The Herschel-Bulkley model describing the rheology of non-Newtonian foods with yield stress (such as tomato paste, chocolate, and butter) is expressed as:
Options:
(A) $\tau = \tau_0 + K \dot{\gamma}^n$
(B) $\tau = \mu \dot{\gamma}$
(C) $\tau = K \dot{\gamma}^n$
(D) $\tau = \tau_0 + \mu \dot{\gamma}$
Answer Key:
A
Step-by-Step Solution & Explanation
Herschel-Bulkley combines yield stress $\tau_0$ with power-law flow behavior index $n$: $\tau = \tau_0 + K \dot{\gamma}^n$. If $n < 1$, the fluid is yield shear-thinning (pseudoplastic with yield stress).