Moisture capillary movement

Capillary movement may take place in any direction upward, downward, or laterally. After moisture has been added to the surface of a packing, capillarity may help in draining it to lower levels conversely, in surface drying, capillarity will draw water from the deeper areas. The rate of downward movement has already been discussed. The movement of moisture upward through a packing is difficult to predetermine, and forms another section of the present chapter. King (1899), in his remarkable memoir on the movements of ground water, states ... 

P.C. Carman, Capillary rise and capillary movement of moisture in fine sands, Soil Sci., 52 (1941) 1-14. 

These studies by Chang et al. (1991) showed that during muscle dehydration, the shifting of the drying mechanisms and drying properties are always possible if the pretreatment and/or drying conditions are varied, which can cause structural modifications in the muscle. If the embedded connective tissue network is intact, capillary movement and external surface vaporization become the major mechanisms for moisture removal. On the other hand, if the connective tissue network is open, below surface and free vaporization become the major mechanisms involved. With meat mixtures of a complex structure, the relative importance of each mechanism depends on the specific structure of the meat and the manipulative changes that... 

Different kinds of plants vary somewhat in their ability to extract water from a dry soil, but these differences are not great. Plant tolerance of drought conditions is a much more important factor. Another important factor in the utilization of soil water is the matter of where the water is located. In soils having moisture contents of less than field capacity water movement is much too slow to meet the requirements of plants that are transpiring rapidly. The rate of capillary movement of water through soils, either horizontally or vertically, is much less rapid than many have supposed. Since the water cannot move readily toward the roots, it is necessary that the roots ramify throughout the soil if the soil water is to be used fully. Water in a reservoir moves readily, but water in soil that is held by capillarity is largely immobile. 

Capillary movement in soil refers to the movement of moisture through the minute pores between the soil particles that act as capillaries. It takes place as a consequence of surface tension, therefore moisture can rise from the water table. This movement, however, can occur in any direction, not just vertically upwards. It occurs whenever evaporation takes place from the surface of the soil, thereby exerting a surface tension pull on the moisture, the forces of surface tension increasing as evaporation proceeds. Accordingly, capillary moisture is in hydraulic continuity with the water table and is raised against the force of gravity. Equilibrium is attained when the forces of gravity and surface tension are balanced. 

Capillary movement in porous solids. When granular and porous solids such as clays, sand, soil, paint pigments, and minerals are being dried, unbound or free moisture moves through the capillaries and voids of the solids by capillary action, not by diffusion. This mechanism, involving surface tension, is similar to the movement of oil in a lamp wick. 

In many instances, however, as mentioned briefly in Section 9.5E, the rate of moisture movement in the falling-rate period is governed by the rate of internal movement of the liquid by liquid diffusion or by capillary movement. These two methods of moisture movement will be considered in more detail and the theories related to experimental data in the falling-rate region. 

A modified form of Poiseuille s equation for laminar flow can be used in conjunction with the capillary-force equation to derive an equation for the rate of drying when flow is by capillary movement. If the moisture movement follows the capillary-flow equations, the rate of drying R will vary linearly with X. Since the mechanism of evaporation during this period is the same as in the constant-rate period, the effects of the variables of the drying gas of gas velocity, temperature of the gas, humidity of the gas, and so on, will be the same as for the constant-rate drying period. 

In porous and granular materials, Hquid movement occurs by capillarity and gravity, provided passages are continuous. Capillary flow depends on the hquid material s wetting property and surface tension. Capillarity appHes to Hquids that are not adsorbed on capillary walls, moisture content greater than fiber saturation in cellular materials, saturated Hquids in soluble materials, and all moisture in nonhygroscopic materials. 

Surface evaporation can be a limiting factor in the manufacture of many types of products. In the drying of paper, chrome leather, certain types of synthetic rubbers and similar materials, the sheets possess a finely fibrous structure which distributes the moisture through them by capillary action, thus securing very rapid diffusion of moisture from one point of the sheet to another. This means that it is almost impossible to remove moisture from the surface of the sheet without having it immediately replaced by capillary diffusion from the interior. The drying of sheetlike materials is essentially a process of surface evaporation. Note that with porous materials, evaporation may occur within the solid. In a porous material that is characterized by pores of diverse sizes, the movement of water may be controlled by capillarity, and not by concentration gradients. 

The capillary theory of drying has been proposed in order to explain the movement of moisture in the bed during surface drying. The basic importance of the pore space between... 

Special considerations apply to the movement of moisture in freeze drying. Since the water is frozen, liquid flow under capillary action is impossible, and movement must be... 

Inputting solid particles at fixed positions, of different sizes simulates a solid phase in the fluid lattice (Fig. 4). The number of fluid particles per node and their interaction law (collisions) affect the physical properties of real fluid such as viscosity. Particle movements are divided into the so called propagation step (spatial shift) and collisions. Not all particles take part in the collisions. It strongly depends on their current positions on the lattice in a certain LGA time step. In order to avoid an additional spurious conservation law [13], a minimum of two- and three-body collisions (FHP1 rule) is necessary to conserve mass and momentum along each lattice line. Collision rules FHP2 (22 collisions) and FHP5 (12 collisions) have been used for most of the previous analyses [1],[2],[14], since the reproduction of moisture flow in capillaries, in comparison to the results from NMR tests [3], is then the most realistic. 

One can state that in the case of moistened capillary-porous materials the friction between grains, moisture movement, grain reformulation and micro-and macrocrack formations all create the sources for emission of acoustic signals. The intensity of acoustic signals, their number and energy, may be used... 

The fourth soil fraction is known as the soil solution, which consists of moisture held by capillary action in the soil particles. The soil solution may be separated by centrifugation. The soil solution contains the ions, which are mobile in soils and is thought to be the main nutrient medium for sustaining plant roots and micro-organisms. The soil is in dynamic equilibrium with the soil solution and the exchange time is of the order of seconds. The movement of the soil solution through the soil after rainfall is responsible for the layered structure of soils. 

An approximate equation for use for materials in which moisture movement is controlled by capillary flow is given as... 

There are three general theories for interpretation of moisture distribution and rate of moisture movement inside poroizs solids. These theories can be listed as (1) diffusion theory, (2) capillary theory, and (3) vaporization-condensation theory. 

Corben and Newitt (C8) showed that the drying characteristics of moist porous granular material are consistent with the capillary theory of moisture movement. The difference in the form of the drying curves are primarily due to the capillary action of the pores. The rate of drying during the constant-rate period is higher for porous than nonporous materials. 

Low rainfall and high moisture losses due to evapotranspiration are typical featuresljf arid regions. Thus, following precipitation events and resultant infiltration of moisture, arid soils often experience net moisture movement upward toward the land surface driven by capillary forces. For such... 

First stage When both surface and core MC are greater than the F.S.P. Moisture movement is by capillary flow. Drying rate is evaporation controlled. 

Moisture flows through porous solids by capillarity - - and to some extent by surface diffusion (see Chap. 25, p. 826). A porous material contains a complicated network of interconnecting pores and channels, the cross sections of which vary greatly. At the surface are the mouths of pores of various sizes. As water is removed by vaporization, a meniscus across each pore is formed, which sets up capillary forces by the interfacial tension between the water and the solid. The capillary forces possess components in the direction perpendicular to the surface of the solid. It is these forces that provide the driving force for the movement of water through the pores toward the surface. 

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