. The elements of railroad engineering . tical discharge through anorifice whose area is the same as the area of the endof thetube. HYDROMECHANICS. 391 If in a compound mouthpiece or tube, such as shown inFig. 181, a b, the narrowest part, be taken as the diameterof the orifice, the coefficient of effluxmay be taken as ; that is, theactual discharge through a com-pound mouthpiece of this shape times the theoretical dischargethrough an orifice whose area is thesame as the area of the smallest sec-tion of the mouthpiece. 1017. When the upper surfaceof the Avater remains at the sam
. The elements of railroad engineering . tical discharge through anorifice whose area is the same as the area of the endof thetube. HYDROMECHANICS. 391 If in a compound mouthpiece or tube, such as shown inFig. 181, a b, the narrowest part, be taken as the diameterof the orifice, the coefficient of effluxmay be taken as ; that is, theactual discharge through a com-pound mouthpiece of this shape times the theoretical dischargethrough an orifice whose area is thesame as the area of the smallest sec-tion of the mouthpiece. 1017. When the upper surfaceof the Avater remains at the sameheight above the orifice, there is said to be a constanthead. The velocity of efflux varies for different pointsin the orifice; it is greater at the bottom of the orificethan at the top, since the head is greater at the bottom thanat the top. A mean velocity may be obtained by dividingthe quantity of ivatcr discharged in feet per second by the area of the orifice, or v,^ = -=^. The theoretical head necessary to give this velocity v^ is. Fig. 181. h = v„ ^g Since the actual velocity is .98 of the theoretical /v V v velocity, the actual head is h= (-7^) -^^g— 1-04—. That is, the actual head must be times the theoreticalhead due to the mean velocity. Let Q = theoretical number of cubic feet discharged persecond;v„^ = theoretical mean velocity through orifice in feet per second = Q -^ A;A = area of orifice in square feet;h = theoretical head necessary to give a mean velo-city 7,„;Qa = actual quantity discharged in cubic feet , for an orifice in a thin plate, or a square-edged ori-fice (the hole itself may be of any shape, triangular, square, 392 HYDROMECHANICS. circular, etc., but the edges must not be rounded), the actualquantity discharged is (2„ = .C15 Q=.G15A v^ = .015 A \^lg/i. (38.) That is, the actual quantity discharged through a square-edged orifice or through a thin plate is .Olo times the theoret-ical discharge, and equals .01> multipli
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
