The air compressor occupies an important position in the gas-turbine power plant equal to that of the turbine in every respect. The net useful output of the plant is the difference between the turbine output and the compressor input. It is clear that an inefficient compressor can largely nullify the gain from a highly efficient turbine. Therefore, the efficient compression of the large volumes of air is the key to an efficient gas turbine cycle. Furthermore, for efficient overall performance it is essential that the turbine characteristics match those of the compressor.
There are many similarities between the compressor and the turbine in as far as the principles of operation are concerned. However, the design application of these principles for the compressor is much more severely restricted because the compressor carries out a diffusion process.
Rapid progress in the development of gas turbines was made during the Second World War, where attention was focused on the simple turbojet unit. German efforts were based on the axial flow compressor, but British developments used the centrifugal compressor. It was recognized in Britain that development time was critical and much experience had already been gained on the design of small high speed Centrifugal compressors for supercharging reciprocating engines. Centrifugal compressors were used in both early British and American fighter aircraft and also original comet airliners which were the first gas turbine powered civil aircraft in regular service. As power requirements grew, it became clear that the axial flow compressor was more suitable for large engines. By the late fifties, however, it is understood that smaller gas turbines would have to use centrifugal compressors, and serious research and development work started again
Description and Operation:
The compression of air can be achieved by two types of compressors.
1. Centrifugal compressor
2. Axial flow compressor
The compressors employed in gas-turbine plants are mostly of the axial and less frequently of the centrifugal type. Whether it is centrifugal compressor or axial flow compressor the fundamental principle is same, that is the compressor adds kinetic energy to the air and then utilizes some sort of diffuser passage to decrease the velocity and convert the kinetic energy into a pressure rise.
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