∆P 5 represents the mean weight of bed material excluding solids in the region between the distributor plate and the first port above it (refer Figure ). On the other hand, standard deviation values increase with increase in flow rate as seen in Figure (bottom). This is observed across all regions and the results are consistent with the previous findings of Bi et al. , Schnitzlein and Weinstein 33 , Grace and Sun 34 and Sobrino et al. . The mean values recorded in the 4-inch and 6-inch test sections follow a similar trend as seen in Figures &. There is negligible change over the range of U/U mf except for ∆P 3 in the 4-inch test section where a slight reduction is noticed. ∆P 3 and σ ∆P 3 are greater than ∆P 2 and σ ∆P 2 in the 4-inch column while they are lesser in the 6-inch column. Also, σ ∆P 2 and σ ∆P 6 measured in 4-inch and 6-inch columns are nearly identical (within measurement uncertainty), where ∆P 6 in these units represents solids in the bed barring the region between distributor plate and the first port above it. It is worth emphasizing that mean and standard deviation of differential pressure are strongly dependent on the location of probes besides operating conditions.