Simultaneous heat and mass transport in paper sheets during moisture sorption from humid air

摘要

A model of simultaneous heat and mass transfer is presented to explain transient moisture sorption by paper sheets from humid air. The model is developed to place parametric dependencies on the mass and heat transfer resistances. The magnitude of these resistances are then estimated by comparing the model to experimental measurements of the moisture and temeprature dynamics of a paper sheet during sorption transients. Several aberrant behaviors are also explained by accounting for nonlinear interactions during transient moisture transport. First, the differences intime to obtain equilibrium when approaching different moisture contents are explained by the nonlinearity of the moisture content isotherm. Second, heat is released during moisture sorption due to the heat of absorption. Temperature excursions of as much as 6 deg C are measured by a remote IR probe. The temeprature changes in the sheet cause the moisture content to change along different isotherms. Dynamic measures of the temperature of the sheet are compared to predictions derived by including thermal effects into the porous sheet model of moisture transport. The effect of these temperature excursions on the shape of the moisture transients is also discussed.