Question 16.15: The diameters of an impeller of a centrifugal pump at inlet ......

Given: D = 30 cm = 0.3 m, D_{1} = 60 cm = 0.6 m, and H_{m} = 20 m
The pressure head developed due to centrifugal force is given by

or         \left\lgroup{\frac{\left(\pi D_{1}N/60\right)^{2}}{2g}}-{\frac{\left(\pi D N/60\right)^{2}}{2g}}\right\rgroup=H_{m}

or         \left\lgroup{\frac{\left(\pi\times0.6N/60\right)^{2}}{2\times9.81}}-{\frac{\left(\pi\times0.3N/60\right)^{2}}{2\times9.81}}\right\rgroup =20

or            N²(0.0000503 – 0.000012575) = 20
or                N²= 530152.4188
Thus,          N = 728.115 rpm