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Research Papers: Gas Turbines: Cycle Innovations

The Brayton Cycle Using Real Air and Polytropic Component Efficiencies

[+] Author and Article Information
W. H. Heiser, T. Huxley, J. W. Bucey

 U.S. Air Force Academy, CO 80840

J. Eng. Gas Turbines Power 133(11), 111702 (May 17, 2011) (9 pages) doi:10.1115/1.4003671 History: Received December 03, 2010; Revised February 07, 2011; Published May 17, 2011; Online May 17, 2011

This paper presents the results of a fundamental, comprehensive, and rigorous analytical and computational examination of the performance of the Brayton propulsion and power cycle employing real air as the working fluid. This approach capitalizes on the benefits inherent in closed cycle thermodynamic reasoning and the behavior of the thermally perfect gas to facilitate analysis. The analysis uses a high fidelity correlation to represent the specific heat at constant pressure of air as a function of temperature and the polytropic efficiency to evaluate the overall efficiency of the adiabatic compression and expansion processes. The analytical results are algebraic, transparent, and easily manipulated, and the computational results present a useful guidance for designers and users. The operating range of design parameters considered covers any current and foreseeable application. The results include some important comparisons with more simplified conventional analyses.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

A typical RABC thermodynamic cycle, showing the four simple processes and station numbering. For this cycle, πc=50, T4/T0=7.0, ec=0.90, and ee=0.90.

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Figure 2

Plot of the specific heat at constant pressure of real air versus absolute temperature for static pressures greater than 1 atm and temperatures between 500°R and 4000°R

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Figure 3

Plot of Cpc¯ as a function of πc and ec

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Figure 4

Plot of Cpa¯ as a function of πc and T4/T0 for ec=0.90

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Figure 5

Plot of Cpe¯ as a function of πe and T4/T0 for πe=πc and ec=ee=0.90

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Figure 6

Plot of Cpr¯ as a function of πe=πc and T4/T0 for ec=ee=0.90

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Figure 7

Plot of the thermal efficiency of the RABC as a function of πc and T4/T0 for ec=ee=0.90

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Figure 8

Plots of the thermal efficiency as a function of πc and T4/T0 for the RABC and for the Brayton cycle with constant Cp=0.240 Btu/lbm°R for ec=ee=0.90. The thermal efficiency of the RABC is shown in lighter lines, and that of the constant Cp Brayton cycle is shown in darker lines.

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Figure 9

Plot of the dimensionless mass specific work of the RABC as a function of πc and T4/T0 for ec=ee=0.90

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Figure 10

Plots of the dimensionless mass specific work as a function of πc and T4/T0 for the RABC and the Brayton cycle with constant Cp=0.240 Btu/lbm°R for ec=ee=0.90. The dimensionless mass specific work of the RABC is shown in lighter lines, and that of the constant Cp Brayton cycle is shown in darker lines.

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