Question

The variation of velocity gradient and shear stress is tabulated as under:
$\begin{array}{ccccc}\frac{du}{dy}\left(rad/sec\right)& 0& 0.2& 0.4& 0.6\\ \tau \left(kPa\right)& 4& 8& 11& 13\end{array}$

the fluid may be classified as:

• A. Bingham plastic
• B. Pseudoplastic
• C. Rheopectic
• D. Thixotropic

Answer 1

The correct option is D Thixotropic

$\begin{array}{ccccc}\frac{du}{dy}& 0& 0.2& 0.4& 0.6\\ \tau & 4& 8& 11& 13\\ \frac{d\tau }{d\left(\frac{du}{dy}\right)}& -& \frac{8-4}{0.2}=\frac{4}{0.2}& \frac{11-8}{0.2}=\frac{3}{0.2}& \frac{13-11}{0.2}=\frac{2}{0.2}\end{array}$

$At\frac{du}{dy}=0\Rightarrow B=4\ne 0$

And slope of $(\tau -\frac{du}{dy})$ is decreasing , $n<1$ hence, the fluid is thixotropic.