Chemical Engineering - Fluid Mechanics - Discussion

I think A is the right answer.

Yes, D is also the right answer.

D is the right answer.

As Perfect gas is ideal gas only which cannot develop shear stress.

A perfect gas can't develop shear stresses.

This is because a perfect gas is assumed to have no intermolecular forces, and therefore, it does not exhibit viscosity, which is responsible for shear stresses in fluids.

The other statements are incorrect:
- A perfect gas does satisfy the equation \(PV = nRT\).
- It is not incompressible; gases are compressible.
- Specific heats can vary with temperature, so they are not necessarily constant.

The correct answer is: can't develop shear stresses.

Explanation:

A perfect gas (also called an ideal gas) is a theoretical gas that follows the ideal gas law perfectly:

PV = nRT
P = ρ R T

But in this question, we're looking at mechanical behaviour, not just thermodynamics.


Key Properties of a Perfect Gas:

1. The ideal gas law is a correct statement.
2. Compressible → NOT incompressible -> incorrect statement
3. Can have variable or constant specific heats depending on assumptions (not necessarily constant)-> correct statement
4. Modelled as having no viscosity → Hence, can't develop shear stress -> correct statement

Shear Stress:

In fluid mechanics, shear stress requires viscosity.
A perfect gas is often assumed to be inviscid (i.e., zero viscosity) → so it cannot support shear stress.

Final Answer: can't develop shear stresses.