Applicability of nanofluids in high flux solar collectors

Abstract

Concentrated solar energy has become the input for an increasing number of experimental and commercial thermal systems over the past 10–15 years [M. Thirugnanasambandam et al., Renewable Sustainable Energy Rev. 14 (2010)]. Recent papers have indicated that the addition of nanoparticles to conventional working fluids (i.e., nanofluids) can improve heat transfer and solar collection [H. Tyagi et al., J. Sol. Energy Eng. 131, 4 (2009); P. E. Phelan et al., Annu. Rev. Heat Transfer 14 (2005)]. This work indicates that power tower solar collectors could benefit from the potential efficiency improvements that arise from using a nanofluid working fluid. A notional design of this type of nanofluid receiver is presented. Using this design, we show a theoretical nanofluid enhancement in efficiency of up to 10% as compared to surface-based collectors when solar concentration ratios are in the range of 100–1000. Furthermore, our analysis shows that graphite nanofluids with volume fractions on the order of 0.001% or less are suitable for 10–100 MWe power plants. Experiments on a laboratory-scale nanofluid dish receiver suggest that up to 10% increase in efficiency is possible (relative to a conventional fluid)—if operating conditions are chosen carefully. Lastly, we use these findings to compare the energy and revenue generated in a conventional solar thermal plant to a nanofluid-based one. It is found that a 100 MWe capacity solar thermal power tower operating in a solar resource similar to Tucson, AZ, could generate ∼$3.5 million more per year by incorporating a nanofluid receiver.