Moisture diffusion coefficient

Measurement of the moisture diffusion coefficient as a function of position in wheat grain was performed [47] the moisture diffusion rate normal to the transverse 1.3 mm section of wheat grain was measured in structural features at a 150 pm resolution. The motion of water was most severely hindered in the endosperm, and water appeared less hindered in the vascular bundles. 

The Moisture Diffusion Coefficient. The one-dimensional moisture flux (/) (g/cm s) of water through wood customarily is given as the product of the moisture diffusion coefficient D (cm /s) and the gradient dcjdx of moisture concentration (g/cm ) in the direction of flow, or... 

Moisture diffusion coefficients as a function of moisture content in soy flour are shown in Figure 46.2. There is a change in the rate of decrease of diffusion coefficient as the material undergoes glass transition. 

Simpson, W.T., Determination and Use of Moisture Diffusion Coefficient to Characterize Drying of Northern Red Oak, Wood Science and Technology, 27(6), 1993, pp.409-420. 

Table 12.1 Typical moisture diffusion coefficients and maximum moisture concentrations of aerospace epoxy matrix resins [8,10]...

Table 3.1 Typical values of moisture diffusion coefficients for resins and composites [3-7]...

Syarief, A.M., Gustafson, R.J., and Morey, R.V, Moisture diffusion coefficients for yeUow-dent com components. Winter Meeting of ASAE, December 11-14, New Orleans, LA, Paper No. 84-3551, 1984. 

Several researches have been carried out to understand the mechanism of moisture movement in clay during drying. Newitt et al. [12] and Wakabayashi [13] investigated the moisture movanent in clay by liquid diffusion and vapor diffusion, which affect the drying characteristics particularly the falling rate. They concluded that the liquid diffusion dominates the movement until about 20%-dry basis in moisture content for stoneware clay and 30% for the mixture of 80% Kibushi clay and 20% feldspar. Wakabayashi [14] also evaluated the effective moisture diffusion coefficient of some sorts of clay such as Kibushi, Gairome, stoneware, feldspar, and their mixtures. The effective diffusion coefficient is available for the brief description of the moisture movement behavior. The effective diffusion coefficient D can be defined by... 

Wakabayashi, K., 1964, Moisture diffusion coefficients of solid during drying process, Kagaku Kogaku, 28(1), 33-38. 

Nilsson et al. [48] find that the apparent moisture diffusion coefficient falls from 5.4 x 10 to 2.1 x 10 ms s as the density increases from 500 kg m (softwood pulp) to 1530 kg m" (coated and calendered paper). 

Dr effective moisture diffusion coefficient AH, heat of sorption... 

The moisture diffusion coefficient within a single wool fiber is of the order 10 [34], When... 

If the effective moisture diffusion coefficients are calculated from Eqs 3.2 and 3.3, it can be noted that the coefficient in the case of SSD would be higher when the medium temperature is higher than 140 °C. This corresponds to the experimental drying rate data shown in Fig. 3.7 it can be seen that the inversion temperature of the whole drying process was approximately 140 °C. 

The moisture diffusion coefficient D is of order 10 mm /s, which for composites and polymers is about 6 and 7 orders of magnitudes smaller, respectively, than the temperature diffusion coefficient. The above processes can thus be decoupled. 

Some specimens (3 samples for each cycle condition and for each material) were aged 70°C/84%R.H. to determine the moisture diffusion coefficient (D) and the relative saturation weight gain (Mco). After moisture saturation the samples were analyzed by DMA to determine the Tg. 

Eq. (13.3.19) can be inserted into Eq. (13.3.18) to give the complete theoretical curve, and this is also shown in Figure 13.7 the fit between Fickian theory and experiment is excellent. It is also remarkable that the addition of such a minute amount of clay is found to reduce the moisture diffusion coefficient by 50%. 

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