Helium permeation rate

Table 4.3 provides a comparison between the helium permeation rates in two films, a laminate incorporating a 6 pm aluminium foil, PET 12 pm/Aluminium 6 pm/HDPE 50 pm (Film B) and a multi-layered barrier composed of four aluminium-sputtered PET sheets laminated onto a 50 pm PE (Film A). Tests were run at 24 °C. From the measurement of... 

Table 4.9 Helium permeation rates through barrier films submitted to different mechanical treatments ...

MPa) helium at a flow rate much in excess of the permeation rate. 

To verify the membrane integrity prior to attempting separations, pure gas permeation rates for nitrogen and helium were determined and compared to the vendor s data supplied with the membrane. Figure 4 and Table V verify the vendor s data reasonably well for the only membrane which survived shipment and startup. The agreement of the nitrogen values is particularly indicative of the membrane s integrity. 

The results of gas permeability, hydrogen, helium, methane, nitrogen, oxygen, argon, and carbon dioxide permeation under pressure of 100 mmHg with Membranes A to C. For all samples, the permeation rates were found to be proportional to the molecular weight powered to -0.5. This means that for all membrane samples, the flow in the pores become a Knudsen-type flow and each membrane sample had a linear plot, indicating the absence of pinholes. 

Fig. 10.8. Temperature variation of the oxygen permeation rate from the air to the helium (30 cm min ) side of disc membranes Lao.6Ao. oo.8Feo.z03.5 (A = Na, Ba, Ca, Sr), 20 mm in diameter and 1.5 mm thick, after Teraoka et al. [38]. Reproduced (data re-scaled) from Teraoka et al. [38].

The so-called carrier-gas method is the most complicated approach to gas permeation monitoring.19 Either pure-component or multicomponent permeation rates through Alms can be monitored using this device, shown in Fig. 20.3-8. A carrier gas such as helium, containing a desired partial pressure of the desired component or components. Hows past the upstressu face of the membrane. A downsttesm sweep gas picks up the permeated components and routes them to a gas chromatograph for analysis of the fluxes of each penetrant. An excellent discussion of such a system has been offered by Pye el al.and comparisons were made with manomeiric cells for pure gas permeation to prove that the results for both celts are essentially identical if care is taken in operation. 

The sweep gas method of Pye etal. (23) was utilized as described earlier (12) to measure the permeation rate of each feed gas species from a 100% relative humidity high pressure feed gas stream Into a completely humidified sweep gas stream of pure helium at near atmospheric pressure. For details, the reader Is referred to our previous work (12). 

Special Test facilities exist at NBS in Boulder, CO. These use cryogenic fluids. A description of these facilities can be found in [14]. In addition, low flow rate helium permeation leaks testing capabilities will be available at NBS in 1986. 

To better estimate gas permeation for high quality barriers a novel technique has been developed [24, 25], which is based on the measurement with a quadrupole mass spectrometer of the helium transmission rate through the sample. 

The estimation of the transmission rates for gases other than helium can also be obtained, provided a preliminary calibration is carried out. This is particularly important for water, which is the main gas permeating through the barrier skin. To run the calibration procedure, the helium transmission rate is measured for various samples having different and known permeation rates for water. The linear correlation between helium and water transmission rates is then established, as shown in Figure 4.8. 

Table 4.3 Helium and water permeation rates through films ...

As a result, the oxygen permeation flux under POM reaction conditions is much higher than that when helium is used as the sweep gas at the same temperature (Gong and Hong, 2011). Furthermore, the POM catalyst has great influence on the oxygen permeation rate of the membrane, although the mechanism is not very clear (Ishihara et al, 2002). 

A linear pressure dependence of the permeation rate is indicated by the results of various observers (24,30,28,31,32). It was immaterial whether the gas was monatomic (He) or diatomic (Hg, Og, Ng), the same linear relation was obtained. There is one contrary result (33), data on the velocity of permeation of helium through pyrex, soda, lead, and Jena 16 ii glasses being reported as conforming to an equation dpjdt = ccp. The values of n were given as follows ... 

The separation factor, also referred to as the selectivity of the gas pair, is the ratio of their permeation rates. For a gas pair, such as helium and nitrogen, the separation factor is given by equation 2. 

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