1. Radial Turbines (Turbo-expanders)
P M V Subbarao
Professor
Mechanical Engineering Department
New Solutions for Distributed Green & Waste Resources…..

2. Classification of Distributed Power Units

3. Steam/Water vs. Organic Rankine Cycle
Water/steam Rankine cycle
Organic Rankine cycle
Has uneconomically low thermal efficiency when exhaust steam temperature drops below 370ᵒC
2.Bulky equipments due to high specific volume of steam
3.High capital cost, safety concerns and complex system due to requirements of high temperature and pressure
Suitable to be powered by low grade heat sources in temperature range of ᵒC
2.Small size due to high fluid density (Steam=2.4kg/m3 ,R245fa=17.6 kg/m3 at 5bar,200ᵒC)
3.Simplicity and alleviation of safety concerns due to low pressure and temperature

4. Steam/Water vs. Organic Rankine Cycle
Water/steam Rankine cycle
Organic Rankine cycle
4.High maintenance cost due to erosion and corrosion of blades caused by steam droplets
5.Unavailability of high temperature heat sources in DMPG
4.Low capital and maintenance cost due to use of non-eroding and non-corrosive working fluids
5.Availability of low grade heat sources when supplied by renewable

5. Resource Vs Principle of Momentum Exchange/Direction of Fluid Flow
Primary characteristics of a source.
Maximum Life created in a Working Fluid.
The cause of Momentum Exchange : Dp or Dh
The Capacity: Flow rate, Q (m3/s ).
Density of fluid: r (kg/m3).

6. Time Scale of a Machine to Resource
Speed: N (rpm) or n (rps) of a turbo machine:
This is named as Specific Speed, Ns

7. Selection of A Turbine

8. General Structure of Radial Flow Turbines

9. Why Radial Flow Turbines
Better ability to guide flow in an optimal direction into the expansion turbine wheel.
Variable inlet guide vanes present the most important advantage of a radial turbine over an axial turbine.
Suitable for highly variable natural sources of energy/waste energy recovery.

10. Compressible Flow Francis Turbine
Through minor modifications standard radial inflow turbines can be optimized for different renewable thermal resources.
They enable to smooth the seasonal variations by maintaining high efficiency levels at off-design conditions through the use of variable inlet guide vanes.
Radial inflow turbines are less sensitive to blade profile in accuracies than axial turbines, which enable high efficiencies to be maintained as size decreases.
Radial-inflow turbines are more robust under increased blade road caused by using high-density fluids as either subcritical or supercritical conditions.

11. Compressible Flow Francis Turbine
Radial inflow turbines are easier to manufacture relative to axial turbines as the blades are attached to the hub.
The rotor dynamic stability of the system is also improved due to a higher stiffness.

12. Parts of A Turbo-expander

13. Design of Spiral Casing
Select a suitable value of mass flow rate.
dpipe
Rcasing Q
Risv

14. At any angle q, the radius of casing is:
A full spiral is generally recommended for high head 300m, semi-spiral is recommended for low head < 50m.
In general k =1.0, however corrected using CFD.

15. Flow Distribution Analysis of Casing
Stay vanes or Guide vanes

16. Degree of Reaction & Anatomy of Stator

17. Parts of A Turbo-expander

18. Water particle
Water from spiral casing

19. Geometrical Description of A Turbo-expander

20. Design of the Details of Stay Vanes
Theory of Relatively Whirling flow:
Bisv
rinlet Stay Vane
Besv
rexit stay Vane

21. Max. Opening Position Closed Position Runner inlet (Φ 0.870m)
Guide vane outlet for designα) (Φ 0.913m)
Max. Opening Position
Closed
Position

22. Operation of Guide Vanes.

23. Design of the Guide Vanes
The outlet angle can be calculated by assuming a vortex from the flow in the gap between the runner and the guide vanes
rigv
Begv
regv
Select appropriate value of n

24. The correlation between the turbine discharge and the guide vane opening angle.

25. Pressure Loss versus guide vane angle

26. Runner Velocity triangles
rri
rre
Uri
Vwi
Vri
Vfi
Vai
Ure
Vwe
Vre
Vfe
Vae bi ai be ae

27. Inlet Velocity Triangles Vs Ns
Low Specific Speed : Slow Runner
Vwi
Vai
Vfi

28. Inlet Velocity Triangles Vs Ns
Medium Specific Speed : Normal Runner

29. Inlet Velocity Triangles Vs Ns
High Specific Speed : Fast Runner

30. Specific Speed Vs Runner Shape

31. Detailed Runner Design

32. Preliminary Design of Runner : Case Study

33. Development of Feasible Design Space

34. 3D Reconstruction of Runner with Blades

35. Study of Velocity distribution on runner for improvement

36. Optimal Selection of Flow and Blade Angles

37. Optimal Selection of Blade Spacing

38. Specifications of A Radial Turbo-Expander