Figure 1-15. A compact micro-tur.ine schematic. (Courtesy Capstone Corpora-tion.)
The micro-turbines to be successful must be compact insize， have lowmanufacturing cost， high efficiencies， quiet operation， quick startups， and minimal emissions.These characteristics， if achieved， would make micro-turbines excellent candidates for providing base-load and cogeneration power to a range of commercial customers. The micro-turbines are largely going to be a collection of technologies that have already been developed. The challenges are in economically packaging these technologies.
The micro-turbines on the market today range from about 20-350 kW.Today"s micro-turbine are using radial flow turbines and compressors， as seen in Figure 1-15. To improve the overall thermal efficiency regeneratorsare used in the micro-turbinedesign， and in combination with absorptioncoolers， or other thermal loads very high efficiencies can be obtained. Figure 1-16 shows a typical cogeneration system package using a micro-turbine. This compact form of distributed power systems has great potential in the years to come.
Figure 1-1.. A co.eneration micro-tur.ine system pac.a.e. (Courtesy In.ersoll Rand Corporation.)
Major Gas Turbine Components
Compressors
A compressor is adevice， which pressurizes a working fluid. The types of compressors fall into three categories as shown in Figure 1-17. The positivedisplacement compressors are used for low flow and high pressure (head)，centrifugal compressors are medium flow and mediumhead， and axial flow compressors are high flow and low pressure. In gas turbines the centrifugalflow， and axial flow compressors， which are continuous flow compressors， are the ones used for compressing the air. Positive displacement compressors such as the gear type units are used for lubrication systems in the gas turbines.
The characteristics of these compressors are given in Table 1-3. The pressure ratio of the axial and centrifugal compressors have been classified into threegroups，industrial， aerospace and research. The aircraft gas turbines because of their thrust to weight ratio considerations have very high loading for each compressor stage. The pressure ratio per each stage
Head
P
O
S
I
T
I
V
E
Centrifugal compressor
D I S P
Axial flow compressor
Flow
Figure 1-1.. Performance characteristics of different types of compressors.
Table 1-.
Compressor Characteristics
Types of Pressure .atio .fficiency Operating
Compressors Industrial .erospace .esearch .ange
Positive Up to 30 - - 75-82% -
Displacemnt
Centrifugal 1.2-1.9 2.0-7.0 13 75-87% Large 25%
Axial 1.05-1.3 1.1-1.45 2.1 80-91% Narrow 3-10%
can reach as high as 1.4 per stage. In the industrial gas turbines， the loading per stage is considerably less and varies between 1.05-1.3 per stage. The adiabatic efficiency of the compressors has also increased and efficiencies in the high 80s have been achieved. Compressor efficiency is very important in the overall performance of the gas turbine as it consumes 55-60% of the power generated by the gas turbine.
The industrial pressure ratio is low for the reasons that the operating range needs to be large. The operating range is the range between the surge point and the choke point. Figure 1-18 shows the operating characteristics of a compressor. The surge point is the point when the flow is reversed in the compressor. The choke point is the point when the flow has reached a孔ach二 1.0 the point where no more flow can get through the unit， a ""stone
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