Second-law based thermodynamic analysis of Brayton/Rankine combined power cycle with reheat A. Khaliq a, *, S.C. Kaushik b a Department of Mechanical Engineering, Faculty of Engineering and Technology, Jamia Millia Islamia, New Delhi 110025, India b Centre for Energy Studies, Indian Institute of Technology, New Delhi 10016, India Accepted 3 August 2003 Abstract The aim of the present paper is to use the second-law approach for the thermodynamic analysis of the reheat combined Brayton/Rankine power cycle. Expressions involving the variables for specific power-output, thermal efficiency, exergy destruction in components of the combined cycle, second-law efficiency of each process of the gas-turbine cycle, and second- law efficiency of the steam power cycle have been derived. The standard approximation for air with constant properties is used for simplicity. The effects of pressure ratio, cycle temperature- ratio, number of reheats and cycle pressure-drop on the combined cycle performance parameters have been investigated. It is found that the exergy destruction in the combustion chamber represents over 50% of the total exergy destruction in the overall cycle. The com- bined cycle efficiency and its power output were maximized at an intermediate pressure-ratio, and increased sharply up to two reheat-stages and more slowly thereafter. # 2003 Elsevier Ltd. All rights reserved. 1. Introduction A development in the search for higher thermal-efficiency of conventional power plant has been the introduction of combined-cycle plants. This is leading to the development of gas turbines dedicated to combined-cycle applications, which has been a subject of great interest in recent years, because of their relatively low initial Applied Energy 78 (2004) 179–197 www.elsevier.com/locate/apenergy 0306-2619/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2003.08.002 * Corresponding author. E-mail addresses: abd_khaliq2001@yahoo.co.in.