Question

Which of the following statements is NOT correct?

• A. As the shear rate increases, the apparent viscosity decreases for a pseudoplastic fluid.
• B. As the shear rate increases, the apparent viscosity increases for a dilatant fluid.
• C. A Bingham fluid requires application of yield stress prior to any response.
• D. Rheopectic and thixotropic are two time independent fluids.

Hint:

Remember: - Time-independent = Newtonian, pseudoplastic, dilatant, Bingham. - Time-dependent = Thixotropic, Rheopectic.

Answer 1

The Correct Option is D

Step 1: Review fluid classifications.
- Pseudoplastic (shear-thinning) fluids: viscosity decreases with increasing shear rate. Statement (A) is correct. - Dilatant (shear-thickening) fluids: viscosity increases with shear rate. Statement (B) is correct. - Bingham plastics: behave like rigid solids until yield stress is applied, after which they flow like a viscous fluid. Statement (C) is correct. - Thixotropic fluids: viscosity decreases with time under constant shear. Rheopectic fluids: viscosity increases with time under constant shear. Both are time-dependent fluids, not time-independent. Statement (D) is incorrect.
Step 2: Conclude.
Therefore, the incorrect statement is that thixotropic and rheopectic fluids are time-independent. Final Answer: \[ \boxed{\text{Rheopectic and thixotropic are NOT time independent fluids.}} \]