I am calculating the relaxation time of a concentrated polymer solution. Based on my steady shear measurement, I used curve fitting that is based on Carreau model to obtain an estimated relaxation time. Ultimately, I am going to use the estimated relaxation time to calculate Weissenberg number. I just want to know whether my polymer flow is more elastic-dominant or inertial-dominant at a particular shear rate.
Thank you.
As one may have guessed, the rheological data (CR mode?) in the form of apparent viscosity as a function of the shear rate you described by the Carreau equation and you have determined the value of its parameters. However, you do not provide information about what method you used and what was the error of estimation. I mean not about R2 but about average relative error. You should also remember that the lamda (relaxation time) is correlated (numerically) to the n (power index).
Having the correct value of relaxation time of course you can calculate the Weissenberg number value.
Regards,
Thank you Prof Miroslaw Grzesik for your reply. I was using plate-plate configuration to perform the rheological measurement with a nano-torque rheometer. The measurement was conducted in a stress-controlled module, in which the shear stress is increasing over time and the corresponding change of shear rate and viscosity is recorded.
I did not ask about the measurement only about the method of determining mathematical model parameters. You could use the rheometer software here and not be interested in it.
To find the value of parameters you can use linear regression (after transforming a function) and you can use nonlinear regression. In the latter case, it is important to choose a proper starting point for the numerical method. Another problem is local minima. There are also other rheological equations
Regards,
You should try transient tests such creep behaviour or stress relaxation in order to get accurate values of relaxation time or its spectrum.
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