The Limit Power of Propelling Machinery with Steam Turbine

Abstract

The power of propelling machinery with steam turbine is restricted not only by the constructionof steam turbine but also by the reduction gearing and propeller. This treatiseargue on the limit of shaft horse power per shaft of merchant ship propelled by steamturbine (condensing, single flow, not extracted) reduced by gearing.As the limit construction of steam turbine, we assume that the turbine efficiency ratio is0.8, the adiabatic heat drop of steam is 300kcal/kg, on the ehe exhaust end of the last stagespecific volume of steam is 26.4m3/kg, velocity ratio is 0.8, peripheral speed is 250m/sec, the ratio of blade length to mean diameter of turbinedisc is 1/5, the coefficient of contractionof exhaust area of blade is 0.95 and the transmission efficiency of reduction gear is 0.96.Let the shaft horse power of propeller shaft per shaft is P HP/shaft, number of revolutionsof shaft is N rev/mn and the reduction ratio of revolutions of low pressure turbine is r.then we can get the limit power restricted by steam turbine asP=13.53×104/(r•N/1000)2 (12)As the limit construction of reduction gear, we assume that the ratio of effective widthof gear to pitch diameter of pinion is 4.5, the tooth pressure per axial gear width in cm. is25 times the square root of pitch diameter in cm., the peripheral speed in pitch circle is43.0m/sec. Let number of turbine cylinders is α, number of revolutions of pinion is np rev/mn. then we can get the limit power restricted by reduction gearing asP=4.613×104×α/(np/1000)3/2 (20)As the limit construction of screw propeller, we assume that the ratio of projected areato disc area of propeller is 0.5 the transmission efficiency of shafting is 0.95, the propellerefficiency behind hull is 0.65, the wake factor is 0.2, the thrust intensity per unit area ofprojected area is 0.9kg/cm2. Let the ship speed is V kn., the peripheral speed of propellertip is us m/sec, then we can get the limit power restricted by propeller asN√ =107.0×us (32)The limit power of propelling machinery with steam turbine is restricted by either of these three equations. Fig. 3 is the nomograph for these equations and show the relative relations for them.The author researched for the relations between N, P, V and us about some actual ships, and got the approximate equationsN√ =-1500+120us. (35) shown by Fig. 2.