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The article focuses on the mixed convective flow of Ag–ethylene glycol nanofluid. The analysis is carried out for a cavity having center as heated. The relatively moving side walls of cavity are retained at low constant temperature while constant heat source is examined in the bottom wall. The rest of the bottom and top walls remain insulated. Cattaneo–Christov heat flux is implemented in the analysis of heat transfer. Heat transfer rate is dig out for the case of Fourier's heat flux, as for the case of Cattaneo–Christov heat flux it gives implicit expression, which is difficult to analyze and simplify. The problem is analyzed numerically via projection method. Higher heat transfer is observed for the Fourier's law as compare to Cattaneo–Christov heat flux. The results are expressed by isotherms, streamlines, velocity field, and average Nusselt numbers. • Nanoparticles in a viscous flow is studied. • The impact of thermal relaxation time is considered. • Comparison of Fourier's and Cattaneo–Christov heat flux is presented. • Thermal relaxation declines the transfer of heat. [ABSTRACT FROM AUTHOR]

Nanofluid, an advanced type of fluid containing small quantity of nanoparticles (usually less than 100 nm), has been proven to provide more efficient heat transfer compared to conventional fluids. The dispersion of a small amount of solid nanoparticles in conventional fluids such as water or ethylene glycol changes their thermal conductivity remarkably. Recently, nanofluid has been used as a heat transfer fluid to enhance the performance of solar collector devices. This paper reviews recent progress and applications of nanofluids in stationary solar collectors. In addition to reviewing the efficiency of solar collectors which use nanofluids, the paper also discusses the impact of nanofluid usage in solar collector based on economic and environmental viewpoints. Finally, the challenges and future trends related to the application of nanofluids in thermal solar collector is discussed. [ABSTRACT FROM AUTHOR]