Expansion turbines radial

The efficiency of expansion turbines (partial admission axial, full admission axial, and radial inflow turbines) is a function of the following four basic parameters. 

For the preliminary estimate of the expected efficiency of expansion turbines, in most cases it is sufficient to neglect Reynolds number effects (Rg > 10 ) and use the efficiency and specific speed correlations shown in Figure 2-12 for partial admission axial impulse, reaction radial inflow and full admission impulse and reaction axial turbines. Due to the economic advantage of the radial turbine, die radial inflow turbine is die best selection when operating in die specific speed range 20 < Nj < 140, whereby die optimum efficiency will be achieved at N, = 80. 

TTiere are two main types of expansion turbines axial flow and radial flow. Axial flow expansion turbines are like conventional steam turbines. They may be single-stage or multistage with impulse or reaction blading, or some combination of the two. Turbines of this type are used as power recovery turbines. They are used where flow rates, inlet temperatures, or total energy drops are very high. 

Radial-flow expansion turbines are normally single-stage, with combination impulse reaction blades and a rotor resembling a centrifugal... 

Valves are often used to reduce the pressure of a gas or liquid process stream. By replacing the valve with a turbine, called an expander, turboexpander, or expansion turbine in the case of a gas and a liquid expander or radial-infiow, power-recovery turbine in the case of a liquid, power can be recovered for use elsewhere. Power recovery from gases is far more common than from liquids because for a given change in pressure and mass flow rate, far more power can be recovered from a gas than from a liquid because of the lower density of the gas. Equations for f.o.b. purchase costs of power recovery devices are included in Table 16.32 in terms of horsepower that can be extracted. Typical efficiencies are 75-85% for gases and 50-60% for liquids. Condensation of gases in expanders up to 20% can be tolerated, but vapor evolution from liquid expansion requires a special design. Whenever more than 100 Hp for a gas and more than 150 Hp for a liquid can be extracted, a power recovery device should be considered. 

To reeap, a turboexpander is a radial inflow turbine. The expansion proeess is aeeomplished in two steps primary and seeondary expansion. Primary expansion oeeurs in the inlet guide vanes and seeondary expansion oeeurs in the radial wheel. The proeess is isentropie and thermally effieient with reeoverable eold energy. Turboexpanders used in dew point eontrol require the following ... 

The overall effieieney of a radial-inflow turbine is a funetion of effieieneies from various eomponents sueh as the nozzle and rotor. A typieal turbine expansion enthalpy/entropy diagram is shown in Figure 8-7. The total enthalpy remains eonstant through the nozzle, sinee neither work nor heat is transferred to or from the fluid. Within the rotor, the total enthalpy ehanges. Downstream of the rotor the total enthalpy remains eonstant. 

Ceramic materials that retain structural integrity to temperatures in the 2100 to 2400°F range have been the subject of research and development for many years. Researchers have in fact created small radial inflow turbines from structural ceramic material for possible use in automotive gas turbines. These experimental units have shown favorable properties in laboratory tests. However, several practical considerations pose potential stumbling blocks to their use in commercial systems, such as coefficients of expansion that are substantially different from those of the metals used in gas turbine construction. One may expect to find ceramic materials in use in industrial gas turbines in the future, first on... 

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