The effects of adding the aluminum oxide to water in the water to water double pipe heat exchanger with six gear disc turbulators are numerically investigated; in which the nanoparticle with a concentration of 1%, 4%, and 6% is added to the hot fluid and streaming inside a tube with the Reynolds range from 3000 to 13000. Water as the cold fluid goes through the shell in Reynolds of 500, and six gear disc turbulators are located at the shell. The results indicate that turbulators enhance thermal effects. The collision of fluid with the surface of the turbulator and breaking of the boundary layer increase the heat transfer and local Nusselt number about 70%. Also, adding nanoparticles in the heat exchanger with turbulators increases the average Nusselt number, the effectiveness, and the number of transfer units. They increase by increasing the concentration of nanofluid. So that at the maximum state, adding nanofluid in the heat exchanger with turbulators increases these parameters by 1.21, 1.19, and 1.20 times compared to the heat exchanger with turbulators and pure water, respectively. Furthermore, from the contour of the number of transfer units is pointed out more useful of the nanofluid at the higher Re number.

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