Flow in the closed channel

Closed channel flow is a part of hydraulics and fluid mechanics and is a type of fluid flow in a closed channel (channel in the sense of a closed pipeline). The second type of liquid flow is the flow in the open channel. These two types of flow, albeit similar in many respects, differ significantly in detail. The flow in the closed channel does not have a free surface, which occurs in the second case. No direct atmospheric pressure is applied to the liquid flowing in the enclosed space, but the liquid itself exerts a hydraulic pressure on the duct wall (pipe or pipe).

Not every liquid movement in the apparently closed conduit is subject to the flow laws of the closed channel. The drain pipes (not to be confused with the gutter) are closed in their design, but usually retain a free surface and are therefore considered to be open channels. The exception is when the storm drainage system is 100% filled, in which case it can be treated as a closed space, and the phenomenon itself is called a hydraulic shock or pressure wave.

The flow energy of the pipe is expressed as the pressure height and is determined by the Bernoulli equation. To illustrate the piezometric height along the flow of liquid in a pipe, the diagrams often show a hydraulic gradient. Liquid flow in the closed channel is subject to frictional losses, as defined by Darcy-Weisbach equation. Flow states

The preservation of the liquid stream in the pipe is mainly regulated by the action of gravity and viscosity in relation to the flow inertia. Depending on the ratio of inertia forces to the viscosity forces represented by the Reynolds number, the flow can be laminar or turbulent. If the Reynolds number is below the critical value of about 2040, the pipe flow will be laminar, above which the value can change into turbulent flow. Furthermore, the transition from laminar flow to turbulent may be susceptible to imperfections and level disturbances.

The flow through pipes can be roughly divided into two parts:

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