Bed Voidage Method

The bed voidage method was developed by Abrahamsen and Geldart11 as a simple alternative to the caking end point method outlined above, when the end point cannot be clearly identified. 

This method is based on an observation that the minimum packed voidage is virtually the same for particles of similar size and particle shape. The procedure is that between 0.2 and 0.25 kg of a control powder c of known particle effective density ppc is poured into a measuring cylinder and tapped until it reaches its minimum volume, corresponding to the maximum bulk density Pbc. This procedure is repeated with the unknown powder x (ideally, several control powders should be used). If the porosity after tapping is assumed to be the same for both powders c and 

As it is not always possible to find known powders of the same shape as the test powder, Abrahamsen and Geldart11 introduced an experimentally-determined factor k which varied from 0.82 to 1.22 for conversion from spherical to angular or the other way round. They tested the method using non-porous powders and compared it with liquid pyknometer results, and found an excellent agreement. 

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