Chemical Engineering - Fluid Mechanics - Discussion

Let’s carefully check each statement one by one:

1. “A forced vortex occurs when fluid rotates as a solid about an axis.” It is correct. In a forced vortex, external torque makes the fluid rotate like a rigid body (solid body rotation).


2. “In laminar flow, Newton's law of viscosity does not apply.” This statement is wrong. In laminar flow, Newton’s law of viscosity does apply (shear stress ∝ velocity gradient).


3. “A free vortex occurs when fluid rotates as a solid.” It is wrong. In a free vortex, there is no external torque; fluid particles move due to pressure difference, and velocity ∝ 1/r, not solid body rotation.


4. “In turbulent flow, there are neither cross-currents nor eddies.” It is also wrong. Turbulent flow is characterised by cross-currents and eddies.

So, the Correct statement is A forced vortex occurs when fluid rotates as a solid about an axis.