Caking end point method

In the petroleum industry, the effective particle density of free-flowing cracking catalysts is measured indirectly by measuring the open pore volume. This consists of adding water or another liquid of low viscosity and volatility, to the powder until the liquid has filled all the open pores and it starts coating the external surfaces of particles the powder cakes-up by surface tension at this point and stops flowing. 

If the volume of water needed to just cake the powder is x cm3/g (assumed to be the pore volume) and pa is the true particle density 

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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. 

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