Evaluation of nanoparticle shape effect on a nanofluid based flat-plate solar collector efficiency

Abstract

Solar thermal energy is a very convenient source of heating which is environmentally benign. Solar collectors convert solar radiation into heat and transfer the heat to a medium. Flat-plate solar collectors are the most common and cost effective devices for exploiting solar energy. However, these systems have relatively low efficiency due to the poor thermo-physical properties of working fluid. Dispersing of nanometer sized particles into the base fluid is proposed as an efficient method to improve heat transfer properties of the working fluid. In order to evaluate the thermal performance of nanofluid in a solar collector, firstly, it is essential to understand the thermo-physical variations of base fluid through addition of nanoparticles. Thermo-physical properties of base fluid vary with parameters such as particle concentration, particle diameter, and particle shape. In this study the effect of these parameters are explored on thermal performance of a flat-plate solar collector theoretically. Investigating shape effect of particles on collector efficiency is a highlight in this study. It is observed that increasing nanoparticles volumetric concentration leads to enhancenement in flat-plate collector efficiency. Reversely, particle size enhancement reduces the efficiency. In addition, particle shape affects collector efficiency. For different shapes of particles, including spherical, brick, cylinders, platelets, and blades, the blade shape particles relatively have the highest efficiency.