Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . degrees like the onein Fig. 35 will exert only about half as much pressure as one turn-ing the steam through nearly180 degrees like the one inFig. 36. A turbine wheel whichwould be called a reactiontype is shown in Fig. 37. Itdiffers from the one in Fig. 36chiefly in the blade section B,shown at the top of the draw-ing. In this type the expan-sion of the steam in the noz-zle is only partial, and theblades are made so that partof the expansion occurs inthem. In the types
Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . degrees like the onein Fig. 35 will exert only about half as much pressure as one turn-ing the steam through nearly180 degrees like the one inFig. 36. A turbine wheel whichwould be called a reactiontype is shown in Fig. 37. Itdiffers from the one in Fig. 36chiefly in the blade section B,shown at the top of the draw-ing. In this type the expan-sion of the steam in the noz-zle is only partial, and theblades are made so that partof the expansion occurs inthem. In the types shownin Figs. 35 and 36, on theother hand, all the expansionis in the nozzles, with no ex-pansion at all in the blades.* The amount of expansion of the steam in the blades marks,therefore, the essential difference between the two importanttypes of steam turbines illustrated by Figs. 36 and 37. In im-pulse turbines there is no expansion in the blades, while in * The turbine wheel illustrated in Fig. 37 is not, however, typical of commercial reaction types in which there are sometimes as many as 60 to 80 pressure Fig. 37. Simple Reaction Wheel. 64 THE STEAM TURBINE reaction turbines expanding blades are used, with the resultthat some of the kinetic energy of the steam is changed tovelocity in flowing through them. From the explanation that has preceded it is obvious that bothof the types represented by the last two figures operate by bothimpulse and reaction. Impulse and Reaction of Fluids. The kinetic energy of afluid jet discharging from a nozzle may be regarded as producedby a constant impulse force I acting upon a weight W of thefluid discharged for one second. During this second the velocityhas changed from zero to V feet per second and has gone througha space of \ V feet. The work done by this force in producing the kinetic energy (K foot-pounds per second) is I X -/which 2 wv2 is equal to K or 2g We have then IV WV2 2 2g i _ wv g In practice the principal distingu
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