Constant Pressure System
The constant pressure system operates by maintaining a constant pressure gradient across a membrane to establish a constant mass flux through the membrane. This system can be used with both pure and mixed gases.
Bronkhorst flow controllers control and record the flow rates of various streams while a mass spectrometer determines the stream compositions.
Constant Volume System
In the constant volume system the membrane cell, upstream and downstream volumes and the major piping are housed in an oven for temperature control. This also provides the ability to test membranes at high temperature.
The constant volume system utilises pure gas and can currently test membranes with a range of gases. An upstream reservoir is filled prior to each experiment. This system can currently test membranes up to 20 bar and 205 °C.
This technique can be used to directly determine both the permeability and diffusivity directly.