"Verbal" notes and sketches for marine engineers : a manual of marine engineering practice, intended for the use of naval and mercantile engineer officers of all grades, and students, and is specially compiled for the use of engineer officers preparing for examinations of competency at home or abroad . nged with expanding nozzles in which the high velocity of dischargeimpinges against a series of small buckets secured on the circumferenceof a large wheel keyed to the driving shaft, the De-Laval turbine beingan example of this t)pe ; and those (2) Impulse-reaction Turbines, inwhich the steam pa
"Verbal" notes and sketches for marine engineers : a manual of marine engineering practice, intended for the use of naval and mercantile engineer officers of all grades, and students, and is specially compiled for the use of engineer officers preparing for examinations of competency at home or abroad . nged with expanding nozzles in which the high velocity of dischargeimpinges against a series of small buckets secured on the circumferenceof a large wheel keyed to the driving shaft, the De-Laval turbine beingan example of this t)pe ; and those (2) Impulse-reaction Turbines, inwhich the steam passes through a number of rings of fixed blades andof moving blades, expanding as it travels, an example of which isfound in the Parsons turbine Work by impulse is produced by high velocities, and as the workis done at the expense of the internal heat, water is formed whichthus diminishes the heat left. The Parsons_turbine is generally called a reaction turbine, althoughthe correct term should be impulse-reaction turbine, as the steamactually does act first by impulse from the guide to the moving bladesand afterwards works by reaction from the moving to the guide blades De-Laval Turbine.—In the specially shaped diverging nozzle olthe De-Laval turbine shown in the sketch, the steam expands down. \^>.^^^^ ARRANGEMENT OF NOZZLE AND VAl,g^ No. I.—De-Laval Turbine. * For more exhaustive information on turbine practice, see authors TheMarine Steam Turbine (published by Messrs Crosby Lockvvood & Son, London). 642 I Appendix 643 to the required exhaust pressure, and the resultant kinetic energyacquired is appHed direct to the small buckets or vanes, the steambeing in consequence at a very high velocity. To obtain the bestefficiency the circumferential velocity of the turbine blades should beequal to about half the velocity of the steam, and this, of course,demands a very high revolution speed. In the De-Laval turbine thespeed is often as 20,000 revolutions pe
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