1054 IV International Conference on Computational Methods for Coupled Problems in Science and Engineering COUPLED PROBLEMS 2011 M. Tahmasebpoor, R. Sotudeh-Gharebagh, R. Zarghami, N. Mostoufi RECURRENCE PLOTS ANALYSIS OF PRESSURE FLUCTUATIONS IN FLUIDIZED BEDS M. Tahmasebpoor, R. Sotudeh-Gharebagh, R. Zarghami, N. Mostoufi Multiple Systems Research Laboratory, School of Chemical Engineering, University of Tehran, Tehran, Iran e-mail: tahmasebpour@ut.ac.ir Key words: Fluidized bed, Recurrence plot, Recurrence quantification analysis, Pressure fluctuation. Summary. Recurrence plot (RP) and recurrence quantification analysis (RQA), as powerful statistical techniques, have been used for studying the dynamic behavior of gas-solids fluidized beds. The method of delays was used to reconstruct the state space attractor to carry out analysis in the reconstructed state space. In this work, variance of recurrence rate, which indicates density of recurrence points in RP, against different epoch lengths (time windows) for time series of pressure fluctuation of fluidized bed was calculated. It was concluded that the characteristic parameters of RPs could reflect the extent of chaos in fluidization behavior. The average cycle frequency and entropy as nonlinear dynamical invariants were evaluated with RQA at different aspect ratios. The estimated entropy showed a similar trend of average cycle frequency for different aspect ratios. The results also indicated that the entropy and average cycle frequency are higher in smaller aspect ratios showing that the importance of the finer structures. In addition, a minimum in average cycle frequency and entropy of the pressure fluctuations indicated a minimum deviation from periodicity or, in other words, a minimum deviation from the larger structures, of the bed. The results of this study allow the deep understanding the fluidized bed hydrodynamics which can then be used for scale up. 1 INTRODUCTION Fluidized bed reactors have a numerous advantages over other reactor types that make them suitable for industrial applications. They have good particle mixing, high heat and mass transfer rates in addition to low pressure drop. However, due to complexity of the hydrodynamics, design and scaling of this type of chemical reactor are still not straightforward [1-3]. The governing equations of fluidized bed system are rather complex. Since the performance of a fluidized bed is dependent on their hydrodynamic states of fluidization, many investigations reported the hydrodynamic properties of fluidized bed properly such as transition velocities, bubble and cluster characteristics. There are many techniques to determine the hydrodynamic properties of fluidized bed such as optical fiber probes, pressure fluctuations measurements and etc. However, a great advantage of the pressure signals is that they are easy to measure consisting different dynamic phenomena taking place in the bed, such as bubble formation, bubble coalescence and splitting, bubble passage as well as particles behaviors [4].