AIR STANDARD BRAYTON CYCLE
Gas turbines function based on Brayton cycles. Figures 30.4 (a), (b) and (c) explain working of a Brayton cycle.
Figure 30.4 (a) (b) and (c) |
The air-standard Brayton cycle consists of
1-2 Isentropic compression of air
2-3 Constant pressure energy addition
3-4 Isentropic expansion
4-1 Constant pressure energy rejection
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(30.10) |
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(30.11) |
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(30.12) |
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(30.13) |
 is the pressure ratio
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(30.14) |
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(30.15) |
and
 or  |
(30.16) |
or,
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(30.17) |
so,
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(30.17) |
or
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(30.18) |
The variation of  as a function of  is shown in Figure 30.5
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(30.19) |
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(30.20) |
But
 &  |
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or
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(30.21) |
The optimum pressure ratio is obtained by differentiating W wrt rp holding T1 and T3 constant, and setting the expression equal to zero. This gives
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