Radial-inflow turbines design

NASA TN D-4384, Rohlik, H. E., Analytical determination of Radial-Inflow Turbine Design Geometry for Maximum Efficiency", (1968)... 

Because high-pressure ratio requirements coincide in most cases with low specific speed designs, only partial admission axial or radial inflow turbines are seriously considered. 

With a lower temperature, the turbine is best used by allowing the baek-pressure to fall and thus obtain more power. In radial inflow turbines, the relative veloeity at the turbine inlet is small. Any ehanges are, therefore, far less signifieant than with high relative veloeity impulse wheels. Commonly, a turboexpander tolerates as mueh as a 30% ehange from its designed enthalpy. The effeet on effieieney was shown earlier in Figure 3-12. 

Radial-Inflow Turbines 329 Turbine Design Considerations... 

To design a radial-inflow turbine of the highest effleieney, the exit veloeity leaving the turbine must be axial. If the exit veloeity is axial, the Euler turbine equation reduees to... 

The boundary layer along the blade surfaces must be well energized so that no separation of the flow occurs. Figure 8-16 shows a schematic of the flow in a radial-inflow impeller. Off-design work indicates that radial-inflow turbine efficiency is not affected by changes in flow and pressure ratio to the extent of an axial-flow turbine. 

Axial-flow turbines are the most widely employed turbines using a eompres-sible fluid. Axial-flow turbines power most gas turbine units—exeept the smaller horsepower turbines—and they are more effieient than radial-inflow turbines in most operational ranges. The axial-flow turbine is also used in steam turbine design however, there are some signifieant differenees between the axial-flow turbine design for a gas turbine and the design for a steam turbine. 

Radial-inflow turbine 8,00(T 0,000 High High med. Lightweight, mature technology, high efficiency High cost, low efficiency at off-design conditions, intolerable two phase... 

Development The following discussion relates specifically to the use of what could be called radial-inflow, centrifugal-pump power-recovery turbines. It does not apply to the type of unit nurtured by the hydroelecti ic industry for the 1 ge-horsepower, large-flow, low- to medium-pressure differential area of hydraulic water turbines of the Felton or Francis runner type. There seems to have been little direct transfer of design concepts between these two fields the major manufacturers in the hydroelectric field have thus far made no effort to sell to the process industries, and the physical arrangement of their units, developed from the requirements of the hydroelectric field, is not suitable to most process-plant applications. 

Miero-turbines are usually referred to units of less than 350 kW. These units are usually powered by either diesel fuel or natural gas. They utilize teehnology already developed. The miero-turbines ean be either axial flow or eentrifugal-radial inflow units. The initial eost, effieieney, and emissions will be the three most important eriterias in the design of these units. 

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