燃气涡轮工程手册 Gas Turbine Engineering Handbook 1(17)

曝光台 注意防骗 网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者

In a typical centrifugal compressor， the fluid is forced through the impeller by rapidly rotating impeller blades. The velocity of the fluid is converted to pressure， partially in the impeller and partially in the stationary diffusers.孔ost of the velocity leaving the impeller is converted into pressure energy inthe diffuser. The diffuser consists essentially of vanes， which are tangential to the impeller. These vane passages diverge to convert the velocity head into pressure energy. The inner edge of the vanes is in line with the direction of the resultant airflow from the impeller.
In the centrifugal or mixed-flow compressor the air enters the compressor in an axial direction and exists in a radial direction into a diffuser. This combination of rotor (or impeller) and diffuser comprises a single stage. The air enters into the centrifugal compressor through an intake duct and can be a given prewhirl by the IGVs as shown in Figure 1-21. The inlet guide vanes give circumferential velocity to the fluid at the inducer inlet. IGVs areinstalled directly in front of the impeller induceror， where an axial entry isnot possible， located radially in an intake duct. The purpose of installing theIGVs is usually to decrease the relative孔ach number at the inducer-tip (impeller eye) inlet because the highest relative velocity at the inducer inlet is at the shroud. When the relative velocity is close to the sonic velocity orgreater thanit， a shock wave takes place in the inducer section. A shock wave produces shock loss and chokes the inducer. The air initially enters the

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Inducer
Figure 1-.1. Schematic of a centrifu.al compressor sta.e.
centrifugal impeller at the inducer. The inducer， usually an integral part ofthe impeller， is very much like an axial-flow compressor rotor.孔any earlier designs kept the inducer separate. The air then goes through a 900 turn andexits into adiffuser， which usually consists of a vaneless space followed by a vaned diffuser. This is especially true if the compressor exit is supersonic as is the case with high-pressure ratio compressors. The vaneless space is used to reduce the velocity leaving the rotor to a value lower than孔ach number二1(孔 <1). From the exit of the diffuser， the air enters a scroll or collector. The centrifugal compressor is slightly less efficient than theaxial-flow compressor， but it has a higher stability. A higher stability means that its operating range is greater (surge-to-choke margin).
.egenerators
Heavy-duty regenerators are designed for applications in large gas tur-bines in the 1-50孔W range. The use of regenerators in conjunction with industrial gas turbines substantially increases cycle efficiency and provides an impetus to energy management by reducing fuel consumption up to 30%. The term ""regenerative heat exchanger"" is used for this system in which the heat transfer between two streams is affected by the exposure of a third medium alternately to the two flows. The heat flows successively into andout of the third medium， which undergoes a cyclic temperature. In a recu-perative heat exchanger each element of head-transferring surface has aconstant temperature and， by arranging the gas paths in contraflow， the temperature distribution in the matrix in the direction of flow is that giving optimum performance for the given heat-transfer conditions. This optimum temperature distribution can be achieved ideally in a contraflow regenerator and approached very closely in a cross-flow regenerator.
Figure 1-22 shows how a regenerator works. In most present-day regen-erative gas turbines ambient air enters the inlet filter and is compressed to about 100 psi (6.8 Bar) and a temperature of 500 0F (260 0C). The air is thenpiped to the regenerator， which heats the air to about 900 0F (482 0C). The heated air then enters the combustor where it is further heated beforeentering the turbine. After the gas has undergone expansion in the turbine， it is about 1000 0F (538 0C) and essentially at ambient pressure. The gas is ducted through the regenerator where the waste heat is transferred to the incoming air. The gas is then discharged into the ambient air through theexhaust stack. In effect， the heat that would otherwise be lost is transferredto theair， decreasing the amount of fuel that must be consumed to operatethe turbine. For a 25孔W turbine， the regenerator heats 10 million pounds of air per day.
　
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