Numerical investigation of heat transfer in flows in two- and three-dimensional channels with a built-in cylinder

Fluid flows and heat transfers have been calculated from continuity, Navier-Stokes and energy equations in two- and three-dimensional channels with a built-in cylinder. The geometrical configuration represents a simplified model of a cross-flow heat exchanger. For small blockage ratio, and for large Reynolds number the flow in cylinder wake becomes periodic. For large blockage ratio, the Nusselt number on the cylinder surface can be much larger than in a flow with infinite medium. The three-dimensional flow is characterized by a large normal component of velocity in the stagnation and near wake region. This, along with the back flow in wake, results in a helical vortical motion of fluid moving backward and upward from the bottom to the middle of the channel in the wake. This results in an increase in Nusselt number for the channel wall, but a reduction for the cylinder.