Q.62 The values of the consistency index ‘K’ and the flow behavior index ‘n’ of a dilatant fluid are 0.415 (in CGS units) and 1.23, respectively. The value of the apparent viscosity (in g.cm−1.s−1) of this fluid at a shear rate of 60 s−1 (rounded off to the nearest integer) is ____________.
Dilatant fluids exhibit shear-thickening behavior, where apparent viscosity increases with shear rate due to their power-law flow characteristics defined by consistency index K and flow behavior index n > 1. For this fluid with K = 0.415 (CGS units, g·cm⁻¹·sⁿ) and n = 1.23 at a shear rate of 60 s⁻¹, the apparent viscosity is calculated using the standard formula μ_a = K × (shear rate)^(n-1).
Step-by-Step Solution
Apparent viscosity: μa = τ / γ̇ = K × γ̇(n-1)
Substituting values: μa = 0.415 × (60)0.23
(log(60) ≈ 1.778 → 0.23×1.778 ≈ 0.409 → 100.409 ≈ 2.817)
Common Errors to Avoid
- Using μ_a = K × γ̇^n (yields ~35, incorrect – this equals shear stress τ, not viscosity)
- Assuming Newtonian η = K (0.415, ignores shear rate dependence)
- Forgetting to subtract 1 from n in the exponent (n-1 = 0.23, not 1.23)
SEO-Friendly Article
Apparent viscosity dilatant fluid calculations are essential for GATE Biotechnology aspirants tackling non-Newtonian flow problems with consistency index K 0.415 and flow behavior index n 1.23 at shear rate 60 s⁻¹. This guide breaks down the power-law formula μ_a = K × γ̇^(n-1), yielding ~1.17 (rounded to 1) in CGS units (g·cm⁻¹·s⁻¹).
Power-Law Fluids Explained
- Dilatant (shear-thickening, n>1): Cornstarch slurry – viscosity increases with shear
- Pseudoplastic (shear-thinning, n<1): Paint, blood – viscosity decreases with shear1):
- Newtonian (n=1): Water, simple oils – constant viscosity
Here, n=1.23 confirms dilatant nature, where viscosity rises with shear rate γ̇.
Detailed Calculation Walkthrough
- Identify formula: μ_a = K γ̇^(n-1)
- Plug in values: γ̇^(0.23) = 60^0.23 ≈ 2.817
- Multiply: 0.415 × 2.817 ≈ 1.169
- Round: 1 (nearest integer)
GATE Exam Relevance
This mirrors GATE BT 2023 Q.62, testing CGS units and rounding for numerical answers. Practice similar problems boosts scores in fluid mechanics/biochemical engineering sections. Perfect for IIT JAM and GATE Biotechnology preparation.
Final Answer: 1
Apparent viscosity = 1 g·cm⁻¹·s⁻¹ (rounded to nearest integer)