. A text book of physics, for the use of students of science and engineering . ed into kinetic energy inthe jets. The water passes in thin layers over the wheel blades 6, C,and the pressure in the wheel passages is kept equal to that of theatmosphere by means of side openings in the rim of the wheel, oneat the back of each blade. It will be noted that the wheel is situatedabove the level of the discharged water in the tail-race E, E ; thewater is therefore discharged at atmospheric pressure from the wheelinto the atmosphere. In Fig. 317 is shown in outline a Jonval reaction turbine. Thearrange
. A text book of physics, for the use of students of science and engineering . ed into kinetic energy inthe jets. The water passes in thin layers over the wheel blades 6, C,and the pressure in the wheel passages is kept equal to that of theatmosphere by means of side openings in the rim of the wheel, oneat the back of each blade. It will be noted that the wheel is situatedabove the level of the discharged water in the tail-race E, E ; thewater is therefore discharged at atmospheric pressure from the wheelinto the atmosphere. In Fig. 317 is shown in outline a Jonval reaction turbine. Thearrangement is similar to the Girard turbine. -Water is suppliedfrom A and passes through a ring of orifices B, B, having guide bladesso as to whirl the water. The wheel C, C has blades so shaped as to 294 DYNAMICS CHAP. eliminate the whirl. The difference between the two types is thatin the Jonval turbine the water passing through the wheel fills com-pletely the passages in the wheel, and may therefore have a pressurenot equal to that of the atmosphere, tn the example illustrated. Fig. 317.—Action in a Jonval reaction turbine. the wheel is below the level of the water in the tail-race E, E, and the pressure in the wheel passages is therefore greater than that of the atmosphere. The difference in free surface levels of the supply water in A. A and of the discharged water in E, E is H ; hence H units of potential energy per unit mass of water are avail-able for conversion into work. Pelton wheel.—To obtain efficientconditions of working in water turbines,the wheel blades must be so formed thatthe water slides on to them withoutimpact. Impact, or shock, alwaysproduces waste of energy (p. ;).Further, the water must be dischargedfrom the wheel with as small a velocityas possible. Both of these conditionswill lie readily understood by referenceto Fig. 318 showing a Pelton wheel. A jet of water is discharged intobuckets which are fixed to the rim of a revolving wheel. In theplan
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