Using Pressure Fluctuation Analysis to Measure the Bubble Size in Pulsed Fluidized Beds

Pulsed fluidization is a special mode of fluidization in which the gas flow-rate varies periodically with time. Our previous studies showed that gas-phase pulsation affects bed pressure drop, local pressure fluctuations, bed expansion and bubbling in fluidized beds . While the gas bubble characteristics can be investigated with direct measurement methods which measure the voidage in a fluidized bed, pressure fluctuations caused by the rising gas bubbles can be used as an indirect measure of bubble size and velocity. This method can be advantageous, because it is a relatively simple, non-intrusive, and inexpensive technique, applicable to a wide range of experimental conditions. However, in addition to the rising of the gas bubbles, there are other sources, an important one of which is gas turbulence/fluctuation, which cause the fluctuations in the pressure. In a pulsed system, in which gas flow rate periodically changes by up to 50%, it might be suspected that using pressure fluctuation to analyse the bubbling would not be possible. In this work, however, we could overcome this problem by decomposing the PSD (Power Spectral Density) of the time series of pressure fluctuations into its different components. It is demonstrated that using this method, the fluctuations caused by the gas pulsation can be successfully recognized and filtered out. The experiments are performed in two-dimensional fluidized beds, using sand particles. This allowed us to apply video analysis, as well as the pressure fluctuation analysis. The validity of the pressure fluctuation method is demonstrated by comparing the results obtained from this method, with those obtained from video analysis method.