Multicomponent Solid Modeling of Continuous and Intermittent Drying of Pinus radiata Sapwood Below the Fiber Saturation Point

Abstract

A multicomponent softwood timber drying model has been created that illustrates both the overall desorption behavior and the desorption behavior of individual timber components (cellulose, hemicellose, and lignin) for moisture contents below the fiber saturation point of 0.3 kg/kg. This model differentiates between the individual timber components by the differences in their thermodynamic properties, including the heat of sorption, the relative humidity above the timber surface, and diffusivity. This model incorporates a “double permeability” structure to simulate moisture moving between the components during drying. This article shows the results of a sensitivity study conducted on this model, which determines the effect of varying diffusivity on both overall and individual component desorption rates. Nonunique solutions have been predicted for some drying conditions, and the ranges of conditions leading to unique and nonunique conditions have been explored using both continuous and intermittent drying schedules. The use of intermittent drying schedules in this multicomponent drying situation has made the problem of parameter estimation less ambiguous. The range of initial conditions for most realistic conditions give predominantly unique results, so the diffusivities and intercomponent mass transfer rates can be determined from experimental drying data.