Laminar forced convection of a nanofluid (water) and in a vertical tube, has been numerically investigated. Two portions of the tube, separated by adiabatic zone, are heated at constant flux. The pipe wall has been non-uniformly heated. The first heated zone is located at the entrance of the tube and the second area is movable. Ansys Fluent has been used to solve the continuity, momentum and energy equations. The effects of nanoparticles volume fraction (0, 1 and 4%), Reynolds number (800-1800) as well as the length of unheated zone (25D, 50D, 75D and 100D) on both heat transfer coefficient and wall temperature have been investigated. Numerical results showed that convective heat transfer coefficient for nanofluids increased with increasing nanoparticles volume fraction and Reynolds number. It reached the highest enhancement with increasing length of non-heated zone. For given Reynolds number and volume fraction it is found that the local convective heat transfer coefficient in the second heated zone is less than those obtained for the first one.