Water-power; an outline of the development and application of the energy of flowing water . to be recommended for heads under 50 feet, nor even inthat case when the head is liable to great variation from back-water. These conditions restrict the application of the wheelto special cases. The regulation of the supply of water and the speed of thesewheels is sometimes attempted by means of cocks in the pipesleading to the nozzles. For a wheel with four nozzles thismethod would not be inconsistent with a good result at fulldischarge, and at three-fourths, one-half, and one-fourth ofsame. But the w
Water-power; an outline of the development and application of the energy of flowing water . to be recommended for heads under 50 feet, nor even inthat case when the head is liable to great variation from back-water. These conditions restrict the application of the wheelto special cases. The regulation of the supply of water and the speed of thesewheels is sometimes attempted by means of cocks in the pipesleading to the nozzles. For a wheel with four nozzles thismethod would not be inconsistent with a good result at fulldischarge, and at three-fourths, one-half, and one-fourth ofsame. But the water from the pipe which was undergoingcontraction would act at a great disachantage on account of THE HUKDY GURDY WHEEL. J j:) the loss of head incident to the action of the cock. For awheel propelled by a single nozzle as at Fig. i6o this mode ofregulation would be wholly inapplicable. The speed of thevanes is fixed by the application or use made of the power andmay be considered invariable. This velocity we may take asthat of greatest efficiency viz., one-half that due the full head. acting on the wheel. In the arrangement of Fig. i6o, if thesupply be controlled wholly by the gate there shown, theissuing stream will be of the full size of the nozzle efflux,irrespective of the extent to which the gate is closed. Thegate acts to diminish the pressure in the space between the 336 TURBINES. gate and efflux, and consequenth- the velocity of the issuingstream. Equation 39 gives for the energy exerted on a cup-shaped vane moving with the velocity ?^ under the action of astream of water, of cross-section a, with the velocity v, Pu = ivav —^—? -, w being the weight of a cubic foot of water. Suppose u to be the velocity of maximum efficienc}, \iZ., 21 = -. If now we suppose the velocity v to be reduced by one-fourth, ?/ remain-ing unchanged, we have Pu = Izcaz^^ ^^ = izvav X ~ ~ = {Q^o X^i = iQw/i. The diminution of the velocit} by one-fourth, therefore,diminishes the power by fiv
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecthydraulicengineering
