AJP - Regulatory, Integrative and Comparative Physiology, Vol 235, Issue 1 3-17, Copyright © 1978 by American Physiological Society
Osmosis, diffusion, convection
H. Soodak and A. Iberall
We present a tutorial on the mechanisms of and connections among osmosis,
diffusion, and convection. For simplicity, we consider only two-component
nonelectrolyte solutions under isothermal conditions. Further, we confine
our attention to laminar convection with application to the case of flow
through narrow channels, as might occur in membranes containing pores or
slits. The application of equilibrium and near-equilibrium thermodynamics
to flow processes is just like considerations of mechanics with friction,
or hydrodynamics. The description of flow processes of more than two
atomistic components, either solutions or suspensions, is identical in the
dilute limit to the description we give, except possibly when the curvature
of the flow field (at the velocity profile) is significant. Flow fields,
therefore, naturally divide into three regimes: 1) "one-dimensional" flow
fields, e.g., solutions or suspensions in extended regions, whose velocity
profile is macroscopically flat (compared to the atomistic curvature); 2)
flow fields with significant curvature, e.g., Poiseuille or turbulent
fields; and 3) high curvature fields, e.g., narrow flow channels.
