Thermal and exergy optimization of a nanofluid-based direct absorption solar collector

Abstract

An experimental study on a nanofluid-based direct absorption solar collector (DASC) was carried out to analyze the effect of its operating conditions on the thermal performance of the collector. Graphite, magnetite and silver nanoparticles dispersed in de-ionized water were used as the heat transfer fluids. Experiments were conducted for various nanoparticle volume fractions of (5<fv<40 ppm); volumetric flow rates (5<Q<10 ml/min) and incident radiation fluxes (600<GT<1000 W/m2) based on Box-Behnken experimental design feature. The acquired data were analyzed according to response surface methodology (RSM) and the relation between the input parameters and responses (thermal and exergy efficiencies) for each nanofluid was expressed by response surface functions. The results show that among nanofluids, magnetite dispersions gained the highest thermal and exergy efficiencies; followed by graphite and silver nanofluids, respectively. Also, optimum operating conditions for each nanofluid revealed that in the given design range, the maximum thermal and exergy efficiencies occurred at fv = 40 ppm, Q = 10 ml/min and GT = 884 W/m2 for magnetite; fv = 40 ppm, Q = 10 ml/min and GT = 884 W/m2 for graphite and fv = 38.6, Q = 10 ml/min and GT = 826 W/m2 for silver nanofluids.