Radial-Inflow Turbines
The radial-inflow turbine has been in use for many years. It first appeared as a practical power-producing unit in the hydraulic turbine field. Basically acentrifugal compressor with reversed flow and oppositerotation, the radial-inflowturbinewasthefirstusedinjetengineflightinthelate 1930s. Itwas considered the natural combination for a centrifugal compressor used in the same engine. Designers thought it easier to match the thrust from the two rotors and that the turbine would have a higher efficiency than the com-pressor for the same rotor because of the accelerating nature of the flow.
The performance of the radial-inflow turbine is now being investigated with more interest by the transportation and chemical industries: in trans-portation, this turbine is used in turbochargers for both spark ignition anddiesel engines; in aviation, the radial-inflow turbine is used as an expander inenvironmental control systems; and in the petrochemicalindustry, it is usedin expander designs, gas liquefaction expanders, and other cryogenic sys-tems. Radial-inflow turbines are also used in various small gas turbines to power helicopters and as standby generating units.
The radial-inflow turbine's greatest advantage is that the work produced by a single stage is equivalent to that of two or more stages in an axial turbine. This phenomenon occurs because a radial-inflow turbine usually has a higher tip speed than an axial turbine. Since the power output is a function ofthe square ofthe tip speed (PαU2) for a given flowrate, the work is greater than in a single-stage axial-flow turbine.
The radial-inflow turbine has another advantage: its cost is much lower than that of a single or multistage axial-flow turbine. The radial-inflow turbine has a lower turbine efficiency than the axial-flow turbine; how-ever, lower initial costs may be an incentive to choosing a radial-inflow turbine.
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