This article explores combined volumetric radiation and natural convection in a square cavity containing a nanofluid for the first time using lattice Boltzmann method -LBM- to consider the absorbing and scattering coefficients of nanoparticles through the nanofluid as a participating medium. Accordingly, the flow, energy and radiative equations are solved by using separate distribution functions in the LBM. Also, the Rayleigh theory is used to obtain the optical properties of nanofluid. Mixtures of Al2O3 nanoparticles suspended in water are considered as the nanofluid. The effects of volumetric radiation at different values of Rayleigh number -103, 104 and 105- and volume concentration -0.1% and 0.3%- on the flow and thermal fields are examined. It is observed that the average Nusselt number is enhanced by considering radiation, but it has a reverse relationship with volume concentration. The present work indicates that the proposed Lattice Boltzmann method can provide new results which will be very helpful in analyzing the radiant enclosures containing nanoparticles.

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