potential of nanodiamond/water nanofluid as working fluid of volumetric solar collectors

In this study, the thermal efficiency of volumetric solar collector is experimentally compared using diamond nanofluid as the working fluid. first, the dispersion stability of prepared nanofluids is considered with zeta potential method. then, the radiative properties of nanofluids, which affect directly the efficiency of volumetric collector, are experimentally determined using spectrophotometry method. two setups for outdoor performance test of volumetric and surface solar collectors have been designed and built based on en12975-2 standard. the tests were performed under different flow rate conditions and nanoparticle weight fractions. the thermal performance tests of volumetric collector reveals that using nanodiamond nanofluid (weight fraction of 0.001 wt%) enhanced the efficiency up to 19.6% compared to water-based one, at the mass flow rate of 0.0225 kg/s. in addition, at low reduced temperature difference, the efficiency of nanofluid-based volumetric collector is found to be 17.8% higher than that of a waterbased surface solar collector, under similar operating conditions. based on the experimental results obtained from this study, the nanofluidbased volumetric solar collector is suitable for utilization in water heating systems of residential buildings, but it will require new solar equipment like pcm or stratified storage tanks to be competitive with surface solar collectors.