impulse turbines - Pelton wheels - Website Staff...
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Transcript of impulse turbines - Pelton wheels - Website Staff...
Dr. Ir. Harinaldi, M.EngMechanical Engineering Department
Faculty of Engineering University of Indonesia
impulse turbines -Pelton wheels
Construction and ComponentConstruction and Component
ConstructionConstruction
Multi Jet
Single Jet
InstallationInstallation
Velocity TriangleVelocity TriangleEuler Equation:
Assume no loss of relative velocity, W1 = W2
For maximum E dE/dU = 0
Velocity TriangleVelocity TriangleIn practice :Surface friction of the bucket W2≠ W1
Losses and EfficiencyLosses and EfficiencyPipeline transmission efficiency pipeline losses, hf
11
1
reservoirat availableenergy pipeline of endat energy
HH
HhH f
trans
Nozzle efficiency nozzle losses, hin
HH
HhH
hHhhH in
f
infN
'inlet nozzleat energy outlet nozzleat energy
1
1
Energy available in jet at nozzle outlet : gCH 2' 21
Nozzle velocity coefficient
gHCCv 2inlet nozzleat ty jet veloci ltheoretica
outlet nozzleat ty jet veloci actual 1 2vN C
Hydraulic efficiency
gCE
HE
H 2'outlet nozzleat jet in availableenergy nsferredenergy tra
21
Losses and EfficiencyLosses and EfficiencyOverall Efficiency
gQHP
o
inlet nozzleat availablePower turbineby the developedPower
Turbine discharge, Q
1
21 4
outlet nozzleat ty jet veloci actual nozzleareaCdAC
Q
d = nozzle diameter
ExampleExampleA Pelton turbine develops 2000 kW under a head of 100 m and with an overall efficiency of 85%. The coefficient of velocity for the nozzle is 0.98. Determine: (a) The theoretical velocity of the jet ?(b) The actual velocity of the jet ?(c) The flow rate ?(d) The diameter of the nozzle
Solution:Given: P = 2000 kW; H = 100 m; ηo = 0.85 ; Cv= 0.98Let : d = diameter of the nozzle ; Q = discharge flow rate of the turbine
(a) The theoretical velocity of the jet
m/s 3.44)100)(81.9(22 gHCtheo
(b) The actual velocity of the jet
smCCgHCC
gHCC
theovv
v
/ 4.433.4498.02
2
1
1
ExampleExample(c) The flow rate
smgH
PQ
gQHP
o
o
/ 4.285.010081.910
10.2000 33
3
(d) The diameter of the nozzle
m
CQd
CdACQ
265.04.43
4.244
4
1
12
1
Design of Pelton WheelsDesign of Pelton Wheels
Pelton wheel is designed to find out the following data:1. Diameter of the wheel (D)2. Diameter of the jet (d)3. Size (i.e. width and depth) of the buckets4. Number of buckets (z)
Pelton wheel is designed with the following input:1. Head of water2. Power to be developed3. Speed of the runner
Pelton wheel is usually designed with the following assumption:1. Overall efficiency, ηo between 80% and 87% 2. Coefficient of velocity, Cv as 0.98 to 0.993. Ratio of peripheral velocity to the jet velocity, U/C1 as 0.43 to 0.48
Design of Pelton WheelsDesign of Pelton WheelsSize of the buckets
16 to11
2.1 to8.0
4 to3
3 to2
dDdTdBdL
Number of the buckets (z)Theoretical :
oz 360
26.05.0cos
DRdRdR
where:
Empirical :
dDz2
15
Characteristics CurvesCharacteristics Curves
Efficiency and jet speed ratio Efficiency vs speed at various nozzle setting
Power vs speed at various nozzle setting Variation of efficiency with load
Load ChangesLoad ChangesIn practice :U must remain constant when the load changes to maintain maximum efficiency U/C1 must stay the same change the input of water power change in Q change in nozzle area A
Load Control : spear valve and deflector plate
Load ChangesLoad Changes