micro turbines : turbo-expanders new solutions for distributed green & waste resources….. p m...
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Micro Turbines : Turbo-expanders
New Solutions for Distributed Green & Waste Resources…..
P M V SubbaraoProfessor
Mechanical Engineering Department
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Selection of An Expander
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In search of A Suitable Principle of Momentum Exchange/Direction of Fluid Flow
• Primary characteristics of a source or need.• The cause/effect: p or h• The Capacity: Flow rate, Q (m3/s ).• Density of fluid: (kg/m3).
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Time Scale of a Machine to Resource
Speed: N (rpm) or n (rps) of a turbo machine:
Scale Time Machine
Scale Time Resourcescale timeessDimensionl
n
T f1
scale timeDimension -Non
This is named as Specific Speed, Ns
4
3
p
QT f
4
3
p
QnN s
4 31000
76
h
QNN s
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Selection of An Expander
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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.
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Turbo-Expanders
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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.
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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.
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Parts of A Turbo-expander
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Design of Spiral Casing
Rcasing
Risv
dpipe
Q
Select a suitable value of mass flow rate.
2
4 pipepipemain dVm
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At any angle , the radius of casing is:
pipeisv dRR
2casing
A full spiral is generally recommended for high head 300m, semi-spiral is recommended for low head < 50m.
2mm
In general =1.0, however corrected using CFD.
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Flow Distribution Analysis of Casing
Stay vanes or Guide vanes
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Parts of A Turbo-expander
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Geometrical Description of A Turbo-expander
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R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanes
R a d i a l v i e wrunner guide vanes and stay vanesR a d i a l v i e wrunner guide vanes and stay vanes
Water from spiral casing
Water particle
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Design of the Details of Stay Vanes
StayVaneinletStayVaneinletwGuideVaneinletGuideVaneinletw rVrV
rexit stay Vane
rinlet Stay Vane
Besv
Theory of Relatively Whirling flow:
Bisv
isvn
wisvisvesvn
wesvesv rVrV
isvSratyVaneinletStayVaneinletf BD
QV
pipemainStayVaneainlet VV
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Guide vanesGuide vanesGuide vanesGuide vanesGuide vanesGuide vanes
Runner inlet (Φ 0.870m)
Guide vane outlet for designα) (Φ 0.913m)
ClosedPosition
Max. Opening Position
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Operation of Guide Vanes
Guide vane at DesignPosition = 12.21°
Guide vane at closed position
Guide vane at Max. openPosition = 18°
.
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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
nwigvigv
nwegvegv igvegv
rVrV
egvegvfegv BD
QV
regv
rigv
Begv
Select appropriate value of n
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The correlation between the turbinedischarge and the guide vane opening angle.
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Pressure drop versus guide vane angle
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Velocity trianglesrri
rre
UriVwi
Vri
Vfi
Vai
UreVwe
Vre
VfeVae
i
i
ee
rU
UU
r
rire
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Inlet Velocity Triangles Vs Ns
Low Specific Speed : Slow Francis Runner
Vwi
Vai
Vfi
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Inlet Velocity Triangles Vs Ns
Low Specific Speed : Normal Francis Runner
Vwi
Vai
Vfi
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Inlet Velocity Triangles Vs Ns
High Specific Speed : Fast Francis Runner
Vwi
Vai
Vfi
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Specfic Speed Vs Runner Shape
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3D Reconstruction of Runner with Blades
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Study of Velocity distribution on runner for improvement
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Design Rule 190
-i
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Design Rule 2
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Design Rule 3