Extensive studies have been devoted to the boundary of Geldart A and B particles due to its great practical relevance, however, consensus on the hydrodynamic characteristics when the A/B boundary is crossed is still lacking. On the basis of extensive discrete particle simulations, it seems that there is no dramatic change with respect to the nature of granular temperature as a function of superficial gas velocity when the A/B boundary is crossed, suggesting a smooth transition from Geldart A particles to Geldart B particles, which is in agreement with some of the experimental studies (Geldart, D., 1973. Powder Technol. 7, 285-292; Grace, JR., 1986. Can. J. Chem. Eng. 64, 353-363; Loezos et al., 2002. Chem. Eng. Sci. 57, 5123-5141), but disagrees with acoustic shot noise (ASN) studies (Cody et al., 1996. Powder Technol. 87, 211-232; and Cody et al., 2008. Powder Technol. 182, 146-170). Finally, we show that the disagreement between the results obtained from present DPM studies and ASN studies may possibly be attributed to the short range of superficial gas velocity in ASN measurement and/or the effect of the reactor size. In view of the various possible sources of uncertainty related to both DPM method and ASN technique, lot of works are needed before making a definite conclusion on the nature of hydrodynamic characteristics of dense gas-fluidized beds when the boundary of Geldart A/B particles was crossed. (C) 2013 Elsevier Ltd. All rights reserved.