Acceleration mass transfer

Rastogi, N.K., Eshtiagi, M.N., and Knorr, D. 1999. Accelerated mass transfer during osmotic dehydration of high intensity electrical field pulse pretreated carrots. J. Food Sci. 64, 1020-1023. 

The composition of volatiles released from a food is different when it is sniffed (via orthonasal route) and when it is eaten (via retronasal route). This is partially due to conditions in the mouth that selectively affect volatility, thus altering the ratio of compounds that volatilize from a food system. Mouth temperature, salivation, mastication, and breath flow have all been shown to affect volatilization (de Roos and Wolswinkel, 1994 Roberts et al., 1994 Roberts and Acree, 1995 van Ruth et al., 1995c). The ideal gas law describes the effects of temperature. Saliva dilutes the sample, affects the pH, and may cause compositional changes through the action of the enzymes present (Burdach and Doty, 1987 Overbosch et al., 1991 Harrison, 1998). Mastication of solid foods affects volatility primarily by accelerating mass transfer out of the solid matrix. The gas flow sweeps over the food, creating a dynamic system. The rate of the gas flow determines the ratio of volatiles primarily based on individual volatilization rates and mass transfer. 

Irrespective of the conditions ensuring the abnormally rapid movement of a liquid in a capillary under acoustic cavitation effect, it is important to note that the sonocapillary effect follows all the major effects of the ultrasonic treatment of melts. Among such phenomena are wetting and activation of solid nonmetallic impurities in a liquid metal as well as fine filtration of a melt through porous filters under action of the ultrasonic cavitation treatment. For both processes, ultrasonic cavitation and sonocapillary effect with formation of cumulative jets provide the accelerated mass transfer of a melt to slots and cracks in the surface of nonwettable solid particles and into capillary channels of fine filters. 

Electrodialysis. The driving force is an external electric field that accelerates mass transference across the membrane. Charged compounds are transferred, whereas uncharged compounds are retained. As the dialysis efficiency depends on the external applied electric field, a potentiostat should be linked to both sides of the membrane. Details are given elsewhere [277,278]. 

One of the expected benefits from using enzymes in supercritical fluids (SCFs) is that mass transfer resistance between the reaction mixture and the active sites in the solid enzyme should be greatly reduced if the reactants and products are dissolved in an SCF instead of running the reaction in a liquid phase. It is expected that the high diffusivity and low viscosity of SCFs will accelerate mass-transfer controlled reactions. 

Sandstone grains with a distorted crystal structure (clearly demonstrated by outcrops of dislocations on grain shears and assessed at 4 x 10 cm (Plates gf, 10b) show a much higher coefficient of diffusion and accelerated mass transfer compared to similar processes in perfect crystals. 

Both theoretical calculations and experimental data document that rapid mass transfer between the mobile and stationary phases and the absence of intraparticular diffusion allow the separations of biomacromolecules to be finished within a few seconds [55]. In addition, a higher working temperature that may easily exceed lOO C further accelerates mass transfer and incieases column efficiency [56,57]. 

Surfactants are widely used to control wetting, capillary penetration, and evaporation. Adsorption of surfactants accelerates mass transfer processes, such as impregnation of hydrophobic porous bodies by aqueous solutions, cleaning of greasy oiled surfaces, and crude oil recovery. Surface modification of adsorbents, membranes, and catalysts by surfactants is often used to control their properties. 

Those techniques which allow direct contact of the phases. Usually, the phases are stirred to accelerate mass transfer. Unfortunately, the influence of transport in either phase is poorly known. For this reason, it has been tried to minimize the transport contribution by vigorous stirring, to reach a regime controlled by the kinetics. 

Accelerated mass transfer during osmotic dehydration of high intensity electrical field pulse pretreated carrots. f Food Sci. 64 1020-1023. 

Erosion corrosion is mainly observed in hydraulic installations (pumps, turbines, or tubes). This form of corrosion appears at a point where the flow velocity of the bulk solution exceeds a critical limit, or where this limit is exceeded by local turbulence. Erosion corrosion results from an interaction between mechanical and chemical influences. Fig. 1-26. One model describing the mechanism of erosion corrosion assumes that local shear forces acting on the metal surface as a result of the high flow velocity forms pores or unprotected areas. Accelerated mass transfer then occurs in these areas and aggravates corrosion damage. 

Again, some points about this result deserve attention. First, the product KA is normally called the diffusing capacity, which is descriptive but conceals its relation to mass transfer. Second, K includes mass transfer resistances in the lung gas, across the alveoli walls, and into the blood. The resistance in the gas is probably small because diffusion in gases is fast. The resistance in the blood may be small because of the fast reaction between CO and hemoglobin which accelerates mass transfer this acceleration is discussed in detail in Chapter 17. The resistance across the membrane may be rate controlling. 

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