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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.


Extinction coefficients - measurements versus modeling for promising water-based "solar nanofluids". The curve which is the lowest on the right part of the graph represents the irradiance directly hitting a normal surface for a mid-latitude summer location in the United States.
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Figure 6: Extinction coefficients - measurements versus modeling for promising water-based "solar nanofluids". The curve which is the lowest on the right part of the graph represents the irradiance directly hitting a normal surface for a mid-latitude summer location in the United States.

Mentions: Conventional solar receivers have fluid depths on the order of 10 cm. Thus, a real nanofluid solar receiver would likely have a similar geometry. Figure 6 shows some characteristic results for several water-based nanofluids which were chosen to absorb > 95% of incoming solar radiation over this fluid depth. Direct normal solar irradiance is also shown over the same wavelengths for comparison in Figure 6. Again, one can see the characteristic high extinction coefficients for the nanoparticles at short wavelength and that of water at longer wavelengths, ≥1.1 μm. For this fluid thickness, the nanoparticles will be absorbing approximately 65% to 70% of the incoming solar energy, with the base fluid, water, absorbing approximately 30%.


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

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

Extinction coefficients - measurements versus modeling for promising water-based "solar nanofluids". The curve which is the lowest on the right part of the graph represents the irradiance directly hitting a normal surface for a mid-latitude summer location in the United States.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Extinction coefficients - measurements versus modeling for promising water-based "solar nanofluids". The curve which is the lowest on the right part of the graph represents the irradiance directly hitting a normal surface for a mid-latitude summer location in the United States.
Mentions: Conventional solar receivers have fluid depths on the order of 10 cm. Thus, a real nanofluid solar receiver would likely have a similar geometry. Figure 6 shows some characteristic results for several water-based nanofluids which were chosen to absorb > 95% of incoming solar radiation over this fluid depth. Direct normal solar irradiance is also shown over the same wavelengths for comparison in Figure 6. Again, one can see the characteristic high extinction coefficients for the nanoparticles at short wavelength and that of water at longer wavelengths, ≥1.1 μm. For this fluid thickness, the nanoparticles will be absorbing approximately 65% to 70% of the incoming solar energy, with the base fluid, water, absorbing approximately 30%.

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.