Radial turbines

Radial-Inflow Turbine The radial-inflow turbine, or inward-flow radial turbine, has been in use for many years. Basically a centrifugal compressor with reversed-flow and opposite rotation, the inward-flow radial turbine is used for smaller loads and over a smaller operational range than the axial turbine. Radial-inflow turbines are only now beginning to be used because little was know about them heretofore. Axial turbines have enjoyed tremendous interest due to their low frontal area, making them suited to the aircraft industiy. However, the axial machine is much longer than the radial machine, making it unsuited for certain vehicular and helicopter applications. Radial turbines are used in turbochargers and in some types of expanders. 

In a radial turbine there are enormous eentrifugal forees aeting radially outward on the stream within the rotor. If this stream eontains... 

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. 

The more reeent eombination of standardized eompressor modules and eustomized eomponents with integrally geared radial turbines has opened new possibilities. Integrally geared radial turboexpanders represent eonsiderable design flexibility and this, in turn, allows... 

In the case of nitrous acid plants, application of integrally geared process gas radial turbines and compressors are used in plants with capacities ranging from 120-600 t/day and higher. For air compression, up to three compressor stages are connected in series. To increase efficiency, the inlet temperature of the individual stages is reduced by using two external intermediate coolers. 

The radial-inflow turbine, or inward-flow radial turbine, has been in use for many years. Basically a centrifugal compressor with reversed flow and opposite rotation, the inward-flow radial turbine is used for smaller loads and over a smaller operational range than the axial turbine. 

The inward-flow radial turbine has many components similar to a centrifugal compressor. There are two types of inward-flow radial turbines the cantilever and the mixed-flow. The cantilever type in Figure 1-34 is similar to an axial-flow turbine, but it has radial blading. However, the cantilever turbine is not popular because of design and production difficulties. 

The nomenelature of the Inward-Flow Radial Turbine is shown in Figure 1-36. These turbines are used beeause of lower produetion eosts, in part beeause the nozzle blading does not require any eamber or airfoil design. 

Knoernschild, E.M., The Radial Turbine for Low Specific Speeds and Low Velocity Factors, Journal of Engineering for Power, Trans ASME, Serial A, Vol. 83, pp. 1-8 (1961). 

Rodgers, C., Efficiency and Performance Characteristics of Radial Turbines, SAE Paper 660754, October, 1966. 

Vavra, M.H., Radial Turbines, Pt 4., AGARD-VKI Lecture Series on Flow in Turbines (Series No. 6), March, 1968. 

The 45° axial-flow turbine is more efficient at all Reynold s numbers than the flat-blade radial turbine. However, as the pitch angle decreases below 45°, the impeller becomes increasingly sensitive to high viscosity. 

On the basis of the information gathered here, three methods are possible for the design of agitated gas dispersion. In all cases the size of the tank, the ratio of impeller and tank diameters and the gas feed rate are specified. The data are for radial turbine impellers with six vertical blades. 

With a gas sparger and a radial turbine of the Rushton type, gas loads of up to 500 m3/(m2h) can be achieved with reasonable energy consumption. This method of dispersing the gas phase is usually employed for fast reactions or in situations where the hourly demand for the gaseous reactant is high, as in industrial fermenters. With such high gas-feed rates, the gas reactant may not react completely, so that eventually the unreacted gas may be recycled externally. 

The solids are kept in suspension if the pumping capacity of the impeller causes strong enough circulation of the liquid. In most processes, complete suspension of the particles is not required. Often, so-called off-bottom suspension is sufficient, which means that all particles are moving above the bottom of the tank with some vertical velocity. Radial flow impellers are usually not very effective in suspending solid particles. Actually, about three times more power is required for a radial turbine to provide the same degree of uniformity compared to an axial turbine. This is because the radial turbines pick up particles from the bottom of the tank by the suction side of the impeller, which is only half of the total flow from the impeller. Due to the appearance of an upper and a lower circulation zone, the contents of the two zones are not sufficiently mixed. Axial impellers are therefore most frequently used for the suspension of solids in stirred tanks [65]. 

It can be seen by comparing T ables 1 and 2 that if mechanical agitation is used and a jacket is desired, then additional internal coils are required. The internal coils can be vertical, like baffles, or helical. Agitation experts state that helical coils can be used with radial turbines if the spaces between the coil loops are 1 to 1.5 pipe diameters, Once helical coils are accepted. Why use ajacket at all Reasons in favor of coils (in addition to the better heat transfer coefficient) are ... 

Unwanted vortex] baffles not high enough (not above liquid level)/no baffles/ poor design/radial turbine selected instead of axial flow impeller/not sufficient baffles/rpm too high/impeller diameter too small. 

Radial compressor Radial wave rotor LPA port HPG port Combustor LPG port HFA port Radial turbine... 

DT 6-blade Scaba radial turbine 3- and 4-blade Scaba axial hydrofoil impellers (multiple impellers) Air-water 6-DT, 6-PTD... 

Sardeing R, Aubin J, Poux M, Xuereb C. (2004a) Gas-liquid mass transfer influence of sparger location. Trans. IChemE, Part A, Chem. Eng. Res. Des., 82(A9) 1161-1168. Sardeing R, Aubin J, Xuereb C. (2004b) Gas-liquid mass transfer a comparison of down- and up-pumping axial flow impellers with radial turbines. Trans. IChemE, 82(A12) 1589-1596. 

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