Liquids transport processes

Vergnaud J. M., 1991. Liquid Transport Processes in Polymeric Materials. Modeling and industrial applications. Prentice Hall, Englewood Cliffs, New Jersey. 

Vergnaud, J.M., Liquid Transport Processes in Poymeric Materials , Prentice Hall, Engelwood Cliffs. 1991. 

A step-by-step simulation of the system can be carried out by numerical calculations when the initial values of capacitances and the values of parameters (constants) are assigned. The calculations have been performed using the model from Table 13.1 after assuming n = A. This value is sufficient [86] to achieve reliable simulation data of typical liquid transport processes under study. However, it should be noted that the increase in the number of layers, i.e., increasing in n will always result in more precise calculations and predictions comparable to those achieved by analytic calculation methods. The n-value equal to 4 should be treated as the lowest limit required for obtaining quantitative data sufficient for the interpretation of the separation effects. The problem of proper compartmentalization can be especially significant when reactions locally attain quasi-equUibrium conditions. 

The transport coefficients have been obtained by Green20 and by Irving and Kirkwood2 in terms of the molecular densities and intermolecular potentials by methods which introduce no assumptions beyond those already discussed herein. A review of the derivation is presented in tJ.S. Air Force Note No. 56—255, Part 2 As this aspect of the liquid transport processes is completely solved, the present discussion will be confined to a brief exposition of the transport coefficients. 

A precise determination of the frictional coefficient C in terms of the intermolecular potential and the radial distribution function at present constitutes the principal unresolved problem of the Brownian motion approach to liquid transport processes. It has been suggested by Kirkwood that an analysis of the molecular basis of self-diffusion might be a fruitful approach. The diffusion constant so calculated would be related to the frictional coefficient through the Einstein equation, Eq. 46. 

The evaporation process is also influenced by the liquid transport process. When liquid water cannot diffuse into the fabric, it can only evaporate at the lower surface of the fabric. As the liquid diffuses into the fabric due to capillary action, evaporation can take place throughout the fabric[39]. 

Moreover, the heat transfer process has significant impact on the evaporation process in cotton fabrics but not in polyester fabrics. The process of moisture sorption is largely affected by water vapor diffusion and liquid water diffusion, but not by heat transfer. When there is liquid diffusion in the fabric, the moisture sorption of fibers is mainly determined by the liquid transport process, because the fiber surfaces are covered by liquid water quickly. Meanwhile, the water content distributions in the fibers are not significantly related to temperature distributions. 

Walters, K. and R. I. Tanner, The motion of a sphere through an elastic liquid. Transport Processes in Bubbles, Drops and Particles (R. P. Chhabra and D. De Kee, eds.), Hemisphere, New York, 1991. 

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