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Saturday, 29 March 2014

Two Basic Type of Gas Turbine Cycles

Two Basic Type of Gas Turbine Cycles Points : Two Basic Type of Gas Turbine Cycles, Open Cycle, Closed Cycle There are two basic types of gas turbine cycles.
1. Open Cycle
2. Closed Cycle
1. Open Cycle In this case fresh atmospheric dir is drawn in to the compressor continuously and heat is added by combustion of fuel in the year itself. The product of combustion are expanded through are expanded through the turbine. And exhaust to atmosphere for a given flow of air there is a limit to amount of fuel. Which can be burnt in the combustion chamber and the maximum amount of fuel which can be added to combustion chamber is governed by the working temp of highly stressed turbine blade which should not be allowed to exceed to a certain limit. Combustion ofa fuel takes place either at the constant volume or at constant pressure constant pressure cycle system is the most satisfactory because in case of constant pressure cycle combustion is a continuous process and valves are not necessary so this system has proves to be quite satisfactory. 2. Closed Cycle In case of closed cycle the sir or some other stable gas is constantly circulated. The fuel is burnt in the combustion chamber and the heat is transferred to the working medium through heat transfer surfaces. Thus the working medium does not mix with the products of combustion. The working medium is cooled in the water cooler before it enters the compressor this minimizes the compressor work. Constant Volume and Constant Pressure Cycle Constant Volume: In the earliest days of the gas turbine, two possible system of combustion were proposed, one at constant pressure the other at constant volume. Theoretically the thermal efficiency of the constant volume cycle is higher than that of the constant pressure cycle but the mechanical difficulties are very much greater with heat addition. At constant volume, valves are necessary to issolarate the combustion chamber from the compressor and turbine. Combustion is therefore intermittent which impairs the smooth running of the machine. It is very difficult to design as turbine to operate efficiently under such conditions.
Constant Pressure Cycle: In the constant pressure gas turbine. Combustion is the continuous process in which valves are necessary and it was soon accepted that the constant pressure cycle had the greater possibilities for failure development.

Gas turbine power plant may be classified according to the following criteria.
1. Type of Load
a) Peak load plants.
b) Base load plants.
c) Stand by plants.

2. Application
a) Air craft.
b) locomotive
c) Marine
d) Transport

3. Cycle
a) Open cycle plants
b) Closed cycle plants.

4. Number of Shafts
a) Single shaft
b) Multi shaft

5. Fuel
a) liquid
b) solid
c) Gas

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