Moisture bound

Fiber saturation point is the bound moisture content of ceUular materials such as wood. 

Bound moisture in a solia is that hquid which exerts a vapor pressure less than that of the pure hquid at the given temperature. Liquid may become bound by retention in small capillaries, by solution in cell or fiber walls, by homogeneous solution throughout the sohd, and by chemical or physical adsorption on solid surfaces. 

Hygroscopic material is material that may contain bound moisture. 

Nonbygroscopic material is material that can contain no bound moisture. 

The plate dryer is limited in its scope of apphcations only in the consistency of the feed material (the products must be friable, free flowing, and not undergo phase changes) and diying temperatures up to 320°C. Applications include speci ty chemicals, pharmaceuticals, foods, polymers, pigments, etc. Initial moisture or volatile level can be as high as 65 percent and the unit is often used as a final dryer to take materials to a bone-dry state, if necessary. The plate dryer can also be used for heat treatment, removal of waters of hydration (bound moisture), solvent removal, and as a product cooler. 

Bound moisture This is moisture retained within the solid such that it exerts a vapour pressure less than that of free solvent (Figure 4.24). Such solvent may be adsorbed on the surface, retained in capillaries or within cells or occlusions of liquor. The latter can be difficult to remove without resorting to high temperatures, which may damage the crystals. 

Bound moisture may be located in various positions within a crystal... 

Boundary managing, in R D, 21 619-620 Boundary spanning, in R D, 21 619 Bound chloride formation, 10 358 Bound moisture, 9 96 Bourdon tube, 20 647-649 Boussinesq approximation, 11 779 Boutique fuels, 12 419 Bovatec, 20 136 Bovine hemoglobin, 4 125 Bovine insulin, 3 817 Bovine serum albumin (BSA), 20 573 properties of standard, 3 836t Bovine somatotropin (BST), 10 871 Bovine spongiform encephalitis/... 

Bound moisture. This is water retained so that it exerts a vapour pressure less than that of free water at the same temperature. Such water may be retained in small capillaries, adsorbed on surfaces, or as a solution in cell walls. 

The interest in mass transfer in high-pressure systems is related to the extraction of a valuable solute with a compressed gas. This is either a volatile liquid or solid deposited within a porous matrix. The compressed fluid is usually a high-pressure gas, often a supercritical fluid, that is, a gas above its critical state. In this condition the gas density approaches a liquid—like value, so the solubility of the solute in the fluid can be substantially enhanced over its value at low pressure. The retention mechanism of the solute in the solid matrix is only physical (that is, unbound, as with the free moisture), or strongly bound to the solid by some kind of link (as with the so-called bound moisture). Crushed vegetable seeds, for example, have a fraction of free, unbound oil that is readily extracted by the gas, while the rest of the oil is strongly bound to cell walls and structures. This bound solute requires a larger effort to be transferred to the solvent phase. 

This procedure is based on the unique response of the hydrogen nuclei (protons) present in bound moisture versus free oil. The physical state of the moisture and oil is a critical factor in experiment design. Since the oil in typical oilseeds is present in a liquid state and moisture is bound under conditions in a mature seed, a simple spin echo pulse sequence can determine the quantities separately. 

As the bound moisture is removed and the material is heated to a temperature of 58 to 62 °C in the falling-speed drying section, the content of methylol groups in batches Nos. 1,2, and 3 slightly increases, which may be due to the effect of agglomerating additives. 

The third stage came with the realization that even small amounts of bound moisture could have a dramatic impact on properties and processes of pharmaceutical interest. In the evolution of this scientific pursuit, it is now evident that the state of moisture is as important as the amount present. Although sophisticated thermodynamic characterization of adsorbates has been the subject of research since the pioneering work of Gibbs, this stage has been enhanced by the ability to examine behavior at the molecular level by using powerful new analytical tools. 

Bound moisture Water associated with a solid exhibiting a vapor pressure less than P. 

In a moisture determination by the physical separation of water from the solid, it is important to recognize that free and bound moisture must be dissociated from the solid by an applied stress, using... 

Bound moisture is water (or other solvents in nonaqueous systems) held by a material in such a manner that it exerts a lower vapor pressure than that of the pure liquid at the same temperature. Water may be chemically or physically bound. Unbound moisture is therefore moisture in association with a solid that exerts the same vapor pressure as the pure liquid. In a discussion of bound versus unbound water, it should be pointed out that are not only different equilibria to be considered, but that the binding energies and kinetics are different. 

Here p is the rate of heat transfer from the heated wall to the solids, and ATtj/s is the temperature driving force. The latent heat of evaporation Xev should allow for bound moisture and heating of solids and vapor to the final temperature. A typical wall-to-solids heat-transfer coefficient h s for the given dryer type should be used. The calculation is less accurate than the one for convective dryers. Again, the heat-transfer rate is assumed to be the overall limiting factor. 

The category of bound moisture comprises water retained in small capillaries in the solid, water absorbed on solid surfaces, water bound as solutions in cells or fiber walls, and water bound as crystal water in chemical combination with the solid. Bound water exerts an equilibrium vapor pressure lower than that of pure water at the same temperature. 

The category of unbound moisture can be described as the moisture in excess of the bound moisture. A hygroscopic material may contain bound as well as unbound moisture. A nonhygroscopic material contains unbound moisture only. The equilibrium vapor pressure of unbound water is equal to that of pure water at the same temperature. 

The free moisture in a particle is the moisture in excess of the equilibrium moisture and may consist of unbound and some bound moisture. Only free moisture can be removed by evaporation during spray drying. 

The presence of unbound moisture in the droplet means that the drying proceeds at a constant high rate as long as the moisture diffusion within the droplet is able to maintain saturated surface conditions. When the diffusional and capillary flows can no longer maintain these conditions, a critical point is reached and the drying rate will decline until equilibrium moisture content is reached. The evaporation of bound moisture is strongly dependent on the nature of the solid matter in the spray droplet. 

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