To increase the uniformity of radial temperature profile for fluid how in square channel and consequently to enhance the heat transfer, the use of filament insert is developed and investigated experimentally and numerically. The metallic filament of very large length-to-diameter ratio installed in the radial direction, without contacting the channel wall, will alter the radial temperature profile. The numerical results for friction factor and Nusselt number are presented for a range of Reynolds number from 200 to 1200. Both numerical and experimental results show that the convective heat transfer is considerably enhanced by the metallic filament insert. It is more important that the values of performance evaluation criterion are raised to 3-8. This implies that the advantage of present approach lies in the less additional pressure drop while heat transfer is enhanced. (C) 2001 Elsevier Science Ltd. All rights reserved.