Evaluation of air-dense medium fluidized beds with pulsatile inlet air

- Significant flow phenomena happen around bubbles with most energy loss, large gradients of pressure and velocity.
- Compared with fluidized beds without pulsation, pulsation incurs pronounced fluctuation, especially at low frequency.
- High frequency decreases bed response and fluctuation, and increases energy transferred from inlet air to beds.

A two-dimensional Eulerian-Eulerian two-fluid model is established to study the effects of pulsatile inlet air on an air-dense medium fluidized bed (ADMFB). The bed-volume expansion and dissipation rate are introduced to evaluate the overall fluidization and energy loss of the bed, respectively. The standard deviation and fast Fourier transform signal processing technique are also employed in the investigation of bed quality. The results show that significant flow phenomena occur around bubbles with both the greatest energy loss and large gradients of pressure and velocity. For inlet air without pulsation, the Reynolds number is the major dimensionless parameter influencing the bed flow. Both the bed-volume expansion and dissipation rate (dimensionless) linearly increase with the Reynolds number. As the inlet air flows faster and more kinetic energy is transferred into the bed, the uniformity of the bed decreases and relatively less energy is lost. For inlet air with pulsation, the Strouhal number is the major influential dimensionless parameter. The bed-volume expansion drops to nearly a constant as the Strouhal number increases. The non-linear effects of the Strouhal number on the dissipation rate of the bed are approximated through a logarithmic function. With an increase in pulsation frequency, the bed fluctuation decreases and more energy is lost. The pulsation amplitude should be small to form an ADMFB with uniformity and relatively low energy loss. In general, pulsation inhibits bed-volume expansion and greater energy loss is incurred. In practice, pulsation might be used to maintain a bubbling state in a bed with high kinetic energy.