Kinetic Theory of Non equiibrium Systems

A volumetric system was used to assess carbon-based adsorbents for evaluation of the gas separation, equilibrium, and kinetics of oxygen (O 2), nitrogen (N 2), and carbon dioxide (CO 2) adsorption on granular activated carbon (GAC) and functionalized GAC at 298, 308, and 318 K under pressures up to 10 bar. The effects of ZnCl 2 , pH, arrangement of the pores, and heat-treatment temperature on the adsorptive capabilities of O 2 , N 2 , and CO 2 were evaluated. High-performance O 2 adsorption resulted with a fine sample (GAC-10-500) generated with a 0.1 wt % loading of ZnCl 2. The optimal sample structure and morphology were characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, and powder X-ray diffraction. On the basis of the adsorption−desorption results, the fine GAC provides a surface area of 719 m 2 /g. Moreover, it possessed an average pore diameter of 1.69 nm and a micropore volume of 0.27 m 3 /g. At 298 K, the adsorption capacity of the GAC-10-500 adsorbent improved by 19.75% for O 2 but was not significantly increased for N 2 and CO 2. Isotherm and kinetic adsorption models were applied to select the model best matching the studied O 2 , N 2 , and CO 2 gas uptake on GAC-10-500 adsorbent. At 298 K and 10 bar, the sip isotherm model with the highest potential adsorption difference sequence and gas adsorption difference compared with pure GAC adsorbent as O 2 > N 2 > CO 2 follows well for GAC-10-500. Eventually, the optimal sample is more effective for O 2 adsorption than other gases.

A reduced description of the three-dimensional effects of rough surfaces on the laminar liquid flow in microchannels is sought. With this outlook a one-dimensional model is proposed, which is built by splitting the channel in two regions: a porous region and a fluid one. The porous region is the wall-adjacent fluid layer and represents the roughness. Special attention is paid to three aspects not fully solved in previous porous-layer approaches. These are: (i) a clear link between existing works on spatial averaging of porous/fluid composite domains and the derivation of the porous layer model (PLM) for laminar liquid flows in rough microchannels, (ii) the development of a simple geometrical procedure to compute the stress model for the porous region only as a function of the geometrical characteristics of the roughness, and (iii) the application of an appropriate treatment to the interface between the fluid and porous regions. The stress model in the porous layer, the jump boundary condition at the interface and the PLM are validated against numerical simulations and experimental data from the literature. In addition, further validation using numerical simulation of wavy, cube- and pyramid-based rough channels is performed. Results show that the PLM is valid to approximate the three-dimensional solution of several fluid-connected rough surfaces with an error below 15% (within the 90% confidence interval) for the following conditions: relative roughness $\tilde{k}\equiv k/H < 0.4,$ relative width $\tilde{L}\equiv L/H <40 $ and porosity ɛ < 0.7. The validation is restricted to Stokes flow.