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Fluid Mechanics - Engineering

Q1:

The specific speed of a pump is defined as the speed of a unit of such a size, that it

A delivers unit discharge at unit head.

B requires unit power for unit head.

C delivers unit discharge at unit power.

D none of these.

ANS:A - delivers unit discharge at unit head.

The specific speed (NsN_sNs​) of a pump is defined as the speed of a unit of such a size that it delivers unit discharge at unit head. Therefore, the correct definition of specific speed is: delivers unit discharge at unit head. Specific speed (NsN_sNs​) is a dimensionless number that characterizes the geometry and performance of a pump. It is defined as: Ns=NQH3/4N_s = \frac{N \sqrt{Q}}{H^{3/4}}Ns​=H3/4NQ​​ where:

  • NNN = rotational speed of the pump (in RPM),
  • QQQ = flow rate (in m³/s or ft³/s),
  • HHH = head developed by the pump (in meters or feet).
The specific speed is used to classify pumps and predict their performance. It represents the speed at which a geometrically similar pump would operate to deliver a specific flow rate at a specific head. Therefore, the correct answer is: delivers unit discharge at unit head.