Research paper A novel method for inlet duct geometry improvement of heat recovery steam generators Pedram Hanafizadeh a , Sajjad Falahatkar a , Pouria Ahmadi b, * , Mojtaba Mirzakhani Siahkalroudi a a Center of Excellence in Design and Optimization of Energy Systems (CEDOES), School of Mechanical Engineering, College of Engineering, University of Tehran, P.O. Box: 11155-4563, Tehran, Iran b Mechatronic System Engineering, Simon Fraser University (SFU), Vancouver, BC, Canada highlights  To suggest geometry improvement of inlet duct of heat recovery steam generators in power plants.  To conduct numerical simulation of fluid flow in inlet duct of heat recovery and its optimization.  To apply the proposed method in a standard inlet duct of a 5 MW HRSG in power plant. article info Article history: Received 26 March 2015 Accepted 28 May 2015 Available online 9 June 2015 Keywords: Combined cycle power plant Exergy Heat recovery steam generator Inlet duct abstract The geometry of inlet duct of HRSGs strongly affects flow uniformity and plays an important role in an increase in the efficiency of combined cycle power plants (CCPPs) where HRSG is the main component. Therefore, using some remedies to create a uniform flow distribution in HRSG inlet duct seems to be required in order to avoid reducing the effective surface temperature. In this research paper, part elimination and lattice search (PELS) method is presented to improve the inlet duct geometry. This is an innovative method which improves the inlet duct shape due to the amelioration of the flow quality. Uniformity of the velocity profile is considered at the exit section by quantifiable performance param- eters of Root Mean Square (RMS). The RMS difference of local velocity from average velocity is used to evaluate the uniformity of the flow. To apply this method, a standard inlet duct of a 5 MW HRSG is considered and improvements for this case are addressed. The terms of uniform velocity and tempera- ture distribution along the HRSG is numerically solved and explained. Finally, the results are reported in order to compare the standard inlet duct and the improved one. The comparison shows that the flow uniformity at the duct exit section in the modified model has been enhanced. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Heat recovery steam generator (HRSG) is a heat exchanger that facilitates the heat exchange between two fluids at two different temperatures. The hot fluid, which can be the exhaust of a gas turbine, passes through inlet duct and enters a HRSG casing as shown in Fig. 1 . The exhaust heat is then utilized and transferred to the cold fluid, working fluid of the Rankine vapor cycle, in indi- vidual parts such as superheater, evaporator and economizer. Fig. 1 also shows a schematic of all the components of a typical HRSG. HRSGs play a significant role in combined cycle power plants as they recover exhaust energy from gas turbines and utilize the heat in order to produce steam in the bottoming cycle to drive a steam turbine to generate electricity. This is hence really important to have and optimized and cost effective HRSG which has the ability to recover more energy to increase the power plant efficiency. The higher the energy recovered, the higher the thermal efficiency of the power plant. In addition to the heat exchanger element along the HRSG, flue gas temperature entering the HRSG, pinch point temperature dif- ference, inlet HRSG duct shape is another major parameter which leads to better performance of the system [1]. In designing an HRSG, having an inlet duct in a way that can create a uniform flow is * Corresponding author. Tel.: þ1 (289) 6009505. E-mail addresses: Pahmadi@sfu.ca, pouryaahmadi81@gmail.com (P. Ahmadi). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng http://dx.doi.org/10.1016/j.applthermaleng.2015.05.075 1359-4311/© 2015 Elsevier Ltd. All rights reserved. Applied Thermal Engineering 89 (2015) 125e133