Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

318 Fluid Mechanics, Thermodynamics of Turbomachinery
Vapour pressure as head of water, m
0.8
0.6
0.4
0.2
According to eqn. (1.12b), when W SS exceeds 4.0 (rad) then cavitation can occur, giving
further confirmation of the above conclusion.
Connection between Thoma’s coefficient, suction specific speed and
specific speed
The definitions of suction specific speed and specific speed are
Combining and using eqn. (9.24), we get
0 10 20 30 40
Temperature, ∞C
FIG. 9.20. Vapour pressure of water as head (m) vs temperature.
(9.26)
Exercise. Verify the value of Thoma’s coefficient in the earlier example using
the values of power specific speed, efficiency and suction specific speed given or
derived.
We use as data WSS = 7.613, WSP = 0.8 and hH = 0.896 so that, from eqn. (1.9c),