The efficiency of a gas turbine is limited by the highest temperature achieved in the combustors. Figures 14.1(a) and 14.1(b) illustrate how a higher turbine inlet temperature decreases the air consumption and increases the efficiency (by decreasing the specific fuel consumption). Materials and alloys that can withstand high temperatures are very expensive. Figure 14.1(c) illustrates the relative cost of raw material. Thus, the cooling methods for the turbine and combustor liners play an important role in reducing the cost of the unit.
Gas and steam turbines experience similar problems. However, the magnitude of these problems is different. Turbine components must operate under different stress, temperature, and corrosive conditions. The temperature in the compressor is relatively low, but the stress on the blades is high. The temperature inside the combustor is relatively high, but the stress is low. The turbine blades experience severe conditions of stress, temperature, and corrosion. In gas turbines, these conditions are more extreme than in steam turbine applications. Therefore, the selection of materials for individual components is based on different criteria in gas and steam turbines.
The success of a design is determined by the performance of the materials selected for the components. In modern, high-performance, long-life gas turbines, the critical components are the combustor liner and the turbine blades. The required material...
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