Bulk density, along with particle size, is used to assess the quality of granular solids. It is defined as the mass of solid divided by the total volume occupied by this solid, including spaces in and between granules. There are, however, several ‘types’ of bulk density that can be measured for any one sample of granular material. Loose poured bulk density is determined by releasing a powder under standard conditions into a container of known volume, with special care taken to avoid any perturbations of the container, which would cause the powder to consolidate. Another bulk density, is tapped bulk density, where the particular solid is consolidated by tapping under standard conditions. For a large number of taps the bulk density will reach a limiting value.
A third bulk density is the bulk density measured of a flowing material. ‘Flowing’ bulk density is particularly useful in the application of control systems for a granulation circuit, because unlike the other two forms of bulk density, the flowing bulk density can be measured continuously and on-line.