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Flow through pipes

Flow through pipes Reynold's number is a dimensionless ratio between inertia and friction in a flowing medium. It is defined as:

In principal there are two types of flow in a pipe. With Re<2000 the viscous forces dominate in the media and the flow becomes laminar. This means that different layers of the medium move in relation to each other in good order. The velocity distribution across the laminar layers is usually parabolic shaped. With R4000 the inertia forces dominate the flowing medium and the flow becomes turbulent, with particles that move randomly in tge flow's cross section. The velocity distribution across a layer with turbulent flow becomes diffuse.

In the critical area, between R<=2000 and R>=4000, the flow conditions are undetermined, either laminar or turbulent or a mixture of the both. The conditions are governed by factors such as the surface smoothness of the pipe or other disturbances.

To start a flow in a pipe requires a specific pressure difference or pressure drop, to overcome the friction in the pipe and couplings.The size of the pressure drop depends on the diameter of the pipe, its length and form as well as the surface smoothness and Reynold's number.