Fans, Blowers and Compressors

1. Fans, Blowers and Compressors P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Machines to Generate Lively Gases….

2. First Law Analysis & ASME Classification SSSF :

3. Nearly Incompressible Flow machines : Fans

4. Anatomy of Large Centrifugal Fan

5. Fluid Dynamics of Centrifugal Fan

6. Centrifugal Fan Operation Fans cause a pressure increase through two methods Centrifugal force is created by the rotation of the column of air trapped between two blades. Kinetic energy is supplied to the air through the impeller Total pressure = static pressure + velocity head Blades are backward-curved, forward curved, or radial (straight) Airfoil-types are complex and expensive but very efficient; they’re used for large systems where the cost is justified.

7. Axial Flow Fans • Common types: propeller, tubeaxial, vaneaxial • Tubeaxial: impeller is inside a tube to guide airflow and improve performance. • Vane axial: like a tube axial except vanes downstream of the impeller are used to reduce swirl and improve performance • Used to deliver large flow rates but small increase in pressure • Examples include fans used for ventilation without ductwork, mobile room fans, and fans used to cool computers. • Tube-axial fan for computer cooling • Tube-axial fan for ventilation • Vane-axial fan for high air resistance electronics cooling • Straightening vanes are located inside tube.

8. Types of Axial Flow Fans

9. Anatomy of Large Axial Flow Fan

10. Thermodynamics of Fans

11. Fan Laws Operational and performance data of different but geometrically similar fans can be cast onto a single universal curve using dimensionless numbers

12. Actual Fan Power

13. Fan Flow Control • Fans rarely are operated continuously at the same pressure and volume discharge rates. • There exists a need for a system which can vary the vane output according to requirements. • Common methods of controlling fan output are: • Damper control • Inlet vane control • Variable speed control. • Axial fans can control flow using variable pitch blades.

14. Characteristic Curves: Radial Vane Centrifugal Fan Static Pressure Efficiency Power

15. Characteristic Curves: Forward Vane Centrifugal Fan Noise Level Static Pressure Power Efficiency

16. Characteristic Curves: Backward Vane Centrifugal Fan Noise Level Power Static Pressure Efficiency

17. Comparison of Fan Characteristic Curves : Static Pressure Static Pressure Backward Forward

18. Characteristic Curves: Axial Fan Noise Level Power Static Pressure Efficiency

19. ASME Classification

20. Classification of Compressors Rotodynamic Compressors Positive Displacement of Compressors Centrifugal Compressors Mixed Compressors Axial Compressors Reciprocating Compressors Rotory Compressors

21. Duty of Compressors • A two step life infusion into gas. • Rotor : Mostly Energy Transfer • The centrifugal compressor consists essentially of a stationary casing containing a rotating impeller which imparts a high velocity to the air. • Only Energy Conversion: • A number of diverging passages (Diffuser) in which the air is decelerated with a consequent rise in static pressure.

22. Centrifugal Compressors • Air is sucked into the impeller eye and whirled round at high speed by the vanes on the impeller disc. • Centripetal acceleration leads to increase in rise of some amount of static pressure. • The remaining increase in rise of pressure occurs in diffuser.

23. Impeller – Diffuser : Rotor - Stator

24. Encapsulated Diffuser

25. Anatomy of A Centrifugal Compressors

26. Performance of centrifugal compressors Total Pressure Ratio Design clue for Blades: The overall or total-to-total efficiency

27. Centrifugal Compressors for High Pressure Ratio

28. Performance of Radial Vane Compressor

29. Vane Geometry : Compressor Characteristics Pressure Ratio Mass Flow

30. Performance of Backward Vane Compressor b2 =90 b2 =75 b2 =60

31. Remarks on Centrifugal Compressors • High pressure ratio per stage (r0p= 3 to 4). • Less flow area per unit mass flow rate. • A multistage centrifugal compressors have shorter lengths. • They are best suited for low mass flow rates. • As the flow is turned by 900, the efficiency of centrifugal compressor is relatively low. • The impeller is an integral unit of blades and a disk. • Even if one blade is damaged the entire unit is to be replaced. • Look for other fluid dynamic phenomenon for ingestion of life into fluids. • Aerofoil Theory.

32. Evolution of Compression Phenomenon Aerofoil Centrifugal Compact & Less Efficient Bulky & More Efficient

33. GE T700

34. AXIAL FLOW COMPRESSORS An Efficient Way to Ingest Life in Gases !!!

35. A Compressor Stage

36. Axial Flow Compressors

37. Axial Flow Fluid Machines The power, P of a fluid Machine

38. Similarity Analysis • Experimental performance curves or maps provide a versatile data for compressor engineers. • The data is translated into most general form. • Data in general form is minimally effected by air speed, altitude etc. • The total pressure ratio of a compressor is: Using dimensional analysis & Buckingham Pi Theorem:

39. Similarity Analysis

40. Test Rig For Centrifugal Compressor

41. Zero Efficiency Points Compressor Characteristics Maximum Efficiency point Supply pipe Compressor exit

42. Centrifugal Compressor Map

43. Small Centrifugal Compressor Maps

44. Axial Compressor Maps

45. Variable Speed Operation

46. Axial Flow Compressors: Current Design Practice Fan or low pressure Compressor

47. Axial Flow Compressors: Current Design Practice High pressure Compressor

48. Multi Stage Hybrid Compressor

49. GE9X : The worlds Next Great Jet Engine : 2020 6-stage turbine 14-stage compressor contributing to an overall engine pressure ratio of 60:1.