Soluble release mass transfer

The overall mass-transfer coefficient. As shown above the resistance-in-series concept provides a means for combining transport processes on either side of the interface. Defined as the ratio of the flux to the concentration on particles, Ks, the overall sediment soluble release mass-transfer coefficient (L/t) is... 

The dispersion term is absent since dividing the reach into Ax completely mixed segments accomplishes dispersion numerically. In equation 1 t is time (t), Ct is soluble, particulate, and colloidal, concentration (M/L ), U is average water velocity (M/t), Ds is particle deposition flux (M/L t), h is water column depth (L), m v is suspended solids concentration (M/L ), fp and fd are fractions chemical on particles and in solution, kf is the soluble fraction bed release mass-transfer coefficient (L/t), Cs is the total, soluble and colloidal, concentration at the sediment-water interface (M/L ), Rs is particle resuspension flux (M/L t), ms is the particulate chemical concentration in the surface sediment (M/L ), fps Cts is the fraction on particles and total chemical concentration in the surface sediment (M/L ), Kl is the evaporation mass-transfer coefficient (L/t), Ca is chemical vapor concentration in air (M/L ), H is Henry s constant (L / L ) and Sx is the chemical lost by reaction (M/L t). It is conventional to use the local or instantaneous equilibrium theory to quantify the dissolved fraction, fd, particulate fraction, fp, and colloidal fraction, fooM in both the water column and bed. The equations needed to quantify these fractions appear elsewhere (4, 5, 6) and are omitted here for brevity. 

The contrast between the zero-order release which we seek and the other orders which we usually get is vividly shown in Fig. 19.1-1. We clearly need other ways to control release. The first-order release rate, which depends on the drug s solubility and mass transfer, is often too fast and decreases with time. The release rate can be slower, but is still time dependent, difficult to change. 

Mass transfer models have been used to describe the leaching of soluble substances from porous particles into solution. Such models include a concentration difference that drives the concentration of soluble components in the solids and solution to equilibrate (14). Application of one such model (14) to track release from a solid into solution results in the following equations when applied to xylan conversion in a batch system ... 

Therefore, steps 2 and 3 can be combined into a single step, and the overall kinetics can then be described in three compositional fractions the permanent (formed from insolubles), the resistant (in capillary pores and sorbed within aggregates), and the labile (in gravitational pores). The contribution of the permanent fraction (the insoluble portion) to the soluble portion in the leachate is proportional to its concentration. The release of the resistant fraction is represented by mass transfer, and the translocation of the labile fraction relates to convection flow and dispersion. 

The effectiveness of absorption depends on water flow rate, drop size, and gas solubility. Fthenakis (1989) developed a simple model for evaluating mass transfer induced by a single water-spray nozzle for a point-source release ... 

The importance of corrosion product mass transfer was realized first in the early operation of NRU. Here the solubility of the oxide formed on the aluminum fuel sheathing led to the production of a colloidal alumina floe in the heavy water. The mechanism for its formation, means to control it, and the role it played in transporting uranium and fission products released from failed fuel were studied (55, 56). 

When an insoluble bubble rises in a deep pool of liquid, its volume increases according to the ideal gas law. However, when a soluble bubble rises from deep submersion, there is a competing action of dissolution that tends to reduce size. Under practical conditions, it has been proved (Rice 1982) that the mass transfer coefficient ikj for spherical particles (or bubbles) in free-fall (or free-rise) is substantially constant. Thus, for sparingly soluble bubbles released from rest, the following material balance is applicable... 

CFaT riverine models were presented for both the water column and bed sediment. They were then simplified to focus onto the non-flow resuspension soluble fraction using the quasi-steady state assumption to isolate the key water-side and sediment-side process elements. Field evidence of soluble release based on CFaT model derived data was reviewed for three rivers. Both the traditional particle background resuspension process and more recent soluble fraction process algorithms data interpretation were covered. Numerical field calibrated resuspension velocities and soluble mass-transfer coefficients were presented. Candidate water-side and sediment-side transport processes, selected from the literature were reviewed. Those that provided the best theoretical explanation and contained laboratory and/or field data support were selected. Finally, the flux and the overall transport coefficient which captures the essential features of the framework were presented. Following this the theoretical mass-transfer coefficients were applied to a site on the Fox River below De Pere Dam. Numerical calculations were made for the transport coefficients for both individual and combined processes. 

ILs are low-melting salts that are attractive for a number of applications as they are relatively nonvolatile, nonflammable, environmentally benign, and exceptionally thermally stable [18], In addition, there are numerous combinations of cations and anions that can be used to produce ILs, and thus chemical and physical properties of ILs can be tuned, which is needed to design an energy-efficient liquid absorbent for CO2 capture. The mechanism for CO2 capture in ILs is often based on physisorption and involves a weak association between the IL and CO2 molecules [19], Once the CO2 has been removed from the gas mixture, it can be released from the ILs (which would be reused) by either a decrease in pressure or an increase in temperature [18], While the viscosity of ILs minimizes solvent loss from the gas stream, this attribute also limits mass transfers, and they often suffer from low rates of absorption. To overcome these shortcomings and increase the capacity of simple ILs, amine-functionalized ILs have been developed, which allow higher rates of sorption to be achieved at pressures relevant to flue streams [ 19,20]. A number of reports have also demonstrated high CO2/N2 selectivity in polymerized ILs, which exhibit enhanced CO2 solubility relative to the monomeric ILs [21]. 

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