Document zzL6o5pobYNEKewKNk2dLQEK7

92^__________ CHAPTER 4 ' ' 1946 Guide of K again are obtainable from Figs. 7, 8, 9, and-10, according to the type of pressure tap. NOZZLE COEFFICIENTS AND EXPANSION FACTORS Nozzles differ from orifices in that the flow is guided to the throat in such a way that contraction of the jet is suppressed, or, in other words, there is no vena contracta. Because of this fact, the coefficients are different from those of orifices, and very close to unity before the velocity of approach factor is added. Also, the expansion factor may be deduced rationally, rather than empirically, as with orifices. Two shapes of nozzles that have been under investigation by the . A.S.M.E. for some time are shown in Figs. 16 and 17. They are referred 0.2 Fig. 19. 0.3 0.4 as 0.6 0.7 08 09 DIAMETER RATIO p Relation of Nozzle Discharge Coefficient, C, for 6-Inch Pipe, To Diameter Ratio and Reynolds Number coefficient for a given nozzle shape is higher if the finish of the surface is smoother. Discharge coefficients, C, for pipes 2, 6, and 10 in. in diameter are given in Figs. 18, 19, and 20, as correlated by Bean, Beitler and Sprenkle6, . as functions of the diameter ratio $ and the Reynolds number referred to the diameter of the throat in feet. to as long-radius nozzles. Their contour is that of a semi-ellipse, and the contracting portion is followed by a cylindrical section of the same area as the throat. The shape shown in Fig. 16 is designed for use with ratios of throat to pipe diameter of 0.53 or less, that of Fig. 17 for ratios of 0.4 to 0.7. The most usual location of pressure taps is 1 pipe diameter up stream and ]/2 diameter downstream, both measured from the plane of the nozzle inlet. In addition, the International Standards Association has adopted still another shape of nozzle, which has a rather sharper approach-than the A.S.M.E. nozzles, and which uses corner taps. Very little use of this nozzle has been made in this country. The formulas already given for orifices apply equally to nozzles except for discharge coefficients, and for the expansion factor, .when it is applied. Discharge coefficients for nozzles, as for orifices, vary with pipe size; they may either increase,r decrease with decreasing sizeof pipes depend- , ing on the sharpness of the approach curvature of the nozzle.. For the A.S.M.E. nozzles, they tend to decrease. Generally speaking, too, the.