Pipes are closely associated with fluid flow. We encounter pipe flows almost everywhere- for water and gas supply at houses and offices, in fluid machinery, for transporting oil over long distances and at many other places.
A flow can be an Internal flow or an External Flow, the distinction being obvious. Internal flows are further classified into Pipe Flows and Open Channel Flows. A pipe flow is one where the fluid fills the conduit completely. The main driving force is pressure although gravity may also be contributing to the flow. On the other hand, an Open Channel Flow is open where the fluid does not fill the conduit completely. The driving force now is gravity.
Figure 7.1: Flow Classification
(c) Aerospace, Mechanical & Mechatronic Engg. 2005
University of Sydney