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Purpose -The purpose of this paper is to study the radiation-natural convection interactions in a vertical divided vented channel. The effects of the surface emissivity, the vent opening position and size on the heat transfer and the flow structures inside the channel were studied. Design/methodology/approach -The governing differential equations are solved by a finite volume method, with adopting the SIMPLER algorithm for pressure-velocity coupling. The view factors were determined by using a boundary elements approximation and a Monte Carlo method. Findings -The effect of the radiation exchange is very important, it increases the average hot wall Nusselt number by more than 100 per cent. The contribution of the channel wall emissivity in the heat transfer is more important than that of the plate emissivity. The average hot wall Nusselt number increases with increasing the vent opening size, only in presence of the radiation exchange, and this increase is more pronounced, particularly when the vent opening is located near the channel inlet.Research limitations/implications -The flow is assumed to be incompressible, laminar and two dimensional. The radiative surfaces are assumed diffuse-grey. The working fluid, air, is considered as transparent with respect to the radiation. Practical implications -The industrial applications of this study are solar collectors, thermal building, electronic cooling, aeronautics, chemical apparatus, nuclear engineering, etc. Originality/value -In comparison to the preceding studies, the originality of this paper is the taking into account of the radiation exchange in a vented and divided channel.