If torque produced on the shaft of the turbine is only due to change in momentum of steam and pressure of steam at inlet and outlet of the turbine being same, it is known as impulse turbine. In this turbine, the expansion of high-pressure steam occurs only in nozzle as shown in Figure 5.8a, b. During passage of steam through blade, its direction changes which results in change in momentum equal to impulse on blade.
Fdt = d (mv); where Fdt is impulse and d (mv) is change in momentum.
Figure 5.8 (a) Impulse Turbine, (b) Pressure and Velocity Diagram
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