Laminar mixed convection in a vertical channel with a finite section of a linearly varying wall temperature is numerically investigated. Dramatic variations of local velocity, temperature, local and average Nusselt numbers are plotted to demonstrate the influences of investigated parameters including Reynolds number, Grashof number and the degree of wall temperature variation. Particular attention is paid to reveal the effects of linearly varying temperature. The results suggest that the average Nusselt number (Nu) over bar increases with Re and Gr. Moreover, (Nu) over bar is higher with a linearly increasing wall temperature than that with a linearly decreasing wall temperature. Finally, an excellent correlation is proposed to predict (Nu) over bar over the wide ranges of investigated parameters. (c) 2006 Elsevier Ltd. All rights reserved.