| A | membrane area, m2 |
| Ae | electrode area, m2 |
| Ea | activation energy, kJ mol−1 |
| Df | measured frequency shift, Hz |
| f 0 | frequency of quartz crystal prior to a mass change, Hz |
| Δm | mass change, g |
| Mi | molecular weights of gas-i, kg mol−1 |
| p/p0 (H2O) | relative pressure of water vapor, dimensionless |
| pH | pressures of gas feed side, Pa |
| pL | pressures of gas permeate side, Pa |
| Qi | permeance of gas-i, mol m−2 s−1 Pa−1 |
| QK ,i | Knudsen permeance of gas-i, mol m−2 s−1 Pa−1 |
| V | permeate molar flow rate, mol s−1 |
| Va(H2O) | maximum amount of water adsorption, cm3(STP) g−1 |
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