LAUSR

Abstract Flow and heat transfer in a single tube of a flat-tube heat exchanger with passive inserts as means of heat transfer enhancement is numerically investigated. The tube geometry is taken from an industrial design with an elaborate pattern of passive inserts (bumps) distributed on the two walls of the channel. The channel is not symmetric in the spanwise direction, leaving a insert-free area on one side of the channel. In order to investigate the heat transfer in such a channel, the incompressible Navier-Stokes and energy equations are solved directly on a very fine computational mesh. These quasi-DNS simulations are carried out at three Reynolds numbers, spanning the threshold where laminar-turbulent regime transition is believed to occur based on previous experiments. Results suggest that turbulence does contribute to heat transfer enhancement at the highest Reynolds number. However, the boundary layer modification, which is the main heat transfer enhancement mechanism, is identically in action in both, laminar and turbulent, regimes. Results also show that the non-symmetric distribution of passive inserts is disadvantageous, particularly in the event of laminar-turbulence regime transition.