SUMMARY
The effect of aspect ratio on the forced convection heat transfer is studied experimentally by construction a device formed mainly from an air duct with sliding surfaces to up or down directions and from a copper tube represents a heat generation source placed inside the air duct. The aspect ratio considered the ratio of the distance between the upper and lower surfaces of the air duct to diameter of the copper tube. The experimental results which obtained from this study show that the Nusselt number decreases with increase of the aspect ratio for Reynolds number range equals to (500 < Re < 3000). From the experimental results, a correlation for Nusselt number calculation is presented that depending on the effect of Reynolds number, Prandtl number, and aspect ratio with an accuracy of ±8%.