Lu and Wang ( 3 ) . This has the advantage that in the absence of quaternary data, the corresponding &jkl may be set to zero to obtain a better approximation than by setting (Eijkl -C i j k l ) to zero.excess Gibbs free energy i, i, k, 1, m, n, p = index representing components n = moles P =pressure R = gas constant = binary two-and three-suffix coefficient T = absolute temperature x = mole fraction y = activity coefficient In a recent article Narsimhan (18) presented a generalized expression for the minimum fluidization velocity by extending the correlation proposed by Leva, Shirai, and Wen (14) into intermediate and turbulent flow reions. Based on a similar approach by employing the &ed-bed pressure drop equation of Ergun (7), an expression for the minimum fluidization velocity quite different from that of Narsimhan has been obtained ( 2 3 ) . It is the purpose of this communication to compare these two correlations and to examine the validity and applicability of each. The generalized expression given by Narsimhan consists of three equations [Equations ( 6 ) , (9), and ( 11) in his communication (18) 1. The correlation obtained by Wen and Yu ( 2 3 ) can be represented by ( N R~)~~ = d ( 3 3 . 7 ) ' + 0.0408 N G~ -33.7 (1)For nonspherical particles, the particle diameter dp is defined as the equivalent diameter of a spherical particle with the same volume. As an approximation, the particle diameter may be calculated from the geometric mean of the two consecutive sieve openings without introducing serious errors ( 2 6 ) .The major differences between the two correlations are the minimum fluidization voidage emf and the shape factor 4%.1. Narsimhan considered that for spherical emf has the value of 0.35 and is independent of e particle diameter, provided that the wall effect can be neglected. From the literature data (16, 20, 2 4 ) , as well as trrticles from the experimental data of the present investigation ( 2 3 ) , emf for spherical particles can be shown to vary from 0.36 to 0.46. Different average values of emf have V Van Heerden, et a l . ( Z Z ) 0 Fancher and Lewis (9) o.ol -Narsimhan's correlation I 0.001 aooz 0.004 aoi aoz 03 dp (in.) 986 emf Fig. 1. Correlation of voidage shape factor function -.(1 -emf)2

A study on the flow of power‐law fluids through a multi‐particle system including both fixed bed and fluidized bed is presented. Equations for the pressure drop, the minimum fluidization velocity, and the bed expansion are obtained by extending the Blake‐Kozeny's equation for the pressure drop through packed beds to power‐law fluids. Bed expansion equations are also obtained by extending the Richard‐son‐Zaki's theory for the drag force in a multiparticle suspension to power‐law fluids. These equations are compared with experimental data.

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