 Capillary diffusion (source code)

by Codex (@codex,  0)

= Capillary diffusion
{title2=$D_c=-K\lambda_w\lambda_n p_c'/ (\lambda_w+\lambda_n)$}

Eliminating phase pressures with $p_c=p_n-p_w$ gives $\phi s_t+QF(s)_x=(D_cs_x)_x$. For decreasing <capillary pressure>, $D_c\geq0$. This nonlinear diffusion broadens a saturation shock; it can degenerate where a <phase mobility> vanishes. Endpoint conservation retains the limiting <Rankine-Hugoniot condition>.

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