Gasdiffusionen

Gasdiffusionen refers to the process by which gas molecules spread from regions of higher concentration to regions of lower concentration due to random thermal motion. It occurs in gases, liquids, and porous solids and is described quantitatively by Fick's laws.

The diffusive flux, J, is described by Fick's first law: J = -D ∂C/∂x, where D is the diffusion coefficient and ∂C/∂x is the concentration gradient. In binary gas mixtures, D depends on temperature, pressure, and the molecular properties of the species involved. Higher temperature generally increases D, while higher pressure can reduce it. Fick's second law, ∂C/∂t = D ∂^2C/∂x^2, describes how concentration changes over time in simple one-dimensional diffusion.

In porous media, diffusion is influenced by porosity and tortuosity. The effective diffusion coefficient De = ε/τ D uses ε for porosity and τ for tortuosity, representing reduced diffusion paths in a convoluted pore structure. When pore sizes are small compared with the gas molecules’ mean free path, Knudsen diffusion becomes important, and the diffusion mechanism deviates from bulk-gas behavior.

Biological and environmental contexts include diffusion across the alveolar membrane in respiration, where oxygen and carbon dioxide exchange depends on surface area, membrane thickness, and the respective gas diffusion coefficients. Diffusion in such systems can be diffusion-limited or perfusion-limited, affecting overall gas exchange rates.

Applications of gasdiffusionen span gas separation, environmental dispersion modeling, and industrial processes that rely on diffusion-driven transport.