chamber was closed and the test gas was allowed to permeate across the specimen for a

sufficient time to purge any residual air at downstream chamber. At this time, only test

gas filled the chambers. When the outlet valve of the upstream chamber was closed, the

upstream pressure increased slowly. The upstream pressure can be adjusted by

controlling the pressure regulator. Sufficient time was allowed for attaining steady state

of moving rate of the liquid indicator before beginning to take readings. The distance of

rise of the liquid indicator was measured while the ambient pressures were recorded.

 Calculations

 The volumetric methodology is used to calculate the permeability by measuring gas

volume transmitted through a specimen. The rate of rise of the liquid indicator is

measured using the capillary tube. The volume flow rate is calculated as follows.

 V = slope xa (4.1)

 where a, is the cross-sectional area of a capillary tube. The slope is the rate of rise

of the liquid indicator in the capillary tube. The gas transmitted rate (GTR) is calculated

using the ideal gas law as follows.


 GTR = o (4.2)
 ART

 where po is ambient pressure, A is transmitting area of a specimen, R is the

universal gas constant (8.3143 x 103 L-Pa/{mol-K}) and T is ambient temperature. The

permeance P is defined by the ratio between the gas transmission rate and pressure

differential across the thickness of a specimen. Therefore, the permeance P is calculated

as follows.


 P G (4.3)
 P-Po