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Nanofluid optical property characterization: towards efficient direct absorption solar collectors.

Taylor RA, Phelan PE, Otanicar TP, Adrian R, Prasher R - Nanoscale Res Lett (2011)

Bottom Line: To determine the effectiveness of nanofluids in solar applications, their ability to convert light energy to thermal energy must be known.A simple addition of the base fluid and nanoparticle extinction coefficients is applied as an approximation of the effective nanofluid extinction coefficient.Thus, nanofluids could be used to absorb sunlight with a negligible amount of viscosity and/or density (read: pumping power) increase.

View Article: PubMed Central - HTML - PubMed

Affiliation: Arizona State University, Tempe, AZ, USA. Rataylo2@asu.edu.

ABSTRACT
Suspensions of nanoparticles (i.e., particles with diameters < 100 nm) in liquids, termed nanofluids, show remarkable thermal and optical property changes from the base liquid at low particle loadings. Recent studies also indicate that selected nanofluids may improve the efficiency of direct absorption solar thermal collectors. To determine the effectiveness of nanofluids in solar applications, their ability to convert light energy to thermal energy must be known. That is, their absorption of the solar spectrum must be established. Accordingly, this study compares model predictions to spectroscopic measurements of extinction coefficients over wavelengths that are important for solar energy (0.25 to 2.5 μm). A simple addition of the base fluid and nanoparticle extinction coefficients is applied as an approximation of the effective nanofluid extinction coefficient. Comparisons with measured extinction coefficients reveal that the approximation works well with water-based nanofluids containing graphite nanoparticles but less well with metallic nanoparticles and/or oil-based fluids. For the materials used in this study, over 95% of incoming sunlight can be absorbed (in a nanofluid thickness ≥10 cm) with extremely low nanoparticle volume fractions - less than 1 × 10-5, or 10 parts per million. Thus, nanofluids could be used to absorb sunlight with a negligible amount of viscosity and/or density (read: pumping power) increase.

No MeSH data available.


Modeled and experimental extinction coefficients for several concentrations of aqueous graphite nanofluids. Experimental results for pure water and water with 5 % surfactant are also plotted for comparison.
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Figure 5: Modeled and experimental extinction coefficients for several concentrations of aqueous graphite nanofluids. Experimental results for pure water and water with 5 % surfactant are also plotted for comparison.

Mentions: To compare the approaches discussed above, Figure 5 shows several concentrations of water-based graphite nanofluids - nominally 30 nm in diameter of spherical particles. Experimental (labeled "EXP") and modeling (labeled "MOD") results are plotted together. Due to the large number of data points, the measured/experimental results are shown as lines while the modeling results are shown as marker curves. Note that the curve labeled "Water_MOD" is essentially data from the reference book by Palik [29]. That is, Equation 16 is used to manipulate reference text data from the complex refractive index, kEXP, to the extinction coefficients shown in the plot. For comparison, pure water with an excessive amount, 5% by volume, of surfactant is also shown. A high volume fraction surfactant was used to exaggerate the absorption of surfactant, which turns out to be very small.


Nanofluid optical property characterization: towards efficient direct absorption solar collectors.

Taylor RA, Phelan PE, Otanicar TP, Adrian R, Prasher R - Nanoscale Res Lett (2011)

Modeled and experimental extinction coefficients for several concentrations of aqueous graphite nanofluids. Experimental results for pure water and water with 5 % surfactant are also plotted for comparison.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211283&req=5

Figure 5: Modeled and experimental extinction coefficients for several concentrations of aqueous graphite nanofluids. Experimental results for pure water and water with 5 % surfactant are also plotted for comparison.
Mentions: To compare the approaches discussed above, Figure 5 shows several concentrations of water-based graphite nanofluids - nominally 30 nm in diameter of spherical particles. Experimental (labeled "EXP") and modeling (labeled "MOD") results are plotted together. Due to the large number of data points, the measured/experimental results are shown as lines while the modeling results are shown as marker curves. Note that the curve labeled "Water_MOD" is essentially data from the reference book by Palik [29]. That is, Equation 16 is used to manipulate reference text data from the complex refractive index, kEXP, to the extinction coefficients shown in the plot. For comparison, pure water with an excessive amount, 5% by volume, of surfactant is also shown. A high volume fraction surfactant was used to exaggerate the absorption of surfactant, which turns out to be very small.

Bottom Line: To determine the effectiveness of nanofluids in solar applications, their ability to convert light energy to thermal energy must be known.A simple addition of the base fluid and nanoparticle extinction coefficients is applied as an approximation of the effective nanofluid extinction coefficient.Thus, nanofluids could be used to absorb sunlight with a negligible amount of viscosity and/or density (read: pumping power) increase.

View Article: PubMed Central - HTML - PubMed

Affiliation: Arizona State University, Tempe, AZ, USA. Rataylo2@asu.edu.

ABSTRACT
Suspensions of nanoparticles (i.e., particles with diameters < 100 nm) in liquids, termed nanofluids, show remarkable thermal and optical property changes from the base liquid at low particle loadings. Recent studies also indicate that selected nanofluids may improve the efficiency of direct absorption solar thermal collectors. To determine the effectiveness of nanofluids in solar applications, their ability to convert light energy to thermal energy must be known. That is, their absorption of the solar spectrum must be established. Accordingly, this study compares model predictions to spectroscopic measurements of extinction coefficients over wavelengths that are important for solar energy (0.25 to 2.5 μm). A simple addition of the base fluid and nanoparticle extinction coefficients is applied as an approximation of the effective nanofluid extinction coefficient. Comparisons with measured extinction coefficients reveal that the approximation works well with water-based nanofluids containing graphite nanoparticles but less well with metallic nanoparticles and/or oil-based fluids. For the materials used in this study, over 95% of incoming sunlight can be absorbed (in a nanofluid thickness ≥10 cm) with extremely low nanoparticle volume fractions - less than 1 × 10-5, or 10 parts per million. Thus, nanofluids could be used to absorb sunlight with a negligible amount of viscosity and/or density (read: pumping power) increase.

No MeSH data available.