For a food fluid obeying the Ostwald-de Waele power law model $\tau = K \dot{\gamma}^n$, when the flow behavior index $n < 1$, the fluid is classified as:
Options:
(A) Pseudoplastic (Shear-thinning)
(B) Dilatant (Shear-thickening)
(C) Bingham plastic
(D) Newtonian
Answer Key:
A
Step-by-Step Solution & Explanation
Under the power law model:
• $n = 1$: Newtonian fluid (constant viscosity).
• $n < 1$: Pseudoplastic / shear-thinning fluid (apparent viscosity decreases with increasing shear rate, e.g. fruit purees, applesauce).
• $n > 1$: Dilatant / shear-thickening fluid (apparent viscosity increases with shear rate, e.g. concentrated starch suspensions).