition, to identify the absorption characteristics of the four nanofluids, the spectral extinction coefficients were measured using an UV-Vis-NIR spectrophotometer. The absorbed sunlight fraction was calculated using the measured spectral extinction coefficient, which enabled an evaluation of the absorption characteristics of the nanofluids. The MWCNT nanofluids were clearly shown to enhance the absorption rate of solar thermal energy. The suspension stability and the absorption characteristics were also strongly affected by the type of surfactant. Moreover, using the absorbed sunlight fraction and suspension-stability factor, we experimentally show the relation between the absorption characteristics and suspension stability in nanofluids.

Keywords: Absorbed sunlight fraction; Extinction coefficient; MWCNTs; Surfactants; Suspension stability; Volumetric solar thermal receivers; Water-based nanofluids containing.

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Conflict of interest statement

Conflict of interest The authors declare that there is no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Nanofluids with (a) volume fraction ϕ=0.0005%, (b) ϕ=0.002% manufactured with various surfactants by the two-step method with wet-milling process.
Fig. 2.
Fig. 2.
Laser transmission apparatus for measuring the suspension-stability factor, ε, of nanofluids.
Fig. 3.
Fig. 3.
Suspension-stability factor, ε of suspension stability on nanofluids.
Fig. 4.
Fig. 4.
Results of the high-temperature suspension-stability test of the nanofluids with ϕ=0.002% (85 °C).
Fig. 5.
Fig. 5.
Suspension-stability factor, ε, at high temperature (85 °C).
Fig. 6.
Fig. 6.
Length of MWCNT manufactured by the planetary ball mill.
Fig. 7.
Fig. 7.
Results of low-temperature suspension-stability test (10 °C).
Fig. 8.
Fig. 8.
Enhancement of the extinction coefficient of water-based MWCNT nanofluids with each of four surfactants (within 3 h after production, 25 °C).
Fig. 9.
Fig. 9.
Extinction coefficient of water-based MWCNT nanofluids.
Fig. 10.
Fig. 10.
Absorbed sunlight fraction according to the suspension-stability factor.
See this image and copyright information in PMC

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