<Li> For Reynolds numbers 2000 <Re <3000, the flow is unstable, varying with time as vortices within the flow form and vanish randomly . This domain of flow is not well modeled, nor are the details well understood . </Li> <P> Factors other than straight pipe flow induce friction loss; these are known as "minor loss": </P> <Ul> <Li> Fittings, such as bends, couplings, valves, or transitions in hose or pipe diameter, or </Li> <Li> Objects intruded into the fluid flow . </Li> </Ul> <Li> Fittings, such as bends, couplings, valves, or transitions in hose or pipe diameter, or </Li>

Loss of head due to friction in viscous flow