tailieunhanh - GasTurbine Engineering HandbookSecond Edition phần 2

Tất cả các chu trình Carnot tua-bin khí chu trình đơn giản có cùng một hiệu quả. Tương tự như vậy, tất cả các chu trình Carnot mà chu kỳ abc-2 tương tự có thể được chia có một giá trị chung hiệu quả thấp hơn so với các chu trình Carnot bao gồm chu kỳ 1-2-3-4-1. Vì vậy, việc bổ sung một mát, có thêm abc-2-một chu kỳ đơn giản, làm giảm hiệu quả của chu kỳ. | Theoretical and Actual Cycle Analysis 67 Figure 2-7. The intercooled gas turbine cycle. these little cycles approach the Carnot cycle as their number increases. The efficiency of such a Carnot cycle is given by the relationship T _ 1 m CARNOT 1 - Ảp 2-17 Notice that if the specific heats are constant then r4 Tp T1 PA Pl 7-1 7 2-18 Tĩ Tm All the Carnot cycles making up the simple gas turbine cycle have the same efficiency. Likewise all of the Carnot cycles into which the cycle a-b-c-2-a might similarly be divided have a common value of efficiency lower than the Carnot cycles which comprise cycle 1-2-3-4-1. Thus the addition of an intercooler which adds a-b-c-2-a to the simple cycle lowers the efficiency of the cycle. The addition of an intercooler to a regenerative gas turbine cycle increases the cycle s thermal efficiency and output work because a larger portion of the heat required for the process c-3 in Figure 2-7 can be obtained from the hot turbine exhaust gas passing through the regenerator instead of from burning additional fuel. The reheat cycle increases the turbine work and consequently the net work of the cycle can be increased without changing the compressor work or the turbine inlet temperature by dividing the turbine expansion into two 68 Gas Turbine Engineering Handbook or more parts with constant pressure heating before each expansion. This cycle modification is known as reheating as seen in Figure 2-8. By reasoning similar to that used in connection with Intercooling it can be seen that the thermal efficiency of a simple cycle is lowered by the addition of reheating while the work output is increased. However a combination of regenerator and reheater can increase the thermal efficiency. Actual Cycle Analysis The previous section dealt with the concepts of the various cycles. Work output and efficiency of all actual cycles are considerably less than those of the corresponding ideal cycles because of the effect of compressor combustor and turbine .