Axial-flow turbines impulse turbine

The axial-flow turbine, like its eounterpart the axial-flow eompressor, has flow, whieh enters and leaves in the axial direetion. There are two types of axial turbines (1) impulse type, and (2) reaetion type. The impulse turbine has its entire enthalpy drop in the nozzle therefore it has a very high veloeity entering the rotor. The reaetion turbine divides the enthalpy drop in the nozzle and the rotor. Figure 1-37 is a sehematie of an axial-flow turbine, also depleting the distribution of the pressure, temperature and the absolute veloeity. 

Most axial flow turbines eonsist of more than one stage, the front stages are usually impulse (zero reaetion) and the later stages have about 50% reaetion. The impulse stages produee about twiee the output of a eompar-able 50% reaetion stage, while the effieieney of an impulse stage is less than that of a 50% reaetion stage. 

Mechanical Impulse The principle of mechanical impulse when applied to fluids is usually combined with one of the other means of imparting motion. As mentioned earher, this is the case in axial-flow compressors and pumps. The turbine or regenerative-type pump is another device which functions partially oy mechanical impulse. 

An example of a typical turboexpander is shown in Fig. 29-46. Radial-flow turbines are normally single-stage and have combination impulse-reaction blades, and the rotor resembles a centrifugal-pump impeller. The gas is jetted tangentially into the outer periphery of the rotor and flows radially inward to the eye, from which the gas is jetted backward by the angle of the rotor blades so that it leaves the rotor without spin and flows axially away. 

The two types of turbines—axial-flow and radial-inflow turbines—can be divided further into impulse or reaction type units. Impulse turbines take their entire enthalpy drop through the nozzles, while the reaction turbine takes a partial drop through both the nozzles and the impeller blades. 

TTiere are two main types of expansion turbines axial flow and radial flow. Axial flow expansion turbines are like conventional steam turbines. They may be single-stage or multistage with impulse or reaction blading, or some combination of the two. Turbines of this type are used as power recovery turbines. They are used where flow rates, inlet temperatures, or total energy drops are very high. 

From an internal design perspective, the steam turbine is either an impulse-or a reaction-type design. In the United States, almost all turbine designs are of the axial flow variety, and only a small number are of the tangential flow variety. In Europe, a significant number of turbines are of the radial flow... 

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