(3) Good agreement lies between numerical and experimental
results. The numerical results show that the application of
porous inserts effectively makes the temperature profiles
of fluid flow become more uniform at the core of tube, which
play a major role in heat transfer enhancement. Moreover,
the porous radius ratio Rrad should be large enough but less
than 1 to obtain a good integrated performance by using
porous inserts for enhancing heat transfer. As a result, heat
transfer is enhanced greatly with an acceptable flow resistance
increase. It shows that unlike the traditional boundary
enhancement, the core flow enhancement is an efficacious
method for enhancing heat transfer. This is also verified
according to the principle of field synergy by the fact that
average synergy angles of the fluid flow can be reduced
notably by the usage of porous inserts compared to the clear
flow cases.