Question

As the value of specific speed of centrifugal pump increases, the pump type changes from

• A. Radial flow to axial flow type and then to mixed flow type
• B. Radial flow to mixed flow type and then to axial flow type
• C. Mixed flow to radial flow type and then to axial flow type
• D. Axial flow to radial flow type and then to mixed flow type

Hint:

Specific speed sequence: Radial (Low $N_s$, High Head) $\rightarrow$ Mixed (Medium $N_s$) $\rightarrow$ Axial (High $N_s$, High Discharge).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Centrifugal pump impeller geometry and hydraulic flow kinematics evolve continuously as dimensionless specific speed increases from low discharge/high head to high discharge/low head designs.
Key Formula or Approach:
\[ N_s = \frac{N \sqrt{Q}}{H^{3/4}} \]

Step 2: Detailed Explanation:
As specific speed (\(N_s\)) increases from low to high values:
1. Low Specific Speed (\(N_s < 2000\) rpm 10--30 metric): Radial Flow Impeller (Flow enters axially and discharges radially perpendicular to shaft; delivers high head at low flow rates).
2. Medium Specific Speed (\(N_s \approx 2000 - 5000\) rpm 30--75 metric): Mixed Flow Impeller (Flow discharges diagonally with both radial and axial velocity components; medium head and medium discharge).
3. High Specific Speed (\(N_s > 5000\) rpm 75--250 metric): Axial Flow Propeller Pump (Flow moves parallel to pump shaft; delivers high discharge against low heads).

Step 3: Final Answer:
Therefore, the pump type changes from Radial flow to mixed flow type and then to axial flow type, matching option (B).