Separation process undertaken in packed columns often displays anisotropic turbulentmass diffusion. The anisotropic turbulent mass diffusion can be characterized rigorously by using the Reynolds mass flux (RMF) model. With the RMF model

the concentration and temperature as well as the velocity distributions can be simulated numerically. Themodeled Reynolds mass flux equation is adopted to close the turbulent mass transfer equation

while themodeled Reynolds heat flux and Reynolds stress equations are used to close the turbulent heat and momentum transfer equations

so that the Boussinesq postulate and the isotropic assumption are abandoned. To validate the presented RMF model

simulation is carried out for CO

2

absorption into aqueous NaOH solutions in a packed column (0.1 m id

packed with 12.7 mm Berl saddles up to a height of 6.55 m). The simulated results are comparedwith the experimental data and satisfactory agreement is found both in concentration and temperature distributions. The sequel Part II extends the model application to the simulation of an unsteady state adsorption process in a packed column.