On the basis of the conservation laws of mass

momentum and energy

the heat transfer and flow resistance characteristics of air in square channels with rib baffle were numerically simulated.The effects of attack angle and slit location on the comprehensive heat transfer performance in the channel were investigated.Moreover

the local fluid flow streamlines

temperature contour

heat flux distribution

absolute vorticity flux and drag factor were also analyzed to reveal the mechanisms of heat transfer enhancement and flow resistance reduction for different square channels.The results show that the attack angle plays an important role in the heat transfer and flow behaviors of the air.The comprehensive heat transfer performance of air in the channel reaches the optimum with attack angle of 30°.On this basis

the slit location on the bottom of rib baffle is in favor of reducing the flow resistance and enhancing the heat transfer rate.The obtained results also present that the rib baffle can induce secondary flow in the flow channel

homogenize the flow and improve the flow mixing between the near wall zone and mainstream zone

which enhances the heat transfer.The absolute vorticity flux can characterize the intensity of single secondary flow in a typical rib baffle square channel while it can not sufficiently describe all heat transfer enhancement mechanism in square channels with slotted baffle.The flow resistance reduction by varying the attack angle and slit location mainly acts on the channel's form drag.