Upper limits for the work extraction by nanofluid-filled selective flat-plate solar collectors

The objective of this paper is to investigate the effect of simultaneous using of nanofluid and selective absorber on the improvement of work extraction by a solar flat-plate collector (FPC). Applying a precise model for the exergy factor of solar incident, it is found that the maximum power generation is higher and lower than that by the Petela-Landesberg-Press (PLP) and Carnot model, respectively. Results showed that the influence of temperature ratio (a) and geometry factor (f) on the exergy efficiency is not such significant when a FPC is working on the Earth's surface. It is also revealed that the key role of the ratio of the absorber plate's emittance to its absorptance must be given attention since only the values lower than 0.174 are allowed by the second law requirements. Furthermore, the exergy efficiency and energy efficiency would experience 10.5% and near 8% enhancement for a 7.5% increase in collector's optical efficiency. Boosting the exergy efficiency by almost 4.1% at 4% volume concentration, demonstrated that nanofluid exploitation instead of plain water would be capable of improving the power generation by the collector.