Steam Turbine Special Aspects of Reaction Turbine &Impulse Turbine
Special Aspects of Reaction Turbine :
There is a difference in pressure across the moving blades the steam will, therefore, tend to leak around. The periphery of the blades in the stand of passing through them blade clearances, therefore, must be kept a minimum.
Also due to the pressure drop across the moving blades, an unbalanced thrust will be developed upon the rotor and same arrangement must be made to balance this.
Impulse Turbine staging :
In order for the steam blades up all its kinetic energy to the moving blades in an impulse turbine, it should leave the blades at zero absolute velocity this condition will exist if the blade velocity is equal to one half of the steam velocity. therefore for good efficiency. The blade velocity should be about one half of the steam velocity.
If the steam was expanded from admission pressure down to final exhaust pressure in a single stage of nozzles (single stage) then the velocity of the steam leaving the nozzle might he in the order of 100m per second in order to have good efficiency the blade velocity would have 10 be about 550m per second which would require excursively hid rev/min of the turbine rotor and failure due to centrifugal force could result.
In addition to this objection, excessively high steam velocity will cause high steam velocity will cause high friction losses in nozzles and blades.