Abstract: The pipeline is the most economical water transporting tool for human daily use. However, it generates many issues, like pipe leakage and break. These damages not only cause massive expenditure in repair work but also affect water quality. It is therefore significant for engineers to investigate the water pipeline system to ensure its effectiveness. Computational Fluid Dynamic (CFD) method is applied to analyse the flow motion in a straight pipe, in terms of flow velocity profile, entrance length and head loss. The result shows that the flow motion passes two regions, entrance region and fully developed region. At the entrance area, the pressure difference over the pipe length is non-linear. Thus, to achieve a precise result, the measurement of flow properties alteration starts at the fully developed region since the fluid properties are stable. Moreover, the consequence of the 98 simulation tests indicates that the larger diameter pipe produces less head loss. It is less possible to generate pipe leakage and break since less energy is consumed. Thus, the large diameter pipes are more economical and reliable to water pipeline application.

Key words: pipe, computational fluid dynamics, entrance length, head loss