. Applied thermodynamics for engineers. = We find values of F as follows : Aty,at m,at A, X 1683 X 2225 X 1507 = ; at w,= ; at B,= ; at v, X X X 2271 = ;= ;= Completing the computation as to the last set of nozzles only, the throatarea is sq. ft., that at the outlet being sq. ft. These corre-spond to diameters of in. The taper may be uniformfrom throat to outlet, the sides mak-ing an angle of 10°. This requiresa l
. Applied thermodynamics for engineers. = We find values of F as follows : Aty,at m,at A, X 1683 X 2225 X 1507 = ; at w,= ; at B,= ; at v, X X X 2271 = ;= ;= Completing the computation as to the last set of nozzles only, the throatarea is sq. ft., that at the outlet being sq. ft. These corre-spond to diameters of in. The taper may be uniformfrom throat to outlet, the sides mak-ing an angle of 10°. This requiresa length from throat to outlet of( - ) -- 2 tan 5° = length from inlet to throat maybe one fourth this, or in., the edge of the inlet being Stage Nozzle. „,^ i • i, • -r>- o-^r The nozzle is shown ni 1 ig. 2o7. The diameter of the bucket wheels at mid-height is obtained from the rotative speed and peripheral velocity. If d be the diameter, d X 1200 = 60 X 500, or d = Fig. 257. Art. 532. PRESSURE TURBINE 381 The forms of bucket are derived from the velocity diagrams. For the firststage, we proceed as in Art. 530, using the relatice angles e and/given in Fig. 255for determining the angles of the backs of the moving blades, and the absoluteangles for determining those of the stationary blades. 533. Utilization of Pressure Energy. Besides the energy of impulseagainst the wheel, unaccompanied by changes in pressure, the steam mayexpand while traversing the buckets, producing work by reaction. Thisinvolves incomplete expansion in the nozzle, and makes the velocities ofthe discharged jets much, less than in a pure impulse turbine. Lowerrotative speeds are therefore practicable. Loss of efficiency is avoided bycarrying the ultimate expansion down to the condenser pressure. In thepure pressure turbine of Parsons, there are no expanding nozzles; all ofthe expansion occurs in the buckets (Art. 524). (See Fig. 247.) Here
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