Monday, November 9, 2015: 5:00 PM
254C (Salt Palace Convention Center)
Despite the importance of minimum bubbling velocity, Umb, in the design and modeling of fluidized bed systems, there continues to be debate as to the relative merits of approaches to measuring it. In this work, we compare measurements of Umb obtained by direct visual observation, with estimates obtained indirectly from pressure fluctuations. We have previously reported observations suggesting that at or close to Umb, the reciprocal of the von Neumann ratio, T, calculated for the fluctuations in the bed pressure drop signal, obtained at incremental changes in superficial velocity, U, rapidly rises to a maximum value, and the standard deviation, σ, of the pressure fluctuations, increases abruptly, though can subsequently exhibit some scatter. These features of plots of T-1 vs U and σ vs U, have been used to obtain estimates of Umb for 12 different powders; with surface-volume mean diameters, d32, spanning the range 36 μm to 223 μm and particle densities, ρp, from 1540 kg m-3 to 3010 kg m-3. The accord between Umb determined visually and the values obtained indirectly, by both the T-1: U method and the σ vs U method was encouraging, with R2 values of ~0.98. However, the use of T-1 is easier to implement, with less potential for ambiguity.