. Applied thermodynamics for engineers. ntlyhave the ratio \J2 : 1 (21). Assume, in this case, that the peripheral speed of the first drum is 130 ft. per sec, and thatof the last drum 350 ft. per sec. Theusual plan is to increase the successivedrum speeds at constant ratio. Thismakes the speeds of the blades on theintermediate drums 181 and 251 ft. persec, respectively. The steam velocity will be usually between 1| and 3 times the blade ve- locitv: it will increase more rapidly as Art. 534, Prob. of ^he lower pressures are reached. The Pressure Turbine. , c,,. -• i, u i_ ^ value of
. Applied thermodynamics for engineers. ntlyhave the ratio \J2 : 1 (21). Assume, in this case, that the peripheral speed of the first drum is 130 ft. per sec, and thatof the last drum 350 ft. per sec. Theusual plan is to increase the successivedrum speeds at constant ratio. Thismakes the speeds of the blades on theintermediate drums 181 and 251 ft. persec, respectively. The steam velocity will be usually between 1| and 3 times the blade ve- locitv: it will increase more rapidly as Art. 534, Prob. of ^he lower pressures are reached. The Pressure Turbine. , c,,. -• i, u i_ ^ value of this ratio should vary between about the same limits for each drum. The curve EA is sketched to represent steam velocities assumed: the ordinateFE may be 130X2 = 260 ft. per second, and the ordinate OA say 973 ft. per shape of this curve is approximately hyperbolic. It is now desirable to lay off on the axis FO distances representing approximatelythe lengths of the various drums. An empirical formula which facilitates this is. Fig n=- C where n = number of rows of blades when the blade speed is it ft. per sec, C = a constant, =1,500,000 for marine turbines, =2,600,000 for turbo-generators. When (as in our case) u is different for different drums, we have Ml being the number of stages on a drum of blade velocity Ui, developing the s pro-portion of the total power. The power developed by the successive drums increasestoward the exhaust end: let the division in this case be i, i, j, f, of the total respect-ively. Then for C = 2,600,000, 2,600,000 ^^r _ Th 2, _1 181^ X: 16, 2,600,000 1_ 25P ^4~^ _ 2,600,000 ^3 _ o-~^502~~><8 ~ ^• The total number of stages is then approximately 60. The distances FC, CD, DB, BO, are then laid off, equal respectively to eo, and Wo of FO. At any point like G, then, the steam velocity is ZG and the blade velocity is that for the drumin question: for G, for example, it is 181 ft. per sec Knowing the steam velocity and peripheral
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