: Results showed that the thermal conductivity and aggregation of the prepared nanofluid were highest and lowest, respectively, under optimal stability conditions. A new method was developed for calculating the extinction coefficient of the binary nanofluids based on the classical electromagnetic theory. It is shown that the extinction coefficients obtained from the analytical and experimental studies are in good agreement. Moreover, the extinction coefficient of the binary nanofluids is found to be approximately equal to the sum of the extinction coefficients of the constituent components. This was confirmed both analytically and experimentally. By increasing the nanoparticles volume fraction, improvements are observed in the extinction coefficient of the constructed binary nanofluids. Also, the analytical and experimental results of the study show that the extinction coefficient of the binary nanoparticles dispersed in water as the “base fluid” is greater than those of the binary nanoparticles dispersed in ethylene glycol or the mixture of ethylene glycol-water. Also, the present study includes the experimental and numerical evaluation of the effects of application of the binary nanofluid on the thermal efficiency of a Direct Absorption Parabolic Trough Collector's (DAPTC). The numerical analysis of DAPTC is based on the power-law with the objective of simulating a turbulent flow in the receiver pipe. Results of the modeling indicate that the average radial temperature and energy generation terms due to the solar irradiance absorbed and scattered by the nanoparticles decrease with increasing distance from the receiver pipe wall. It is also found that the solar irradiance is absorbed and converted into a significant amount of sensible heat along the length of the receiver pipe. Finally, the results of both numerical and experimental investigations of the DAPTC collector show that the thermal efficiency of the system improves as a result of increased nanoparticle volume fraction and nanofluid flow rate. keywords: Binary nanofluid, Electromagnatic field, Extiction coefficient, Thermal efficiency, Direct Absorption Parabolic Trough Collector (DAPTC)
