For flow in a pipe or tube, the Reynolds number (Re) is generally defined with fluid velocity, tube diameter, and kinematic viscosity. With a certain value of Re, the flow will become unstable and turbulent. This instability occurs with different fluids, usually when Re is over 2000. The laminar flow is stable if Re is less than 2000. In the interval between 2000 and 4000, laminar and turbulent flows are possible and are called "transition" flows, depending on other factors, such as pipe roughness and flow uniformity.
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