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Research Papers

Predicted Efficiency of a Low-Temperature Nanofluid-Based Direct Absorption Solar Collector

[+] Author and Article Information
Himanshu Tyagi, Ravi Prasher

School of Mechanical, Aerospace, Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287-6106

Patrick Phelan1

School of Mechanical, Aerospace, Chemical and Materials Engineering, National Center of Excellence on SMART Innovations, Arizona State University, Tempe, AZ 85287-6106phelan@asu.edu

1

Corresponding author.

J. Sol. Energy Eng 131(4), 041004 (Sep 17, 2009) (7 pages) doi:10.1115/1.3197562 History: Received July 11, 2007; Revised September 24, 2008; Published September 17, 2009

Due to its renewable and nonpolluting nature, solar energy is often used in applications such as electricity generation, thermal heating, and chemical processing. The most cost-effective solar heaters are of the “flat-plate” type, but these suffer from relatively low efficiency and outlet temperatures. The present study theoretically investigates the feasibility of using a nonconcentrating direct absorption solar collector (DAC) and compares its performance with that of a typical flat-plate collector. Here a nanofluid—a mixture of water and aluminum nanoparticles—is used as the absorbing medium. A two-dimensional heat transfer analysis was developed in which direct sunlight was incident on a thin flowing film of nanofluid. The effects of absorption and scattering within the nanofluid were accounted for. In order to evaluate the temperature profile and intensity distribution within the nanofluid, the energy balance equation and heat transport equation were solved numerically. It was observed that the presence of nanoparticles increases the absorption of incident radiation by more than nine times over that of pure water. According to the results obtained from this study, under similar operating conditions, the efficiency of a DAC using nanofluid as the working fluid is found to be up to 10% higher (on an absolute basis) than that of a flat-plate collector. Generally a DAC using nanofluids as the working fluid performs better than a flat-plate collector, however, much better designed flat-plate collectors might be able to match or outperform a nanofluids based DAC under certain conditions.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 7

Collector efficiency (Eq. 11) as a function of the collector length (L) (D=5 nm and fv=0.8%)

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Figure 6

Collector efficiency (Eq. 11) as a function of the collector height (H) (D=5 nm and fv=0.8%)

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Figure 5

Collector efficiency (Eq. 11) as a function of the particle volume fraction (fv)(D=5 nm)

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Figure 4

Collector efficiency (Eq. 11) as a function of the particle size (D)(fv=0.8%)

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Figure 3

Temperature distribution within the solar collector (D=5 nm and fv=0.8%)

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Figure 2

Spectral radiant intensity within the solar collector at various depths (D=5 nm and fv=0.8%)

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Figure 1

Schematic of the nanofluid-based direct absorption solar collector

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Figure 8

Collector efficiency (Eq. 11) as a function of the normalized fluid inlet temperature, (Tin−Tamb)/GT, at different values of fluid thickness (H) and particle volume fraction (fv)(D=5 nm). Shown for comparison are results for a conventional flat-plate collector (16-17).

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