The scaling rules using dimensionless groups are investigated using CFD simulations of two scaled fluidized beds with diameters of 15 and 36 cm. Three sets of dimensionless groups are used: the simplified set, the full set, and the full set extended with a dimensionless pressure group. Voidage and pressure data for the two scales are compared using different analysis techniques. The full set gives the largest differences between the two scales. The simplified set and the extended set perform better, but neither lead to complete similarity between the two scales. (C) 2006 Elsevier B.V. All rights reserved.