Three-dimensional simulation of rotary air preheater in steam power plant Armin Heidari-Kaydan, Ebrahim Hajidavalloo * Mechanical Engineering Department, Shahid Chamran University, Ahvaz 61357, Iran highlights  Three-dimensional thermal simulation of full-scale rotary air preheater is presented.  Variation of isothermal lines in the air preheater are shown.  Effect of separator plate on the temperature distribution is restricted to center of the matrix.  Rotational speed of matrix has important role in the performance of preheater until certain limit. article info Article history: Received 10 April 2014 Accepted 3 August 2014 Available online 8 August 2014 Keywords: Rotary air preheater Thermal simulation Matrix Preheater performance abstract In this study, thermal behavior of a full-scale rotary air preheater is investigated using three-dimensional approach and treating preheater matrix as a porous media. Mass, momentum and energy equations are solved using moving reference frame (MRF) to incorporate the effect of rotational speed of the matrix. Temperature distributions of the matrix at different conditions have been presented and the effect of essential parameters such as rotational speed of the matrix, fluid mass flow, matrix material and tem- perature of inlet air on the performance of preheater have been discussed. Numerical results which are confirmed by experimental data show the significant effect of rotational speed, separator plate, fluid flow rate on the performance and temperature distribution of preheater. Increasing the rotational speed of the air heater increases the efficiency up to certain limit, after which it does not significantly change. It was also found that the effect of material change on the efficiency is very limited. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Rotary air preheater is one of the important energy recovery systems in the steam power plant which was first introduced in 1920 by Ljungstrom [1]. It transfers heat from the hot fluid to the cold one by using a rotating matrix of compact plates as shown in Fig. 1 . Considering the important effect of the air preheater on the cycle efficiency, there are many studies addressing preheater effi- ciency. Warren [2] published his studies on Ljungstrom as a particular type of air to air exchanger and base on the experimental results confirmed a minimum reduction of 10% in power plants fuel consumption. Skiepko [3,4] investigated the effects of heat con- duction in the matrix, Peclet number and the length of the matrix on the preheater performance [5,6]. Investigating on the effect of separator plate on the preheater performance, Worsoe-Schmidt [7] stated that although the separator decreases the efficiency of the exchanger, but it cannot be removed due to its role in the reduction of the fluid leakage. Based on the several experimental and nu- merical analyses, Ghodsipour and Sadrameli [8] studied the effect of mass flow rate and rotational speed of the matrix on the pre- heater performance and showed that the flow rate effect was more significant than the rotational speed. Drobnic and Tuma [9] used both numerical and experimental methods to estimate the pattern of Ljungstrom exhaust gas tem- perature. Sanaye et al. [10] specified the importance of optimizing the speeds of rotation and mass flow rate by using analytical re- lationships and empirical models. Using a three-dimensional rotary preheater model, Wang et al. [11] obtained the temperature dis- tribution in the exchanger through a semi-analytical method. Passandideh-Fard et al. [12] modeled the exchanger and studied the effects of fluid flow rates and speed by using a two-dimensional finite volume method and periodic boundary conditions. Despite many studies in this area, there are more rooms for better understanding of the periodic nature of heat transfer process * Corresponding author. Tel.: þ98 3738532; fax: þ98 611 3336642. E-mail addresses: hajidae_1999@yahoo.com, hajidae@scu.ac.ir (E. Hajidavalloo). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng http://dx.doi.org/10.1016/j.applthermaleng.2014.08.013 1359-4311/© 2014 Elsevier Ltd. All rights reserved. Applied Thermal Engineering 73 (2014) 397e405