Classification of steam turbine pdf fluid acts on the blades so that they move and impart rotational energy to the rotor. Claude Burdin, built the first practical water turbine. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. Impulse turbines do not require a pressure casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blades on the rotor.
Impulse turbines are most efficient for use in cases where the flow is low and the inlet pressure is high. The pressure of the gas or fluid changes as it passes through the turbine rotor blades. For compressible working fluids, multiple turbine stages are usually used to harness the expanding gas efficiently. In the case of steam turbines, such as would be used for marine applications or for land-based electricity generation, a Parsons-type reaction turbine would require approximately double the number of blade rows as a de Laval-type impulse turbine, for the same degree of thermal energy conversion.
Whilst this makes the Parsons turbine much longer and heavier, the overall efficiency of a reaction turbine is slightly higher than the equivalent impulse turbine for the same thermal energy conversion. In practice, modern turbine designs use both reaction and impulse concepts to varying degrees whenever possible. Wind turbines also gain some energy from the impulse of the wind, by deflecting it at an angle. Turbines with multiple stages may utilize either reaction or impulse blading at high pressure. Steam turbines were traditionally more impulse but continue to move towards reaction designs similar to those used in gas turbines. At low pressure the operating fluid medium expands in volume for small reductions in pressure. Under these conditions, blading becomes strictly a reaction type design with the base of the blade solely impulse.
The reason is due to the effect of the rotation speed for each blade. As the volume increases, the blade height increases, and the base of the blade spins at a slower speed relative to the tip. This change in speed forces a designer to change from impulse at the base, to a high reaction-style tip. Classical turbine design methods were developed in the mid 19th century. Vector analysis related the fluid flow with turbine shape and rotation. Graphical calculation methods were used at first. As with most engineering calculations, simplifying assumptions were made.
The velocity triangles are constructed using these various velocity vectors. Modern turbine design carries the calculations further. These tools have led to steady improvements in turbine design over the last forty years. This number describes the speed of the turbine at its maximum efficiency with respect to the power and flow rate.