A drilling fluid following the power law model is circulated in a wellbore at a rate of 600 gal/min. The internal diameter (Di) of the drill pipe is 4.276 inches, and the power law flow behaviour index n for the fluid is 0.67.
The wall shear rate is given by \[ \dot{\gamma}_w = \left(\frac{3n+1}{4n}\right)\frac{8V}{D_i} \] where V is the average velocity of the drilling fluid inside the drill pipe.
[Given: 1 gallon = 3785.4 cm3, 1 inch = 2.54 cm]
The wall shear rate (in s^-1) is __________ (rounded off to one decimal place).