220
6 Steam Turbines
Conclusions are:
• Optimum overall efficiency is reached with R s = 0.5 and the corresponding speed
ratio λ ≈ 0.70. Inlet and outlet flow are very near to the axial direction.
• For a somewhat lower speed ratio, as λ = 0.60, internal efficiency is at its lowest
at R s = 0.5. This shows that the optimum in the efficiency variation is very weak.
• With axial inlet and outlet, optimum speed ratio increases with the degree of
reaction.
Table 6.3 Internal efficiency with varying degree of reaction
R s
l o ( − 1.5 %) h o
b o
η ( λ = 0.60) l ( b = 0)
h ( b = 0)
0
0.53
0.908
0.119
0.918
0.46
0.888
0.25
0.62
0.918
0.104
0.915
0.54
0.902
0.50
0.70
0.928
0.019
0.907
0.68
0.925
0.75
0.64
0.922
-0.212
0.915
0.97
0.937
Table 6.2 Internal efficiency as a function of speed ratio with varying degree of reaction;
a
v v b
v v
1u
s
2 u
s
= = / ,
/ (Soderberg correlation AR = 4; 1 72
°
=
a
)
R s = 0.0
R s = 0.25
l
h
a
b
l
h
a
b
0.40
0.8605
0.959
− 0.117
0.50
0.8898
0.830
-0.060
0.45
0.8836
0.960
− 0.022
0.55
0.9042
0.834
0.012
0.50
0.9006
0.968
0.068
0.60
0.9149
0.841
0.079
0.53
0.9080
0.975
0.119
0.62
0.9182
0.845
0.104
0.60
0.9184
0.998
0.233
0.65
0.9223
0.852
0.142
0.65
0.9218
1.019
0.310
0.70
0.9371
0.865
0.203
0.70
0.9232
1.044
0.385
0.75
0.9301
0.880
0.260
0.72
0.9232
1.055
0.414
0.80
0.9318
0.898
0.312
0.75
0.9230
1.072
0.456
0.87
0.9325
0.926
0.390
0.80
0.9217
1.102
0.526
0.90
0.9324
0.939
0.421
0.90
0.9166
1.169
0.659
1.00
0.9303
0.986
0.521
R s = 0.50
R s = 0.75
l
h
a
b
l
h
a
b
0.60
0.9070
0.678
− 0.078
0.60
0.9150
0.519
− 0.244
0.65
0.9187
0.678
− 0.028
0.64
0.9220
0.508
− 0.212
0.70
0.9280
0.681
0.019
0.70
0.9284
0.495
− 0.168
0.75
0.9348
0.687
0.063
0.75
0.9316
0.488
− 0.134
0.80
0.9393
0.694
0.106
0.80
0.9338
0.483
− 0.101
0.85
0.9418
0.702
0.148
0.85
0.9354
0.480
− 0.070
0.90
0.9428
0.712
0.188
0.90
0.9364
0.479
− 0.041
0.94
0.9430
0.721
0.219
0.95
0.9369
0.480
− 0.013
1.00
0.9423
0.736
0.264
0.97
0.9369
0.481
− 0.002
1.05
0.9411
0.749
0.301
1.05
0.9361
0.485
0.039
1.10
0.9396
0.764
0.336
1.10
0.9348
0.488
0.063
6 Steam Turbines
Conclusions are:
• Optimum overall efficiency is reached with R s = 0.5 and the corresponding speed
ratio λ ≈ 0.70. Inlet and outlet flow are very near to the axial direction.
• For a somewhat lower speed ratio, as λ = 0.60, internal efficiency is at its lowest
at R s = 0.5. This shows that the optimum in the efficiency variation is very weak.
• With axial inlet and outlet, optimum speed ratio increases with the degree of
reaction.
Table 6.3 Internal efficiency with varying degree of reaction
R s
l o ( − 1.5 %) h o
b o
η ( λ = 0.60) l ( b = 0)
h ( b = 0)
0
0.53
0.908
0.119
0.918
0.46
0.888
0.25
0.62
0.918
0.104
0.915
0.54
0.902
0.50
0.70
0.928
0.019
0.907
0.68
0.925
0.75
0.64
0.922
-0.212
0.915
0.97
0.937
Table 6.2 Internal efficiency as a function of speed ratio with varying degree of reaction;
a
v v b
v v
1u
s
2 u
s
= = / ,
/ (Soderberg correlation AR = 4; 1 72
°
=
a
)
R s = 0.0
R s = 0.25
l
h
a
b
l
h
a
b
0.40
0.8605
0.959
− 0.117
0.50
0.8898
0.830
-0.060
0.45
0.8836
0.960
− 0.022
0.55
0.9042
0.834
0.012
0.50
0.9006
0.968
0.068
0.60
0.9149
0.841
0.079
0.53
0.9080
0.975
0.119
0.62
0.9182
0.845
0.104
0.60
0.9184
0.998
0.233
0.65
0.9223
0.852
0.142
0.65
0.9218
1.019
0.310
0.70
0.9371
0.865
0.203
0.70
0.9232
1.044
0.385
0.75
0.9301
0.880
0.260
0.72
0.9232
1.055
0.414
0.80
0.9318
0.898
0.312
0.75
0.9230
1.072
0.456
0.87
0.9325
0.926
0.390
0.80
0.9217
1.102
0.526
0.90
0.9324
0.939
0.421
0.90
0.9166
1.169
0.659
1.00
0.9303
0.986
0.521
R s = 0.50
R s = 0.75
l
h
a
b
l
h
a
b
0.60
0.9070
0.678
− 0.078
0.60
0.9150
0.519
− 0.244
0.65
0.9187
0.678
− 0.028
0.64
0.9220
0.508
− 0.212
0.70
0.9280
0.681
0.019
0.70
0.9284
0.495
− 0.168
0.75
0.9348
0.687
0.063
0.75
0.9316
0.488
− 0.134
0.80
0.9393
0.694
0.106
0.80
0.9338
0.483
− 0.101
0.85
0.9418
0.702
0.148
0.85
0.9354
0.480
− 0.070
0.90
0.9428
0.712
0.188
0.90
0.9364
0.479
− 0.041
0.94
0.9430
0.721
0.219
0.95
0.9369
0.480
− 0.013
1.00
0.9423
0.736
0.264
0.97
0.9369
0.481
− 0.002
1.05
0.9411
0.749
0.301
1.05
0.9361
0.485
0.039
1.10
0.9396
0.764
0.336
1.10
0.9348
0.488
0.063