Experimental investigation of thermal performance for direct absorption solar parabolic trough collector (DASPTC) based on binary nanofluids
Nanofluids can be utilized to capture and distribute effectively solar radiation due to the capability of their nanoparticles in the liquid medium to scatter and absorb solar radiation. Hence, nanofluid-based solar collectors have the potential to harness solar radiant energy. Proper nanofluids can be selected for solar applications based on their potential optical properties. Binary nanofluids as a new class of nanofluids comprising a base fluid and two different nanoparticles may exhibit a behavior different from any of their components. The behavior of such nanofluids has not yet been extensively investigated. The present experimental study was, therefore, designed and implemented to investigate the absorption and thermal conductivity of binary nanofluids and to evaluate the factors involved in their optimal stability. For this purpose, two dissimilar nanoparticles, i.e. CuO (with high absorption properties) and γ-Al2O3 (with high scattering properties) were chosen to prepare a binary nanofluid. Results showed that the thermal conductivity and aggregation of the prepared nanofluid were highest and lowest, respectively, under optimal stability conditions. As another main goal of this study, the effect of the binary nanofluid on the thermal efficiency of direct absorption solar parabolic trough collectors (DASPTCs) was evaluated. Results showed that solar irradiance is absorbed and converted into a significant amount of sensible heat along the length of the receiver pipe. Experiments with the DASTPC collector also revealed that the thermal efficiency of the system could be enhanced by increasing nanoparticle volume fraction and nanofluid flow rate.