Post on 18-Jan-2016
transcript
Jets & Buckets for Pelton Wheels
Means to Complete the Second Law of Power Retrieval…….
P M V SubbaraoProfessor
Mechanical Engineering Department
Geometrical Relations for Nozzle
dO
2dO – 2.4dO
5dO – 9dO
0.8dO – 0.9dO
1.2dO – 1.4dO
1.1dO – 1.3dO
Numerical Computation of Total Pressure Variation
gHKV vactualVCjet 21:, 99.098.0 1 vK
Jet carrying a discharge of Q to deliver a power P
gHKdQ vVCjet 24 1
2,
To generate a discharge of Q, we need a least jet diameter of
gHK
Qd
v
VCjet2
4
1
,
QgHP turbine
Acceptable Performance of Nozzle
Diameter of the Jet at the outlet, do
gHKdQ voo 24
2
83.081.0 vOK
It is important to find out the VC and outlet jet diameters/areas
The Diameter of Jet before Reaching Bucket
A Set of Relations
• A jet of finite velocity needs to have a relation with peripheral velocity of wheel.
• A jet of finite area need to have a relation with dimensions of bucket.
• A bucket of finite dimensions and shape should have a relation with wheel.
Jet Vs Mean Diameter of Pelton Runner
Mean diameter or Pitch circle diameter:Dwheel
Circumferential velocity of the wheel, Uwheel
gHU wheel 2
gHKUwheeluwheel 2
Dwheel
Jet Power & Conditions for Maximum Power
ei
bijetbbijetb
UVkUVUmP
180coscos
coscos
e
i
jet
bi
bjet
bi
jet
bVU
kV
U
V
UmP
180cos
cos
cos
cos
Define, Blade Speed Ratio asjet
bb V
UC
ei
bibbib
CkCCmP
180cos
cos
coscos
0
bC
P
602.max
wheelwheelpoweruwheel
NDgHKU
wheel
wheel
uwheel D
gHKN wheel
260
4 5gH
PN
Nwheel
s
gHKdQ vVCjet 2
4 12
,
QgHP turbine
Implication of Maximum Power Condition
jet
wheelpowerforb V
UC max,
turbinevVCjet gHKdgHP 24 1
2,
4 5
12
, 24260
gH
gHKdgH
D
gHK
N
vVCjetturbine
wheel
u
s
wheel
12
,42
260vVCjetturbine
wheel
us Kd
D
KN wheel
wheel
VCjetvturbine
us D
dK
KN wheel ,
14 52
60
2
,
2
12
VCjet
wheels
vturbine d
DN
KK
C
wheelu
For maximum efficiency
Optimal values of Wheel diameter to jet diameter
Ns
jet
wheeld
D
Experimental values of Best values of Wheel diameter to jet diameter
Dwheel /djet,VC 6.5 7.5 10 20
Ns (rpm) 35 32 24 10
turbine 0.82 0.86 0.89 0.90
45
H
PNN s P in hp, H in meters and N in rpm
Essential to have a minimum of 10 for acceptable turbine efficiency.
The highest ratio used in the world is 110 (Kt. Glauraus Power House in Switzerland).
Specifications of this Pelton wheel are:
Power 3000HP (2.24MW) Speed: 500 rpmDwheel= 5.36m djet,VC=48.77mmHead =1,650 m
6.2
1650
30005004 54 5
gH
PN
Nwheel
s
Extreme Engineering Conditions
The Second Relation : Jet Vs Bucket
External stroboscopic flow visualization
Runner with Advanced Buckets
Bucket Displacement Diagram
• A notch made near the edge of the outer rim of each bucket is carefully sharpened to ensure a loss-free entry of the jet into the buckets,
• i.e., the path of the jet is not obstructed by the incoming buckets.
BUCKET GEOMETRIC DEFINITIONS
Geometric Details of Bucket
The hydraulic efficiency depends more on the main bucket dimensions (length (A), width (B) and depth (C)).The shape of the outer part of its rim or on the lateral surface curvature also has marginal effect on hydraulic efficiency.