A 2 D numerical investigation was carried out to study the effect of spacing between ribs on nanofluid flow and heat transfer inside a horizontal micro-channel. Two identical ribs were placed at the lower wall of micro channel with variable spacing between them. The alumina oxide nan oparticles was suspended in water as based fluid at different volume fraction 0, 2 a nd 4%. The finite volume method was used to solve the continuity, momentum and energy equations. The effects of different parameters such as nanoparticles volume fraction,
Reynolds number, and the spacing between ribs has been evaluated. The results showed that increasing nanoparticles volume fraction and Reynolds number significantly enhanced the heat transfer and the Poiseuille number . The presence of ribs improves the heat transfer. However, increasing the spacing between ribs leads to decrease the heat transfer rate.