On the Role of the Harmonic Mean Isentropic Exponent in the Analysis of the Closed-Cycle Gas Turbine

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.

Optimum Heat Conductance Distribution for Power Optimization of a Regenerated Closed Brayton Cycle

“…The analytical results about dimensionless power output ( ) with of this paper replicate the results given in recent literatures (Woods, 1991;Woods et al, 1991;Frost et al, 1992;Horlock and Woods, 2000) by using conventional method in which irreversible Brayton cycles without external heat transfer irreversibility were examined.…”

Thermodynamic analysis and parametric study of an intercooled–reheat closed-cycle gas turbine on the basis of a new isentropic exponent

“…The gas-based Brayton cycle thermal power plant is represented by a system of algebraic equations which is based on a modified, semi-perfect gas model of the closed-cycle GT as investigated by Woods (1991). Here, the same gas-based Brayton cycle thermal power plant with intercooler and reheater is modelled by the following algebraic equations.…”

“…This may be compared with ψ and φ , the values given for the maximum non-dimensional net work given by Equations (11) and (10) in Woods et al (1991) and Woods (1991), respectively:…”

“…The pressure ratios at which these maximum values occur are different; the maximum power output occurs at a lower pressure ratio than that for a maximum efficiency. Woods (1991) investigated the role of a harmonic mean isentropic exponent in the analysis of the closed-cycle GT. He analysed by taking account of the variation of specific heats of the working fluid by treating the flow through the compressor and the turbine as different perfect gases.…”

“…An analytical expression is derived for the pressure ratio corresponding to maximum power, which is 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. In the present paper, the same type of investigations as done by Woods (1991) is extended for the closed-cycle GT power plant with a single intercooler and a single reheater, for semi-perfect gases. An analytical expression for the pressure ratio corresponding to maximum power, zero output and for the maximum net power is obtained.…”