Figure 13 . The nondimensionalized mean and standard deviation of bed height for LDPE and 100 wood pellets binary mixture with varying initial bed height.
Figure 13 shows the effects of initial bed height on the mean and standard deviation of bed height for LDPE and 100 wood pellets binary mixture. After non-dimensionalizing the mean bed height and standard deviation with the initial bed height (Hb0), both curves are well collapsed on a straight line from 1.5Umf to 3Umf range, with both the nondimensionalized bed height and standard deviation increase with the increase of the superficial gas velocity. The experimental data above 3Umf is only available for shallower bed cases due to pressure constraints for the facility, which shows that the mean bed height remains almost constant at 3.7 Umf. This trend is consistent with the pressure drop data reported in Li et al.25. Figure 14 shows the effects of initial bed height on the temporal evolution of the spatially averaged vertical velocity. In presenting the data, <v>FOV is non-dimensionalized using the characteristic velocity (gΔH)1/2, where ΔH=Hb-Hb0, is the difference between expanded and initial bed height. The time is non-dimensionalized using the characteristic time for the particle to travel ΔH, i.e. τ=(2ΔH/g)1/2. The non-dimensionalized periods are at ~3. Specifically, it is 3.25 at 2Umf and 2.66 at 3Umf for the shallower bed and 2.89 at 2Umf and 3.10 at 3Umf for the deeper bed. The non-dimensionalized amplitude is 1.71 and 1.36 at 2Umf and 3umf respectively for the deep bed. The value decreases to 0.78 and 0.92 at 2Umf and 3Umf respectively for the shallow bed. In general, the nondimensionalization works reasonably well for each static bed height with varying superficial gas velocity, yet works less satisfactory when static bed height is changed. This is possibly due to the internal flow structure change due to the increase of the static bed height.