Centrifugal compressor impeller blade shape strongly affects stability and efficiency. Which statement best reflects the industry-standard behavior of backward-curved blades?

Introduction / Context:
Impeller blade geometry (backward-curved, radial/straight, or forward-curved) determines the characteristic curves of centrifugal compressors and fans, affecting efficiency, surge margin, and power characteristics. This question checks recognition of the typical stability advantage of backward-curved blades.

Given Data / Assumptions:

• Comparison among common blade shapes at similar operating conditions.
• Focus is on qualitative behavior regarding stability and efficiency trends.

Concept / Approach:
Backward-curved blades generally provide higher efficiency and a non-overloading power characteristic with a relatively flat or drooping pressure-flow curve that is more stable. Forward-curved blades tend to offer higher pressure rise at low speeds in fans but commonly at lower efficiency and with overloading characteristics, which can reduce stability in compressor applications.

Step-by-Step Solution:

Verification / Alternative check:
Typical compressor maps and design texts show backward-curved impellers used widely for their efficiency and stability advantages, especially in industrial compressors where surge avoidance is important.

Why Other Options Are Wrong:

• Poor efficiency (backward-curved): Opposite of typical behavior.
• Forward-curved higher efficiency: Usually not; forward-curved are less efficient and more prone to overloading.
• Forward-curved lower pressure ratio: They often show higher head at low speeds; statement is misleading.
• Straight radial blades always highest efficiency: Not universally true; they can be robust but not necessarily most efficient.

Common Pitfalls:
Generalizing fan behavior to compressor maps without considering Mach effects and diffusion limits; ignoring surge margin and power characteristics when judging “performance.”

Final Answer:
Backward curved blades lead to stable performance