Analytical model-based energy and exergy analysis of a gas microturbine at part-load operation Leszek Malinowski a, * , Monika Lewandowska b a Faculty of Maritime Technology and Transport, West Pomeranian University of Technology, 71-065 Szczecin, Al. Piastów 41, Poland b Institute of Physics, West Pomeranian University of Technology, 70-311 Szczecin, Al. Piastów 48, Poland highlights  Analytical model for part-load operation of a gas microturbine is elaborated.  The model is based on heuristic part-load performance formulas.  The model is validated by comparison with experimental and manufacturer’s data.  Exergy destruction or loss for each microturbine component is calculated. article info Article history: Received 30 September 2012 Accepted 23 March 2013 Available online 10 April 2013 Keywords: Gas microturbine Part load operation Analytical model Energy and exergy analysis abstract In this paper a universal analytical model for part-load operation of gas microturbines has been elabo- rated which is subsequently used in the energy and exergy analysis of a sample device. The model, based on the Brayton cycle and heuristic part-load performance formulas, takes into account: the temperature variation of working ﬂuid speciﬁc heat at constant pressure in calculations of adiabatic processes, enthalpy, and exergy, the non-linear dependence of pressure drop on ﬂow rate, and the cooling of generator by intake air. The model is validated using the manufacturer data for a commercially available microturbine of 30 kWe and results of measurements. The agreement is very good as for such a general simple analytical model. Exergy calculations based on the elaborated model show that the greatest potential for improving the efﬁciency of the microturbine lies in the combustion chamber and recu- perator, as these components are characterized by the largest exergy destruction and loss. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Small gas turbines whose mechanical power do not exceed several hundred kilowatts are classiﬁed as microturbines. In gen- eral gas microturbines operate according to the open Brayton cycle with or without heat regeneration. A typical microturbine is a single shaft design with the turbine, compressor and generator mounted on the same shaft. The pressure ratio is of the order 3.5 to 4.0 and the microturbine is controlled by fuel delivery alone. Usu- ally, during load changes the rotational speed of the microturbine also changes while the temperature of the exhaust gas leaving the turbine is kept constant. Gas microturbines are increasingly used as a primary source of electricity and heat for individual objects, such as: hotels, sports facilities, greenhouses, ofﬁces, small businesses, small houses and others. Such micro plants operate under varying demand for elec- tricity and heat. However, running the microturbine at a reduced load results in loss of efﬁciency. In the literature, some attention has been paid to the problem of modeling of gas turbines operated at part load and to the analysis of their performance based on the ﬁrst and second laws of thermo- dynamics. Zhang et al. [1] formulated an analytical model of a constant rotating speed single shaft gas turbine operated at part load and determined basic part-load characteristics of the turbine. Wang et al. [2] extended the model presented in Reference 1 for microturbines operated with variable rotational speed. They derived the optimal rotational speed for part-load operation and analyzed the effect of pressure and temperature ratios on the off- design performance. Song et al. [3] presented an exergy-based performance analysis of a 150 MWe gas turbine based power plant for part-load operation. They investigated numerically the inﬂuence of the variable inlet guide vane and the blade cooling on * Corresponding author. Tel.: þ48 91 449 4827. E-mail addresses: leszmali@gmail.com, lmal@zut.edu.pl (L. Malinowski). Contents lists available at SciVerse ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.applthermaleng.2013.03.057 Applied Thermal Engineering 57 (2013) 125e132