## THERMAL SCIENCE

International Scientific Journal

### DETAILED ANALYSIS OF THE EFFECT OF THE TURBINE AND COMPRESSOR ISENTROPIC EFFICIENCY ON THE THERMAL AND EXERGY EFFICIENCY OF A BRAYTON CYCLE

**ABSTRACT**

Energy and exergy analysis of a Brayton cycle with an ideal gas is given. The irreversibility of the adiabatic processes in turbine and compressor is taken into account through their isentropic efficiencies. The net work per cycle, the thermal efficiency and the two exergy efficiencies are expressed as functions of the four dimensionless variables: the isentropic efficiencies of turbine and compressor, the pressure ratio, and the temperature ratio. It is shown that the maximal values of the net work per cycle, the thermal and the exergy efficiency are achieved when the isentropic efficiencies and temperature ratio are as high as possible, while the different values of pressure ratio that maximize the net work per cycle, the thermal and the exergy efficiencies exist. These pressure ratios increase with the increase of the temperature ratio and the isentropic efficiency of compressor and turbine. The increase of the turbine isentropic efficiency has a greater impact on the increase of the net work per cycle and the thermal efficiency of a Brayton cycle than the same increase of compressor isentropic efficiency. Finally, two goal functions are proposed for thermodynamic optimization of a Brayton cycle for given values of the temperature ratio and the compressor and turbine isentropic efficiencies. The first maximizes the sum of the net work per cycle and thermal efficiency while the second the net work per cycle and exergy efficiency. In both cases the optimal pressure ratio is closer to the pressure ratio that maximizes the net work per cycle.

**KEYWORDS**

PAPER SUBMITTED: 2013-12-02

PAPER REVISED: 2014-04-24

PAPER ACCEPTED: 2014-04-28

PUBLISHED ONLINE: 2014-09-06

**THERMAL SCIENCE** YEAR

**2014**, VOLUME

**18**, ISSUE

**Issue 3**, PAGES [843 - 852]

- Mikulandric, A., et al., Improvement of Environmental Aspects of Thermal Power Operation by Advanced Control Concepts, Thermal science, 16 (2012), 3, pp. 759-772
- Garafulic, E., Klarin B., Acceptable Concept of Carbon Dioxide Storage, Tehnicki vjesnik, 20 (2013), 1, pp. 161-165
- Zaporowski, B., Szczerbowski, R., Energy Analysis of Technological Systems of Natural Gas Fired Combined Heat-and-Power Plants, Applied Energy, 75 (2003), 1-2, pp. 43-50
- Wu, C., et al., Performance of a Regenerative Brayton Heat Engine, Energy, 21 (1996), 2, pp. 71-76
- Sanchez - Orguz, S., et al., Thermodynamic Model and Optimization of Multi-Step Irreversible Brayton Cycle, Energy Conversion and Management, 51 (2010), 11, pp. 2134-2143
- Ferdelji, N., et al., Exergy Analysis of a Co-Generation Plant, Thermal science, 12 (2008), 4, pp. 75-88
- Haseli, Y., Optimization of Regenerative Brayton Cycle by Maximization of Newly Defined Second Law Efficiency, Energy Conversion and Management, 68 (2013), Apr., pp. 133-140
- Thong, W., et al., Power and Efficiency Optimization for Combined Brayton and Inverse Brayton Cycle, Applied Thermal Engineering, 29 (2009), 14-15, pp. 2885-2894
- Cheng, C. Y.,. Chen, C. K., Power Optimization of an Endoreversible Regenerative Brayton Cycle, Energy, 21 (1996), 4, pp. 241-247
- Haseli, Y., et al., Unified Approach to Exergy Efficiency, Environmental Impact and Sustainable Development for Standard Thermodynamic Cycles, International Journal of Green Energy, 5 (2008), 1-2, pp.105-119
- Ehyaei, M., et al., Exergetic Analysis of an Aircraft Turbojet Engine with an Afterburner, Thermal science, 17 (2013), 4, pp. 1181-1194
- M. Kanoglu, Y. A., et al., Efficiency Evaluation of Energy Systems, Springer Briefs in Energy, Springer Verlag, New York, 2012
- Hernandez, A.C., et al., Power and Efficiency in a Regenerative Gas-Turbine Cycle with Multiple Reheating and Intercooling Stages, J Phys D Appl Phys, 29 (1996), pp. 1462-1468