Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . away in the dischargedsteam, the energy available for work would be Wamit+J£=JdtMaA (B) 2g 2g Effi . = actual work done (A) = V22+Vr32-V^2-V32 * ( , °ienCy total work possible (B) V22+Vr32-Vr22 In the same way the efficiency can be calculated for any numberof rows of blades. Equation (19) expresses the efficiency foronly two rows of blades — one stationary and one moving — or,in other words, for one stage. We shall now obtain the efficiencyfor three stages, that is, for
Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . away in the dischargedsteam, the energy available for work would be Wamit+J£=JdtMaA (B) 2g 2g Effi . = actual work done (A) = V22+Vr32-V^2-V32 * ( , °ienCy total work possible (B) V22+Vr32-Vr22 In the same way the efficiency can be calculated for any numberof rows of blades. Equation (19) expresses the efficiency foronly two rows of blades — one stationary and one moving — or,in other words, for one stage. We shall now obtain the efficiencyfor three stages, that is, for six rows of blades. The correspond-ing velocity diagram is shown in Fig. 47. V 2 — — = kinetic energy developed in the first stationary blades. * Efficiency of a single stage approaches its maximum value as Vz is Vz could be made zero, the efficiency would be 100 per cent. 86 THE STEAM TURBINE VrZ2 - Vr*2 2? kinetic energy developed in the first moving blades. JV 2gblades. = kinetic energy in steam leaving the second stationary Vrb2 ~ Vr*2 2g kinetic energy developed in the second moving Fig. 47. Velocity Diagrams for Three Stages of a Reaction Turbine. 2g blades. 1 = kinetic energy in steam leaving the third stationary Vrl2 - Vr&2 2S kinetic energy developed in the third moving blades. V 9 —— = kinetic energy carried away in the discharged steam 2g final residual velocity. STEAM TURBINE TYPES AND BLADE DESIGN 87 We observe here that the velocities Va3 and V&3 are not lostbut represent velocities that can be effective in the succeedingstages. For this reason their energies do not enter the discussionof efficiency. The actual work in moving the blades is then Wk = ry^2+v*2 - v^2i+ry^,2+^ - v„n L2g 2g J L^g 2g J | rVc22 | V^-VreH Vc32 *L2g 2g J 2g Now, in designing a reaction turbine it is desirable to assumethat the blade velocities and the corresponding angles of theblades are the same and that equal steam velocities are devel-oped in each
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