Phase field equation in the singular limit of the Stefan problem

Abstract

The classical Stefan problem is reduced as the singular limit of phase-field equations. These equations are for temperature $u$ and the phase-field $\varphi$, consists of a heat equation: $$ u_t+\ell\varphi_t=\Delta u, $$ and a Ginzburg-Landau equation: $$ \epsilon\varphi_t=\epsilon\Delta\varphi -\frac{1}{\epsilon}W^\prime (\varphi )+\ell (\varphi )u, $$ where $\ell$ is a latent heat and $W$ is a double-well potential whose wells, of equal depth, correspond to the solid and liquid phases. When $\epsilon\to 0$, the velocity of the moving boundary $v$ in one dimension and that of the radius in the cylinder or sphere are shown as the following Stefan problem,\\ $$ \left\{ \begin{array}{l} u_t-\Delta u =0\\\\ \displaystyle v=\frac{1}{2}\left[\frac{\partial u}{\partial n}\right]_\Gamma \displaystyle u=-\frac{m}{2\ell}[\kappa -\alpha v]_\Gamma \end{array} \right. $$ where $\alpha$ is a positive parameter, $[\frac{\partial u}{\partial n}]_\Gamma$ is the jump of the normal derivatives of $u$ (from solid to liquid), and $m=\int_{-1}^1\left(2W(\varphi)\right)^{1/2}d\varphi$. Since it is sufficient to describe the phase transition of single component by the phase-field equation, we analyze the phase-field equation, and investigate whether the equation shows the Stefan problem or not. The velocity of the moving boundary in the cylinder and sphere are determined and the result of the simulation of the equation is also presented. Next, we consider the velocity of interface which depends on the temperature. The control of width of diffusion layer by the parameter of phase-field equations is investigated in order to realize the singular limit of phase field equations by the numerical method.