Local differential pressure analysis in a slugging bed using deterministic chaos theory

Abstract

Local instantaneous pressure signals obtained in a slugging bed have been analyzed using both classical and advanced signal analysis methods. Dual static pressure probes (DSPP) have been used in prior research to collect the local axial differential pressure signals, which can deliver the necessary information about the presence of the bubbles or slugs in the bed. For the data considered in this work, nylon spheres with a diameter of 0.3 cm were used as a fluidization material. The data were captured at a frequency of 100 Hz. Evaluation of the dominant slug frequency was completed using the autocorrelation coefficient and power spectrum. The pseudo-phase space and mutual information function were used as a preliminary analysis for deterministic chaos in the experimental data. Since the mutual information does not demand any particular functional relationships between the data points, it is a better method (when compared with the autocorrelation coefficient) for measuring the predictability of nonlinear systems. The correlation integral was used to evaluate the fractal dimension, embedding dimension and the degrees of freedom of the system. One may characterize both slugs and particle motion in the system with the correlation coefficient if the dominant steady slug motion is mixed with the irregular particle motion. The Kolmogorov entropy, which is a quantitative measure of the amount of information lost or gained by a system as it evolves, is evaluated via the correlation integral to determine the multi-dimensional nature of the signal. Both the Kolmogorov entropy and the correlation coefficient showed similar trends for the changes in the system parameters.