In this study,we applied the variational model to fluidization of small spherical particles.Fluidization experiments were carried out for spherical particles with 13 diameters between dp =0.13 and 5.00 mm.We propose a generalized form of our variational model to predict the superficial velocity U and interphase drag coefficient β by introducing an exponent n to describe the different dependences of the drag force Fd on fluid velocity for different particle sizes (different flow regimes).By comparing the predictions with the experimental results,we conclude that n=1 should be used for small particles (dp ＜ 1 mm) and n =2 for larger particles (dp＞ 1 mm).This conclusion is generalized by proposing n =1 for particles with Ret ＜ 160 and n =2 for particles with Ret ＞ 160.The average mean absolute error was 5.49％ in calculating superficial velocity for different bed voidages using the modified variational model for all of the particles examined.The calculated values ofβ were compared with values of literature models for particles with dp ＜ 1.0 mm.The average mean absolute error of the modified variational model was 8.02％ in calculating β for different bed voidages for all of the particles examined.