The elastic and moisture transfer properties of polyethylene and polypropylene membranes for use in liquid-to-air energy exchangers

The elastic and moisture transfer properties of membrane materials are required when designing liquid-to-air energy exchangers composed of a series of pressurized membrane channels. Elastic properties are needed to ensure minimal deflections and moisture transfer properties are needed to ensure high moisture transfer rates between the liquid desiccant and air streams. In this research, two ASTM tension test standards (D 882 and D 4595) and circular and square bulge tests are used to determine the elastic moduli of two membranes; the dynamic moisture permeation cell is used to determine the water vapour resistance. The experimental data show the effects of membrane orientation, strain rate and relative humidity on the elastic properties and the effect of humidity on the water vapour resistance. Results show that the bulge test is best suited for the proposed application of a pressurized membrane channel since it includes biaxial effects and gives accurate data that are easy to measure and more closely represent a membrane channel under uniform pressure. The measured elastic moduli and water vapour resistances are applied to estimate the deflections of a pressurized membrane channel supported by a screen with square openings and the energy transfer effectiveness of an energy recovery system consisting of two liquid-to-air membrane energy exchangers.