Question

A centrifugal pump has an impeller of 30 cm outer diameter. The vane tips are radial at the outlet. For a rotative speed of 1450 rpm, what is the manometric head developed?

(Assume a manometric efficiency of 82% and take g = 9.81 m/s²)

1. 37.24 m
2. 43.38 m
3. 29.46 m
4. 32.88 m
5.

Answer 1

Correct Answer - Option 2 : 43.38 m

Concept:

Manometric Efficiency (ηman)

\({\eta _{man}} = \frac{{{H_m}}}{{\frac{{{V_{w2}}{u_2}}}{g}}} = \frac{{g{H_m}}}{{{V_{w2}}{u_2}}}\)

Calculation:

Given:

D₂ = 30 cm, N₂ = 1450 rpm, η_man = 82%, g = 9.81 m/s2

\(u_2=\frac{\pi D_2N_2}{60}\)

\(u_2=\frac{\pi \times 0.3\times 1450}{60}=22.765\;m/s\)

For radial outlet V_w2 = u₂

\({\eta _{man}} = \frac{{g{H_m}}}{{{}{u_2}^2}}\)

\(0.82 = \frac{{9.81 \times {H_m}}}{{{}{22.765}^2}}\)

H_m = 43.32 m