How does the blade angle impact the efficiency of a reaction-type steam turbine?

In a reaction-type steam turbine, the blade angle significantly impacts efficiency by influencing the steam's expansion and velocity as it passes through the rotor. Unlike impulse turbines where the pressure drop occurs primarily in the nozzles, reaction turbines feature a gradual pressure drop across both the stationary blades (nozzles) and the moving rotor blades. The blade angle determines how effectively the steam expands and accelerates as it moves through the rotor. A properly designed blade angle ensures optimal steam velocity relative to the blade speed. If the blade angle is too small, the steam may not expand sufficiently, resulting in a lower velocity and reduced energy extraction. This leads to decreased turbine efficiency. Conversely, if the blade angle is too large, the steam velocity may become excessively high. This can cause increased friction losses as the steam flows through the rotor, reducing efficiency and potentially leading to erosion of the blade material. The ideal blade angle is carefully calculated based on factors such as the steam's inlet pressure and temperature, the desired turbine speed, and the stage's pressure ratio. Turbine designers aim to create a blade profile that maximizes the steam's kinetic energy while minimizing losses due to turbulence and friction. The blade angle is also crucial for maintaining a smooth and uniform steam flow, which further contributes to higher efficiency and reduced wear.