To find the reasons of heat transfer enhancement of a laminar convective heat transfer process in a channel at a uniform heat flux boundary when a pair of longitudinal vortex generators (VGs) is mounted on the bottom wall, the laminar convective heat transfer process in the channel is investigated numerically in a frame built up by the convective transport equation of the heat flux. The results show that longitudinal vortices greatly increase the local convection contribution terms that determine the local intensity of the convective transport of the heat flux component in the span direction, and that the increased local contribution terms intensify the local convective transport of the heat flux component in the same direction. This process increases the convection contribution terms that determine the convective transports of the heat flux components in the main stream direction and in the normal direction of the channel walls. The increase in these convection contribution terms results in an enhancement of the convective heat transfer ability on the channel walls, and then, the heat transfer is enhanced by longitudinal vortices. When the span-averaged characteristic is numerically counted, longitudinal vortices are found to have no contribution on the span-averaged convective transport of the heat flux in the span direction.

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