Differentiate between laminar flow and turbulent flow and hence define critical velocity.
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Answer:
Laminar flow (smooth flow) tends to occur at lower flow rates through smaller pipes. In essence, the fluid particles flow in cylinders. The outermost cylinder, touching the pipe wall, does not move due to viscosity. The next cylinder flows against the unmoving fluid cylinder, which exhibits less frictional “pull” than the pipe wall. This cylinder will move the slowest. This continues, with the centermost cylinder having the greatest velocity.
Turbulent flow is by nature chaotic. The fluid mixes irregularly during turbulent flow. Constant changes in the flow’s behavior (wakes, vortexes, eddies) make flow rates difficult, if not impossible, to accurately measure. Turbulent flow usually occurs at high flow rates and/or in larger diameter pipes. Turbulent flow is usually desirable when solids must remain suspended in the fluid to prevent settling or blockages.
Critical velocity is the speed and direction at which the flow of a liquid through a tube changes from smooth, or "laminar," to turbulent. Calculating critical velocity depends on multiple variables, but it is the Reynolds number that characterizes the flow of the liquid through a tube as either laminar or turbulent.