Figure 3.
The energy loss in a straight tube will be determined by the friction loss (ΔEfr). This can be calculated with Poiseuille’s law. Bends give extra energy loss almost entirely caused by eddies, which originate because the flow has to separate from the wall due to a sharp bend (separation). Because of the increase in centrifugal overpressure (Pco) on section AB in the outside bend and the decrease in the underpressure (Pci) on section CD in the inside bend, areas will be built up where the flow may separate from the wall; this is accompanied by eddies and extra energy losses (ΔEsep).25 The fastest particles are pressed outwards by the centrifugal effect, the original symmetrical velocity profile will be asymmetrical and perpendicular to the main flow a secondary transverse flow is generated.