Advantages and Features of Closed Impellers in Centrifugal Compressors
1. Key Advantages
✅ High Efficiency (85~92%)
Fully enclosed flow path design significantly reduces gas leakage, achieving much higher energy conversion efficiency than open/semi-open impellers.
✅ High-Pressure Capability
Can withstand working conditions >5MPa, making it the preferred choice for high-pressure applications like natural gas pipeline compression and air separation.
✅ Low Turbulence Loss
Smooth enclosed flow path optimizes airflow, reducing vortex and friction losses.
✅ Long Service Life
Shrouds protect blades from direct media erosion, ideal for continuous industrial operations (e.g., refinery compressors).
2. Structural Features
🔧 Dual-Shroud Design
Front shroud + back shroud fully enclose the blades, forming a sealed flow channel.
🔧 Precision Manufacturing
Typically produced via 5-axis milling or investment casting, ensuring flow path dimensional tolerance ≤±0.05mm.
🔧 Material Selection
Clean gases: Stainless steel (SS304/316)
Corrosive environments: Titanium alloy (Ti-6Al-4V) or Nickel-based alloy (Inconel 718)
3. Typical Applications
⚙️ High-Pressure Clean Gases
Natural gas compression
Air separation units
Refrigeration cycles
⚙️ High-Speed Conditions
Centrifugal refrigeration compressors (>20,000 RPM)
Aircraft auxiliary power units (APUs)
4. Comparison with Open Impellers
| Feature | Closed Impeller | Open Impeller |
|---|---|---|
| Efficiency | ★★★★★ (92% max) | ★★★☆☆ (82% max) |
| Clog Resistance | ★☆☆☆☆ (clean media only) | ★★★★★ (tolerates particles/fibers) |
| Maintenance Cost | High (requires casing disassembly) | Low (direct blade access) |
| Typical Cost | High (complex structure) | Low (simplified design) |
5. Selection Guidelines
Prefer Closed Impellers When:
Media is clean (solid content <0.1%)
High efficiency or high-pressure output is required
Long-term continuous operation is needed (e.g., petrochemical main compressors)
Avoid in These Scenarios:
Dusty/viscous media (use open or semi-open impellers)
Frequent cleaning requirements