In this paper transient natural convection in a vertical convergent channel with or without saturated porous medium is studied numerically. The investigation is carried out in laminar, two dimensional regime and employing the Brinkman-Forchheimer-extended Darcy model. The physical domain consists of two non-parallel plates which form a convergent channel. Both plates are heated at uniform heat flux. The solutions are achieved using the commercial code FLUENT. A finite-extension computational domain is employed to simulate the free-stream condition. The results are obtained for different convergence angles, for 0° to 5°, and porosity coefficient (0.4, 0.6 and 0.9), a channel aspect ratio equal to 10, a Rayleigh number equal to 104 and a Darcy number equal to 0.01. The dimensionless results are reported in terms of average and maximum wall temperatures, average Nusselt number as a function of time and at steady state wall temperature, local Nusselt number and temperature and stream function fields. The cases with porous medium in the channel shows that in conductive regime dominant, at initial time, average and maximum wall temperatures are lower than the case without porous medium in the channel. For the convective regime dominant, the lowest average and maximum wall temperatures are attained for the case without porour medium in the channel. At steady state, in the inlet zone the cases with porous medium present wall temperature lower than the no porous case. In the other part of the channel the opposite behaviour is detected.

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