Question 7.P.2: A three-bladed propeller is used to mix a fluid in the lamin...

For mixing in the laminar region, the power requirement is:

P =k^{\prime} N^2 D^3                (equation 7.17)

where k^{\prime}=1964 for a propeller and 1748 for a flat paddle.
Thus, for a propeller 0.3 m in diameter rotating at 1.5 Hz:

P =\left(1964 \times 1.5^2 \times 0.3^2\right)=\underline{119.3  W }

and for a paddle, 0.75 m in diameter using the same motor:

119.3=\left(1748 N^2 \times 0.75^3\right) and N=\underline{\underline{0.403  Hz }} (24 rpm)