Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . bladesrespectively, d2 is the steam density in pounds per cubicfoot at the discharge from the stationary blades, d3 is the steamdensity in pounds per cubic foot at the discharge from themovable blades, and V2 and Vr3 are the corresponding steamvelocities (feet per second) as previously defined. This expres-sion gives the effective steam flow; that is, the amount of steamflowing between the blades and doing useful work. The leak- STEAM TURBINE TYPES AND BLADE DESIGN 91 ag
Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . bladesrespectively, d2 is the steam density in pounds per cubicfoot at the discharge from the stationary blades, d3 is the steamdensity in pounds per cubic foot at the discharge from themovable blades, and V2 and Vr3 are the corresponding steamvelocities (feet per second) as previously defined. This expres-sion gives the effective steam flow; that is, the amount of steamflowing between the blades and doing useful work. The leak- STEAM TURBINE TYPES AND BLADE DESIGN 91 age steam at the tip of the blades in the clearance space will beconsidered later. It should be noted that the expression (Vr2 COS |8 + Vr3 cos 7) V& g (22a) gives the useful output in foot-pounds per pound of steam; andthat similarly the useful output in per pound of steam isgiven by (7,3cos/3 + Fr3cos7) Vb2X778 (22b) As already stated above, in using these formulas the relativevelocities V& and Vr3 at the entrance and discharge sides of themoving row are respectively actual values after proper allowances. Fig. 47c. Illustration of a Practical Example. are made for frictional losses in the stationary and moving rowsof blades. Proper coefficients to allow for these friction losseswill be given later. It is sufficient to say here that the kineticenergy actually developed in either the stationary or movingblades is about .8 to .85 of the available energy, that is fE2=V2y2g) JEz 2g 92 ; THE STEAM TURBINE where f is a fraction equal to .8 to .85. The relative velocityat the entrance to the moving blade V^ is of course computed bymeans of simple trigonometric formula applied to the velocitydiagram illustrated in Fig. 46. Example. Consider a common blade section (Fig. 47b) forboth stationary and moving blades, having a discharge angle aof 200 and an entrance angle (3 of 700. Referring to Fig. 47c,the following relations are obvious, 7* 7^ Vh , sin no° sin 20° — . 0 • •
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