Chemical Engineering - Fluid Mechanics - Discussion

For open channel flow,

If Re <500 or 600. laminar
> 2000 or 2100. turbulent.
Here, Re=rho*v*R/mu...R=hydraulic gradient.

For circular pipe flow,

If Re <2000. laminar.
> 4000. turbulent.
Here, Re=rho*v*d/mu...d=dia of pipe.

Here both formulae are important to keep in mind. because sometime this may confuse you.

Laminar flow is in linear motion and having re less than 2100, after increase the re the turbulence is so that velocity increase.

Re below 2100 is laminar flow in case of circular pipes.

Let is assume the question is for circular pipe based on options given. But, the question is when will the Laminar flow cease? I think, once the fully turbulent flow is achieved, which is after crossing Re 4000. Then only we can say there is no laminar flow.