Earlier analytical and graphical treatments of gas turbine performance, assuming the working fluid to be a perfect gas, are developed to allow for ‘non-perfect’ gas effects and pressure losses. The pressure ratios for maximum power and maximum thermal efficiency are determined analytically; the graphical presentations of performance based on the earlier approach are also modified. It is shown that the optimum conditions previously determined from the ‘air standard’ analyses may be changed quite substantially by the inclusion of the ‘real’ effects.

No abstract

This technical note presents a development of the perfect gas analysis of the simple, closed-cycle, gas turbine reported by Hawthorne and Davis. Some comments on perfect and semi-perfect gases are included for clarification. The new analysis takes account of the variation of specific heats of the working fluid by treating the flow through the compressor and the flow through the turbine as different perfect gases. An analytical expression is derived for the pressure ratio corresponding to maximum power. This expression is shown to be the same as that derived previously, except that the isentropic exponent has to be replaced by the harmonic mean of those used for the compressor and the turbine. The note shows that the new method leads to significantly higher pressure ratios for the maximum power.