Exploring a non‐dimensional varying exponent equation relating minimum spouting velocity to maximum spoutable bed depth

The equation $U_{{\rm ms}} /U_{{\rm mf}} = (H/H_{\rm m} )^{1 - (0.5\,H/H_{\rm m} )}$ was critically examined for spouting both in small conical‐cylindrical columns ( D c  < 0.5 m) and large cone‐base or flat‐bottom cylindrical columns ( D c  ≥ 0.5 m). For small columns, a data base of 36 points with experimental measurements of both H m and U m (= U ms at H  =  H m ) afforded some insights into the components of this equation and to the merits of the equation itself. For large columns, in the absence of verifiable methods of predicting H m , correlation of U ms / U mf as a function of H / H m , using the available experimental data on U ms , has not been achieved.