Constant volume permeameters

Two types of instruments are employed to determine the specific surface area by permea-metry. Those of the first type are called constant pressure systems, and the Fisher subsieve sizer is a typical example that belongs to such systems. Instruments of the second type are known as constant volume permeameters, and the apparatus devised by Blain is an example. 

The measured specific surface has been found to decreases with increasing porosity. One way of eliminating this effect, using a constant volume permeameter, is to use equation (1.37) in the form ... 

Commercial permeameters can be divided into constant flow rate and constant volume instruments. 

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