Diffusion coefficient, abbreviated as \(D\), quantifies the rate at which atoms, ions, molecules, or particles spread through a medium, such as concrete, soil, water, or air, solely due to random thermal motion driven by a concentration gradient, without any bulk flow or external force.
Diffusion Coefficient Formula |
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\( D \;=\; \dfrac{ k_b \cdot T_a }{ \mu } \) (Diffusion Coefficient) \( k_b \;=\; \dfrac{ D \cdot \mu }{ t_a }\) \( T_a \;=\; \dfrac{ D \cdot \mu }{ k_b }\) \( \mu \;=\; \dfrac{ k_b \cdot T_a }{ D }\) |
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| Symbol | English | Metric |
| \( D \) = Diffusion Coefficient | \(ft^2 \;/\; sec\) | \(m^2 \;/\; s\) |
| \( k_b \) (Greek symbol sigma) = Boltzmann Constant | \(lbm-ft^2 \;/\; sec^2\) | \(kJ \;/\; molecule-K\) |
| \( T_a \) = Absolute Temperature | \(^\circ R\) | \(^\circ K\) |
| \( \mu \) (Greek symbol mu) = Friction Coefficient | \(dimensionless\) | \(dimensionless\) |
The diffusion coefficient can be calculated using Fick's laws of diffusion, which describe the behavior of particles as they move from areas of high concentration to areas of low concentration. The first law of diffusion states that the flux of particles is proportional to the concentration gradient, while the second law states that the rate of change of concentration over time is proportional to the second derivative of the concentration with respect to position.
The diffusion coefficient depends on the properties of the material or medium being diffused, as well as the temperature and pressure of the system. It is commonly used in fields such as chemistry, physics, and engineering to model the behavior of gases, liquids, and solids in various systems.
