Sorption-desorption moisture transfer model

Water is introduced into closed pharmaceutical systems either accompanying the input materials or in the headspace as relative humidity [79]. Whatever water is contained within the dosage form and its container will ultimately equilibrate among the components according to its affinity for the solid ingredients and the number of association sites. The Sorption-Desorption Moisture Transfer model has been used to evaluate the thermodynamically favored state that will result after the equilibration process is complete [79]. 

Badway, S. I. F., Gawronski, A. J., and Alvarez, F. J. (2001), Application of sorption-desorption moisture transfer modeling to the study of chemical stability of a moisture sensitive drug product in different packaging configurations, Int. J. Pharm., 223(1-2), 1-13. 

Desiccants are often used to eliminate moisture in packaging when the moisture resistance of the packaging is not sufficient to prevent exposure. The utility of desiccants has been assessed based on a sorption-desorption moisture transfer model [20]. 

Combining solids that have previously been equilibrated at different relative humidities results in a system that is thermodynamically unstable because there will be a tendency for moisture to distribute in the system so that a single relative humidity is attained in the headspace. As shown in Fig. 6, moisture will desorb into the headspace from the component initially equilibrated at a higher relative humidity and sorb to the component initially equilibrated at a lower relative humidity. This process will continue until both solids have equilibrated at the final relative humidity. The final relative humidity can be predicted a priori by the sorption-desorption moisture transfer model (SDMT) model if one has moisture uptake isotherms for each of the solid components, their initial... 

M. J. Kontny, S. Koppenol, and E. T. Graham, Use of the sorption-desorption moisture transfer model to assess the utility of a desiccant in a solid product, Int. J. Pharm. 84, 261-271(1992). 

Fan and Luo [12] incorporated the new two-stage moisture sorption/ desorption model of fibers into the dynamic heat and moisture transfer model for porous clothing assemblies. They considered the radiation heat transfer and the efFect of water content of fibers on the thermal conductivity of fiber material. Further, Fan and his co-woricers improved the model by introducing moisture bulk flow, which was caused by the vapor-pressure gradients and supersaturation state [12]. This improvement made up for the ignorance of liquid water diffusion in the porous textile material in previous models. The equations of the model are listed as follows ... 

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