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About the Hershel-Bulkley model of Non-Newtonian fluidsHi,everyone!
Lately I have been using the Herschel-Bulkley model to model the behaviors of a Non-Newtonian fluid. The model states that if the stress of the fluid is less than the yield stress tau0,then the fluid would act like rigid(pseudoplastic). The mathematical description of the HB model is tau=tau0+k*gamma^n,in which tau is the stress, tau0 is the yield stress,gamma is the shear rate and k and n are fluid constants. Here is the question. In some fluid field, if I don't previously know in which area the shear stress would be smaller than tau0 (plug area), how can I find it out? I mean, according to the HB equation, because gamma and tau, tau0 point to the same direction, so no matter what value set gamma to be, the absolute value of tau is always no less than that of tau0. (tau,tau0 and gamma always have the same sign.) For example, if k=1,n=1,gamma>0, then tau(positive)=tau0(positive)+gamma(positive), tau>tau0;if gamma<0, then tau(negative)=tau0(negative)+gamma(negative),abs(t au)>abs(tau0). In both case, there would be no plug area in the fluid. Can anyone help me? Thanks! |

Quote:
Thank you triple_r! I know sometimes my fundamental concepts are ambiguous. I referred to some text books and scientific papers, and found out that usually the shear rate is calculated first and then then shear stress is calculated with the constitution equation. In some simple cases, like in a tube or between two plates, the shear stress can be obtained when knowing the pressure distribution. Is this always the way to find out the shear stress without the shear rate? |

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