Estimation of the apparent anisotropic water diffusivity on spruce evaluated with a simplified derivative approach and as a function of the flow rate

The anisotropic apparent diffusivity as a function of the flow rate was determined in a series of Dynamic Vapor Sorption (DVS) experiments on spruce samples in the three orthotropic directions. Four different fitting procedures were applied for the evaluation of the time-sorption isotherms, i.e., the double-stretched exponential (DSE), the Ritger-Peppas (RP), and the Fickian and double-Fickian (SUM/DSUM) fitting methods, together with a derivative (DER) method for the determination of the apparent diffusivity. The results confirm that the DER method delivers similar results to the DSE fitting procedure, i.e., 1.98·10− 10, 0.94·10− 10 and 1.00·10− 10 m2/s for the longitudinal, radial and tangential direction, respectively, with a maximum of 10% deviation, in a much simpler manner.