Fluid Mechanics MCQ Questions & Answers | Chemical Engineering

Pascal's law states that the pressure applied to a confined fluid is transmitted undiminished in all directions throughout the fluid.

This law is only valid when the fluid is at rest because any motion would introduce additional forces such as viscosity and turbulence.

A frictionless fluid in motion would not follow Pascal's law due to the influence of dynamic pressure changes.

The correct answer is Option C: Remain unchanged
Here's why:
NRe stands for Reynolds Number, which is a dimensionless number that helps predict flow patterns in fluids.
It's calculated as: NRe = (density * velocity * diameter) / viscosity
At a Reynolds number of 2100, the flow is considered laminar flow.
In laminar flow, the fluid flows in smooth layers, and the friction is mainly due to the viscosity of the fluid.
The surface roughness has very little impact on friction in laminar flow because the layers of fluid slide past each other in an ordered fashion, and the irregularities of the wall are hidden under a smooth flowing layer.
Since the flow is already laminar at NRe = 2100, further smoothening the pipe (reducing roughness) won't change the flow pattern or the friction factor.
Therefore, the friction factor (f1) will remain unchanged.