Specific speed range and outlet flow type for centrifugal pumps Which pump configuration is preferred for a specific speed between 80 and 160 rpm (metric specific speed class)?

Introduction / Context:
Specific speed groups centrifugal pumps by how head and discharge scale with speed and impeller diameter. As specific speed increases, the outlet flow pattern transitions from radial to mixed and then to axial. Selecting the right outlet type within a specific speed band ensures good efficiency and cavitation performance.

Given Data / Assumptions:

• Specific speed Ns in the range 80–160 (metric convention).
• Water service and standard pump designs.

Concept / Approach:
Low Ns (≈10–80) favors radial-flow impellers (high head, low flow). Mid-to-high Ns (≈80–160) corresponds to mixed-flow designs that combine radial and axial components for improved capacity at moderate heads. Very high Ns (>160–300+) trends toward axial-flow (propeller) pumps.

Step-by-Step Solution:
Recognize Ns = 80–160 lies above the classic radial-flow band.Map Ns to outlet pattern: this band aligns with mixed-flow impellers.Therefore the preferred configuration is a high-speed, mixed-flow pump.

Verification / Alternative check:
Manufacturer selection charts plot efficiency islands vs. Ns, showing mixed-flow optima in this range.

Why Other Options Are Wrong:
Options (a) and (b) indicate radial-flow suited to lower Ns. Option (c) keeps radial discharge at high Ns, which is inefficient. Option (e) corresponds to yet higher Ns typical of axial pumps.

Common Pitfalls:
Confusing rotational speed in rpm with specific speed; ignoring that Ns is a non-dimensionalized grouping that dictates geometry trends.

Final Answer:
high-speed pump with mixed flow at outlet