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bingham papanastasiou pipe
Posted Apr 22, 2016, 5:25 a.m. EDT 0 Replies
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I'm currently working on a 3D model of a pipe, using the Bingham model (with the Papanastasiou correction). According to it, the viscosity can be written like it follows:
n = np + tau0*(1-exp(-m*gamapoint))/gamapoint
n - viscosity
np - dynamic viscosity
m - factor that determines whether the model is more similar to the newtonian solution (when m is 0) or to the Bingham solution ( when m tends to infinite). In this case, I've imposed m = 10000 to be able to compare results with the Bingham theory.
tau0 - yield shear stresss
gamapoint - shear rate
In COMSOL, I've inserted the equation by specifying the values as parameters and by writing the shear rate with the internal variable "spf.sr". However, the comparison between the theorical maximum speed and the value provided by the software shows a big difference between results.
VISCOSITY EQUATION WRITTEN IN COMSOL:
n = np + tau0*(1-exp(-m*spf.sr[s]))/spf.sr
THEORICAL EQUATION FOR THE BINGHAM VELOCITY PROFILE:
vz (r) = P*(R^2 - r^2)/(4*np*L) + Tau0*(R - r)/np
L - length of the pipe
R - radius of the pipe
Could someone help me here, telling me whether I've correcty implemented the model or if I've made a mistake somewhere?
Thank you in advance!
Hello Hanna Freitas
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