【Mechanical Equipment Technology Exchange Edition】Mechanical Equipment 【Daily Question】20190924

Based on the number of pressure stages, they can be divided into single-stage and multi-speed stages； Based on their different functions, blades can be divided into regulating stages and pressure stages. In a pure impulse stage, the reaction degree is zero; the steam expands only within the nozzle, converting its thermal energy into kinetic energy ； It does not expand within the moving blades; these blades are subjected only to the force exerted by the steam, which converts kinetic energy into mechanical work. Its structural feature is that the blade profile of the moving blades is basically symmetrical. A pure impulse stage has high working capacity but lower efficiency. For impulse stages with reactivity, the reactivity ranges from 0.2 to 0.3; most of the steam expansion occurs within the nozzle, with only a small portion taking place in the rotor blades. Its working capacity is greater than that of a reaction stage, and its efficiency is higher than that of a pure impulse stage, making it widely used in steam turbines. The regenerative stage is an improved version based on the single-row impulse stage, that is, a row of guide vanes and a row of moving vanes are added behind the single row of moving vanes. The working capacity of a compound speed stage is greater than that of a single impulse stage. Compound stages are typically used when the enthalpy drop per stage is large and the velocity at the nozzle exit is high. To improve the efficiency of the regenerative stage, its moving blades can also be designed with a certain degree of reaction. When the exit velocity of the second row of moving vanes is still high, another row of guide vanes and moving vanes can be added to form three rows of speed stages. For the reaction stage, the reaction degree is 0.5; as steam flows through the rotor blades, in addition to exerting a thrust on them, it also exerts a significant reaction force on the rotor blades due to the further expansion and acceleration of the steam within those blades. The ideal enthalpy drop in the steam turbine cascade is equal to the enthalpy drop in the static cascade. The static and dynamic blades of the reaction stage have the same airfoil shape and are symmetrical. The efficiency of the reaction stage is higher than that of the impulse stage, but its working capacity is lower.

Three main categories: pure impulse stage, impulse stage with a small reaction degree (abbreviated as impulse stage), and reaction stage

Based on their working principle, they can be divided into impulse stages and reaction stages; the impulse stages can further be classified into pure impulse stages, impulse stages with a degree of reaction, and compound speed stages

Based on their degree of reaction, turbine stages are classified into three types: pure impulse stages, impulse stages, and reaction stages

1. In a pure impulse stage, the reaction degree is zero; the steam expands only within the nozzle, converting its thermal energy into kinetic energy； It does not expand within the moving blades; these blades are subjected only to the force exerted by the steam, which converts kinetic energy into mechanical work. Its structural feature is that the blade profile of the moving blades is basically symmetrical. A pure impulse stage has high working capacity but lower efficiency. 2. For impulse stages with reaction degree, the reaction degree is between 0.2 and 0.3; most of the steam expansion occurs within the nozzle, with only a small portion taking place in the rotor blades. Its working capacity is greater than that of a reaction stage, and its efficiency is higher than that of a pure impulse stage, making it widely used in steam turbines. 3. The regenerative stage is an improved version based on the single-row impulse stage, that is, a row of guide vanes and a row of moving vanes are added behind the single row of moving vanes. The working capacity of a compound speed stage is greater than that of a single impulse stage. Compound stages are typically used when the enthalpy drop per stage is large and the velocity at the nozzle exit is high. To improve the efficiency of the regenerative stage, its moving blades can also be designed with a certain degree of reaction. When the exit velocity of the second row of moving vanes is still high, another row of guide vanes and moving vanes can be added to form three rows of speed stages. 4. For the reaction stage, with a reaction degree of 0.5, as steam flows through the rotor blades, in addition to exerting a thrust on them, the continued expansion and acceleration of the steam within the rotor blades also results in a significant reactive force being applied to them. The ideal enthalpy drop in the steam turbine cascade is equal to the enthalpy drop in the static cascade. The static and dynamic blades of the reaction stage have the same airfoil shape and are symmetrical. The efficiency of the reaction stage is higher than that of the impulse stage, but its working capacity is lower.

1) Pure impulse stage: The steam expands only in the nozzle cascade, while it does not expand in the rotor cascade. It uses only impact force to do work. In this grade: p1 hbD = p2 ； =0 ； Ωm=0. (2) Reaction stage: Half of the steam expansion occurs in the nozzle, and the other half takes place in the rotor blades. In its moving blade cascade, not only is there an impact force, but the expansion of steam within the moving blades also generates a significant reaction force that does work. The flow efficiency of the reaction stage is higher than that of a pure impulse stage, but its working capacity is lower. In this level: p1 > ht ； Ωm=0.5. Dhb≈0.5Dhn≈Dp2 ； (3) Impulse stage with reaction degree: Most of the steam expansion occurs in the nozzle cascade, with only a small portion taking place in the rotor cascade. This stage possesses the characteristics of both impulse and reaction stages; its flow efficiency is higher than that of a pure impulse stage, while its performance capacity is higher than that of a reaction stage. In this level: p1 > hnDp2 ； >hbD >0 ； Ωm=0.05～0.35. (4) Compound stage: A compound stage consists of two rows of moving vanes. Modern compound stages have a certain degree of reaction, meaning that in addition to expanding in the nozzles, the steam also expands appropriately within the two rows of moving vanes and guide vanes. Since the compound speed stage uses two rows of moving vanes, its operating capacity is greater than that of a single-row impulse stage.

Based on their working principle, they can be divided into impulse stages and reaction stages; the impulse stages can further be classified into pure impulse stages, impulse stages with a degree of reaction, and compound speed stages

1. Pure impulse stage 2. Reaction stage 3. Impulse stage with reaction

1. Pure impulse stage 2. Reaction stage 3. Impulse stage with reaction

Pure impulse stage, impulse stage, and reaction stage