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research-article

Analysis of Nanofluid-Based Parabolic Trough Collectors for Solar Thermal Applications

[+] Author and Article Information
Justin P Freedman

Energy Storage and Distributed Resources Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720
justinfreedman@justinfreedman.com

Hao Wang

Energy Storage and Distributed Resources Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720
hwang204@asu.edu

Dr. Ravi Prasher

Energy Storage and Distributed Resources Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720Department of Mechanical Engineering, University of California, Berkeley, CA 94720
RSPrasher@lbl.gov

1Corresponding author.

ASME doi:10.1115/1.4039988 History: Received November 26, 2017; Revised March 31, 2018

Abstract

Solar-to-thermal energy conversion technologies are an increasingly promising segment of our renewable energy technology future. Today, concentrated solar power plants provide a method to efficiently store and distribute solar energy. Current industrial solar-to-thermal energy technologies employ selective solar absorber coatings to collect solar radiation, which suffer from low solar-to-thermal efficiencies at high temperatures due to increased thermal emission from selective absorbers. Solar absorbing nanofluids (a heat transfer fluid seeded with nanoparticles), which can be volumetrically heated, are one method to improve solar-to-thermal energy conversion at high temperatures. To date, radiative analyses of nanofluids via the radiative transfer equation have been conducted for low temperature applications and for flow conditions and geometries that are not representative of the technologies used in the field. In this work, we present the first comprehensive analysis of nanofluids for concentrated solar power plants in a parabolic trough configuration. This geometry was chosen because parabolic troughs are the most prevelant CSP technologies. We demonstrate that the solar-to-thermal energy conversion efficiency can be optimized by tuning the nanoparticle volume fraction, the temperature of the nanofluid, and the incident solar concentration. Moreover, we demonstrate that direct solar absorption receivers have a unique advantage over current surface-based solar coatings at large tube diameters. This is because of a nanofluid’s tunability, which allows for high solar-to-thermal efficiencies across all tube diameters enabling small pressure drops to pump the heat transfer fluid at large tube diameters.

Copyright (c) 2018 by ASME
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