Investigating the hydrodynamics of high temperature fluidized bed by recurrence plot

Abstract

Effect of temperature on the hydrodynamics of bubbling gas–solid fluidized beds was investigated using recurrence plot (RP) and recurrence quantification analysis (RQA) due to their capabilities for determining the whole bed complexity in a simple way. For this purpose, pressure fluctuations of a fluidized bed of sand particle were measured at various gas velocities and temperatures. Recurrence quantification analysis showed that by increasing the temperature up to 300°C, both determinism and laminarity increase due to formation of larger bubbles whereas entropy and recurrence rate decrease. To better detecting the different structures of in the bed recurrence plot at higher temperature, pressure fluctuations were also decomposed through wavelet transform. It was shown that at low gas velocity, the macro structures became dominate with increasing the bed temperature due to increase in the rate of bubble coalescence. The bubble diameter was estimated from the incoherent component of the cross power spectra of pressure signals at various temperatures and velocities. The incoherent results and standard deviation of measured pressure fluctuations confirmed that by increasing the bed temperature up to 300°C, bubbles grow up to a maximum diameter, after which they became smaller. In addition, the trend of the largest positive Lyapunov exponent was estimated through the recurrence plot patterns. It was shown that a bubbling fluidized bed is a chaotic system at higher temperatures. It was found a maximum in the estimated largest positive Lyapunov exponent at 300°C corresponds to the larger bubbles.