A numerical study of heat transfer and fluid flow past single tube using computational fluid dynamic (FLUENT 6.0) to predict the heat transfer and pressure drop characteristics of turbulent flow past single tube is presented in this work. The results show that the pressure drop decreases as the aspect ratio increases. The fluid is heated in the near wall and wake regions and the predicted temperatures serve as excellent benchmark data for assessing computational fluid dynamic predictive accuracy for the selected cases. The maximum velocity increases as the aspect ratio increases. The overall performance of the single tube with a lower aspect ratio is preferable since it provides a higher heat transfer rate. Higher turbulence kinetic energy is at the inlet and outlet computation domain of the lowest aspect ratio, and near the upper side and the first upper corner of the external surface of the tube with the case L/D = 2.0.