Natural convection in an inclined cavity with time-periodic temperature boundary conditions using nanofluids: Application in solar collectors

•Time natural convective flow and heat transfer of a nanofluid is studied.•An inclined cavity with time-periodic temperature boundary conditions has been considered.•A growth of boundary temperature oscillating frequency leads to an increase in the average Nusselt number oscillation amplitude and reduction of oscillation period.•The cavity inclination angle and periodic thermal boundary conditions can be very good control parameters for heat and fluid flow inside the cavity. Natural convection of alumina-water nanofluid inside a square cavity with time-sinusoidal temperature is studied numerically. The domain of interest is an inclined square cavity having isothermal wall at x¯=L, while temperature of the wall x¯=0 is changed as a sinusoidal function of time, other walls are adiabatic. Dimensionless governing equations formulated using stream function, vorticity and temperature have been solved by finite difference method of the second order accuracy. The effects of Rayleigh number, oscillating frequency, cavity inclination angle and nanoparticles volume fraction on fluid flow and heat transfer have been analyzed. It has been found that a growth of boundary temperature oscillating frequency leads to an increase in the average Nusselt number oscillation amplitude and reduction of oscillation period. At the same time, the boundary temperature oscillating frequency is a very good control parameter that allows to intensify convective flow and heat transfer.