In this paper, we investigate the unsteady MHD mixed convection flows of SWCNT-water and Au-water nanofluids within a horizontal grooved channel with two heat generating solid cylinders. These flows may be used to model a wide range of engineering problems such as the flow of fluid in tubular heat exchangers and the cooling of nuclear fuel rods. The fluid is initially at rest and the initial temperature throughout the channel is constant. The flow velocity at the inlet is suddenly raised to a constant value and the inlet of the channel is maintained at the initial temperature. The mixed finite element method with polynomial pressure projection stabilization is used to solve the governing equations with the corresponding initial and boundary conditions. The effects of time t, groove geometry, cylinder radius r,, groove area Ag, Reynolds number Re, Grashof number Gr, Hartmann number Ha and solid volume fraction 0 on the fluid flow and heat transfer are examined. (C) 2016 Elsevier Ltd. All rights reserved.