# Fluid dynamics question

1. Mar 11, 2016

### datf

1) (Assume that pump similarity laws are valid and that the effects of Reynolds number (Re) are small.)
A centrifugal pump operating at speed N is combined in series with an identical centrifugal pump operating at speed 2N. The head rise across the pump operating at the lower speed is H, which is below its maximum head. Which of the following statements is/are valid?
I. Under steady state conditions, the flowrate through both pumps is identical.
II. Under steady state conditions, the head rise across the pump operating at the higher speed is 4H.

a. None of the other options is valid.
b. I only.
c. II only.
d. I and II.

I'm thinking it's I and II.

2) The efficiency n of a centrifugal pump with impeller diameter D operating at a specified speed is given by n = 16(Q – 10Q^2), where Q is the volume flow rate in m^3/s. Ignoring the effects of Reynolds number, the efficiency of a homologous centrifugal pump of impeller diameter 2D is given by

a. n = 128(Q – 10Q^2)
b. n = 16(Q – 10Q^2)
c. None of the other options is valid.
d. n = 2Q – 2.5Q^2

I'm thinking it's n = 2Q – 2.5Q^2

2. Mar 11, 2016

Hello datf,