Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . theory that if theareas at the throatand at the mouthwere of the right size,the shape of the wallsbetween was of noconsequence, and, infact, that the steamof itself would takethe correct by preventingthe steam particlesfrom touching thewalls the frictionlosses in the nozzleshould be reduced. Itwill be observed, how-ever, from the curvein the figure deter-mined from some experiments with this nozzle that the pres-sure first drops abruptly in the throat to .58
Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . theory that if theareas at the throatand at the mouthwere of the right size,the shape of the wallsbetween was of noconsequence, and, infact, that the steamof itself would takethe correct by preventingthe steam particlesfrom touching thewalls the frictionlosses in the nozzleshould be reduced. Itwill be observed, how-ever, from the curvein the figure deter-mined from some experiments with this nozzle that the pres-sure first drops abruptly in the throat to .58 of the initial,as in any other nozzle, and then forms a series of waves, fromwhich it appears that the particles of steam strike the walls andrebound, to meet again at a point, as at A, where an increasedpressure is produced, and so on till the mouth is reached. Theprobable path of the steam is shown by the dotted lines in thedrawing of the nozzle. These experiments show therefore thatthe steam will not take the correct passage through a nozzle with-out the provision of properly designed walls of gradually increasing. Fig. 25. —>- Distance along Axis of NozzJeExpansion Curve in an Abnormal Nozzle. 54 THE STEAM TURBINE area corresponding to the expansion required. The importanceof careful workmanship in the manufacture of nozzles is thereforeobvious. The results shown by Fig. 25 bring up naturally the discussionof the proper length for a nozzle, as the one in this figure wasobviously much too long. Probably the best designers of the Curtis types of turbines makethe length of the nozzle depend only on the initial pressure. Inother words, the length of a nozzle for 150 pounds per square inchinitial pressure is usually made the same for a given type regard-less of the final pressure. And if it happens that there iscrowding for space, one or more of the nozzles is sometimesmade a little shorter than the others. Designers of De Laval nozzles follow practically the sameelastic m
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