Question

The speed in revolutions per minute of a geometrically similar centrifugal pump of such a size that under corresponding conditions, it would deliver 1 litre of liquid per second against a head of 1 m is known as

• A. Pump capacity
• B. Pump efficiency
• C. Pump head
• D. Specific speed of pump

Hint:

Specific speed of pump $N_s = \frac{N\sqrt{Q}}{H^{3/4}}$.
Low $N_s$ $\rightarrow$ Radial flow (High head, low flow). High $N_s$ $\rightarrow$ Axial flow (Low head, high flow).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Specific speed (\(N_s\)) is a dimensionless or unit-calibrated speed parameter that characterizes the geometrical shape and hydrodynamic performance of a pump impeller irrespective of physical size.
Key Formula or Approach:
\[ N_s = \frac{N \sqrt{Q}}{H^{3/4}} \]

Step 2: Detailed Explanation:
By definition, the specific speed of a pump is the rotational speed in rpm of a geometrically similar model pump of such a size that it would discharge unit flow rate (e.g., \(1\text{ L/s}\) or \(1\text{ m}^3\text{/s}\)) when operating against a unit total head (\(1\text{ m}\)).
It serves as the primary criterion for classifying pump impellers into radial flow, mixed flow, or axial flow designs.

Step 3: Final Answer:
Thus, this characteristic parameter is the Specific speed of pump, corresponding to option (D).