50 years of Geldart classification

Journal article, 2023

The Geldart classification reported in 1973 is widely acknowledged as one of the seminal papers on fluidization. Today, it remains the most used classification for particle fluidization. This is a simple comparison of the differential between particle and air densities versus Sauter-mean diameter, which successfully demarcates all particles into four distinctly different fluidization behaviors. To commemorate the 50th anniversary of this classification, an overview of the fluidization characteristics of the four Geldart groups is presented along with other such classifications, providing perspectives on why the Geldart classification is so universal. Some of the precautions that need to be considered when using this classification are also highlighted. This study is a tribute to the Geldart classification and is expected to be valuable as a summary of the advancements in the understanding of the Geldart groups to date.