Studies of the process of moisture exchange across a membrane using irreversible thermodynamics

On the basis of non-equilibrium thermodynamic theory, the coupling phenomena of heat and mass transfer during the process of moisture exchange across a membrane were studied and the relevant physical and mathematical models were established. Formulae for calculating the four characteristic parameters included in the non-equilibrium thermodynamic model were derived, and the dependences of these parameters on the temperatures and concentrations on the two sides of the membrane were analyzed, providing a basis for calculating the heat and mass fluxes. The effects of temperature and concentration differences between the two sides of membrane and the membrane average temperature on the transmembrane mass and heat fluxes were investigated. The results show that for a given membrane average temperature, a larger concentration difference or a smaller temperature difference leads to a higher mass flux. For fixed concentration and temperature differences and with the mass flux predominantly caused by the concentration difference, a higher membrane average temperature yields a higher mass flux. The ratio of the heat of sorption induced by mass flow to total heat relates not only to the temperature and concentration differences between the two sides of membrane but also to the membrane average temperature and the ratio increases when the temperature difference is reduced.