THE REACTION TURBINE

THE REACTION TURBINE:
Construction of the reaction turbine is somewhat different from that of the impulse turbine. Essentially, the reaction turbine consists of row of blades on drum .These drum blades are separated by row of fixed blade mounted in the casing. Unlike the impulse turbine, no nozzle as such are mounted in a reaction turbine. The fixed blades act as nozzles in which velocity of steam in increased and they directed the steam correctly onto the moving blade.


The pressure and velocity variation across a reaction turbine is shown in fig(1) .
The steam also expands in the moving blades of reaction turbine with consequent pressure drop and velocity increase in the these moving blades. This is unlike the impulse turbine where the pressure drop takes place in the nozzle only and not in the turbine .This expansion in the moving blade of reaction turbine gives an extra reaction to the moving blade over that which would be obtained if the blades were impulse.
In a reaction turbine a stage is made up of a row of fixed blades followed by a row of moving blades. Steam acceleration usually occurs in both the fixed and moving the blades of reaction turbine differ from that of impulse turbine.
There is an enthalpy drop in the steam during its passage through the blades which produced the acceleration the extent to which the enthalpy drop occurs in the moving blades is called the " Degree of reaction"
If (50%) of enthalpy drop occurs in moving blades ,the stage will be said (50%) reaction stage.
A (50 %) reaction stage is more common in reaction turbine .But in an impulse turbine, the entire enthalpy drop occurs in fixed blade.

VELOCITY DIAGRAM FOR REACTION TURBINE STAGE:
The diagram illustrated is symmetrical ,showing equal acceleration in both fixed and moving blades and hence this diagram illustrates the condition of (50%) reaction.