Types Of Turbines

Three types of turbines will be discussed: propeller (fixed and adjustable blades), Francis, and impulse. Figures 4 to 7 are illustrations of these turbine runners. Figure 8 shows a complete Francis turbine unit. The fixed- and adjustable-blade propellers and runners are essentially the same, with the exception that the adjustable is suited to a much wider range of loading conditions. This versatility is reflected in a higher manufacturing cost for the adjustable blade. The Francis runner is much like a centrifugal pump impeller running backward. The impulse runner (or Pelton wheel) is for high-head applications. The water is first channeled through a nozzle that directs a jet of water into the bowl-shaped runner buckets. This jet then discharges into the atmosphere. When a high back pressure is present in the housing, the impulse wheel cannot discharge properly. The performance drops off rapidly as the back pressure is increased. However, it is sometimes possible to admit low air pressure into the impulse runner housing to lower the level of the liquid surface to below the level of the runner. When the high turbine back pressure cannot be eliminated, a Francis turbine will perform much better than an impulse turbine. Figure 9 illustrates the relative efficiencies of the different types of runners. The fixed-blade propeller and Francis runners operate most efficiently in a range near full load, and operating time should be limited at low loads. The impulse and adjustable-blade runners, however, are designed for high efficiencies over a large load range. The adjustable-blade propeller accomplishes this by changing the angle of its blades by means of linkage in the hub of the runner. With the impulse runner, the size of the jet is controlled by the nozzle needle, which enables the runner to maintain high efficiencies at low loads.

FIGURE 3 Double-suction single-stage pump driven FIGURE 4 Mixed flow propeller runner (Voith by a Francis turbine (Voith Siemens Hydro) Siemens Hydro)
Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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