. Applied thermodynamics for engineers. impulse turbine with three pressure stages, havingtwo moving wheels in each pressure stage. Initial pressure, 150 lb. absolute;temperature, 600 F.; final pressure, 2 lb. absolute; entering stream angles, 20°;peripheral velocity, 500 ft. per second ; 1200 revolutions per minute. By reproducing as in Fig. 240 a portion of the Mollier heat chart, we obtainthe expansive path .4i?, and the heat drop is - = B. t. u. Divid-ing this into three equal parts, the heat drop per stage becomes -^ 3 = t. u. This is without correction fo
. Applied thermodynamics for engineers. impulse turbine with three pressure stages, havingtwo moving wheels in each pressure stage. Initial pressure, 150 lb. absolute;temperature, 600 F.; final pressure, 2 lb. absolute; entering stream angles, 20°;peripheral velocity, 500 ft. per second ; 1200 revolutions per minute. By reproducing as in Fig. 240 a portion of the Mollier heat chart, we obtainthe expansive path .4i?, and the heat drop is - = B. t. u. Divid-ing this into three equal parts, the heat drop per stage becomes -^ 3 = t. u. This is without correction for friction, and we may expect a somewhatunequal division to appear as friction is considered. To include friction in deter-mining the change of condition during flow through the nozzle, we lay off, in Fig- 240, AH= , HG =^^^, and project GE, finding j9 = 50, ^ = 380°, at the out-lets of the first set of nozzles. The velocity attained (with 10 per cent loss ofavailable heat by friction) is y = = 2225 ft. per T n 11 f Fig. 255. Art. 532. — Multi-stage Velocity Diagram. We now lay ofT the velocity diagram, Fig. 249, making a = 20°, w = 5U0,y = 2225. The exit velocity x may be variously drawn; we will assume it so that 378 APPLIED THERMODYNAMICS the relative angles e and/are equal, and, allowing 10 per cent for bucket friction,will make x = V. For the second wheel, the angle a is again 20°, while v, onaccount of friction along the stationary or guide blades, is Y. After locatingVf if the angles e and/ were made equal, there would in some cases be a back-ward impulse upon the wheel, tending to stop it, at the emergence of the jet aloDgY. On the other hand, if the angle/ were made too acute, the stream would beunable to get away from the moving buckets. With the particular angles andvelocities chosen, some backward impulse is inevitable. We will limit it by mak-ing/ = 30°. The rotative components of the absolute velocities may be computedas
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