Where does the pressure drop occur in an impulse turbine?

Only in the nozzles; pressure is constant over moving blades

Equally in fixed and moving blades

What force acts on the blades of a reaction turbine?

Impulse plus reaction from steam accelerating in the blade passage

Which statement is correct?

Impulse turbines have symmetrical blades and may use partial admission; reaction turbines have aerofoil blades, full admission and more stages

Reaction turbines have fewer stages and partial admission

Both use identical blade profiles

Impulse turbines have higher efficiency and more stages

2080 Baisakh · 4+4 marks

Rankine efficiency and impulse versus reaction

Short answer

Efficiency rises with higher boiler pressure, superheating, lower condenser pressure, reheating, and regenerative feed heating. In impulse turbines, pressure drops only in nozzles with constant moving-blade pressure; reaction turbines drop pressure in both fixed and moving blades, yielding higher efficiency but more stages.

What are the ways by which efficiency of the Rankine cycle can be increased? Differentiate between impulse and reaction steam turbine.

Ways to increase the efficiency of the Rankine cycle

Rankine efficiency $\eta = \dfrac{W_T - W_P}{Q_s}$ increases when heat is added at a higher mean temperature or rejected at a lower temperature:

Higher boiler pressure - higher saturation temperature during boiling.
Superheating to a higher turbine inlet temperature.
Lower condenser pressure - lower heat rejection temperature (limited by cooling water temperature).
Reheating the partly expanded steam.
Regenerative feed heating with bled steam.
Recovering flue gas heat with economiser and air preheater; using supercritical pressure or combined/binary cycles.

Impulse vs reaction steam turbine

Point	Impulse turbine	Reaction turbine
Pressure drop	Whole drop occurs in the nozzles only	Drop occurs in both fixed and moving blades
Pressure on moving blades	Constant over the moving blades	Falls continuously across moving blades
Force on blades	Impulse of high-velocity jet only	Impulse + reaction of steam accelerating in the blade passage
Blade profile	Symmetrical, constant passage area	Aerofoil shape, converging passage
Fixed element	Nozzles	Fixed (guide) blades acting as nozzles
Steam admission	Partial or full (nozzle arcs)	Full admission all round
Blade velocity / speed	Very high speed per stage (needs compounding)	Lower speed, many stages
Number of stages	Fewer	More (for same pressure drop)
Efficiency	Lower	Higher
Size / cost	Smaller, cheaper for given power	Larger, costlier (more stages)
Tip leakage	Small (no pressure difference across blades)	Larger, needs close clearances and dummy piston
Example	De Laval, Curtis, Rateau	Parsons turbine

✓ Answer checked by Claude Opus 5.5 (high effort)

Reheat Rankine cycle: 20 MPa, 500°C · Power Plant Equipment, chapter 7
Impulse versus reaction turbines · Power Plant Equipment, chapter 7 · asked 2×
Throttled reheat cycle with 50 bar steam · Power Plant Equipment, chapter 7
Open cycle gas turbine with intercooling · Power Plant Equipment, chapter 6
Open cycle gas turbine on heavy oil · Power Plant Equipment, chapter 6
Reheat cycle at 14 bar: ideal efficiency · Power Plant Equipment, chapter 7
Impulse and reaction steam turbines compared · Fluid Machines, chapter 5
Rankine cycle plots and efficiency · Fundamental of Thermodynamics & Heat Transfer, chapter 6
Rankine cycle 2 MPa: efficiency vs Carnot · Fundamental of Thermodynamics & Heat Transfer, chapter 6
Single-stage impulse turbine blade work and efficiency · Fluid Machines, chapter 5

All Power Plant Equipment chapter 7 questions →

Rankine efficiency and impulse versus reaction

Ways to increase the efficiency of the Rankine cycle

Impulse vs reaction steam turbine

Related questions