Moisture profile

Moisture gradient is the moisture profile ia a material at a specific moment duriag dryiag, which usually reveals the mechanisms of moisture movement ia the material up to the moment of measurement. 

When clay or similar material is dried, often a pressure gradient is developed by the forces of repulsion between particles as shrinkage brings the particles close together (25). This gradient forces Hquid toward the surface and the resulting moisture profile resembles that characteristic of Hquid diffusion. 

Figure 4-38 Possible Moisture Profiles through the Laminate Thickness (Adapted from Pipes, Vinsor), and Chou [4-6])...

This measurement methodology and data analysis is general and can be extended to other porous media. The results from MRI moisture profiles can also be used to measure moisture diffusivity that enable moisture transport models to be developed for a wide range of materials. 

Fig. 4.7.8 Moisture distribution in lasagna three sheets. The image data at one time point pasta as a function of distance from the surface is shown by the insert. The lighter gray is to the center (0.1 cm). The moisture profiles directly proportional to moisture content and are extracted from the central sheet of a set of occurs at the edge of the pasta sheet.

Figure 19 Representative in-process moisture profile for granulation.

The change of moisture profile in barley and soybean seeds during maturation was measured using NMR imaging [30]. The process of seed maturation was discussed in relation to the biological and morphological characteristics of the crop. 

Figure 3. Moisture profiles measured during drying of a fired-clay brick sample of 45 mm length after 0, 1,3, 6, 9, 12, and 15 days. The drying surface is at 0 mm.

We have performed experiments on fired-clay bricks, because they show almost no adsorption of ions at the pore wall. As an example of a typical experiment, we first discuss the results for a 3 M NaCl solution. A few representative moisture profiles are shown in figure 3. This figure shows that the moisture profiles are nearly flat, which indicates that the moisture distribution within the sample remains homogeneous during this evaporation experiment, i.e., up... 

Several workers measured tritium concentrations in profiles of soil moisture. The samples were collected in most cases by means of a hand drill the profile samples were carefully wrapped to avoid drying or exchange with tritium in the air. In the laboratory the soil moisture was extracted by distillation, weighted (to get a moisture profile), and measured for the tritium concentration. 

Fig. 10.9 Tritium in soil moisture profiles in the southern Kalahari, South Africa. The measurements were done in 1978, and 10 TU was taken to mark the 1963 recharge. B.H. 3 was profiled under a large camel thorn tree. (From Verhagen et al., 1979.)...

It has been reeognized that microwaves could perform a useful fimction in textile drying in the leveling out of moisture profiles across a wet sample. This is not surprising because water is more reaetive than any other material to dielectric heating so that water removal is aeeelerated. An exponential model presented here. [7] can be used to describe the drying eurves. 

Biochemical Degradation Biochemical degradation is another harmful transformation that occurs with most biological products. There are four key reactions to consider lipid oxidation, Maillard browning, protein denaturation, and various enzyme reactions. These reactions are both heat- and moisture-dependent such that control of temperature and moisture profiles can be very important during drying. 

With impermeable woods - and heartwood - the supply of moisture from the interior eaimot keep paee with evaporation of water vapour from the surface, because mass flow of water is not possible and diffusion is a much slower process. Thus the surfaee moisture eontent quiekly falls below fibre saturation and the evaporative front starts reeeding into the wood. Figure 8.6 shows the parabolic moisture content profile for a slowly air-dried impermeable hardwood. Similarly for permeable softwoods that have been dried below the irreducible moisture content, Stamm (1964, 1967b) reported parabolic moisture profiles that are consistent with diffusion of both water vapour and bound water. 

The diffusion coefficient is sensitive to moisture content. The amount of water entering the slab (Jmi = Dmi- A. (5M/5x)mi) on one side of Figure 8.7 must equal the amount of water leaving the slab (Jm2 Dm2 A. (5M/5x)m2) on the other side under steady state conditions, otherwise the moisture profile within the wood would have to change and the system would not be in steady state. Thus ... 

Figure 8.16. (a) Strains in 50 mm red oak during air-drying (McMillen, 1955). (b) Transverse movement in partially dried timber when stresses are released by cutting in sections parallel to the surface, (c) Moisture profile through the timber during drying (McMillen, 1955). 

Seepage of water through the piles is not uniform. It is greatest during a rain but almost ceases during dry periods. This results in irregular moisture profiles in the piles, with wet and dry layers alternating within the piles. This moisture pattern has been observed previously [7]. 

FIGURE 2.1 Moisture profiles in the breading (B) and core (C) regions of chicken nnggets dnring deep-fat frying at different temperatures. (From Ngadi, M. et al., Int. J. Food Eng., 2(3), Art. 8, 1, 2006.)... 

Peck, A.J. (1964) Moisture profile development and air compression during water uptake by bounded porous bodies 3. Vertical columns. Soil Science 100 (1), 44-51. 

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