This paper performs the lattice Boltzmann simulation combined with unknown-index algorithm for the convective heat transfer problems of an impeller stirred tank. Three types of motion of the heating impeller are adopted in this study, including rotation with constant angular velocity, oscillation and oscillating rotation, which are denoted as Types I, II, and III stirrings respectively. Because the flow structures in rotation stirring case are concentric vertical, the heat transfer efficiency of the tank walls is lower than those of the other two types of stirrings. The other two types of stirrings, the flow structures include complex vortices and present better field synergy of the fluid velocity and temperature gradient, which positively contributes to the convective heat transfer efficiency. The results also indicate that a large swing process angle of the impeller with oscillating rotation stirring does not have significant advantage, because the flow phenomena would be similar to that of constant angular velocity stirring case. Basically, the Type III stirred tank can be considered as an improved Type II stirred tank by choosing appropriate process angle. (C) 2015 Elsevier Ltd. All rights reserved.